Seata源码—6.Seata AT模式的数据源代理

庾签 · 2025-6-2 23:56:34

大纲
1.Seata的Resource资源接口源码
2.Seata数据源连接池代理的实现源码
3.Client向Server发起注册RM的源码
4.Client向Server注册RM时的交互源码
5.数据源连接代理与SQL句柄代理的初始化源码
6.Seata基于SQL句柄代理执行SQL的源码
7.执行SQL语句前取消自动提交事务的源码
8.执行SQL语句前后构建数据镜像的源码
9.构建全局锁的key和UndoLog数据的源码
10.Seata Client发起分支事务注册的源码
11.Seata Server处理分支事务注册请求的源码
12.将UndoLog写入到数据库与提交事务的源码
13.通过全局锁重试策略组件执行事务的提交
14.注册分支事务时获取全局锁的入口源码
15.Seata Server获取全局锁的具体逻辑源码
16.全局锁和分支事务及本地事务总结
17.提交全局事务以及提交各分支事务的源码
18.全局事务回滚的过程源码

1.Seata的Resource资源接口源码
数据源代理DataSourceProxy不仅实现了Seata的Resource资源接口，同时还继承了实现了SeataDataSourceProxy接口的抽象类AbstractDataSourceProxy。

由于SeataDataSourceProxy接口又继承自JDK提供的DataSource接口，所以通过数据源连接池DataSource接口的方法，可以获取数据源的连接。

注意：这里的数据源==数据库。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {
...
}
public abstract class AbstractDataSourceProxy implements SeataDataSourceProxy {
...
}
public interface SeataDataSourceProxy extends DataSource {
...
}
public interface DataSource extends CommonDataSource, Wrapper {
//获取数据源连接
Connection getConnection() throws SQLException;
Connection getConnection(String username, String password) throws SQLException;
}

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Seata的Resource资源接口有三个方法：

一.getResourceGroupId()方法用来获取资源分组
比如主从节点同属一个分组。

二.getResourceId()方法用来获取数据源ID
比如数据源连接URL可作为数据源ID。

三.getBranchType()方法用来获取分支事务类型
比如类型有：AT、TCC、SAGA、XA。

//Resource that can be managed by Resource Manager and involved into global transaction.
//资源是由RM资源管理组件来负责管理的
//RM资源管理器组件会负责把一个个的资源纳入到全局事务里去
//比如RM可以管理数据库资源，把一个数据库本地事务纳入到全局事务里去
public interface Resource {
//Get the resource group id.
//e.g. master and slave data-source should be with the same resource group id.
//获取到资源分组ID
//主从架构的数据源关联到同一个资源分组ID
//比如MySQL部署了主从架构，主节点和从节点是两个数据源，但是关联到一个分组ID
String getResourceGroupId();
//Get the resource id.
//e.g. url of a data-source could be the id of the db data-source resource.
//比如数据源连接URL可以作为数据源的ID
String getResourceId();
//get resource type, AT, TCC, SAGA and XA
//branchType表示分支事务类型：AT、TCC、SAGA、XA
BranchType getBranchType();
}

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2.Seata数据源连接池代理的实现源码
(1)Seata的数据源连接池代理接口SeataDataSourceProxy
(2)Seata的数据源连接池代理抽象类AbstractDataSourceProxy
(3)Seata的数据源连接池代理DataSourceProxy的变量和初始化

(1)Seata的数据源连接池代理接口SeataDataSourceProxy
SeataDataSourceProxy数据源代理在继承DataSource数据源连接池的基础上，增加了两个方法：一个是获取代理的目标数据源连接池的方法，一个是获取代理的目标数据源连接池对应的分支事务类型的方法。

public interface SeataDataSourceProxy extends DataSource {
//Gets target data source.
//获取代理的目标数据源连接池
DataSource getTargetDataSource();
//Gets branch type.
//获取代理的目标数据源连接池对应的分支事务类型
BranchType getBranchType();
}

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(2)Seata的数据源连接池代理抽象类AbstractDataSourceProxy
AbstractDataSourceProxy抽象类的主要工作是封装代理的目标数据源连接池targetDataSource。

//The type Abstract data source proxy.
//AbstractDataSourceProxy主要的工作就是：
//封装了代理的目标数据源连接池targetDataSource
public abstract class AbstractDataSourceProxy implements SeataDataSourceProxy {
//The Target data source.
//代理目标的连接池，可以通过targetDataSource来获取连接
protected DataSource targetDataSource;
//Instantiates a new Abstract data source proxy.
public AbstractDataSourceProxy(){ }
//Instantiates a new Abstract data source proxy.
public AbstractDataSourceProxy(DataSource targetDataSource) {
this.targetDataSource = targetDataSource;
}
//Gets target data source.
@Override
public DataSource getTargetDataSource() {
return targetDataSource;
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return targetDataSource.unwrap(iface);
}
//判断目标连接池targetDataSource是否包装了指定的接口iface
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return targetDataSource.isWrapperFor(iface);
}
@Override
public PrintWriter getLogWriter() throws SQLException {
return targetDataSource.getLogWriter();
}
@Override
public void setLogWriter(PrintWriter out) throws SQLException {
targetDataSource.setLogWriter(out);
}
@Override
public void setLoginTimeout(int seconds) throws SQLException {
targetDataSource.setLoginTimeout(seconds);
}
@Override
public int getLoginTimeout() throws SQLException {
return targetDataSource.getLoginTimeout();
}
@Override
public Logger getParentLogger() throws SQLFeatureNotSupportedException {
return targetDataSource.getParentLogger();
}
}

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(3)Seata的数据源连接池代理DataSourceProxy的变量和初始化
初始化数据源连接池代理DataSourceProxy的具体逻辑是：首先从目标数据库连接池dataSource中获取一个数据库连接，然后根据这个数据库连接Connection去初始化jdbcUrl和dbType，接着根据数据库连接地址jdbcUrl初始化resourceId，然后把当前数据库连接池代理DataSourceProxy作为一个资源注册到默认的RM即DefaultResourceManager里去，最后设置RootContext上下文即线程本地变量副本中的分支事务类型。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {
private static final Logger LOGGER = LoggerFactory.getLogger(DataSourceProxy.class);
//默认资源分组ID
private static final String DEFAULT_RESOURCE_GROUP_ID = "DEFAULT";
//Enable the table meta checker，默认是不启用的
private static boolean ENABLE_TABLE_META_CHECKER_ENABLE = ConfigurationFactory.getInstance().getBoolean(ConfigurationKeys.CLIENT_TABLE_META_CHECK_ENABLE, DEFAULT_CLIENT_TABLE_META_CHECK_ENABLE);
//Table meta checker interval，默认是60s
private static final long TABLE_META_CHECKER_INTERVAL = ConfigurationFactory.getInstance().getLong(ConfigurationKeys.CLIENT_TABLE_META_CHECKER_INTERVAL, DEFAULT_TABLE_META_CHECKER_INTERVAL);
//资源组ID，比如MySQL部署了主从架构，主节点和从节点是两个数据源，但是关联到一个分组ID
private String resourceGroupId;
//代理的目标数据源连接url，这个数据源连接url也可以作为resourceId
private String jdbcUrl;
//数据源ID，比如数据库连接url就可以作为一个数据源ID
private String resourceId;
//数据源类型
private String dbType;
//数据源连接用户名
private String userName;
//定时调度的线程池，定时检查表里的元数据
private final ScheduledExecutorService tableMetaExecutor = new ScheduledThreadPoolExecutor(1, new NamedThreadFactory("tableMetaChecker", 1, true));
//Instantiates a new Data source proxy.
public DataSourceProxy(DataSource targetDataSource) {
this(targetDataSource, DEFAULT_RESOURCE_GROUP_ID);
}
//Instantiates a new Data source proxy.
//@param targetDataSource the target data source
//@param resourceGroupId the resource group id
public DataSourceProxy(DataSource targetDataSource, String resourceGroupId) {
if (targetDataSource instanceof SeataDataSourceProxy) {
LOGGER.info("Unwrap the target data source, because the type is: {}", targetDataSource.getClass().getName());
targetDataSource = ((SeataDataSourceProxy) targetDataSource).getTargetDataSource();
}
this.targetDataSource = targetDataSource;
init(targetDataSource, resourceGroupId);
}
//初始化数据源连接池代理DataSourceProxy
private void init(DataSource dataSource, String resourceGroupId) {
//资源分组ID
this.resourceGroupId = resourceGroupId;
//从目标数据库连接池dataSource中，获取一个数据库连接
try (Connection connection = dataSource.getConnection()) {
//获取数据库连接connection里的元数据的连接url
jdbcUrl = connection.getMetaData().getURL();
//根据连接url获取到数据库类型
dbType = JdbcUtils.getDbType(jdbcUrl);
if (JdbcConstants.ORACLE.equals(dbType)) {
//如果数据库类型等于oracle，则需要获取数据库连接connection的元数据的用户名
userName = connection.getMetaData().getUserName();
} else if (JdbcConstants.MARIADB.equals(dbType)) {
//如果数据库类型等于mariadb，则需要对数据库类型进行赋值为MySQL
dbType = JdbcConstants.MYSQL;
}
} catch (SQLException e) {
throw new IllegalStateException("can not init dataSource", e);
}
//初始化资源ID，也就是获取数据库连接url来初始化resourceID
initResourceId();
//把当前数据库连接池代理，作为一个资源，注册到默认的RM里，也就是DefaultResourceManager
DefaultResourceManager.get().registerResource(this);
if (ENABLE_TABLE_META_CHECKER_ENABLE) {
tableMetaExecutor.scheduleAtFixedRate(() -> {
try (Connection connection = dataSource.getConnection()) {
TableMetaCacheFactory.getTableMetaCache(DataSourceProxy.this.getDbType()).refresh(connection, DataSourceProxy.this.getResourceId());
} catch (Exception ignore) {
}
}, 0, TABLE_META_CHECKER_INTERVAL, TimeUnit.MILLISECONDS);
}
//Set the default branch type to 'AT' in the RootContext.
//设置RootContext上下文，即线程本地变量副本中的分支事务类型
RootContext.setDefaultBranchType(this.getBranchType());
}
private void initResourceId() {
if (JdbcConstants.POSTGRESQL.equals(dbType)) {
initPGResourceId();
} else if (JdbcConstants.ORACLE.equals(dbType) && userName != null) {
initDefaultResourceId();
resourceId = resourceId + "/" + userName;
} else if (JdbcConstants.MYSQL.equals(dbType)) {
initMysqlResourceId();
} else {
initDefaultResourceId();
}
}
private void initMysqlResourceId() {
String startsWith = "jdbc:mysql:loadbalance://";
if (jdbcUrl.startsWith(startsWith)) {
String url;
if (jdbcUrl.contains("?")) {
url = jdbcUrl.substring(0, jdbcUrl.indexOf('?'));
} else {
url = jdbcUrl;
}
resourceId = url.replace(",", "|");
} else {
initDefaultResourceId();
}
}
...
}

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3.Client向Server发起注册RM的源码
初始化数据源连接池代理DataSourceProxy时，会将数据库连接池代理作为资源，注册到DefaultResourceManager资源管理器中。

而初始化DefaultResourceManager时，会通过SPI机制加载所有的ResourceManager。

因此在执行DataSourceProxy的init()方法进行初始化时，由于会调用DefaultResourceManager的registerResource()方法，所以最后会执行到DataSourceManager的registerResource()方法。

在DataSourceManager的registerResource()方法中，首先会把数据源连接池代理DataSourceProxy放入一个Map中进行缓存，然后通过RmNettyRemotingClient构造一个注册RM的请求把数据源连接池代理DataSourceProxy作为资源注册到Seata Server中。

public class DefaultResourceManager implements ResourceManager {
//all resource managers
protected static Map<BranchType, ResourceManager> resourceManagers = new ConcurrentHashMap<>();
private static class SingletonHolder {
private static DefaultResourceManager INSTANCE = new DefaultResourceManager();
}
//Get resource manager.
public static DefaultResourceManager get() {
return SingletonHolder.INSTANCE;
}
private DefaultResourceManager() {
initResourceManagers();
}
protected void initResourceManagers() {
//init all resource managers
//通过SPI加载所有的ResourceManager资源管理器
//比如：DataSourceManager、TCCResourceManager、SagaResourceManager、ResourceManagerXA
List<ResourceManager> allResourceManagers = EnhancedServiceLoader.loadAll(ResourceManager.class);
if (CollectionUtils.isNotEmpty(allResourceManagers)) {
for (ResourceManager rm : allResourceManagers) {
resourceManagers.put(rm.getBranchType(), rm);
}
}
}
@Override
public void registerResource(Resource resource) {
getResourceManager(resource.getBranchType()).registerResource(resource);
}
public ResourceManager getResourceManager(BranchType branchType) {
ResourceManager rm = resourceManagers.get(branchType);
if (rm == null) {
throw new FrameworkException("No ResourceManager for BranchType:" + branchType.name());
}
return rm;
}
...
}
//The type Data source manager.
//DataSourceManager是AT模式下的资源管理器
public class DataSourceManager extends AbstractResourceManager {
//异步化worker
private final AsyncWorker asyncWorker = new AsyncWorker(this);
//RM负责管理的一些resource资源
private final Map<String, Resource> dataSourceCache = new ConcurrentHashMap<>();
...
@Override
public void registerResource(Resource resource) {
DataSourceProxy dataSourceProxy = (DataSourceProxy) resource;
//根据资源ID和数据源代理，把数据源连接池代理DataSourceProxy放入到map里去
dataSourceCache.put(dataSourceProxy.getResourceId(), dataSourceProxy);
super.registerResource(dataSourceProxy);
}
...
}
public abstract class AbstractResourceManager implements ResourceManager {
...
@Override
public void registerResource(Resource resource) {
//通过RmNettyRemotingClient把RM注册到Seata Server中
RmNettyRemotingClient.getInstance().registerResource(resource.getResourceGroupId(), resource.getResourceId());
}
...
}

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4.Client向Server注册RM时的交互源码
(1)Client异步发送注册RM的请求给Server
(2)Server收到注册RM的请求后的处理及异步响应

(1)Client异步发送注册RM的请求给Server

public final class RmNettyRemotingClient extends AbstractNettyRemotingClient {
...
//Register new db key.
public void registerResource(String resourceGroupId, String resourceId) {
//Resource registration cannot be performed until the RM client is initialized
if (StringUtils.isBlank(transactionServiceGroup)) {
return;
}
if (getClientChannelManager().getChannels().isEmpty()) {
getClientChannelManager().reconnect(transactionServiceGroup);
return;
}
synchronized (getClientChannelManager().getChannels()) {
//向每一个Server发起注册
for (Map.Entry<String, Channel> entry : getClientChannelManager().getChannels().entrySet()) {
String serverAddress = entry.getKey();
Channel rmChannel = entry.getValue();
if (LOGGER.isInfoEnabled()) {
LOGGER.info("will register resourceId:{}", resourceId);
}
sendRegisterMessage(serverAddress, rmChannel, resourceId);
}
}
}
public void sendRegisterMessage(String serverAddress, Channel channel, String resourceId) {
RegisterRMRequest message = new RegisterRMRequest(applicationId, transactionServiceGroup);
message.setResourceIds(resourceId);
try {
//异步发送注册RM的请求
super.sendAsyncRequest(channel, message);
} catch (FrameworkException e) {
if (e.getErrcode() == FrameworkErrorCode.ChannelIsNotWritable && serverAddress != null) {
getClientChannelManager().releaseChannel(channel, serverAddress);
if (LOGGER.isInfoEnabled()) {
LOGGER.info("remove not writable channel:{}", channel);
}
} else {
LOGGER.error("register resource failed, channel:{},resourceId:{}", channel, resourceId, e);
}
}
}
...
}
public abstract class AbstractNettyRemotingClient extends AbstractNettyRemoting implements RemotingClient {
...
@Override
public void sendAsyncRequest(Channel channel, Object msg) {
if (channel == null) {
LOGGER.warn("sendAsyncRequest nothing, caused by null channel.");
return;
}
RpcMessage rpcMessage = buildRequestMessage(msg, msg instanceof HeartbeatMessage
? ProtocolConstants.MSGTYPE_HEARTBEAT_REQUEST
: ProtocolConstants.MSGTYPE_RESQUEST_ONEWAY);
if (rpcMessage.getBody() instanceof MergeMessage) {
mergeMsgMap.put(rpcMessage.getId(), (MergeMessage) rpcMessage.getBody());
}
super.sendAsync(channel, rpcMessage);
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
//rpc async request.
protected void sendAsync(Channel channel, RpcMessage rpcMessage) {
channelWritableCheck(channel, rpcMessage.getBody());
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("write message:" + rpcMessage.getBody() + ", channel:" + channel + ",active?" + channel.isActive() + ",writable?" + channel.isWritable() + ",isopen?" + channel.isOpen());
}
doBeforeRpcHooks(ChannelUtil.getAddressFromChannel(channel), rpcMessage);
channel.writeAndFlush(rpcMessage).addListener((ChannelFutureListener) future -> {
if (!future.isSuccess()) {
destroyChannel(future.channel());
}
});
}
...
}

