Seata源码—5.全局事务的创建与返回处理

梢疠 · 2025-6-2 23:52:39

大纲
1.Seata开启分布式事务的流程总结
2.Seata生成全局事务ID的雪花算法源码
3.生成xid以及对全局事务会话进行持久化的源码
4.全局事务会话数据持久化的实现源码
5.Seata Server创建全局事务与返回xid的源码
6.Client获取Server的响应与处理的源码
7.Seata与Dubbo整合的过滤器源码

1.Seata开启分布式事务的流程总结
(1)Seata分布式事务执行流程
(2)开启一个全局事务的流程

(1)Seata分布式事务执行流程
Seata Client在执行添加了全局事务注解@GlobalTransactional的方法时，实际执行的是根据全局事务拦截器创建该方法所在Bean的动态代理方法，于是会执行GlobalTransactionalInterceptor的invoke()方法。此时，添加了全局事务注解@GlobalTransactional的方法就会被全局事务拦截器拦截了。

GlobalTransactionalInterceptor全局事务拦截器拦截目标方法的调用后，会由事务执行模版TransactionalTemplate的excute()方法来执行目标方法。

在事务执行模版TransactionalTemplate的excute()方法中，首先会判断Propagation全局事务传播级别，然后开启一个全局事务(也就是打开一个全局事务)，接着才执行具体的业务目标方法。

执行具体的业务目标方法时，会通过Dubbo的RPC调用来传递全局事务的xid给其他的Seata Client。其他的Seata Client通过Dubbo过滤器获取到RPC调用中的xid后，会将xid放入线程本地变量副本中。之后执行SQL时就会获取数据库连接代理来对SQL进行拦截，数据库连接代理就可以从线程本地变量副本中获取xid，然后开启分支事务。

各个分支事务都执行完毕后，开启全局事务的Seata Client就会提交事务、处理全局锁、资源清理。

(2)开启一个全局事务的流程
Seata Server收到Seata Client发送过来的RpcMessage对象消息后，RpcMessage对象消息首先会由ServerOnRequestProcessor的process()方法处理，然后会由DefaultCoordinator的onRequest()方法进行处理，接着会由GlobalBeginRequest的handle()方法进行处理，然后会由DefaultCoordinator的doGlobalBegin()方法来处理，最后给到DefaultCore的begin()方法来进行处理。

在DefaultCore的begin()方法中，首先就会创建一个全局事务会话，然后将全局事务会话的xid通过MDC放入线程本地变量副本中，接着对该全局事务会话添加一个全局事务会话的生命周期监听器，最后打开该全局事务会话、发布会话开启事件并返回全局事务会话的xid。

在创建一个全局事务会话GlobalSession时，首先会由uuid生成组件UUIDGenerator来生成全局事务id(transactionId)，然后根据生成的全局事务id(transactionId)来继续生成xid。

2.Seata生成全局事务ID的雪花算法源码
(1)通过UUIDGenerator生成全局事务ID
(2)IdWorker实现的雪花算法生成的ID的组成
(3)IdWorker实现的雪花算法对时钟回拨的处理

(1)通过UUIDGenerator生成全局事务ID
Seata在创建全局事务会话时会通过UUIDGenerator来生成全局事务ID，UUIDGenerator在生成ID时是通过Seata自己实现的雪花算法来生成的。