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(2)Server收到注册RM的请求后的处理及异步响应

public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {
...
@ChannelHandler.Sharable
class ServerHandler extends ChannelDuplexHandler {
@Override
public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
if (!(msg instanceof RpcMessage)) {
return;
}
//接下来调用processMessage()方法对解码完毕的RpcMessage对象进行处理
processMessage(ctx, (RpcMessage) msg);
}
...
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
//Rpc message processing.
protected void processMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(String.format("%s msgId:%s, body:%s", this, rpcMessage.getId(), rpcMessage.getBody()));
}
Object body = rpcMessage.getBody();
if (body instanceof MessageTypeAware) {
MessageTypeAware messageTypeAware = (MessageTypeAware) body;
//根据消息类型获取到一个Pair对象，该Pair对象是由请求处理组件和请求处理线程池组成的
//processorTable里的内容，是NettyRemotingServer在初始化时，通过调用registerProcessor()方法put进去的
final Pair<RemotingProcessor, ExecutorService> pair = this.processorTable.get((int) messageTypeAware.getTypeCode());
if (pair != null) {
if (pair.getSecond() != null) {
try {
pair.getSecond().execute(() -> {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
} finally {
MDC.clear();
}
});
} catch (RejectedExecutionException e) {
...
}
} else {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
}
}
} else {
LOGGER.error("This message type [{}] has no processor.", messageTypeAware.getTypeCode());
}
} else {
LOGGER.error("This rpcMessage body[{}] is not MessageTypeAware type.", body);
}
}
...
}
public class RegRmProcessor implements RemotingProcessor {
...
@Override
public void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
onRegRmMessage(ctx, rpcMessage);
}
private void onRegRmMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) {
RegisterRMRequest message = (RegisterRMRequest) rpcMessage.getBody();
//获取请求的发送地址
String ipAndPort = NetUtil.toStringAddress(ctx.channel().remoteAddress());
boolean isSuccess = false;
String errorInfo = StringUtils.EMPTY;
try {
if (null == checkAuthHandler || checkAuthHandler.regResourceManagerCheckAuth(message)) {
//通过Channel管理组件ChannelManager，注册RM网络连接
ChannelManager.registerRMChannel(message, ctx.channel());
Version.putChannelVersion(ctx.channel(), message.getVersion());
isSuccess = true;
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("RM checkAuth for client:{},vgroup:{},applicationId:{} is OK", ipAndPort, message.getTransactionServiceGroup(), message.getApplicationId());
}
} else {
if (LOGGER.isWarnEnabled()) {
LOGGER.warn("RM checkAuth for client:{},vgroup:{},applicationId:{} is FAIL", ipAndPort, message.getTransactionServiceGroup(), message.getApplicationId());
}
}
} catch (Exception exx) {
isSuccess = false;
errorInfo = exx.getMessage();
LOGGER.error("RM register fail, error message:{}", errorInfo);
}
RegisterRMResponse response = new RegisterRMResponse(isSuccess);
if (StringUtils.isNotEmpty(errorInfo)) {
response.setMsg(errorInfo);
}
//返回响应给客户端
remotingServer.sendAsyncResponse(rpcMessage, ctx.channel(), response);
if (isSuccess && LOGGER.isInfoEnabled()) {
LOGGER.info("RM register success,message:{},channel:{},client version:{}", message, ctx.channel(), message.getVersion());
}
}
...
}
public class ChannelManager {
...
public static void registerRMChannel(RegisterRMRequest resourceManagerRequest, Channel channel) throws IncompatibleVersionException {
Version.checkVersion(resourceManagerRequest.getVersion());
Set<String> dbkeySet = dbKeytoSet(resourceManagerRequest.getResourceIds());
RpcContext rpcContext;
if (!IDENTIFIED_CHANNELS.containsKey(channel)) {
rpcContext = buildChannelHolder(NettyPoolKey.TransactionRole.RMROLE, resourceManagerRequest.getVersion(),
resourceManagerRequest.getApplicationId(), resourceManagerRequest.getTransactionServiceGroup(),
resourceManagerRequest.getResourceIds(), channel);
rpcContext.holdInIdentifiedChannels(IDENTIFIED_CHANNELS);
} else {
rpcContext = IDENTIFIED_CHANNELS.get(channel);
rpcContext.addResources(dbkeySet);
}
if (dbkeySet == null || dbkeySet.isEmpty()) {
return;
}
for (String resourceId : dbkeySet) {
String clientIp;
ConcurrentMap<Integer, RpcContext> portMap =
CollectionUtils.computeIfAbsent(RM_CHANNELS, resourceId, key -> new ConcurrentHashMap<>())
.computeIfAbsent(resourceManagerRequest.getApplicationId(), key -> new ConcurrentHashMap<>())
.computeIfAbsent(clientIp = ChannelUtil.getClientIpFromChannel(channel), key -> new ConcurrentHashMap<>());
rpcContext.holdInResourceManagerChannels(resourceId, portMap);
updateChannelsResource(resourceId, clientIp, resourceManagerRequest.getApplicationId());
}
}
...
}
public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {
...
@Override
public void sendAsyncResponse(RpcMessage rpcMessage, Channel channel, Object msg) {
Channel clientChannel = channel;
if (!(msg instanceof HeartbeatMessage)) {
clientChannel = ChannelManager.getSameClientChannel(channel);
}
if (clientChannel != null) {
RpcMessage rpcMsg = buildResponseMessage(rpcMessage, msg, msg instanceof HeartbeatMessage
? ProtocolConstants.MSGTYPE_HEARTBEAT_RESPONSE : ProtocolConstants.MSGTYPE_RESPONSE);
super.sendAsync(clientChannel, rpcMsg);
} else {
throw new RuntimeException("channel is error.");
}
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
//rpc async request.
protected void sendAsync(Channel channel, RpcMessage rpcMessage) {
channelWritableCheck(channel, rpcMessage.getBody());
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("write message:" + rpcMessage.getBody() + ", channel:" + channel + ",active?" + channel.isActive() + ",writable?" + channel.isWritable() + ",isopen?" + channel.isOpen());
}
doBeforeRpcHooks(ChannelUtil.getAddressFromChannel(channel), rpcMessage);
channel.writeAndFlush(rpcMessage).addListener((ChannelFutureListener) future -> {
if (!future.isSuccess()) {
destroyChannel(future.channel());
}
});
}
...
}

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5.数据源连接代理与SQL句柄代理的初始化源码
(1)数据库操作的三剑客之连接、句柄和结果
(2)数据源连接代理的初始化
(3)数据源连接代理对SQL进行预编译
(4)SQL句柄代理的初始化
(5)SQL句柄代理执行SQL

(1)数据库操作的三剑客之连接、句柄和结果
Seata Client或者Seata Server进行数据库操作的大致流程如下所示：

public class LogStoreDataBaseDAO implements LogStore {
//The Log store data source. 数据源连接池
protected DataSource logStoreDataSource = null;
...
@Override
public GlobalTransactionDO queryGlobalTransactionDO(long transactionId) {
String sql = LogStoreSqlsFactory.getLogStoreSqls(dbType).getQueryGlobalTransactionSQLByTransactionId(globalTable);
Connection conn = null;//连接
PreparedStatement ps = null;//句柄
ResultSet rs = null;//结果
try {
//1.从数据源连接池中获取数据源连接
conn = logStoreDataSource.getConnection();
conn.setAutoCommit(true);
//2.对sql语句进行预编译
ps = conn.prepareStatement(sql);
ps.setLong(1, transactionId);
//3.执行sql语句
rs = ps.executeQuery();
if (rs.next()) {
return convertGlobalTransactionDO(rs);
} else {
return null;
}
} catch (SQLException e) {
throw new DataAccessException(e);
} finally {
IOUtil.close(rs, ps, conn);
}
}
...
}

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(2)数据源连接代理的初始化
Seata Client或者Seata Server进行数据库操作时，首先会通过数据库连接池代理DataSourceProxy获取数据库连接，也就是会通过DataSourceProxy的getConnection()方法获取数据源连接代理ConnectionProxy，其中就会根据获取到的一个数据源连接Connection初始化一个数据源连接代理ConnectionProxy。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {
...
@Override
public ConnectionProxy getConnection() throws SQLException {
//从目标数据源连接池中获取一个数据库连接，然后封装到ConnectionProxy数据源连接代理中，并进行返回
Connection targetConnection = targetDataSource.getConnection();
return new ConnectionProxy(this, targetConnection);
}
@Override
public ConnectionProxy getConnection(String username, String password) throws SQLException {
//从目标数据源连接池中获取一个数据库连接，然后封装到ConnectionProxy数据源连接代理中，并进行返回
Connection targetConnection = targetDataSource.getConnection(username, password);
return new ConnectionProxy(this, targetConnection);
}
...
}
public class ConnectionProxy extends AbstractConnectionProxy {
//Instantiates a new Connection proxy.
public ConnectionProxy(DataSourceProxy dataSourceProxy, Connection targetConnection) {
super(dataSourceProxy, targetConnection);
}
...
}
public abstract class AbstractConnectionProxy implements Connection {
//The Data source proxy. 数据源连接池代理
protected DataSourceProxy dataSourceProxy;
//The Target connection. 目标数据源连接
protected Connection targetConnection;
//Instantiates a new Abstract connection proxy.
public AbstractConnectionProxy(DataSourceProxy dataSourceProxy, Connection targetConnection) {
this.dataSourceProxy = dataSourceProxy;
this.targetConnection = targetConnection;
}
...
}

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(3)数据源连接代理对SQL进行预编译
数据源连接代理ConnectionProxy在进行数据库操作时，获取到数据库连接Connection之后，就需要对要执行的SQL进行预编译，也就是会调用AbstractConnectionProxy的prepareStatement()方法。

public abstract class AbstractConnectionProxy implements Connection {
...
//对SQL进行预编译
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
String dbType = getDbType();
//support oracle 10.2+
PreparedStatement targetPreparedStatement = null;
//如果是AT模式
if (BranchType.AT == RootContext.getBranchType()) {
List<SQLRecognizer> sqlRecognizers = SQLVisitorFactory.get(sql, dbType);
if (sqlRecognizers != null && sqlRecognizers.size() == 1) {
SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);
if (sqlRecognizer != null && sqlRecognizer.getSQLType() == SQLType.INSERT) {
TableMeta tableMeta = TableMetaCacheFactory.getTableMetaCache(dbType).getTableMeta(
getTargetConnection(),
sqlRecognizer.getTableName(), getDataSourceProxy().getResourceId()
);
String[] pkNameArray = new String[tableMeta.getPrimaryKeyOnlyName().size()];
tableMeta.getPrimaryKeyOnlyName().toArray(pkNameArray);
targetPreparedStatement = getTargetConnection().prepareStatement(sql, pkNameArray);
}
}
}
if (targetPreparedStatement == null) {
targetPreparedStatement = getTargetConnection().prepareStatement(sql);
}
//返回一个SQL句柄代理
return new PreparedStatementProxy(this, targetPreparedStatement, sql);
}
...
}

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(4)SQL句柄代理的初始化
SQL句柄代理PreparedStatementProxy的初始化主要是设置目标SQL、目标句柄和数据源连接代理。

public class PreparedStatementProxy extends AbstractPreparedStatementProxy implements PreparedStatement, ParametersHolder {
//Instantiates a new Prepared statement proxy.
public PreparedStatementProxy(AbstractConnectionProxy connectionProxy, PreparedStatement targetStatement, String targetSQL) throws SQLException {
super(connectionProxy, targetStatement, targetSQL);
}
...
}
public abstract class AbstractPreparedStatementProxy extends StatementProxy<PreparedStatement> implements PreparedStatement {
protected Map<Integer, ArrayList<Object>> parameters;
private void initParameterHolder() {
this.parameters = new HashMap<>();
}
//Instantiates a new Abstract prepared statement proxy.
public AbstractPreparedStatementProxy(AbstractConnectionProxy connectionProxy, PreparedStatement targetStatement, String targetSQL) throws SQLException {
super(connectionProxy, targetStatement, targetSQL);
initParameterHolder();
}
...
}
public class StatementProxy<T extends Statement> extends AbstractStatementProxy<T> {
//Instantiates a new Statement proxy.
public StatementProxy(AbstractConnectionProxy connectionWrapper, T targetStatement, String targetSQL) throws SQLException {
super(connectionWrapper, targetStatement, targetSQL);
}
...
}
public abstract class AbstractStatementProxy<T extends Statement> implements Statement {
//The Connection proxy.
protected AbstractConnectionProxy connectionProxy;
//The Target statement.
protected T targetStatement;
//The Target sql.
protected String targetSQL;
...
//Instantiates a new Abstract statement proxy.
public AbstractStatementProxy(AbstractConnectionProxy connectionProxy, T targetStatement, String targetSQL) throws SQLException {
this.connectionProxy = connectionProxy;
this.targetStatement = targetStatement;
this.targetSQL = targetSQL;
}
...
}

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(5)SQL句柄代理执行SQL
从数据源连接池中获取到数据源连接，以及对SQL语句进行预编译后，就可以调用SQL句柄代理PreparedStatementProxy的executeQuery()等方法执行SQL语句。

6.Seata基于SQL句柄代理执行SQL的源码
(1)Spring的JdbcTemplate操作数据库的三剑客
(2)基于SQL句柄代理执行SQL的流程

(1)Spring的JdbcTemplate操作数据库的三剑客
连接、句柄和结果。

@Disabled
public class LocalTransactionWithGlobalLockDataSourceBasicTest {
private static ClassPathXmlApplicationContext context;
private static JdbcTemplate jdbcTemplate;
@BeforeAll
public static void before() {
context = new ClassPathXmlApplicationContext("basic-test-context.xml");
jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");
}
@Test
public void testInsert() {
RootContext.bindGlobalLockFlag();
jdbcTemplate.update("insert into user0 (id, name, gmt) values (?, ?, ?)", new Object[]{2, "xxx", new Date()});
}
...
}
public class JdbcTemplate extends JdbcAccessor implements JdbcOperations {
...
@Override
public int update(String sql, @Nullable Object... args) throws DataAccessException {
return update(sql, newArgPreparedStatementSetter(args));
}
@Override
public int update(String sql, @Nullable PreparedStatementSetter pss) throws DataAccessException {
return update(new SimplePreparedStatementCreator(sql), pss);
}
protected int update(final PreparedStatementCreator psc, @Nullable final PreparedStatementSetter pss) throws DataAccessException {
logger.debug("Executing prepared SQL update");
return updateCount(execute(psc, ps -> {
try {
if (pss != null) {
pss.setValues(ps);
}
//PreparedStatement执行SQL
int rows = ps.executeUpdate();
if (logger.isTraceEnabled()) {
logger.trace("SQL update affected " + rows + " rows");
}
return rows;
} finally {
if (pss instanceof ParameterDisposer) {
((ParameterDisposer) pss).cleanupParameters();
}
}
}, true));
}
@Nullable
private <T> T execute(PreparedStatementCreator psc, PreparedStatementCallback<T> action, boolean closeResources) throws DataAccessException {
Assert.notNull(psc, "PreparedStatementCreator must not be null");
Assert.notNull(action, "Callback object must not be null");
if (logger.isDebugEnabled()) {
String sql = getSql(psc);
logger.debug("Executing prepared SQL statement" + (sql != null ? " [" + sql + "]" : ""));
}
//1.获取连接
Connection con = DataSourceUtils.getConnection(obtainDataSource());
PreparedStatement ps = null;
try {
//2.创建句柄
ps = psc.createPreparedStatement(con);
applyStatementSettings(ps);
//3.执行SQL的结果
T result = action.doInPreparedStatement(ps);
handleWarnings(ps);
return result;
} catch (SQLException ex) {
if (psc instanceof ParameterDisposer) {
((ParameterDisposer) psc).cleanupParameters();
}
String sql = getSql(psc);
psc = null;
JdbcUtils.closeStatement(ps);
ps = null;
DataSourceUtils.releaseConnection(con, getDataSource());
con = null;
throw translateException("PreparedStatementCallback", sql, ex);
} finally {
if (closeResources) {
if (psc instanceof ParameterDisposer) {
((ParameterDisposer) psc).cleanupParameters();
}
JdbcUtils.closeStatement(ps);
DataSourceUtils.releaseConnection(con, getDataSource());
}
}
}
...
}