public class GlobalSession implements SessionLifecycle, SessionStorable {
...
//创建全局事务会话
public static GlobalSession createGlobalSession(String applicationId, String txServiceGroup, String txName, int timeout) {
GlobalSession session = new GlobalSession(applicationId, txServiceGroup, txName, timeout, false);
return session;
}
public GlobalSession(String applicationId, String transactionServiceGroup, String transactionName, int timeout, boolean lazyLoadBranch) {
//全局事务id是通过UUIDGenerator来生成的
this.transactionId = UUIDGenerator.generateUUID();
this.status = GlobalStatus.Begin;
this.lazyLoadBranch = lazyLoadBranch;
if (!lazyLoadBranch) {
this.branchSessions = new ArrayList<>();
}
this.applicationId = applicationId;
this.transactionServiceGroup = transactionServiceGroup;
this.transactionName = transactionName;
this.timeout = timeout;
//根据UUIDGenerator生成的transactionId + XID工具生成最终的xid
this.xid = XID.generateXID(transactionId);
}
...
}
public class UUIDGenerator {
private static volatile IdWorker idWorker;
//generate UUID using snowflake algorithm
public static long generateUUID() {
//Double Check + volatile，实现并发场景下只创建一次idWorker对象
if (idWorker == null) {
synchronized (UUIDGenerator.class) {
if (idWorker == null) {
init(null);
}
}
}
//正常情况下，每次都会通过idWorker生成一个id
return idWorker.nextId();
}
//init IdWorker
public static void init(Long serverNode) {
idWorker = new IdWorker(serverNode);
}
}

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(2)IdWorker实现的雪花算法生成的ID的组成
IdWorker就是Seata自己实现的基于雪花算法的ID生成器。IdWorker的nextId()方法通过雪花算法生成的transactionId一共是64位，用64个bit拼接出一个唯一的ID。

一.最高位始终是0，占1个bit

二.接着的10个bit是workerId
一台机器就是一个worker，每个worker都会有一个自己的workerId。生成workerId时，是基于本机网络地址里的Mac地址来生成的。

三.接着的41个bit是时间戳
表示可以为某台机器的每一毫秒，分配一个自增长的ID。毫秒时间戳有13位数，转换为2进制需要2的41次方。

四.最后的12个bit是序列号
如果一台机器在一毫秒内需要为很多线程生成ID，就可以通过自增长的12个bit的Sequence为每个线程分配ID。

(3)IdWorker实现的雪花算法对时钟回拨的处理
在执行IdWorker的nextId()方法时，会对包含序列号和时间戳的timestampAndSequence进行累加，也就是对timestampAndSequence的某一个毫秒内的Sequence序列号进行累加。

如果出现大量的线程并发获取ID，此时可能会导致timestampAndSequence中某一个毫秒内的Sequence序列号快速累加，并且将代表Sequence序列号的12个bit全部累加完毕，最后便会导致包含序列号和时间戳的timestampAndSequence中的毫秒时间戳也进行累加。

但当前的实际时间其实还是这一毫秒，而timestampAndSequence里的毫秒时间戳已经累加到下一个毫秒去了，出现时钟回拨问题，于是就需要调用waitIfNecessary()方法进行处理。

所以，在IdWorker的waitIfNecessary()方法中，如果获取ID的QPS过高，导致当前时间戳对应的Sequence序列号被耗尽，那么就需要阻塞当前线程5毫秒。

//IdWorker就是Seata自己实现的基于雪花算法的ID生成器
public class IdWorker {
private final long twepoch = 1588435200000L;//Start time cut (2020-05-03)
private final int workerIdBits = 10;//The number of bits occupied by workerId
private final int timestampBits = 41;//The number of bits occupied by timestamp
private final int sequenceBits = 12;//The number of bits occupied by sequence
private final int maxWorkerId = ~(-1 << workerIdBits);//Maximum supported machine id, the result is 1023
//business meaning: machine ID (0 ~ 1023)
//actual layout in memory:
//highest 1 bit: 0
//middle 10 bit: workerId
//lowest 53 bit: all 0
private long workerId;
//timestampAndSequence是64位的、支持CAS操作的Long型的、包含了Sequence序列号的时间戳
//它的最高位是11个bit，没有使用
//中间有41个bit，是时间戳
//最低位有12个bit，是序列号
//timestampAndSequence可以认为是把时间戳和序列号混合在了一个long型数字里
//timestamp and sequence mix in one Long
//highest 11 bit: not used
//middle 41 bit: timestamp
//lowest 12 bit: sequence
private AtomicLong timestampAndSequence;
//mask that help to extract timestamp and sequence from a long
//可以帮忙从一个long数字里提取出一个包含Sequence序列号的时间戳
private final long timestampAndSequenceMask = ~(-1L << (timestampBits + sequenceBits));
//instantiate an IdWorker using given workerId
public IdWorker(Long workerId) {
//初始化timestampAndSequence
initTimestampAndSequence();
//初始化workerId
initWorkerId(workerId);
}
//init first timestamp and sequence immediately
private void initTimestampAndSequence() {
//获取相对于twepoch的最新时间戳
long timestamp = getNewestTimestamp();
//将最新时间戳和sequenceBits进行位运算(左移)，从而得到一个混合了sequence的时间戳
long timestampWithSequence = timestamp << sequenceBits;
//把混合了sequence的时间戳，赋值给timestampAndSequence
this.timestampAndSequence = new AtomicLong(timestampWithSequence);
}
//init workerId
private void initWorkerId(Long workerId) {
if (workerId == null) {
workerId = generateWorkerId();
}
if (workerId > maxWorkerId || workerId < 0) {
String message = String.format("worker Id can't be greater than %d or less than 0", maxWorkerId);
throw new IllegalArgumentException(message);
}
//将workerId与timestampBits+sequenceBits的和进行位运算(左移)，获取一个workerId
this.workerId = workerId << (timestampBits + sequenceBits);
}
//通过snowflake雪花算法来生成transactionId
//一共是64位，用64个bit拼接出一个唯一的ID，最高位始终是0，占1个bit
//接着的10个bit是workerId，一台机器就是一个worker，每个worker都会有一个自己的workerId
//接着的41个bit是时间戳，表示可以为某台机器的每一毫秒，分配一个自增长的id，毫秒时间戳有13位数，转换为2进制就需要2的41次方，2的20次方是一个7位数的数字
//最后的12个bit是序列号，如果一台机器在一毫秒内需要为很多线程生成id，就可以通过自增长的12个bit的Sequence为每个线程分配id
//get next UUID(base on snowflake algorithm), which look like:
//highest 1 bit: always 0
//next 10 bit: workerId
//next 41 bit: timestamp