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(2)基于SQL句柄代理执行SQL的流程
SQL句柄代理PreparedStatementProxy在调用execute()方法执行SQL时，就会调用到ExecuteTemplate执行模版的execute()方法。

而ExecuteTemplate执行模版的execute()方法，如果发现不需要全局锁 + 没有开启全局事务，那么就普通执行本地事务。否则，最终就会调用到BaseTransactionalExecutor的excute()方法。

在BaseTransactionalExecutor的excute()方法中，首先会从线程本地变量副本中获取xid，然后再执行SQL。

public class PreparedStatementProxy extends AbstractPreparedStatementProxy implements PreparedStatement, ParametersHolder {
...
@Override
public boolean execute() throws SQLException {
return ExecuteTemplate.execute(this, (statement, args) -> statement.execute());
}
@Override
public ResultSet executeQuery() throws SQLException {
return ExecuteTemplate.execute(this, (statement, args) -> statement.executeQuery());
}
@Override
public int executeUpdate() throws SQLException {
return ExecuteTemplate.execute(this, (statement, args) -> statement.executeUpdate());
}
...
}
public class ExecuteTemplate {
...
public static <T, S extends Statement> T execute(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, Object... args) throws SQLException {
return execute(null, statementProxy, statementCallback, args);
}
public static <T, S extends Statement> T execute(List<SQLRecognizer> sqlRecognizers, StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, Object... args) throws SQLException {
//如果发现不需要全局锁，而且没有开启AT模式下的全局事务，那么就普通执行本地事务
if (!RootContext.requireGlobalLock() && BranchType.AT != RootContext.getBranchType()) {
//Just work as original statement
return statementCallback.execute(statementProxy.getTargetStatement(), args);
}
//获取到DB的类型
String dbType = statementProxy.getConnectionProxy().getDbType();
if (CollectionUtils.isEmpty(sqlRecognizers)) {
sqlRecognizers = SQLVisitorFactory.get(statementProxy.getTargetSQL(), dbType);
}
Executor<T> executor;
if (CollectionUtils.isEmpty(sqlRecognizers)) {
executor = new PlainExecutor<>(statementProxy, statementCallback);
} else {
if (sqlRecognizers.size() == 1) {
SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);
switch (sqlRecognizer.getSQLType()) {
case INSERT:
//通过SPI机制加载InsertExecutor
executor = EnhancedServiceLoader.load(InsertExecutor.class, dbType, new Class[]{StatementProxy.class, StatementCallback.class, SQLRecognizer.class}, new Object[]{statementProxy, statementCallback, sqlRecognizer});
break;
case UPDATE:
executor = new UpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);
break;
case DELETE:
executor = new DeleteExecutor<>(statementProxy, statementCallback, sqlRecognizer);
break;
case SELECT_FOR_UPDATE:
executor = new SelectForUpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);
break;
case INSERT_ON_DUPLICATE_UPDATE:
switch (dbType) {
case JdbcConstants.MYSQL:
case JdbcConstants.MARIADB:
executor = new MySQLInsertOrUpdateExecutor(statementProxy, statementCallback, sqlRecognizer);
break;
default:
throw new NotSupportYetException(dbType + " not support to INSERT_ON_DUPLICATE_UPDATE");
}
break;
default:
executor = new PlainExecutor<>(statementProxy, statementCallback);
break;
}
} else {
executor = new MultiExecutor<>(statementProxy, statementCallback, sqlRecognizers);
}
}
T rs;
try {
//比如下面最终会调用BaseTransactionalExecutor.excute()方法
rs = executor.execute(args);
} catch (Throwable ex) {
if (!(ex instanceof SQLException)) {
// Turn other exception into SQLException
ex = new SQLException(ex);
}
throw (SQLException) ex;
}
return rs;
}
...
}
@LoadLevel(name = JdbcConstants.MYSQL, scope = Scope.PROTOTYPE)
public class MySQLInsertExecutor extends BaseInsertExecutor implements Defaultable {
...
//Instantiates a new Abstract dml base executor.
public MySQLInsertExecutor(StatementProxy statementProxy, StatementCallback statementCallback, SQLRecognizer sqlRecognizer) {
super(statementProxy, statementCallback, sqlRecognizer);
}
...
}
public abstract class BaseInsertExecutor<T, S extends Statement> extends AbstractDMLBaseExecutor<T, S> implements InsertExecutor<T> {
...
public BaseInsertExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {
super(statementProxy, statementCallback, sqlRecognizer);
}
...
}
public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {
...
public AbstractDMLBaseExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {
super(statementProxy, statementCallback, sqlRecognizer);
}
@Override
public T doExecute(Object... args) throws Throwable {
AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
//判断是否是自动提交本地事务，默认情况本地事务都是自动提交的，此时需要阻止自动提交
if (connectionProxy.getAutoCommit()) {
return executeAutoCommitTrue(args);
} else {
return executeAutoCommitFalse(args);
}
}
...
}
public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {
//The Statement proxy.
protected StatementProxy<S> statementProxy;
//The Statement callback.
protected StatementCallback<T, S> statementCallback;
//The Sql recognizer.
protected SQLRecognizer sqlRecognizer;
...
public BaseTransactionalExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback,
SQLRecognizer sqlRecognizer) {
this.statementProxy = statementProxy;
this.statementCallback = statementCallback;
this.sqlRecognizer = sqlRecognizer;
}
...
@Override
public T execute(Object... args) throws Throwable {
//获取xid
String xid = RootContext.getXID();
if (xid != null) {
statementProxy.getConnectionProxy().bind(xid);
}
statementProxy.getConnectionProxy().setGlobalLockRequire(RootContext.requireGlobalLock());
return doExecute(args);
}
//Do execute object.
protected abstract T doExecute(Object... args) throws Throwable;
...
}

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7.执行SQL语句前取消自动提交事务的源码
执行ExecuteTemplate执行模版的execute()方法时，最终会调用到BaseTransactionalExecutor基础事务执行器的excute()方法。

执行BaseTransactionalExecutor的execute()方法时，又会执行到AbstractDMLBaseExecutor的doExecute()方法。该方法会判断目标数据库连接是否会自动提交本地事务，默认情况下本地事务都是自动提交的。如果是，则取消自动提交本地事务。

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {
//The Statement proxy.
protected StatementProxy<S> statementProxy;
//The Statement callback.
protected StatementCallback<T, S> statementCallback;
//The Sql recognizer.
protected SQLRecognizer sqlRecognizer;
...
public BaseTransactionalExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback,
SQLRecognizer sqlRecognizer) {
this.statementProxy = statementProxy;
this.statementCallback = statementCallback;
this.sqlRecognizer = sqlRecognizer;
}
...
@Override
public T execute(Object... args) throws Throwable {
//获取xid
String xid = RootContext.getXID();
if (xid != null) {
statementProxy.getConnectionProxy().bind(xid);
}
statementProxy.getConnectionProxy().setGlobalLockRequire(RootContext.requireGlobalLock());
return doExecute(args);
}
//Do execute object.
protected abstract T doExecute(Object... args) throws Throwable;
...
}
public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {
...
public AbstractDMLBaseExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {
super(statementProxy, statementCallback, sqlRecognizer);
}
@Override
public T doExecute(Object... args) throws Throwable {
AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
//判断是否是自动提交本地事务，默认情况本地事务都是自动提交的，此时需要阻止自动提交
if (connectionProxy.getAutoCommit()) {
return executeAutoCommitTrue(args);
} else {
return executeAutoCommitFalse(args);
}
}
...
}
public abstract class AbstractConnectionProxy implements Connection {
...
@Override
public boolean getAutoCommit() throws SQLException {
//判断目标数据库连接是否是自动提交，默认情况是都是自动提交的
return targetConnection.getAutoCommit();
}
...
}
public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {
...
//Execute auto commit true t.
protected T executeAutoCommitTrue(Object[] args) throws Throwable {
ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
try {
//修改自动提交事务的设置，此时需要阻止自动提交事务
connectionProxy.changeAutoCommit();
return new LockRetryPolicy(connectionProxy).execute(() -> {
T result = executeAutoCommitFalse(args);//执行SQL语句
connectionProxy.commit();//手动提交本地事务
return result;
});
} catch (Exception e) {
//when exception occur in finally,this exception will lost, so just print it here
LOGGER.error("execute executeAutoCommitTrue error:{}", e.getMessage(), e);
if (!LockRetryPolicy.isLockRetryPolicyBranchRollbackOnConflict()) {
connectionProxy.getTargetConnection().rollback();
}
throw e;
} finally {
connectionProxy.getContext().reset();
connectionProxy.setAutoCommit(true);
}
}
...
}
public class ConnectionProxy extends AbstractConnectionProxy {
private final ConnectionContext context = new ConnectionContext();
...
//change connection autoCommit to false by seata
public void changeAutoCommit() throws SQLException {
getContext().setAutoCommitChanged(true);
setAutoCommit(false);
}
//Gets context.
public ConnectionContext getContext() {
return context;
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
if ((context.inGlobalTransaction() || context.isGlobalLockRequire()) && autoCommit && !getAutoCommit()) {
//change autocommit from false to true, we should commit() first according to JDBC spec.
doCommit();
}
//把目标数据源连接的自动提交事务设置为false
targetConnection.setAutoCommit(autoCommit);
}
...
}

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8.执行SQL语句前后构建数据镜像的源码
(1)AbstractDMLBaseExecutor的doExecute()方法的执行流程
(2)以UpdateExecuto为例构建前后镜像

(1)AbstractDMLBaseExecutor的doExecute()方法的执行流程
一.首先设置数据源连接阻止其自动提交事务
二.根据目标SQL语句构建beforeImage前镜像
三.执行目标SQL语句(但还没提交其对应的事务)
四.根据beforeImage前镜像构建afterImage后镜像
五.根据前镜像和后镜像构建UndoLog数据
六.手动提交数据源连接代理的事务

public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {
...
//Execute auto commit true t.
protected T executeAutoCommitTrue(Object[] args) throws Throwable {
ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
try {
//修改数据源连接的自动提交事务的设置，此时需要阻止自动提交事务
connectionProxy.changeAutoCommit();
return new LockRetryPolicy(connectionProxy).execute(() -> {
T result = executeAutoCommitFalse(args);//执行SQL语句
connectionProxy.commit();//手动提交本地事务
return result;
});
} catch (Exception e) {
// when exception occur in finally,this exception will lost, so just print it here
LOGGER.error("execute executeAutoCommitTrue error:{}", e.getMessage(), e);
if (!LockRetryPolicy.isLockRetryPolicyBranchRollbackOnConflict()) {
connectionProxy.getTargetConnection().rollback();
}
throw e;
} finally {
connectionProxy.getContext().reset();
connectionProxy.setAutoCommit(true);
}
}
//Execute auto commit false t.
protected T executeAutoCommitFalse(Object[] args) throws Exception {
if (!JdbcConstants.MYSQL.equalsIgnoreCase(getDbType()) && isMultiPk()) {
throw new NotSupportYetException("multi pk only support mysql!");
}
//根据目标SQL语句构建beforeImage，表示目标SQL执行前的数据镜像
TableRecords beforeImage = beforeImage();
//接下来真正去执行这条SQL语句，但是此时本地事务还不会提交
T result = statementCallback.execute(statementProxy.getTargetStatement(), args);
int updateCount = statementProxy.getUpdateCount();
if (updateCount > 0) {
//根据beforeImage构建afterImage，表示目标SQL执行后的数据镜像
TableRecords afterImage = afterImage(beforeImage);
//根据beforeImage和afterImage准备undoLog数据到数据源连接代理中
prepareUndoLog(beforeImage, afterImage);
}
return result;
}
...
}

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(2)以UpdateExecutor为例构建前后镜像

public class TableRecords implements java.io.Serializable {
//表的元数据
private transient TableMeta tableMeta;
//表的名称
private String tableName;
//表的多行数据
private List<Row> rows = new ArrayList<Row>();
...
}
public class UpdateExecutor<T, S extends Statement> extends AbstractDMLBaseExecutor<T, S> {
private static final Configuration CONFIG = ConfigurationFactory.getInstance();
private static final boolean ONLY_CARE_UPDATE_COLUMNS = CONFIG.getBoolean(ConfigurationKeys.TRANSACTION_UNDO_ONLY_CARE_UPDATE_COLUMNS, DefaultValues.DEFAULT_ONLY_CARE_UPDATE_COLUMNS);
//Instantiates a new Update executor.
public UpdateExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {
super(statementProxy, statementCallback, sqlRecognizer);
}
@Override
protected TableRecords beforeImage() throws SQLException {
ArrayList<List<Object>> paramAppenderList = new ArrayList<>();
TableMeta tmeta = getTableMeta();
//根据主键ID值拼接一个SQL语句，查询这条数据更新前的镜像
String selectSQL = buildBeforeImageSQL(tmeta, paramAppenderList);
return buildTableRecords(tmeta, selectSQL, paramAppenderList);
}
private String buildBeforeImageSQL(TableMeta tableMeta, ArrayList<List<Object>> paramAppenderList) {
SQLUpdateRecognizer recognizer = (SQLUpdateRecognizer) sqlRecognizer;
List<String> updateColumns = recognizer.getUpdateColumns();
StringBuilder prefix = new StringBuilder("SELECT ");
StringBuilder suffix = new StringBuilder(" FROM ").append(getFromTableInSQL());
String whereCondition = buildWhereCondition(recognizer, paramAppenderList);
String orderByCondition = buildOrderCondition(recognizer, paramAppenderList);
String limitCondition = buildLimitCondition(recognizer, paramAppenderList);
if (StringUtils.isNotBlank(whereCondition)) {
suffix.append(WHERE).append(whereCondition);
}
if (StringUtils.isNotBlank(orderByCondition)) {
suffix.append(" ").append(orderByCondition);
}
if (StringUtils.isNotBlank(limitCondition)) {
suffix.append(" ").append(limitCondition);
}
suffix.append(" FOR UPDATE");
StringJoiner selectSQLJoin = new StringJoiner(", ", prefix.toString(), suffix.toString());
if (ONLY_CARE_UPDATE_COLUMNS) {
if (!containsPK(updateColumns)) {
selectSQLJoin.add(getColumnNamesInSQL(tableMeta.getEscapePkNameList(getDbType())));
}
for (String columnName : updateColumns) {
selectSQLJoin.add(columnName);
}
//The on update xxx columns will be auto update by db, so it's also the actually updated columns
List<String> onUpdateColumns = tableMeta.getOnUpdateColumnsOnlyName();
onUpdateColumns.removeAll(updateColumns);
for (String onUpdateColumn : onUpdateColumns) {
selectSQLJoin.add(ColumnUtils.addEscape(onUpdateColumn, getDbType()));
}
} else {
for (String columnName : tableMeta.getAllColumns().keySet()) {
selectSQLJoin.add(ColumnUtils.addEscape(columnName, getDbType()));
}
}
return selectSQLJoin.toString();
}
@Override
protected TableRecords afterImage(TableRecords beforeImage) throws SQLException {
TableMeta tmeta = getTableMeta();
if (beforeImage == null || beforeImage.size() == 0) {
return TableRecords.empty(getTableMeta());
}
String selectSQL = buildAfterImageSQL(tmeta, beforeImage);
ResultSet rs = null;
try (PreparedStatement pst = statementProxy.getConnection().prepareStatement(selectSQL)) {
SqlGenerateUtils.setParamForPk(beforeImage.pkRows(), getTableMeta().getPrimaryKeyOnlyName(), pst);
rs = pst.executeQuery();
return TableRecords.buildRecords(tmeta, rs);
} finally {
IOUtil.close(rs);
}
}
private String buildAfterImageSQL(TableMeta tableMeta, TableRecords beforeImage) throws SQLException {
StringBuilder prefix = new StringBuilder("SELECT ");
String whereSql = SqlGenerateUtils.buildWhereConditionByPKs(tableMeta.getPrimaryKeyOnlyName(), beforeImage.pkRows().size(), getDbType());
String suffix = " FROM " + getFromTableInSQL() + " WHERE " + whereSql;
StringJoiner selectSQLJoiner = new StringJoiner(", ", prefix.toString(), suffix);
if (ONLY_CARE_UPDATE_COLUMNS) {
SQLUpdateRecognizer recognizer = (SQLUpdateRecognizer) sqlRecognizer;
List<String> updateColumns = recognizer.getUpdateColumns();
if (!containsPK(updateColumns)) {
selectSQLJoiner.add(getColumnNamesInSQL(tableMeta.getEscapePkNameList(getDbType())));
}
for (String columnName : updateColumns) {
selectSQLJoiner.add(columnName);
}
//The on update xxx columns will be auto update by db, so it's also the actually updated columns
List<String> onUpdateColumns = tableMeta.getOnUpdateColumnsOnlyName();
onUpdateColumns.removeAll(updateColumns);
for (String onUpdateColumn : onUpdateColumns) {
selectSQLJoiner.add(ColumnUtils.addEscape(onUpdateColumn, getDbType()));
}
} else {
for (String columnName : tableMeta.getAllColumns().keySet()) {
selectSQLJoiner.add(ColumnUtils.addEscape(columnName, getDbType()));
}
}
return selectSQLJoiner.toString();
}
}