//lowest 12 bit: sequence
public long nextId() {
waitIfNecessary();
//对包含Sequence序列号的时间戳timestampAndSequence进行累加，也就是对timestampAndSequence的某一个毫秒内的Sequence进行累加
//如果出现大量的线程并发获取id，此时可能会导致timestampAndSequence的某一个毫秒内的Sequence快速累加，并且将12个bit全部累加完毕
//最终导致timestampAndSequence的毫秒时间戳也进行累加了
//但当前的实际时间其实还是这一毫秒，而timestampAndSequence里的毫秒时间戳已经累加到下一个毫秒去了，于是就需要waitIfNecessary()进行处理
long next = timestampAndSequence.incrementAndGet();
//把最新的包含Sequence序列号的时间戳next与timestampAndSequenceMask进行位运算，获取真正的包含Sequence序列号的时间戳timestampWithSequence
long timestampWithSequence = next & timestampAndSequenceMask;
//对包含Sequence序列号的时间戳与workerId通过位运算拼接在一起
return workerId | timestampWithSequence;
}
//block current thread if the QPS of acquiring UUID is too high that current sequence space is exhausted
//如果获取UUID的QPS过高，导致当前时间戳对应的Sequence序列号被耗尽了，那么就需要阻塞当前线程5毫秒
private void waitIfNecessary() {
//先获取包含Sequence序列号的当前时间戳
long currentWithSequence = timestampAndSequence.get();
//将currentWithSequence与sequenceBits进行位运算(右移)，获取到当前时间戳
long current = currentWithSequence >>> sequenceBits;
//获取相对于twepoch的最新时间戳
long newest = getNewestTimestamp();
//如果当前的时间戳大于最新的时间戳，说明获取UUID的QPS过高，导致timestampAndSequence增长太快了(出现时钟回拨问题)
if (current >= newest) {
try {
//如果获取UUID的QPS过高，导致当前时间戳对应的Sequence序列号被耗尽了，那么就需要阻塞当前线程5毫秒
Thread.sleep(5);
} catch (InterruptedException ignore) {
//don't care
}
}
}
//get newest timestamp relative to twepoch
private long getNewestTimestamp() {
//通过当前毫秒单位的时间戳减去一个固定的时间twepoch，得到的就是相对于twepoch的最新时间戳
return System.currentTimeMillis() - twepoch;
}
//auto generate workerId, try using mac first, if failed, then randomly generate one
private long generateWorkerId() {
try {
//生成一个workerId，默认是基于网络的Mac地址来生成的
return generateWorkerIdBaseOnMac();
} catch (Exception e) {
return generateRandomWorkerId();
}
}
//use lowest 10 bit of available MAC as workerId
private long generateWorkerIdBaseOnMac() throws Exception {
//获取所有的网络接口
Enumeration<NetworkInterface> all = NetworkInterface.getNetworkInterfaces();
//遍历每一个网络接口
while (all.hasMoreElements()) {
NetworkInterface networkInterface = all.nextElement();
boolean isLoopback = networkInterface.isLoopback();
boolean isVirtual = networkInterface.isVirtual();
//如果是虚拟的、回环的地址，那么这个地址就跳过，不能使用
if (isLoopback || isVirtual) {
continue;
}
//获取本机网络地址里的Mac地址，基于Mac地址来生成一个workerid
byte[] mac = networkInterface.getHardwareAddress();
return ((mac[4] & 0B11) << 8) | (mac[5] & 0xFF);
}
throw new RuntimeException("no available mac found");
}
//randomly generate one as workerId
private long generateRandomWorkerId() {
return new Random().nextInt(maxWorkerId + 1);
}
}