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9.构建全局锁的key和UndoLog数据的源码
(1)prepareUndoLog()方法会构建全局锁的key和UndoLog数据
(2)构建全局锁的key的源码
(3)构建UndoLog数据的源码

(1)prepareUndoLog()方法会构建全局锁的key和UndoLog数据
在基础事务执行器BaseTransactionalExecutor的prepareUndoLog()方法中，会构建全局锁的key和构建UndoLog数据，并把它们设置到数据源连接代理ConnectionProxy中。

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {
...
//prepare undo log.
//@param beforeImage the before image
//@param afterImage the after image
protected void prepareUndoLog(TableRecords beforeImage, TableRecords afterImage) throws SQLException {
if (beforeImage.getRows().isEmpty() && afterImage.getRows().isEmpty()) {
return;
}
if (SQLType.UPDATE == sqlRecognizer.getSQLType()) {
if (beforeImage.getRows().size() != afterImage.getRows().size()) {
throw new ShouldNeverHappenException("Before image size is not equaled to after image size, probably because you updated the primary keys.");
}
}
ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
TableRecords lockKeyRecords = sqlRecognizer.getSQLType() == SQLType.DELETE ? beforeImage : afterImage;
//构建全局锁的key
//比如更新了一批数据，那么需要针对这批数据的主键ID，来构建这批数据的全局锁的key
String lockKeys = buildLockKey(lockKeyRecords);
if (null != lockKeys) {
//将全局锁key设置到数据源连接代理ConnectionProxy中
connectionProxy.appendLockKey(lockKeys);
//构建UndoLog
SQLUndoLog sqlUndoLog = buildUndoItem(beforeImage, afterImage);
//将UndoLog设置到数据源连接代理ConnectionProxy中
connectionProxy.appendUndoLog(sqlUndoLog);
}
}
...
}

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(2)构建全局锁的key的源码

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {
...
//build lockKey
//@param rowsIncludingPK the records
//@return the string as local key. the local key example(multi pk): "t_user:1_a,2_b"
protected String buildLockKey(TableRecords rowsIncludingPK) {
if (rowsIncludingPK.size() == 0) {
return null;
}
//构建出来的全局锁的key形式为：table_name:id_11001
StringBuilder sb = new StringBuilder();
sb.append(rowsIncludingPK.getTableMeta().getTableName());
sb.append(":");
int filedSequence = 0;
//pksRows指的是，更新的每一行数据主键字段和主键的值
List<Map<String, Field>> pksRows = rowsIncludingPK.pkRows();
//获取到主键字段名称，主键可能是联合主键，主键字段的名称可能有多个
List<String> primaryKeysOnlyName = getTableMeta().getPrimaryKeyOnlyName();
//rowMap就是一行数据，rowMap中的key是字段名称，value是字段值
for (Map<String, Field> rowMap : pksRows) {
int pkSplitIndex = 0;
//遍历和提取这行数据里多个主键字段的名称
for (String pkName : primaryKeysOnlyName) {
if (pkSplitIndex > 0) {
sb.append("_");
}
//获取到多个主键字段的value，然后拼接在一起
sb.append(rowMap.get(pkName).getValue());
pkSplitIndex++;
}
filedSequence++;
if (filedSequence < pksRows.size()) {
sb.append(",");
}
}
//最终拼成的key形如：table_name:1101_aadd,table_name:xxxx_xxx
return sb.toString();
}
...
}

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(3)构建UndoLog数据的源码

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {
...
//build a SQLUndoLog
//@param beforeImage the before image
//@param afterImage the after image
protected SQLUndoLog buildUndoItem(TableRecords beforeImage, TableRecords afterImage) {
SQLType sqlType = sqlRecognizer.getSQLType();
String tableName = sqlRecognizer.getTableName();
SQLUndoLog sqlUndoLog = new SQLUndoLog();
sqlUndoLog.setSqlType(sqlType);//SQL的类型可能为insert、update、delete
sqlUndoLog.setTableName(tableName);//表的名称
sqlUndoLog.setBeforeImage(beforeImage);//SQL执行前的数据镜像
sqlUndoLog.setAfterImage(afterImage);//SQL执行后的数据镜像
return sqlUndoLog;
}
...
}
public class SQLUndoLog implements java.io.Serializable {
private SQLType sqlType;
private String tableName;
private TableRecords beforeImage;
private TableRecords afterImage;
...
}

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10.Seata Client发起分支事务注册的源码
(1)ConnectionProxy.commit()提交事务
(2)ConnectionProxy.register()注册分支事务

(1)ConnectionProxy.commit()提交事务
执行数据源连接代理ConnectionProxy的commit()方法提交事务的时候，首先会先调用数据源连接代理ConnectionProxy的register()方法注册分支事务。

public class ConnectionProxy extends AbstractConnectionProxy {
private final ConnectionContext context = new ConnectionContext();
...
@Override
public void commit() throws SQLException {
try {
//通过全局锁重试策略组件来执行本地事务的提交
lockRetryPolicy.execute(() -> {
doCommit();
return null;
});
} catch (SQLException e) {
if (targetConnection != null && !getAutoCommit() && !getContext().isAutoCommitChanged()) {
rollback();
}
throw e;
} catch (Exception e) {
throw new SQLException(e);
}
}
private void doCommit() throws SQLException {
if (context.inGlobalTransaction()) {
processGlobalTransactionCommit();
} else if (context.isGlobalLockRequire()) {
processLocalCommitWithGlobalLocks();
} else {
targetConnection.commit();
}
}
private void processLocalCommitWithGlobalLocks() throws SQLException {
//检查全局锁keys
checkLock(context.buildLockKeys());
try {
//目标数据源连接提交事务
targetConnection.commit();
} catch (Throwable ex) {
throw new SQLException(ex);
}
context.reset();
}
private void processGlobalTransactionCommit() throws SQLException {
try {
//注册分支事务
register();
} catch (TransactionException e) {
recognizeLockKeyConflictException(e, context.buildLockKeys());
}
try {
UndoLogManagerFactory.getUndoLogManager(this.getDbType()).flushUndoLogs(this);
//目标数据源连接提交事务
targetConnection.commit();
} catch (Throwable ex) {
LOGGER.error("process connectionProxy commit error: {}", ex.getMessage(), ex);
report(false);
throw new SQLException(ex);
}
if (IS_REPORT_SUCCESS_ENABLE) {
report(true);
}
context.reset();
}
...
}

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(2)ConnectionProxy.register()注册分支事务
执行数据源连接代理ConnectionProxy的register()方法注册分支事务的时候，会调用资源管理器DefaultResourceManager的branchRegister()方法，然后会继续调用AbstractResourceManager的branchRegister()方法来注册分支事务。

在AbstractResourceManager的branchRegister()方法中，首先会构造分支事务注册请求，然后通过RmNettyRemotingClient将分支事务注册请求发送给Seata Server。

//The type Connection proxy.
//数据源连接代理
public class ConnectionProxy extends AbstractConnectionProxy {
private final ConnectionContext context = new ConnectionContext();
...
private void register() throws TransactionException {
if (!context.hasUndoLog() || !context.hasLockKey()) {
return;
}
//分支事务注册
Long branchId = DefaultResourceManager.get().branchRegister(
BranchType.AT,//事务类型
getDataSourceProxy().getResourceId(),//资源id，资源是已经注册过了的
null,
context.getXid(),
context.getApplicationData(),
context.buildLockKeys()//注册分支事物时带上全局锁keys
);
context.setBranchId(branchId);
}
...
}
public class DefaultResourceManager implements ResourceManager {
protected static Map<BranchType, ResourceManager> resourceManagers = new ConcurrentHashMap<>();
private static class SingletonHolder {
private static DefaultResourceManager INSTANCE = new DefaultResourceManager();
}
public static DefaultResourceManager get() {
return SingletonHolder.INSTANCE;
}
private DefaultResourceManager() {
initResourceManagers();
}
protected void initResourceManagers() {
//通过SPI加载所有的ResourceManager资源管理器
//比如：DataSourceManager、TCCResourceManager、SagaResourceManager、ResourceManagerXA
List<ResourceManager> allResourceManagers = EnhancedServiceLoader.loadAll(ResourceManager.class);
if (CollectionUtils.isNotEmpty(allResourceManagers)) {
for (ResourceManager rm : allResourceManagers) {
resourceManagers.put(rm.getBranchType(), rm);
}
}
}
//注册分支事务
@Override
public Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {
return getResourceManager(branchType).branchRegister(branchType, resourceId, clientId, xid, applicationData, lockKeys);
}
public ResourceManager getResourceManager(BranchType branchType) {
ResourceManager rm = resourceManagers.get(branchType);
if (rm == null) {
throw new FrameworkException("No ResourceManager for BranchType:" + branchType.name());
}
return rm;
}
...
}
public abstract class AbstractResourceManager implements ResourceManager {
...
@Override
public Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {
try {
BranchRegisterRequest request = new BranchRegisterRequest();
request.setXid(xid);//xid是全局事务id
request.setLockKey(lockKeys);//这次分支事务要更新数据全局锁key
request.setResourceId(resourceId);//分支事务对应的资源id
request.setBranchType(branchType);//分支事务类型
request.setApplicationData(applicationData);//应用数据
BranchRegisterResponse response = (BranchRegisterResponse) RmNettyRemotingClient.getInstance().sendSyncRequest(request);
if (response.getResultCode() == ResultCode.Failed) {
throw new RmTransactionException(response.getTransactionExceptionCode(), String.format("Response[ %s ]", response.getMsg()));
}
return response.getBranchId();
} catch (TimeoutException toe) {
throw new RmTransactionException(TransactionExceptionCode.IO, "RPC Timeout", toe);
} catch (RuntimeException rex) {
throw new RmTransactionException(TransactionExceptionCode.BranchRegisterFailed, "Runtime", rex);
}
}
...
}

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11.Seata Server处理分支事务注册请求的源码
(1)Seata Server收到分支事务注册请求后的处理
(2)BranchRegisterRequest.handle()的处理
(3)DefaultCore.branchRegister()的处理

(1)Seata Server收到分支事务注册请求后的处理
Seata Server收到Seata Client发送过来的分支事务注册请求后，首先会将分支事务注册请求交给ServerOnRequestProcessor的process()方法进行处理，然后再将请求交给DefaultCoordinator的onRequest()方法进行处理。

public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {
...
@ChannelHandler.Sharable
class ServerHandler extends ChannelDuplexHandler {
@Override
public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
if (!(msg instanceof RpcMessage)) {
return;
}
//接下来调用processMessage()方法对解码完毕的RpcMessage对象进行处理
processMessage(ctx, (RpcMessage) msg);
}
}
}
public abstract class AbstractNettyRemoting implements Disposable {
...
protected void processMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(String.format("%s msgId:%s, body:%s", this, rpcMessage.getId(), rpcMessage.getBody()));
}
Object body = rpcMessage.getBody();
if (body instanceof MessageTypeAware) {
MessageTypeAware messageTypeAware = (MessageTypeAware) body;
//根据消息类型获取到一个Pair对象，该Pair对象是由请求处理组件和请求处理线程池组成的
//processorTable里的内容，是NettyRemotingServer在初始化时，通过调用registerProcessor()方法put进去的
//所以下面的代码实际上会由ServerOnRequestProcessor的process()方法进行处理
final Pair<RemotingProcessor, ExecutorService> pair = this.processorTable.get((int) messageTypeAware.getTypeCode());
if (pair != null) {
if (pair.getSecond() != null) {
try {
pair.getSecond().execute(() -> {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
} finally {
MDC.clear();
}
});
} catch (RejectedExecutionException e) {
...
}
} else {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
}
}
} else {
LOGGER.error("This message type [{}] has no processor.", messageTypeAware.getTypeCode());
}
} else {
LOGGER.error("This rpcMessage body[{}] is not MessageTypeAware type.", body);
}
}
...
}
public class ServerOnRequestProcessor implements RemotingProcessor, Disposable {
private final RemotingServer remotingServer;
...
@Override
public void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (ChannelManager.isRegistered(ctx.channel())) {
onRequestMessage(ctx, rpcMessage);
} else {
try {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("closeChannelHandlerContext channel:" + ctx.channel());
}
ctx.disconnect();
ctx.close();
} catch (Exception exx) {
LOGGER.error(exx.getMessage());
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info(String.format("close a unhandled connection! [%s]", ctx.channel().toString()));
}
}
}
private void onRequestMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) {
Object message = rpcMessage.getBody();
//RpcContext线程本地变量副本
RpcContext rpcContext = ChannelManager.getContextFromIdentified(ctx.channel());
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("server received:{},clientIp:{},vgroup:{}", message, NetUtil.toIpAddress(ctx.channel().remoteAddress()), rpcContext.getTransactionServiceGroup());
} else {
try {
BatchLogHandler.INSTANCE.getLogQueue().put(message + ",clientIp:" + NetUtil.toIpAddress(ctx.channel().remoteAddress()) + ",vgroup:" + rpcContext.getTransactionServiceGroup());
} catch (InterruptedException e) {
LOGGER.error("put message to logQueue error: {}", e.getMessage(), e);
}
}
if (!(message instanceof AbstractMessage)) {
return;
}
//the batch send request message
if (message instanceof MergedWarpMessage) {
...
} else {
//the single send request message
final AbstractMessage msg = (AbstractMessage) message;
//最终调用到DefaultCoordinator的onRequest()方法来处理RpcMessage
//此时传入的msg其实就是客户端发送请求时的BranchRegisterRequest对象
AbstractResultMessage result = transactionMessageHandler.onRequest(msg, rpcContext);
//返回响应给客户端
remotingServer.sendAsyncResponse(rpcMessage, ctx.channel(), result);
}
}
...
}
public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
...
@Override
public AbstractResultMessage onRequest(AbstractMessage request, RpcContext context) {
if (!(request instanceof AbstractTransactionRequestToTC)) {
throw new IllegalArgumentException();
}
//此时传入的request其实就是客户端发送请求时的BranchRegisterRequest对象
AbstractTransactionRequestToTC transactionRequest = (AbstractTransactionRequestToTC) request;
transactionRequest.setTCInboundHandler(this);
return transactionRequest.handle(context);
}
...
}