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(3)将全局事务会话持久化到File文件的实现

public class XID {
private static int port;
private static String ipAddress;
...
//Generate xid string.
public static String generateXID(long tranId) {
//首先获取当前机器的IP地址
//然后拼接上一个冒号、接着拼接一个端口号、再拼接一个冒号
//最后再拼接事务id，以此来生成xid
//所以xid是通过ip:port:transactionId拼接出来的
return new StringBuilder().append(ipAddress).append(IP_PORT_SPLIT_CHAR).append(port).append(IP_PORT_SPLIT_CHAR).append(tranId).toString();
}
...
}

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public class DefaultCore implements Core {
...
@Override
public String begin(String applicationId, String transactionServiceGroup, String name, int timeout) throws TransactionException {
//创建一个全局事务会话
GlobalSession session = GlobalSession.createGlobalSession(applicationId, transactionServiceGroup, name, timeout);
//通过slf4j的MDC把xid放入线程本地变量副本里去
MDC.put(RootContext.MDC_KEY_XID, session.getXid());
//添加一个全局事务会话的生命周期监听器
session.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
//打开Session，其中会对全局事务会话进行持久化
session.begin();
//transaction start event，发布会话开启事件
MetricsPublisher.postSessionDoingEvent(session, false);
//返回全局事务会话的xid
return session.getXid();
}
...
}
public class GlobalSession implements SessionLifecycle, SessionStorable {
...
@Override
public void begin() throws TransactionException {
this.status = GlobalStatus.Begin;
this.beginTime = System.currentTimeMillis();
this.active = true;
for (SessionLifecycleListener lifecycleListener : lifecycleListeners) {
lifecycleListener.onBegin(this);
}
}
...
}
public abstract class AbstractSessionManager implements SessionManager, SessionLifecycleListener {
...
@Override
public void onBegin(GlobalSession globalSession) throws TransactionException {
addGlobalSession(globalSession);
}
@Override
public void addGlobalSession(GlobalSession session) throws TransactionException {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("MANAGER[{}] SESSION[{}] {}", name, session, LogOperation.GLOBAL_ADD);
}
writeSession(LogOperation.GLOBAL_ADD, session);
}
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)) {
if (LogOperation.GLOBAL_ADD.equals(logOperation)) {
throw new GlobalTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to store global session");
} else if (LogOperation.GLOBAL_UPDATE.equals(logOperation)) {
throw new GlobalTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to update global session");
} else if (LogOperation.GLOBAL_REMOVE.equals(logOperation)) {
throw new GlobalTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to remove global session");
} else if (LogOperation.BRANCH_ADD.equals(logOperation)) {
throw new BranchTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to store branch session");
} else if (LogOperation.BRANCH_UPDATE.equals(logOperation)) {
throw new BranchTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to update branch session");
} else if (LogOperation.BRANCH_REMOVE.equals(logOperation)) {
throw new BranchTransactionException(TransactionExceptionCode.FailedWriteSession, "Fail to remove branch session");
} else {
throw new BranchTransactionException(TransactionExceptionCode.FailedWriteSession, "Unknown LogOperation:" + logOperation.name());
}
}
}
...
}

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//The type Database transaction store manager.
public class DataBaseTransactionStoreManager extends AbstractTransactionStoreManager implements TransactionStoreManager {
private static volatile DataBaseTransactionStoreManager instance;
protected LogStore logStore;
...
//Get the instance.
public static DataBaseTransactionStoreManager getInstance() {
if (instance == null) {
synchronized (DataBaseTransactionStoreManager.class) {
if (instance == null) {
instance = new DataBaseTransactionStoreManager();
}
}
}
return instance;
}
//Instantiates a new Database transaction store manager.
private DataBaseTransactionStoreManager() {
logQueryLimit = CONFIG.getInt(ConfigurationKeys.STORE_DB_LOG_QUERY_LIMIT, DEFAULT_LOG_QUERY_LIMIT);
String datasourceType = CONFIG.getConfig(ConfigurationKeys.STORE_DB_DATASOURCE_TYPE);
//init dataSource，通过SPI机制加载DataSourceProvider
DataSource logStoreDataSource = EnhancedServiceLoader.load(DataSourceProvider.class, datasourceType).provide();
logStore = new LogStoreDataBaseDAO(logStoreDataSource);
}
@Override
public boolean writeSession(LogOperation logOperation, SessionStorable session) {
if (LogOperation.GLOBAL_ADD.equals(logOperation)) {
return logStore.insertGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));
} else if (LogOperation.GLOBAL_UPDATE.equals(logOperation)) {
return logStore.updateGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));
} else if (LogOperation.GLOBAL_REMOVE.equals(logOperation)) {
return logStore.deleteGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));
} else if (LogOperation.BRANCH_ADD.equals(logOperation)) {
return logStore.insertBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));
} else if (LogOperation.BRANCH_UPDATE.equals(logOperation)) {
return logStore.updateBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));
} else if (LogOperation.BRANCH_REMOVE.equals(logOperation)) {
return logStore.deleteBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));
} else {
throw new StoreException("Unknown LogOperation:" + logOperation.name());
}
}
...
}
public class LogStoreDataBaseDAO implements LogStore {
protected DataSource logStoreDataSource = null;
protected String globalTable;
protected String branchTable;
private String dbType;
...
public LogStoreDataBaseDAO(DataSource logStoreDataSource) {
this.logStoreDataSource = logStoreDataSource;
globalTable = CONFIG.getConfig(ConfigurationKeys.STORE_DB_GLOBAL_TABLE, DEFAULT_STORE_DB_GLOBAL_TABLE);
branchTable = CONFIG.getConfig(ConfigurationKeys.STORE_DB_BRANCH_TABLE, DEFAULT_STORE_DB_BRANCH_TABLE);
dbType = CONFIG.getConfig(ConfigurationKeys.STORE_DB_TYPE);
if (StringUtils.isBlank(dbType)) {
throw new StoreException("there must be db type.");
}
if (logStoreDataSource == null) {
throw new StoreException("there must be logStoreDataSource.");
}
//init transaction_name size
initTransactionNameSize();
}
@Override
public boolean insertGlobalTransactionDO(GlobalTransactionDO globalTransactionDO) {
String sql = LogStoreSqlsFactory.getLogStoreSqls(dbType).getInsertGlobalTransactionSQL(globalTable);
Connection conn = null;
PreparedStatement ps = null;
try {
int index = 1;
conn = logStoreDataSource.getConnection();
conn.setAutoCommit(true);
ps = conn.prepareStatement(sql);
ps.setString(index++, globalTransactionDO.getXid());
ps.setLong(index++, globalTransactionDO.getTransactionId());
ps.setInt(index++, globalTransactionDO.getStatus());
ps.setString(index++, globalTransactionDO.getApplicationId());
ps.setString(index++, globalTransactionDO.getTransactionServiceGroup());
String transactionName = globalTransactionDO.getTransactionName();
transactionName = transactionName.length() > transactionNameColumnSize ? transactionName.substring(0, transactionNameColumnSize) : transactionName;
ps.setString(index++, transactionName);
ps.setInt(index++, globalTransactionDO.getTimeout());
ps.setLong(index++, globalTransactionDO.getBeginTime());
ps.setString(index++, globalTransactionDO.getApplicationData());
return ps.executeUpdate() > 0;
} catch (SQLException e) {
throw new StoreException(e);
} finally {
IOUtil.close(ps, conn);
}
}
...
}