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(2)BranchRegisterRequest.handle()的处理
在DefaultCoordinator的onRequest()方法中，会调用BranchRegisterRequest的handle()方法来处理分支事务注册请求，该handle()方法又会调用DefaultCoordinator的doBranchRegister()方法，所以最后会调用DefaultCore的branchRegister()方法来具体处理分支事务注册请求。

public class BranchRegisterRequest extends AbstractTransactionRequestToTC {
...
@Override
public AbstractTransactionResponse handle(RpcContext rpcContext) {
return handler.handle(this, rpcContext);
}
...
}
public interface TCInboundHandler {
...
//Handle branch register response.
BranchRegisterResponse handle(BranchRegisterRequest branchRegister, RpcContext rpcContext);
}
public abstract class AbstractTCInboundHandler extends AbstractExceptionHandler implements TCInboundHandler {
...
@Override
public BranchRegisterResponse handle(BranchRegisterRequest request, final RpcContext rpcContext) {
BranchRegisterResponse response = new BranchRegisterResponse();
exceptionHandleTemplate(new AbstractCallback<BranchRegisterRequest, BranchRegisterResponse>() {
@Override
public void execute(BranchRegisterRequest request, BranchRegisterResponse response) throws TransactionException {
try {
doBranchRegister(request, response, rpcContext);
} catch (StoreException e) {
throw new TransactionException(TransactionExceptionCode.FailedStore, String.format("branch register request failed. xid=%s, msg=%s", request.getXid(), e.getMessage()), e);
}
}
}, request, response);
return response;
}
//Do branch register.
protected abstract void doBranchRegister(BranchRegisterRequest request, BranchRegisterResponse response, RpcContext rpcContext) throws TransactionException;
...
}
public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
private final DefaultCore core;
...
@Override
protected void doBranchRegister(BranchRegisterRequest request, BranchRegisterResponse response, RpcContext rpcContext) throws TransactionException {
MDC.put(RootContext.MDC_KEY_XID, request.getXid());
//调用DefaultCore的branchRegister()方法处理分支事务注册请求
response.setBranchId(core.branchRegister(request.getBranchType(), request.getResourceId(), rpcContext.getClientId(), request.getXid(), request.getApplicationData(), request.getLockKey()));
}
...
}

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(3)DefaultCore.branchRegister()的处理
DefaultCore的branchRegister()方法其实会继续调用其抽象父类AbstractCore的branchRegister()方法来处理注册分支事务请求，具体的过程如下：

一.根据xid获取全局事务会话
二.根据全局事务会话创建分支事务会话
三.通过MDC将分支事务ID存到线程本地变量副本
四.注册分支事务需要先获取全局锁
五.把分支事务会话加入到全局事务会话中并持久化

public class DefaultCore implements Core {
private static Map<BranchType, AbstractCore> coreMap = new ConcurrentHashMap<>();
public DefaultCore(RemotingServer remotingServer) {
List allCore = EnhancedServiceLoader.loadAll(AbstractCore.class, new Class[] {RemotingServer.class}, new Object[] {remotingServer});
if (CollectionUtils.isNotEmpty(allCore)) {
for (AbstractCore core : allCore) {
coreMap.put(core.getHandleBranchType(), core);
}
}
}
@Override
public Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {
return getCore(branchType).branchRegister(branchType, resourceId, clientId, xid, applicationData, lockKeys);
}
public AbstractCore getCore(BranchType branchType) {
AbstractCore core = coreMap.get(branchType);
if (core == null) {
throw new NotSupportYetException("unsupported type:" + branchType.name());
}
return core;
}
...
}
public abstract class AbstractCore implements Core {
protected RemotingServer remotingServer;
public AbstractCore(RemotingServer remotingServer) {
if (remotingServer == null) {
throw new IllegalArgumentException("remotingServer must be not null");
}
this.remotingServer = remotingServer;
}
//注册分支事务
@Override
public Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {
//1.根据xid获取全局事务会话GlobalSession
GlobalSession globalSession = assertGlobalSessionNotNull(xid, false);
return SessionHolder.lockAndExecute(globalSession, () -> {
globalSessionStatusCheck(globalSession);
globalSession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
//2.创建分支事务会话BranchSession，根据全局事务开启一个分支事务
//传入的参数依次是：全局事务会话、事务类型、资源ID、应用数据、全局锁keys、客户端ID
BranchSession branchSession = SessionHelper.newBranchByGlobal(globalSession, branchType, resourceId, applicationData, lockKeys, clientId);
//3.把分支事务的ID存放到线程本地变量副本中，也就是MDC中
MDC.put(RootContext.MDC_KEY_BRANCH_ID, String.valueOf(branchSession.getBranchId()));
//4.注册分支事务时会获取全局锁
//分支事务会话branchSession尝试获取一个全局锁，获取失败会抛异常，说明分支事务注册失败
branchSessionLock(globalSession, branchSession);
try {
//5.把分支事务会话加入到全局事务会话中
globalSession.addBranch(branchSession);
} catch (RuntimeException ex) {
branchSessionUnlock(branchSession);
throw new BranchTransactionException(FailedToAddBranch, String.format("Failed to store branch xid = %s branchId = %s", globalSession.getXid(), branchSession.getBranchId()), ex);
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Register branch successfully, xid = {}, branchId = {}, resourceId = {} ,lockKeys = {}", globalSession.getXid(), branchSession.getBranchId(), resourceId, lockKeys);
}
return branchSession.getBranchId();
});
}
private GlobalSession assertGlobalSessionNotNull(String xid, boolean withBranchSessions) throws TransactionException {
//根据xid寻找全局事务会话GlobalSession
GlobalSession globalSession = SessionHolder.findGlobalSession(xid, withBranchSessions);
if (globalSession == null) {
throw new GlobalTransactionException(TransactionExceptionCode.GlobalTransactionNotExist, String.format("Could not found global transaction xid = %s, may be has finished.", xid));
}
return globalSession;
}
//获取全局锁，获取全局锁失败则抛异常
protected void branchSessionLock(GlobalSession globalSession, BranchSession branchSession) throws TransactionException {
}
...
}
public class SessionHolder {
...
//根据xid获取全局事务会话GlobalSession
public static GlobalSession findGlobalSession(String xid, boolean withBranchSessions) {
return getRootSessionManager().findGlobalSession(xid, withBranchSessions);
}
...
}
@LoadLevel(name = "db", scope = Scope.PROTOTYPE)
public class DataBaseSessionManager extends AbstractSessionManager implements Initialize {
...
//根据xid获取全局事务会话GlobalSession
@Override
public GlobalSession findGlobalSession(String xid, boolean withBranchSessions) {
return transactionStoreManager.readSession(xid, withBranchSessions);
}
...
}
public class DataBaseTransactionStoreManager extends AbstractTransactionStoreManager implements TransactionStoreManager {
...
//根据xid获取全局事务会话GlobalSession
@Override
public GlobalSession readSession(String xid, boolean withBranchSessions) {
//global transaction
GlobalTransactionDO globalTransactionDO = logStore.queryGlobalTransactionDO(xid);
if (globalTransactionDO == null) {
return null;
}
//branch transactions
List<BranchTransactionDO> branchTransactionDOs = null;
//reduce rpc with db when branchRegister and getGlobalStatus
if (withBranchSessions) {
branchTransactionDOs = logStore.queryBranchTransactionDO(globalTransactionDO.getXid());
}
return getGlobalSession(globalTransactionDO, branchTransactionDOs);
}
...
}
public class SessionHelper {
...
//创建分支事务会话
public static BranchSession newBranchByGlobal(GlobalSession globalSession, BranchType branchType, String resourceId, String applicationData, String lockKeys, String clientId) {
BranchSession branchSession = new BranchSession();
branchSession.setXid(globalSession.getXid());
branchSession.setTransactionId(globalSession.getTransactionId());
branchSession.setBranchId(UUIDGenerator.generateUUID());
branchSession.setBranchType(branchType);
branchSession.setResourceId(resourceId);
branchSession.setLockKey(lockKeys);
branchSession.setClientId(clientId);
branchSession.setApplicationData(applicationData);
return branchSession;
}
...
}
public class GlobalSession implements SessionLifecycle, SessionStorable {
private List<BranchSession> branchSessions;
...
//把分支事务会话加入到全局事务会话中
@Override
public void addBranch(BranchSession branchSession) throws TransactionException {
for (SessionLifecycleListener lifecycleListener : lifecycleListeners) {
lifecycleListener.onAddBranch(this, branchSession);
}
branchSession.setStatus(BranchStatus.Registered);
add(branchSession);
}
//把分支事务会话加入到全局事务会话中
public boolean add(BranchSession branchSession) {
if (null != branchSessions) {
return branchSessions.add(branchSession);
} else {
//db and redis no need to deal with
return true;
}
}
...
}
public abstract class AbstractSessionManager implements SessionManager, SessionLifecycleListener {
...
@Override
public void onAddBranch(GlobalSession globalSession, BranchSession branchSession) throws TransactionException {
addBranchSession(globalSession, branchSession);
}
@Override
public void addBranchSession(GlobalSession session, BranchSession branchSession) throws TransactionException {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("MANAGER[{}] SESSION[{}] {}", name, branchSession, LogOperation.BRANCH_ADD);
}
writeSession(LogOperation.BRANCH_ADD, branchSession);
}
//持久化全局事务会话
private void writeSession(LogOperation logOperation, SessionStorable sessionStorable) throws TransactionException {
//transactionStoreManager.writeSession()会对全局事务会话进行持久化
if (!transactionStoreManager.writeSession(logOperation, sessionStorable)) {
...
}
}
...
}

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12.将UndoLog写入到数据库与提交事务的源码
在数据源连接代理ConnectionProxy的processGlobalTransactionCommit()方法中：
一.首先会注册完分支事务
二.然后会将UndoLog写入到数据库
三.最后才提交目标数据源连接的事务

//数据源连接代理
public class ConnectionProxy extends AbstractConnectionProxy {
private final LockRetryPolicy lockRetryPolicy = new LockRetryPolicy(this);
...
@Override
public void commit() throws SQLException {
try {
//通过全局锁重试策略组件LockRetryPolicy来执行本地事务的提交
lockRetryPolicy.execute(() -> {
doCommit();
return null;
});
} catch (SQLException e) {
if (targetConnection != null && !getAutoCommit() && !getContext().isAutoCommitChanged()) {
rollback();
}
throw e;
} catch (Exception e) {
throw new SQLException(e);
}
}
private void doCommit() throws SQLException {
if (context.inGlobalTransaction()) {
processGlobalTransactionCommit();
} else if (context.isGlobalLockRequire()) {
processLocalCommitWithGlobalLocks();
} else {
targetConnection.commit();
}
}
private void processLocalCommitWithGlobalLocks() throws SQLException {
//检查全局锁keys
checkLock(context.buildLockKeys());
try {
//目标数据源连接提交事务
targetConnection.commit();
} catch (Throwable ex) {
throw new SQLException(ex);
}
context.reset();
}
private void processGlobalTransactionCommit() throws SQLException {
try {
//1.注册分支事务
register();
} catch (TransactionException e) {
recognizeLockKeyConflictException(e, context.buildLockKeys());
}
try {
//2.将UndoLog写入到数据库
UndoLogManagerFactory.getUndoLogManager(this.getDbType()).flushUndoLogs(this);
//3.目标数据源连接提交事务
targetConnection.commit();
} catch (Throwable ex) {
LOGGER.error("process connectionProxy commit error: {}", ex.getMessage(), ex);
report(false);
throw new SQLException(ex);
}
if (IS_REPORT_SUCCESS_ENABLE) {
report(true);
}
context.reset();
}
...
}
public class UndoLogManagerFactory {
private static final Map<String, UndoLogManager> UNDO_LOG_MANAGER_MAP = new ConcurrentHashMap<>();
//获取UndoLog管理器
public static UndoLogManager getUndoLogManager(String dbType) {
return CollectionUtils.computeIfAbsent(UNDO_LOG_MANAGER_MAP, dbType,
key -> EnhancedServiceLoader.load(UndoLogManager.class, dbType));
}
}
public abstract class AbstractUndoLogManager implements UndoLogManager {
...
@Override
public void flushUndoLogs(ConnectionProxy cp) throws SQLException {
ConnectionContext connectionContext = cp.getContext();
if (!connectionContext.hasUndoLog()) {
return;
}
String xid = connectionContext.getXid();
long branchId = connectionContext.getBranchId();
BranchUndoLog branchUndoLog = new BranchUndoLog();
branchUndoLog.setXid(xid);
branchUndoLog.setBranchId(branchId);
branchUndoLog.setSqlUndoLogs(connectionContext.getUndoItems());
UndoLogParser parser = UndoLogParserFactory.getInstance();
byte[] undoLogContent = parser.encode(branchUndoLog);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Flushing UNDO LOG: {}", new String(undoLogContent, Constants.DEFAULT_CHARSET));
}
CompressorType compressorType = CompressorType.NONE;
if (needCompress(undoLogContent)) {
compressorType = ROLLBACK_INFO_COMPRESS_TYPE;
undoLogContent = CompressorFactory.getCompressor(compressorType.getCode()).compress(undoLogContent);
}
//插入UndoLog到数据库
insertUndoLogWithNormal(xid, branchId, buildContext(parser.getName(), compressorType), undoLogContent, cp.getTargetConnection());
}
//insert uodo log when normal
protected abstract void insertUndoLogWithNormal(String xid, long branchId, String rollbackCtx, byte[] undoLogContent, Connection conn) throws SQLException;
...
}
@LoadLevel(name = JdbcConstants.MYSQL)
public class MySQLUndoLogManager extends AbstractUndoLogManager {
...
@Override
protected void insertUndoLogWithNormal(String xid, long branchId, String rollbackCtx, byte[] undoLogContent, Connection conn) throws SQLException {
insertUndoLog(xid, branchId, rollbackCtx, undoLogContent, State.Normal, conn);
}
private void insertUndoLog(String xid, long branchId, String rollbackCtx, byte[] undoLogContent, State state, Connection conn) throws SQLException {
try (PreparedStatement pst = conn.prepareStatement(INSERT_UNDO_LOG_SQL)) {
pst.setLong(1, branchId);
pst.setString(2, xid);
pst.setString(3, rollbackCtx);
pst.setBytes(4, undoLogContent);
pst.setInt(5, state.getValue());
pst.executeUpdate();
} catch (Exception e) {
if (!(e instanceof SQLException)) {
e = new SQLException(e);
}
throw (SQLException) e;
}
}
...
}

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13.通过全局锁重试策略组件执行事务的提交
当设置完禁止自动提交事务、构建前镜像、执行SQL、构建后镜像，执行到数据源连接代理ConnectionProxy的commit()方法提交本地事务时，便会通过全局锁重试策略LockRetryPolicy来执行本地事务的提交。