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public class FileTransactionStoreManager extends AbstractTransactionStoreManager implements TransactionStoreManager, ReloadableStore {
private ReentrantLock writeSessionLock = new ReentrantLock();
...
@Override
public boolean writeSession(LogOperation logOperation, SessionStorable session) {
long curFileTrxNum;
writeSessionLock.lock();
try {
if (!writeDataFile(new TransactionWriteStore(session, logOperation).encode())) {
return false;
}
lastModifiedTime = System.currentTimeMillis();
curFileTrxNum = FILE_TRX_NUM.incrementAndGet();
if (curFileTrxNum % PER_FILE_BLOCK_SIZE == 0 && (System.currentTimeMillis() - trxStartTimeMills) > MAX_TRX_TIMEOUT_MILLS) {
return saveHistory();
}
} catch (Exception exx) {
LOGGER.error("writeSession error, {}", exx.getMessage(), exx);
return false;
} finally {
writeSessionLock.unlock();
}
flushDisk(curFileTrxNum, currFileChannel);
return true;
}
private boolean writeDataFile(byte[] bs) {
if (bs == null || bs.length >= Integer.MAX_VALUE - 3) {
return false;
}
if (!writeDataFrame(bs)) {
return false;
}
return flushWriteBuffer(writeBuffer);
}
private boolean writeDataFrame(byte[] data) {
if (data == null || data.length <= 0) {
return true;
}
int dataLength = data.length;
int bufferRemainingSize = writeBuffer.remaining();
if (bufferRemainingSize <= INT_BYTE_SIZE) {
if (!flushWriteBuffer(writeBuffer)) {
return false;
}
}
bufferRemainingSize = writeBuffer.remaining();
if (bufferRemainingSize <= INT_BYTE_SIZE) {
throw new IllegalStateException(String.format("Write buffer remaining size %d was too small", bufferRemainingSize));
}
writeBuffer.putInt(dataLength);
bufferRemainingSize = writeBuffer.remaining();
int dataPos = 0;
while (dataPos < dataLength) {
int dataLengthToWrite = dataLength - dataPos;
dataLengthToWrite = Math.min(dataLengthToWrite, bufferRemainingSize);
writeBuffer.put(data, dataPos, dataLengthToWrite);
bufferRemainingSize = writeBuffer.remaining();
if (bufferRemainingSize == 0) {
if (!flushWriteBuffer(writeBuffer)) {
return false;
}
bufferRemainingSize = writeBuffer.remaining();
}
dataPos += dataLengthToWrite;
}
return true;
}
private boolean flushWriteBuffer(ByteBuffer writeBuffer) {
writeBuffer.flip();
if (!writeDataFileByBuffer(writeBuffer)) {
return false;
}
writeBuffer.clear();
return true;
}
private void flushDisk(long curFileNum, FileChannel currFileChannel) {
if (FLUSH_DISK_MODE == FlushDiskMode.SYNC_MODEL) {
SyncFlushRequest syncFlushRequest = new SyncFlushRequest(curFileNum, currFileChannel);
writeDataFileRunnable.putRequest(syncFlushRequest);
syncFlushRequest.waitForFlush(MAX_WAIT_FOR_FLUSH_TIME_MILLS);
} else {
writeDataFileRunnable.putRequest(new AsyncFlushRequest(curFileNum, currFileChannel));
}
}
...
}
public class TransactionWriteStore implements SessionStorable {
private SessionStorable sessionRequest;
private LogOperation operate;
public TransactionWriteStore(SessionStorable sessionRequest, LogOperation operate) {
this.sessionRequest = sessionRequest;
this.operate = operate;
}
@Override
public byte[] encode() {
byte[] bySessionRequest = this.sessionRequest.encode();
byte byOpCode = this.getOperate().getCode();
int len = bySessionRequest.length + 1;
byte[] byResult = new byte[len];
ByteBuffer byteBuffer = ByteBuffer.wrap(byResult);
byteBuffer.put(bySessionRequest);
byteBuffer.put(byOpCode);
return byResult;
}
...
}