全局锁重试策略LockRetryPolicy，会确保先获取到全局锁才提交本地事务。也就是如果获取不到全局锁，则重试获取。此外，注册分支事务时，获取到全局锁才能注册成功。

public class ConnectionProxy extends AbstractConnectionProxy {
private final LockRetryPolicy lockRetryPolicy = new LockRetryPolicy(this);
...
@Override
public void commit() throws SQLException {
try {
//通过全局锁重试策略组件LockRetryPolicy来执行本地事务的提交
lockRetryPolicy.execute(() -> {
doCommit();
return null;
});
} catch (SQLException e) {
if (targetConnection != null && !getAutoCommit() && !getContext().isAutoCommitChanged()) {
rollback();
}
throw e;
} catch (Exception e) {
throw new SQLException(e);
}
}
...
public static class LockRetryPolicy {
protected static final boolean LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT = ConfigurationFactory.getInstance().
getBoolean(ConfigurationKeys.CLIENT_LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT, DEFAULT_CLIENT_LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT);
protected final ConnectionProxy connection;
public LockRetryPolicy(ConnectionProxy connection) {
this.connection = connection;
}
public <T> T execute(Callable<T> callable) throws Exception {
//the only case that not need to retry acquire lock hear is
//LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT == true && connection#autoCommit == true
//because it has retry acquire lock when AbstractDMLBaseExecutor#executeAutoCommitTrue
if (LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT && connection.getContext().isAutoCommitChanged()) {
//不需要重试
return callable.call();
} else {
//LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT == false
//or LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT == true && autoCommit == false
return doRetryOnLockConflict(callable);
}
}
protected <T> T doRetryOnLockConflict(Callable<T> callable) throws Exception {
LockRetryController lockRetryController = new LockRetryController();
while (true) {
try {
return callable.call();
} catch (LockConflictException lockConflict) {
onException(lockConflict);
//AbstractDMLBaseExecutor#executeAutoCommitTrue the local lock is released
if (connection.getContext().isAutoCommitChanged() && lockConflict.getCode() == TransactionExceptionCode.LockKeyConflictFailFast) {
lockConflict.setCode(TransactionExceptionCode.LockKeyConflict);
}
//休眠一会再去重试
lockRetryController.sleep(lockConflict);
} catch (Exception e) {
onException(e);
throw e;
}
}
}
//Callback on exception in doLockRetryOnConflict.
protected void onException(Exception e) throws Exception {
}
}
...
}
public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {
...
private static class LockRetryPolicy extends ConnectionProxy.LockRetryPolicy {
LockRetryPolicy(final ConnectionProxy connection) {
super(connection);
}
@Override
public <T> T execute(Callable<T> callable) throws Exception {
if (LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT) {
return doRetryOnLockConflict(callable);
} else {
return callable.call();
}
}
@Override
protected void onException(Exception e) throws Exception {
ConnectionContext context = connection.getContext();
//UndoItems can't use the Set collection class to prevent ABA
context.removeSavepoint(null);
//回滚目标数据源连接对SQL的执行
connection.getTargetConnection().rollback();
}
public static boolean isLockRetryPolicyBranchRollbackOnConflict() {
return LOCK_RETRY_POLICY_BRANCH_ROLLBACK_ON_CONFLICT;
}
}
...
}

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14.注册分支事务时获取全局锁的入口源码
在Seata Server中，只有当全局锁获取成功后，分支事务才能注册成功。AbstractCore的branchRegister()方法会通过调用ATCore的branchSessionLock()方法来获取全局锁，而ATCore的branchSessionLock()方法最终则是靠调用AbstractLockManager的acquireLock()方法来尝试获取全局锁的。获取全局锁失败会抛出异常，说明注册分支事务失败。

public abstract class AbstractCore implements Core {
...
//注册分支事务
@Override
public Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {
//1.根据xid获取全局事务会话GlobalSession
GlobalSession globalSession = assertGlobalSessionNotNull(xid, false);
return SessionHolder.lockAndExecute(globalSession, () -> {
globalSessionStatusCheck(globalSession);
globalSession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
//2.创建分支事务会话，根据全局事务开启一个分支事务
//传入的参数依次是：全局事务会话、事务类型、资源ID、应用数据、全局锁keys、客户端ID
BranchSession branchSession = SessionHelper.newBranchByGlobal(globalSession, branchType, resourceId, applicationData, lockKeys, clientId);
//3.把分支事务的ID存放到线程本地变量副本中，也就是MDC中
MDC.put(RootContext.MDC_KEY_BRANCH_ID, String.valueOf(branchSession.getBranchId()));
//4.注册分支事务时会加全局锁
//分支事务会话branchSession尝试获取一个全局锁，获取失败会抛异常，说明分支事务注册失败
branchSessionLock(globalSession, branchSession);
try {
//5.把分支事务会话加入到全局事务会话中
globalSession.addBranch(branchSession);
} catch (RuntimeException ex) {
branchSessionUnlock(branchSession);
throw new BranchTransactionException(FailedToAddBranch, String.format("Failed to store branch xid = %s branchId = %s", globalSession.getXid(), branchSession.getBranchId()), ex);
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Register branch successfully, xid = {}, branchId = {}, resourceId = {} ,lockKeys = {}", globalSession.getXid(), branchSession.getBranchId(), resourceId, lockKeys);
}
return branchSession.getBranchId();
});
}
...
}
public class ATCore extends AbstractCore {
...
@Override
protected void branchSessionLock(GlobalSession globalSession, BranchSession branchSession) throws TransactionException {
//从应用程序数据里提取出一些属性进行属性赋值
String applicationData = branchSession.getApplicationData();
boolean autoCommit = true;
boolean skipCheckLock = false;
if (StringUtils.isNotBlank(applicationData)) {
if (objectMapper == null) {
objectMapper = new ObjectMapper();
}
try {
//ObjectMapper是一个对象映射框架，它可以把ApplicationData对象里的属性值读取出来，然后写入到HashMap里
Map<String, Object> data = objectMapper.readValue(applicationData, HashMap.class);
Object clientAutoCommit = data.get(AUTO_COMMIT);
if (clientAutoCommit != null && !(boolean)clientAutoCommit) {
autoCommit = (boolean)clientAutoCommit;
}
Object clientSkipCheckLock = data.get(SKIP_CHECK_LOCK);
if (clientSkipCheckLock instanceof Boolean) {
skipCheckLock = (boolean)clientSkipCheckLock;
}
} catch (IOException e) {
LOGGER.error("failed to get application data: {}", e.getMessage(), e);
}
}
try {
//分支事务会话branchSession尝试获取一个全局锁，获取失败会抛异常，说明分支事务注册失败
if (!branchSession.lock(autoCommit, skipCheckLock)) {
throw new BranchTransactionException(LockKeyConflict, String.format("Global lock acquire failed xid = %s branchId = %s", globalSession.getXid(), branchSession.getBranchId()));
}
} catch (StoreException e) {
if (e.getCause() instanceof BranchTransactionException) {
throw new BranchTransactionException(((BranchTransactionException)e.getCause()).getCode(), String.format("Global lock acquire failed xid = %s branchId = %s", globalSession.getXid(), branchSession.getBranchId()));
}
throw e;
}
}
...
}
public class BranchSession implements Lockable, Comparable<BranchSession>, SessionStorable {
...
public boolean lock(boolean autoCommit, boolean skipCheckLock) throws TransactionException {
if (this.getBranchType().equals(BranchType.AT)) {
//尝试获取全局锁
return LockerManagerFactory.getLockManager().acquireLock(this, autoCommit, skipCheckLock);
}
return true;
}
...
}
public class LockerManagerFactory {
private static final Configuration CONFIG = ConfigurationFactory.getInstance();
private static volatile LockManager LOCK_MANAGER;
public static LockManager getLockManager() {
if (LOCK_MANAGER == null) {
init();
}
return LOCK_MANAGER;
}
public static void init() {
init(null);
}
public static void init(String lockMode) {
if (LOCK_MANAGER == null) {
synchronized (LockerManagerFactory.class) {
if (LOCK_MANAGER == null) {
if (StringUtils.isBlank(lockMode)) {
lockMode = CONFIG.getConfig(ConfigurationKeys.STORE_LOCK_MODE, CONFIG.getConfig(ConfigurationKeys.STORE_MODE, SERVER_DEFAULT_STORE_MODE));
}
if (StoreMode.contains(lockMode)) {
LOCK_MANAGER = EnhancedServiceLoader.load(LockManager.class, lockMode);
}
}
}
}
}
}
public abstract class AbstractLockManager implements LockManager {
...
@Override
public boolean acquireLock(BranchSession branchSession, boolean autoCommit, boolean skipCheckLock) throws TransactionException {
if (branchSession == null) {
throw new IllegalArgumentException("branchSession can't be null for memory/file locker.");
}
String lockKey = branchSession.getLockKey();
if (StringUtils.isNullOrEmpty(lockKey)) {
//no lock
return true;
}
//get locks of branch
//获取到分支事务里需要的所有行锁
List<RowLock> locks = collectRowLocks(branchSession);
if (CollectionUtils.isEmpty(locks)) {
//no lock
return true;
}
//具体进行获取锁
return getLocker(branchSession).acquireLock(locks, autoCommit, skipCheckLock);
}
@Override
public List<RowLock> collectRowLocks(BranchSession branchSession) {
if (branchSession == null || StringUtils.isBlank(branchSession.getLockKey())) {
return Collections.emptyList();
}
String lockKey = branchSession.getLockKey();
String resourceId = branchSession.getResourceId();
String xid = branchSession.getXid();
long transactionId = branchSession.getTransactionId();
long branchId = branchSession.getBranchId();
return collectRowLocks(lockKey, resourceId, xid, transactionId, branchId);
}
protected List<RowLock> collectRowLocks(String lockKey, String resourceId, String xid, Long transactionId, Long branchID) {
List<RowLock> locks = new ArrayList<>();
String[] tableGroupedLockKeys = lockKey.split(";");
for (String tableGroupedLockKey : tableGroupedLockKeys) {
int idx = tableGroupedLockKey.indexOf(":");
if (idx < 0) {
return locks;
}
String tableName = tableGroupedLockKey.substring(0, idx);
String mergedPKs = tableGroupedLockKey.substring(idx + 1);
if (StringUtils.isBlank(mergedPKs)) {
return locks;
}
String[] pks = mergedPKs.split(",");
if (pks == null || pks.length == 0) {
return locks;
}
for (String pk : pks) {
if (StringUtils.isNotBlank(pk)) {
RowLock rowLock = new RowLock();
rowLock.setXid(xid);
rowLock.setTransactionId(transactionId);
rowLock.setBranchId(branchID);
rowLock.setTableName(tableName);
rowLock.setPk(pk);
rowLock.setResourceId(resourceId);
locks.add(rowLock);
}
}
}
return locks;
}
...
}
public class RowLock {
private String xid;//全局事务xid
private Long transactionId;//全局事务ID
private Long branchId;//分支事务ID
private String resourceId;//资源ID
private String tableName;//表名称
private String pk;//主键
private String rowKey;//行键
private String feature;//功能特性
...
}

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15.Seata Server获取全局锁的具体逻辑源码
调用AbstractLockManager的acquireLock()方法获取全局锁时，其实调用的是DataBaseLocker的acquireLock()方法 -> LockStoreDataBaseDAO的acquireLock()方法。

在LockStoreDataBaseDAO的acquireLock()方法中，首先会查询数据库中是否存在要申请的全局锁的记录，然后根据这些锁记录 + xid判断是否由当前全局事务获取的(这是核心)。

如果不是，则说明其他全局事务先获取到了要申请的全局锁，此时当前事务获取全局锁失败。

如果是，则把当前事务已经获取过的全局锁过滤出来，然后尝试写入当前分支事务还需获取的全局锁记录到数据库。如果写入成功，则表示当前分支事务成功获取到全局锁。如果写入失败，则表示其他分支事务已经获取到全局锁。

@LoadLevel(name = "db")
public class DataBaseLockManager extends AbstractLockManager implements Initialize {
private Locker locker;
@Override
public void init() {
//init dataSource
String datasourceType = ConfigurationFactory.getInstance().getConfig(ConfigurationKeys.STORE_DB_DATASOURCE_TYPE);
DataSource lockStoreDataSource = EnhancedServiceLoader.load(DataSourceProvider.class, datasourceType).provide();
locker = new DataBaseLocker(lockStoreDataSource);
}
@Override
public Locker getLocker(BranchSession branchSession) {
return locker;
}
...
}
public class DataBaseLocker extends AbstractLocker {
private LockStore lockStore;
public DataBaseLocker(DataSource logStoreDataSource) {
lockStore = new LockStoreDataBaseDAO(logStoreDataSource);
}
...
@Override
public boolean acquireLock(List<RowLock> locks, boolean autoCommit, boolean skipCheckLock) {
if (CollectionUtils.isEmpty(locks)) {
//no lock
return true;
}
try {
//通过执行MySQL来获取全局锁
return lockStore.acquireLock(convertToLockDO(locks), autoCommit, skipCheckLock);
} catch (StoreException e) {
throw e;
} catch (Exception t) {
LOGGER.error("AcquireLock error, locks:{}", CollectionUtils.toString(locks), t);
return false;
}
}
...
}
public class LockStoreDataBaseDAO implements LockStore {
...
@Override
public boolean acquireLock(List<LockDO> lockDOs, boolean autoCommit, boolean skipCheckLock) {
//数据库操作三剑客：连接、句柄、结果
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
Set<String> dbExistedRowKeys = new HashSet<>();
boolean originalAutoCommit = true;
if (lockDOs.size() > 1) {
lockDOs = lockDOs.stream().filter(LambdaUtils.distinctByKey(LockDO::getRowKey)).collect(Collectors.toList());
}
try {
//从全局锁数据源里获取到一个连接
conn = lockStoreDataSource.getConnection();
//关闭自动提交事务
if (originalAutoCommit = conn.getAutoCommit()) {
conn.setAutoCommit(false);
}
//需要获取的锁，有可能多个
List<LockDO> unrepeatedLockDOs = lockDOs;
//check lock
if (!skipCheckLock) {
boolean canLock = true;
//query，针对全局锁表查询某个数据加了全局锁的全局事务xid
//LockStoreSqlFactory是全局锁存储的SQL工厂
String checkLockSQL = LockStoreSqlFactory.getLogStoreSql(dbType).getCheckLockableSql(lockTable, lockDOs.size());
ps = conn.prepareStatement(checkLockSQL);
for (int i = 0; i < lockDOs.size(); i++) {
ps.setString(i + 1, lockDOs.get(i).getRowKey());
}
//执行查询
rs = ps.executeQuery();
//获取到当前要加全局锁的事务xid
String currentXID = lockDOs.get(0).getXid();
boolean failFast = false;
//如果查询到的结果rs是空，则表示当前全局锁没有被事务获取占用
while (rs.next()) {
String dbXID = rs.getString(ServerTableColumnsName.LOCK_TABLE_XID);
//如果获取到全局锁的是别的全局事务xid，那么获取全局锁失败，设置canLock为false
if (!StringUtils.equals(dbXID, currentXID)) {
if (LOGGER.isInfoEnabled()) {
String dbPk = rs.getString(ServerTableColumnsName.LOCK_TABLE_PK);
String dbTableName = rs.getString(ServerTableColumnsName.LOCK_TABLE_TABLE_NAME);
long dbBranchId = rs.getLong(ServerTableColumnsName.LOCK_TABLE_BRANCH_ID);
LOGGER.info("Global lock on [{}:{}] is holding by xid {} branchId {}", dbTableName, dbPk, dbXID, dbBranchId);
}
if (!autoCommit) {
int status = rs.getInt(ServerTableColumnsName.LOCK_TABLE_STATUS);
if (status == LockStatus.Rollbacking.getCode()) {
failFast = true;
}
}
canLock = false;
break;
}
dbExistedRowKeys.add(rs.getString(ServerTableColumnsName.LOCK_TABLE_ROW_KEY));
}
if (!canLock) {
conn.rollback();
if (failFast) {
throw new StoreException(new BranchTransactionException(LockKeyConflictFailFast));
}
return false;
}
//If the lock has been exists in db, remove it from the lockDOs
if (CollectionUtils.isNotEmpty(dbExistedRowKeys)) {
//过滤当前事务已经获取过的全局锁
unrepeatedLockDOs = lockDOs.stream().filter(lockDO -> !dbExistedRowKeys.contains(lockDO.getRowKey())).collect(Collectors.toList());
}
if (CollectionUtils.isEmpty(unrepeatedLockDOs)) {
conn.rollback();
return true;
}
}
//lock
if (unrepeatedLockDOs.size() == 1) {
LockDO lockDO = unrepeatedLockDOs.get(0);
//尝试加锁，表示全局锁被当前的分支事务获取了
if (!doAcquireLock(conn, lockDO)) {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Global lock acquire failed, xid {} branchId {} pk {}", lockDO.getXid(), lockDO.getBranchId(), lockDO.getPk());
}
conn.rollback();
return false;
}
} else {
if (!doAcquireLocks(conn, unrepeatedLockDOs)) {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Global lock batch acquire failed, xid {} branchId {} pks {}", unrepeatedLockDOs.get(0).getXid(), unrepeatedLockDOs.get(0).getBranchId(), unrepeatedLockDOs.stream().map(lockDO -> lockDO.getPk()).collect(Collectors.toList()));
}
conn.rollback();
return false;
}
}
conn.commit();
return true;
} catch (SQLException e) {
throw new StoreException(e);
} finally {
IOUtil.close(rs, ps);
if (conn != null) {
try {
if (originalAutoCommit) {
conn.setAutoCommit(true);
}
conn.close();
} catch (SQLException e) {
}
}
}
}
protected boolean doAcquireLock(Connection conn, LockDO lockDO) {
PreparedStatement ps = null;
try {
//insert
String insertLockSQL = LockStoreSqlFactory.getLogStoreSql(dbType).getInsertLockSQL(lockTable);
ps = conn.prepareStatement(insertLockSQL);
ps.setString(1, lockDO.getXid());//全局事务xid
ps.setLong(2, lockDO.getTransactionId());//全局事务id
ps.setLong(3, lockDO.getBranchId());//分支事务id
ps.setString(4, lockDO.getResourceId());//资源id
ps.setString(5, lockDO.getTableName());//表名称
ps.setString(6, lockDO.getPk());//主键
ps.setString(7, lockDO.getRowKey());//rowkey
ps.setInt(8, LockStatus.Locked.getCode());//locked
return ps.executeUpdate() > 0;
} catch (SQLException e) {
throw new StoreException(e);
} finally {
IOUtil.close(ps);
}
}
...
}

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16.全局锁和分支事务及本地事务总结
获取到全局锁，才能注册分支事务成功，否则LockRetryPolicy重试。获取到全局锁，才能提交本地事务成功，否则LockRetryPolicy重试。

全局锁没有被其他事务(xid)获取，则当前事务(xid)才能获取全局锁成功。获取全局锁，会将当前分支事务申请全局锁的记录写入到数据库中。

17.提交全局事务以及提交各分支事务的源码
(1)Seata Client发起提交全局事务的请求
(2)Server向Client发送提交分支事务的请求
(3)Seata Client处理提交分支事务的请求
(4)全局事务的提交主要就是让各个分支事务把本地的UndoLog删除

(1)Seata Client发起提交全局事务的请求

-> TransactionalTemplate.execute()发起全局事务的提交
-> TransactionalTemplate.commitTransaction()
-> DefaultGlobalTransaction.commit()
-> DefaultTransactionManager.commit()
-> DefaultTransactionManager.syncCall()
-> TmNettyRemotingClient.sendSyncRequest()
把全局事务提交请求GlobalCommitRequest发送给Seata Server进行处理

复制代码

//Template of executing business logic with a global transaction. 全局事务执行模版
public class TransactionalTemplate {
private static final Logger LOGGER = LoggerFactory.getLogger(TransactionalTemplate.class);
public Object execute(TransactionalExecutor business) throws Throwable {
//1.Get transactionInfo
TransactionInfo txInfo = business.getTransactionInfo();
if (txInfo == null) {
throw new ShouldNeverHappenException("transactionInfo does not exist");
}
//1.1 Get current transaction, if not null, the tx role is 'GlobalTransactionRole.Participant'.
//根据线程本地变量副本，获取当前线程本地变量副本里是否存在xid，如果存在则创建一个全局事务
//刚开始在开启一个全局事务的时候，是没有全局事务的
GlobalTransaction tx = GlobalTransactionContext.getCurrent();
//1.2 Handle the transaction propagation.
//从全局事务配置里，可以获取到全局事务的传播级别，默认是REQUIRED
//也就是如果存在一个全局事务，就直接执行业务；如果不存在一个全局事务，就开启一个新的全局事务；
Propagation propagation = txInfo.getPropagation();
//不同的全局事务传播级别，会采取不同的处理方式
//比如挂起当前事务 + 开启新的事务，或者是直接不使用事务执行业务，挂起其实就是解绑当前线程的xid
//可以通过@GlobalTransactional注解，定制业务方法的全局事务，比如指定业务方法全局事务的传播级别
SuspendedResourcesHolder suspendedResourcesHolder = null;
try {
switch (propagation) {
...
}
//1.3 If null, create new transaction with role 'GlobalTransactionRole.Launcher'.
if (tx == null) {
tx = GlobalTransactionContext.createNew();
}
//set current tx config to holder
GlobalLockConfig previousConfig = replaceGlobalLockConfig(txInfo);
try {
//2. If the tx role is 'GlobalTransactionRole.Launcher', send the request of beginTransaction to TC,
//else do nothing. Of course, the hooks will still be triggered.
//开启一个全局事务
beginTransaction(txInfo, tx);
Object rs;
try {
//Do Your Business
//执行业务方法，把全局事务xid通过Dubbo RPC传递下去，开启并提交一个一个分支事务
rs = business.execute();
} catch (Throwable ex) {
//3. The needed business exception to rollback.
//发生异常时需要完成的事务
completeTransactionAfterThrowing(txInfo, tx, ex);
throw ex;
}
//4. everything is fine, commit.
//如果一切执行正常就会在这里提交全局事务
commitTransaction(tx);
return rs;
} finally {
//5. clear
//执行一些全局事务完成后的回调，比如清理等工作
resumeGlobalLockConfig(previousConfig);
triggerAfterCompletion();
cleanUp();
}
} finally {
//If the transaction is suspended, resume it.
if (suspendedResourcesHolder != null) {
//如果之前挂起了一个全局事务，此时可以恢复这个全局事务
tx.resume(suspendedResourcesHolder);
}
}
}
//提交事务
private void commitTransaction(GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
try {
triggerBeforeCommit();
tx.commit();
triggerAfterCommit();
} catch (TransactionException txe) {
// 4.1 Failed to commit
throw new TransactionalExecutor.ExecutionException(tx, txe, TransactionalExecutor.Code.CommitFailure);
}
}
...
}
//The type Default global transaction. 默认的全局事务
public class DefaultGlobalTransaction implements GlobalTransaction {
private TransactionManager transactionManager;
DefaultGlobalTransaction(String xid, GlobalStatus status, GlobalTransactionRole role) {
this.transactionManager = TransactionManagerHolder.get();//全局事务管理者
this.xid = xid;
this.status = status;
this.role = role;
}
...
@Override
public void commit() throws TransactionException {
if (role == GlobalTransactionRole.Participant) {
//Participant has no responsibility of committing
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Ignore Commit(): just involved in global transaction [{}]", xid);
}
return;
}
assertXIDNotNull();
int retry = COMMIT_RETRY_COUNT <= 0 ? DEFAULT_TM_COMMIT_RETRY_COUNT : COMMIT_RETRY_COUNT;
try {
while (retry > 0) {
try {
retry--;
status = transactionManager.commit(xid);
break;
} catch (Throwable ex) {
LOGGER.error("Failed to report global commit [{}],Retry Countdown: {}, reason: {}", this.getXid(), retry, ex.getMessage());
if (retry == 0) {
throw new TransactionException("Failed to report global commit", ex);
}
}
}
} finally {
if (xid.equals(RootContext.getXID())) {
suspend();
}
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info("[{}] commit status: {}", xid, status);
}
}
...
}
public class TransactionManagerHolder {
...
private TransactionManagerHolder() {
}
private static class SingletonHolder {
private static TransactionManager INSTANCE = null;
static {
try {
INSTANCE = EnhancedServiceLoader.load(TransactionManager.class);
LOGGER.info("TransactionManager Singleton {}", INSTANCE);
} catch (Throwable anyEx) {
LOGGER.error("Failed to load TransactionManager Singleton! ", anyEx);
}
}
}
//Get transaction manager.
public static TransactionManager get() {
if (SingletonHolder.INSTANCE == null) {
throw new ShouldNeverHappenException("TransactionManager is NOT ready!");
}
return SingletonHolder.INSTANCE;
}
...
}
public class DefaultTransactionManager implements TransactionManager {
...
@Override
public GlobalStatus commit(String xid) throws TransactionException {
GlobalCommitRequest globalCommit = new GlobalCommitRequest();
globalCommit.setXid(xid);
GlobalCommitResponse response = (GlobalCommitResponse) syncCall(globalCommit);
return response.getGlobalStatus();
}
private AbstractTransactionResponse syncCall(AbstractTransactionRequest request) throws TransactionException {
try {
//TMNettyRemotingClient会和Seata Server基于Netty建立长连接
return (AbstractTransactionResponse) TmNettyRemotingClient.getInstance().sendSyncRequest(request);
} catch (TimeoutException toe) {
throw new TmTransactionException(TransactionExceptionCode.IO, "RPC timeout", toe);
}
}
...
}

复制代码

(2)Server向Client发送提交分支事务的请求
ServerHandler的channelRead()方法会将收到的请求进行层层传递：首先交给DefaultCoordinator的onRequest()方法来进行处理，然后交给GlobalCommitRequest的handle()方法来进行处理，接着交给AbstractTCInboundHandler的handle()方法来进行处理，最后交给DefaultCoordinator的doGlobalCommit()方法来进行处理，也就是调用DefaultCore的commit()方法来提交全局事务。

public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {
...
@ChannelHandler.Sharable
class ServerHandler extends ChannelDuplexHandler {
@Override
public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
if (!(msg instanceof RpcMessage)) {
return;
}
//接下来调用processMessage()方法对解码完毕的RpcMessage对象进行处理
processMessage(ctx, (RpcMessage) msg);
}
...
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
protected void processMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(String.format("%s msgId:%s, body:%s", this, rpcMessage.getId(), rpcMessage.getBody()));
}
Object body = rpcMessage.getBody();
if (body instanceof MessageTypeAware) {
MessageTypeAware messageTypeAware = (MessageTypeAware) body;
//根据消息类型获取到一个Pair对象，该Pair对象是由请求处理组件和请求处理线程池组成的
//processorTable里的内容，是NettyRemotingServer在初始化时，通过调用registerProcessor()方法put进去的
//所以下面的代码实际上会由ServerOnRequestProcessor的process()方法进行处理
final Pair<RemotingProcessor, ExecutorService> pair = this.processorTable.get((int) messageTypeAware.getTypeCode());
if (pair != null) {
if (pair.getSecond() != null) {
try {
pair.getSecond().execute(() -> {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
} finally {
MDC.clear();
}
});
} catch (RejectedExecutionException e) {
...
}
} else {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
}
}
} else {
LOGGER.error("This message type [{}] has no processor.", messageTypeAware.getTypeCode());
}
} else {
LOGGER.error("This rpcMessage body[{}] is not MessageTypeAware type.", body);
}
}
...
}
public class ServerOnRequestProcessor implements RemotingProcessor, Disposable {
private final RemotingServer remotingServer;
...
@Override
public void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (ChannelManager.isRegistered(ctx.channel())) {
onRequestMessage(ctx, rpcMessage);
} else {
try {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("closeChannelHandlerContext channel:" + ctx.channel());
}
ctx.disconnect();
ctx.close();
} catch (Exception exx) {
LOGGER.error(exx.getMessage());
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info(String.format("close a unhandled connection! [%s]", ctx.channel().toString()));
}
}
}
private void onRequestMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) {
Object message = rpcMessage.getBody();
//RpcContext线程本地变量副本
RpcContext rpcContext = ChannelManager.getContextFromIdentified(ctx.channel());
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("server received:{},clientIp:{},vgroup:{}", message, NetUtil.toIpAddress(ctx.channel().remoteAddress()), rpcContext.getTransactionServiceGroup());
} else {
try {
BatchLogHandler.INSTANCE.getLogQueue().put(message + ",clientIp:" + NetUtil.toIpAddress(ctx.channel().remoteAddress()) + ",vgroup:" + rpcContext.getTransactionServiceGroup());
} catch (InterruptedException e) {
LOGGER.error("put message to logQueue error: {}", e.getMessage(), e);
}
}
if (!(message instanceof AbstractMessage)) {
return;
}
//the batch send request message
if (message instanceof MergedWarpMessage) {
...
} else {
//the single send request message
final AbstractMessage msg = (AbstractMessage) message;
//最终调用到DefaultCoordinator的onRequest()方法来处理RpcMessage
AbstractResultMessage result = transactionMessageHandler.onRequest(msg, rpcContext);
//返回响应给客户端
remotingServer.sendAsyncResponse(rpcMessage, ctx.channel(), result);
}
}
...
}
public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
...
@Override
public AbstractResultMessage onRequest(AbstractMessage request, RpcContext context) {
if (!(request instanceof AbstractTransactionRequestToTC)) {
throw new IllegalArgumentException();
}
//传入的request其实就是客户端发送请求时的GlobalCommitRequest
AbstractTransactionRequestToTC transactionRequest = (AbstractTransactionRequestToTC) request;
transactionRequest.setTCInboundHandler(this);
return transactionRequest.handle(context);
}
...
}
public class GlobalCommitRequest extends AbstractGlobalEndRequest {
@Override
public short getTypeCode() {
return MessageType.TYPE_GLOBAL_COMMIT;
}
@Override
public AbstractTransactionResponse handle(RpcContext rpcContext) {
return handler.handle(this, rpcContext);
}
}
public abstract class AbstractTCInboundHandler extends AbstractExceptionHandler implements TCInboundHandler {
...
@Override
public GlobalCommitResponse handle(GlobalCommitRequest request, final RpcContext rpcContext) {
GlobalCommitResponse response = new GlobalCommitResponse();
response.setGlobalStatus(GlobalStatus.Committing);
exceptionHandleTemplate(new AbstractCallback<GlobalCommitRequest, GlobalCommitResponse>() {
@Override
public void execute(GlobalCommitRequest request, GlobalCommitResponse response) throws TransactionException {
try {
doGlobalCommit(request, response, rpcContext);
} catch (StoreException e) {
throw new TransactionException(TransactionExceptionCode.FailedStore, String.format("global commit request failed. xid=%s, msg=%s", request.getXid(), e.getMessage()), e);
}
}
@Override
public void onTransactionException(GlobalCommitRequest request, GlobalCommitResponse response, TransactionException tex) {
super.onTransactionException(request, response, tex);
checkTransactionStatus(request, response);
}
@Override
public void onException(GlobalCommitRequest request, GlobalCommitResponse response, Exception rex) {
super.onException(request, response, rex);
checkTransactionStatus(request, response);
}
}, request, response);
return response;
}
protected abstract void doGlobalCommit(GlobalCommitRequest request, GlobalCommitResponse response, RpcContext rpcContext) throws TransactionException;
...
}
public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
private final DefaultCore core;
...
@Override
protected void doGlobalCommit(GlobalCommitRequest request, GlobalCommitResponse response, RpcContext rpcContext) throws TransactionException {
MDC.put(RootContext.MDC_KEY_XID, request.getXid());
//调用DefaultCore.commit()方法提交全局事务
response.setGlobalStatus(core.commit(request.getXid()));
}
...
}

复制代码

DefaultCore的commit()方法会调用DefaultCore的doGlobalCommit()方法，而doGlobalCommit()方法会获取全局事务的所有分支事务并进行遍历，然后把提交分支事务的请求BranchCommitRequest发送到Seata Client中。

public class DefaultCore implements Core {
...
@Override
public GlobalStatus commit(String xid) throws TransactionException {
GlobalSession globalSession = SessionHolder.findGlobalSession(xid);
if (globalSession == null) {
return GlobalStatus.Finished;
}
globalSession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
//just lock changeStatus
boolean shouldCommit = SessionHolder.lockAndExecute(globalSession, () -> {
if (globalSession.getStatus() == GlobalStatus.Begin) {
//Highlight: Firstly, close the session, then no more branch can be registered.
globalSession.closeAndClean();
if (globalSession.canBeCommittedAsync()) {
globalSession.asyncCommit();
MetricsPublisher.postSessionDoneEvent(globalSession, GlobalStatus.Committed, false, false);
return false;
} else {
globalSession.changeGlobalStatus(GlobalStatus.Committing);
return true;
}
}
return false;
});
if (shouldCommit) {
boolean success = doGlobalCommit(globalSession, false);
//If successful and all remaining branches can be committed asynchronously, do async commit.
if (success && globalSession.hasBranch() && globalSession.canBeCommittedAsync()) {
globalSession.asyncCommit();
return GlobalStatus.Committed;
} else {
return globalSession.getStatus();
}
} else {
return globalSession.getStatus() == GlobalStatus.AsyncCommitting ? GlobalStatus.Committed : globalSession.getStatus();
}
}
@Override
public boolean doGlobalCommit(GlobalSession globalSession, boolean retrying) throws TransactionException {
boolean success = true;
//start committing event
MetricsPublisher.postSessionDoingEvent(globalSession, retrying);
if (globalSession.isSaga()) {
success = getCore(BranchType.SAGA).doGlobalCommit(globalSession, retrying);
} else {
//获取到全局事务的所有分支事务，并进行遍历提交
Boolean result = SessionHelper.forEach(globalSession.getSortedBranches(), branchSession -> {
//if not retrying, skip the canBeCommittedAsync branches
if (!retrying && branchSession.canBeCommittedAsync()) {
return CONTINUE;
}
BranchStatus currentStatus = branchSession.getStatus();
if (currentStatus == BranchStatus.PhaseOne_Failed) {
SessionHelper.removeBranch(globalSession, branchSession, !retrying);
return CONTINUE;
}
try {
//发送请求给Seata Client提交分支事务
BranchStatus branchStatus = getCore(branchSession.getBranchType()).branchCommit(globalSession, branchSession);
if (isXaerNotaTimeout(globalSession,branchStatus)) {
LOGGER.info("Commit branch XAER_NOTA retry timeout, xid = {} branchId = {}", globalSession.getXid(), branchSession.getBranchId());
branchStatus = BranchStatus.PhaseTwo_Committed;
}
switch (branchStatus) {
case PhaseTwo_Committed:
SessionHelper.removeBranch(globalSession, branchSession, !retrying);
return CONTINUE;
case PhaseTwo_CommitFailed_Unretryable:
//not at branch
SessionHelper.endCommitFailed(globalSession, retrying);
LOGGER.error("Committing global transaction[{}] finally failed, caused by branch transaction[{}] commit failed.", globalSession.getXid(), branchSession.getBranchId());
return false;
default:
if (!retrying) {
globalSession.queueToRetryCommit();
return false;
}
if (globalSession.canBeCommittedAsync()) {
LOGGER.error("Committing branch transaction[{}], status:{} and will retry later", branchSession.getBranchId(), branchStatus);
return CONTINUE;
} else {
LOGGER.error("Committing global transaction[{}] failed, caused by branch transaction[{}] commit failed, will retry later.", globalSession.getXid(), branchSession.getBranchId());
return false;
}
}
} catch (Exception ex) {
StackTraceLogger.error(LOGGER, ex, "Committing branch transaction exception: {}", new String[] {branchSession.toString()});
if (!retrying) {
globalSession.queueToRetryCommit();
throw new TransactionException(ex);
}
}
return CONTINUE;
});
//Return if the result is not null
if (result != null) {
return result;
}
//If has branch and not all remaining branches can be committed asynchronously,
//do print log and return false
if (globalSession.hasBranch() && !globalSession.canBeCommittedAsync()) {
LOGGER.info("Committing global transaction is NOT done, xid = {}.", globalSession.getXid());
return false;
}
if (!retrying) {
//contains not AT branch
globalSession.setStatus(GlobalStatus.Committed);
}
}
//if it succeeds and there is no branch, retrying=true is the asynchronous state when retrying. EndCommitted is
//executed to improve concurrency performance, and the global transaction ends..
if (success && globalSession.getBranchSessions().isEmpty()) {
SessionHelper.endCommitted(globalSession, retrying);
LOGGER.info("Committing global transaction is successfully done, xid = {}.", globalSession.getXid());
}
return success;
}
...
}
public abstract class AbstractCore implements Core {
protected RemotingServer remotingServer;
...
@Override
public BranchStatus branchCommit(GlobalSession globalSession, BranchSession branchSession) throws TransactionException {
try {
BranchCommitRequest request = new BranchCommitRequest();
request.setXid(branchSession.getXid());
request.setBranchId(branchSession.getBranchId());
request.setResourceId(branchSession.getResourceId());
request.setApplicationData(branchSession.getApplicationData());
request.setBranchType(branchSession.getBranchType());
return branchCommitSend(request, globalSession, branchSession);
} catch (IOException | TimeoutException e) {
throw new BranchTransactionException(FailedToSendBranchCommitRequest, String.format("Send branch commit failed, xid = %s branchId = %s", branchSession.getXid(), branchSession.getBranchId()), e);
}
}
protected BranchStatus branchCommitSend(BranchCommitRequest request, GlobalSession globalSession, BranchSession branchSession) throws IOException, TimeoutException {
BranchCommitResponse response = (BranchCommitResponse) remotingServer.sendSyncRequest(branchSession.getResourceId(), branchSession.getClientId(), request);
return response.getBranchStatus();
}
...
}
public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {
...
@Override
public Object sendSyncRequest(Channel channel, Object msg) throws TimeoutException {
if (channel == null) {
throw new RuntimeException("client is not connected");
}
RpcMessage rpcMessage = buildRequestMessage(msg, ProtocolConstants.MSGTYPE_RESQUEST_SYNC);
return super.sendSync(channel, rpcMessage, NettyServerConfig.getRpcRequestTimeout());
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
protected Object sendSync(Channel channel, RpcMessage rpcMessage, long timeoutMillis) throws TimeoutException {
if (timeoutMillis <= 0) {
throw new FrameworkException("timeout should more than 0ms");
}
if (channel == null) {
LOGGER.warn("sendSync nothing, caused by null channel.");
return null;
}
//把发送出去的请求封装到MessageFuture中，然后存放到futures这个Map里
MessageFuture messageFuture = new MessageFuture();
messageFuture.setRequestMessage(rpcMessage);
messageFuture.setTimeout(timeoutMillis);
futures.put(rpcMessage.getId(), messageFuture);
channelWritableCheck(channel, rpcMessage.getBody());
//获取远程地址
String remoteAddr = ChannelUtil.getAddressFromChannel(channel);
doBeforeRpcHooks(remoteAddr, rpcMessage);
//异步化发送数据，同时对发送结果添加监听器
//如果发送失败，则会对网络连接Channel进行销毁处理
channel.writeAndFlush(rpcMessage).addListener((ChannelFutureListener) future -> {
if (!future.isSuccess()) {
MessageFuture messageFuture1 = futures.remove(rpcMessage.getId());
if (messageFuture1 != null) {
messageFuture1.setResultMessage(future.cause());
}
destroyChannel(future.channel());
}
});
try {
//然后通过请求响应组件MessageFuture同步等待Seata Server返回该请求的响应
Object result = messageFuture.get(timeoutMillis, TimeUnit.MILLISECONDS);
doAfterRpcHooks(remoteAddr, rpcMessage, result);
return result;
} catch (Exception exx) {
LOGGER.error("wait response error:{},ip:{},request:{}", exx.getMessage(), channel.remoteAddress(), rpcMessage.getBody());
if (exx instanceof TimeoutException) {
throw (TimeoutException) exx;
} else {
throw new RuntimeException(exx);
}
}
}
...
}

复制代码

(3)Seata Client处理提交分支事务的请求
ClientHandler的channelRead()方法收到提交分支事务的请求后，会由RmBranchCommitProcessor的handleBranchCommit()方法进行处理。

-> AbstractRMHandler.onRequest()
-> BranchCommitRequest.handle()
-> AbstractRMHandler.handle()
-> AbstractRMHandler.doBranchCommit()
-> DataSourceManager.branchCommit()
-> AsyncWorker.branchCommit()异步化提交分支事务

复制代码

public abstract class AbstractNettyRemotingClient extends AbstractNettyRemoting implements RemotingClient {
...
@Sharable
class ClientHandler extends ChannelDuplexHandler {
@Override
public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
if (!(msg instanceof RpcMessage)) {
return;
}
processMessage(ctx, (RpcMessage) msg);
}
...
}
...
}
public abstract class AbstractNettyRemoting implements Disposable {
...
protected void processMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(String.format("%s msgId:%s, body:%s", this, rpcMessage.getId(), rpcMessage.getBody()));
}
Object body = rpcMessage.getBody();
if (body instanceof MessageTypeAware) {
MessageTypeAware messageTypeAware = (MessageTypeAware) body;
//根据消息类型获取到一个Pair对象，该Pair对象是由请求处理组件和请求处理线程池组成的
final Pair<RemotingProcessor, ExecutorService> pair = this.processorTable.get((int) messageTypeAware.getTypeCode());
if (pair != null) {
if (pair.getSecond() != null) {
try {
pair.getSecond().execute(() -> {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
} finally {
MDC.clear();
}
});
} catch (RejectedExecutionException e) {
...
}
} else {
try {
pair.getFirst().process(ctx, rpcMessage);
} catch (Throwable th) {
LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);
}
}
} else {
LOGGER.error("This message type [{}] has no processor.", messageTypeAware.getTypeCode());
}
} else {
LOGGER.error("This rpcMessage body[{}] is not MessageTypeAware type.", body);
}
}
...
}
public class RmBranchCommitProcessor implements RemotingProcessor {
...
@Override
public void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
String remoteAddress = NetUtil.toStringAddress(ctx.channel().remoteAddress());
Object msg = rpcMessage.getBody();
if (LOGGER.isInfoEnabled()) {
LOGGER.info("rm client handle branch commit process:" + msg);
}
handleBranchCommit(rpcMessage, remoteAddress, (BranchCommitRequest) msg);
}
private void handleBranchCommit(RpcMessage request, String serverAddress, BranchCommitRequest branchCommitRequest) {
BranchCommitResponse resultMessage;
resultMessage = (BranchCommitResponse) handler.onRequest(branchCommitRequest, null);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("branch commit result:" + resultMessage);
}
try {
this.remotingClient.sendAsyncResponse(serverAddress, request, resultMessage);
} catch (Throwable throwable) {
LOGGER.error("branch commit error: {}", throwable.getMessage(), throwable);
}
}
...
}
public abstract class AbstractRMHandler extends AbstractExceptionHandler implements RMInboundHandler, TransactionMessageHandler {
...
@Override
public AbstractResultMessage onRequest(AbstractMessage request, RpcContext context) {
if (!(request instanceof AbstractTransactionRequestToRM)) {
throw new IllegalArgumentException();
}
AbstractTransactionRequestToRM transactionRequest = (AbstractTransactionRequestToRM)request;
transactionRequest.setRMInboundMessageHandler(this);
return transactionRequest.handle(context);
}
...
}
public class BranchCommitRequest extends AbstractBranchEndRequest {
@Override
public short getTypeCode() {
return MessageType.TYPE_BRANCH_COMMIT;
}
@Override
public AbstractTransactionResponse handle(RpcContext rpcContext) {
return handler.handle(this);
}
}
public abstract class AbstractRMHandler extends AbstractExceptionHandler implements RMInboundHandler, TransactionMessageHandler {
@Override
public BranchCommitResponse handle(BranchCommitRequest request) {
BranchCommitResponse response = new BranchCommitResponse();
exceptionHandleTemplate(new AbstractCallback<BranchCommitRequest, BranchCommitResponse>() {
@Override
public void execute(BranchCommitRequest request, BranchCommitResponse response) throws TransactionException {
doBranchCommit(request, response);
}
}, request, response);
return response;
}
protected void doBranchCommit(BranchCommitRequest request, BranchCommitResponse response) throws TransactionException {
String xid = request.getXid();
long branchId = request.getBranchId();
String resourceId = request.getResourceId();
String applicationData = request.getApplicationData();
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Branch committing: " + xid + " " + branchId + " " + resourceId + " " + applicationData);
}
BranchStatus status = getResourceManager().branchCommit(request.getBranchType(), xid, branchId, resourceId, applicationData);
response.setXid(xid);
response.setBranchId(branchId);
response.setBranchStatus(status);
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Branch commit result: " + status);
}
}
...
}
//The type Data source manager. DataSourceManager是AT模式下的资源管理器
public class DataSourceManager extends AbstractResourceManager {
//异步化worker
private final AsyncWorker asyncWorker = new AsyncWorker(this);
...
@Override
public BranchStatus branchCommit(BranchType branchType, String xid, long branchId, String resourceId, String applicationData) throws TransactionException {
//通过asyncWorker，异步化提交分支事务
return asyncWorker.branchCommit(xid, branchId, resourceId);
}
...
}

复制代码

(4)全局事务的提交主要就是让各个分支事务把本地的UndoLog删除

public class AsyncWorker {
...
public BranchStatus branchCommit(String xid, long branchId, String resourceId) {
Phase2Context context = new Phase2Context(xid, branchId, resourceId);
addToCommitQueue(context);
return BranchStatus.PhaseTwo_Committed;
}
private void addToCommitQueue(Phase2Context context) {
if (commitQueue.offer(context)) {
return;
}
CompletableFuture.runAsync(this::doBranchCommitSafely, scheduledExecutor).thenRun(() -> addToCommitQueue(context));
}
void doBranchCommitSafely() {
try {
doBranchCommit();
} catch (Throwable e) {
LOGGER.error("Exception occur when doing branch commit", e);
}
}
private void doBranchCommit() {
if (commitQueue.isEmpty()) {
return;
}
//transfer all context currently received to this list
List<Phase2Context> allContexts = new LinkedList<>();
commitQueue.drainTo(allContexts);
//group context by their resourceId
Map<String, List<Phase2Context>> groupedContexts = groupedByResourceId(allContexts);
groupedContexts.forEach(this::dealWithGroupedContexts);
}
private void dealWithGroupedContexts(String resourceId, List<Phase2Context> contexts) {
DataSourceProxy dataSourceProxy = dataSourceManager.get(resourceId);
if (dataSourceProxy == null) {
LOGGER.warn("failed to find resource for {} and requeue", resourceId);
addAllToCommitQueue(contexts);
return;
}
Connection conn = null;
try {
conn = dataSourceProxy.getPlainConnection();
UndoLogManager undoLogManager = UndoLogManagerFactory.getUndoLogManager(dataSourceProxy.getDbType());
//split contexts into several lists, with each list contain no more element than limit size
List<List<Phase2Context>> splitByLimit = Lists.partition(contexts, UNDOLOG_DELETE_LIMIT_SIZE);
//全局事务的提交，就是让各个分支事务把本地的undo logs删除掉即可
for (List<Phase2Context> partition : splitByLimit) {
deleteUndoLog(conn, undoLogManager, partition);
}
} catch (SQLException sqlExx) {
addAllToCommitQueue(contexts);
LOGGER.error("failed to get connection for async committing on {} and requeue", resourceId, sqlExx);
} finally {
IOUtil.close(conn);
}
}
...
}

复制代码

18.全局事务回滚的过程源码
全局事务的回滚流程和提交流程几乎一样：
一.Seata Client发起全局事务回滚请求
二.Server向Client发送分支事务回滚请求
三.Seata Client处理分支事务回滚的请求

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Seata源码—6.Seata AT模式的数据源代理

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