复制代码

public class RedisTransactionStoreManager extends AbstractTransactionStoreManager implements TransactionStoreManager {
private static volatile RedisTransactionStoreManager instance;
//Map for LogOperation Global Operation
public static volatile ImmutableMap<LogOperation, Function<GlobalTransactionDO, Boolean>> globalMap;
//Map for LogOperation Branch Operation
public static volatile ImmutableMap<LogOperation, Function<BranchTransactionDO, Boolean>> branchMap;
...
public static RedisTransactionStoreManager getInstance() {
if (instance == null) {
synchronized (RedisTransactionStoreManager.class) {
if (instance == null) {
instance = new RedisTransactionStoreManager();
}
}
}
return instance;
}
public RedisTransactionStoreManager() {
super();
initGlobalMap();
initBranchMap();
logQueryLimit = CONFIG.getInt(STORE_REDIS_QUERY_LIMIT, DEFAULT_LOG_QUERY_LIMIT);
if (logQueryLimit > DEFAULT_LOG_QUERY_LIMIT) {
logQueryLimit = DEFAULT_LOG_QUERY_LIMIT;
}
}
public void initGlobalMap() {
if (CollectionUtils.isEmpty(branchMap)) {
globalMap = ImmutableMap.<LogOperation, Function<GlobalTransactionDO, Boolean>>builder()
.put(LogOperation.GLOBAL_ADD, this::insertGlobalTransactionDO)
.put(LogOperation.GLOBAL_UPDATE, this::updateGlobalTransactionDO)
.put(LogOperation.GLOBAL_REMOVE, this::deleteGlobalTransactionDO)
.build();
}
}
public void initBranchMap() {
if (CollectionUtils.isEmpty(branchMap)) {
branchMap = ImmutableMap.<LogOperation, Function<BranchTransactionDO, Boolean>>builder()
.put(LogOperation.BRANCH_ADD, this::insertBranchTransactionDO)
.put(LogOperation.BRANCH_UPDATE, this::updateBranchTransactionDO)
.put(LogOperation.BRANCH_REMOVE, this::deleteBranchTransactionDO)
.build();
}
}
//Insert the global transaction.
private boolean insertGlobalTransactionDO(GlobalTransactionDO globalTransactionDO) {
String globalKey = buildGlobalKeyByTransactionId(globalTransactionDO.getTransactionId());
try (Jedis jedis = JedisPooledFactory.getJedisInstance(); Pipeline pipelined = jedis.pipelined()) {
Date now = new Date();
globalTransactionDO.setGmtCreate(now);
globalTransactionDO.setGmtModified(now);
pipelined.hmset(globalKey, BeanUtils.objectToMap(globalTransactionDO));
pipelined.rpush(buildGlobalStatus(globalTransactionDO.getStatus()), globalTransactionDO.getXid());
pipelined.sync();
return true;
} catch (Exception ex) {
throw new RedisException(ex);
}
}
//Insert branch transaction
private boolean insertBranchTransactionDO(BranchTransactionDO branchTransactionDO) {
String branchKey = buildBranchKey(branchTransactionDO.getBranchId());
String branchListKey = buildBranchListKeyByXid(branchTransactionDO.getXid());
try (Jedis jedis = JedisPooledFactory.getJedisInstance(); Pipeline pipelined = jedis.pipelined()) {
Date now = new Date();
branchTransactionDO.setGmtCreate(now);
branchTransactionDO.setGmtModified(now);
pipelined.hmset(branchKey, BeanUtils.objectToMap(branchTransactionDO));
pipelined.rpush(branchListKey, branchKey);
pipelined.sync();
return true;
} catch (Exception ex) {
throw new RedisException(ex);
}
}
@Override
public boolean writeSession(LogOperation logOperation, SessionStorable session) {
if (globalMap.containsKey(logOperation) || branchMap.containsKey(logOperation)) {
return globalMap.containsKey(logOperation) ?
globalMap.get(logOperation).apply(SessionConverter.convertGlobalTransactionDO(session)) :
branchMap.get(logOperation).apply(SessionConverter.convertBranchTransactionDO(session));
} else {
throw new StoreException("Unknown LogOperation:" + logOperation.name());
}
}
...
}
public class SessionConverter {
...
public static GlobalTransactionDO convertGlobalTransactionDO(SessionStorable session) {
if (session == null || !(session instanceof GlobalSession)) {
throw new IllegalArgumentException("The parameter of SessionStorable is not available, SessionStorable:" + StringUtils.toString(session));
}
GlobalSession globalSession = (GlobalSession)session;
GlobalTransactionDO globalTransactionDO = new GlobalTransactionDO();
globalTransactionDO.setXid(globalSession.getXid());
globalTransactionDO.setStatus(globalSession.getStatus().getCode());
globalTransactionDO.setApplicationId(globalSession.getApplicationId());
globalTransactionDO.setBeginTime(globalSession.getBeginTime());
globalTransactionDO.setTimeout(globalSession.getTimeout());
globalTransactionDO.setTransactionId(globalSession.getTransactionId());
globalTransactionDO.setTransactionName(globalSession.getTransactionName());
globalTransactionDO.setTransactionServiceGroup(globalSession.getTransactionServiceGroup());
globalTransactionDO.setApplicationData(globalSession.getApplicationData());
return globalTransactionDO;
}
public static BranchTransactionDO convertBranchTransactionDO(SessionStorable session) {
if (session == null || !(session instanceof BranchSession)) {
throw new IllegalArgumentException("The parameter of SessionStorable is not available, SessionStorable:" + StringUtils.toString(session));
}
BranchSession branchSession = (BranchSession)session;
BranchTransactionDO branchTransactionDO = new BranchTransactionDO();
branchTransactionDO.setXid(branchSession.getXid());
branchTransactionDO.setBranchId(branchSession.getBranchId());
branchTransactionDO.setBranchType(branchSession.getBranchType().name());
branchTransactionDO.setClientId(branchSession.getClientId());
branchTransactionDO.setResourceGroupId(branchSession.getResourceGroupId());
branchTransactionDO.setTransactionId(branchSession.getTransactionId());
branchTransactionDO.setApplicationData(branchSession.getApplicationData());
branchTransactionDO.setResourceId(branchSession.getResourceId());
branchTransactionDO.setStatus(branchSession.getStatus().getCode());
return branchTransactionDO;
}
...
}

复制代码

-> ServerHandler.channelRead()接收Seata Client发送过来的请求；
-> AbstractNettyRemoting.processMessage()处理RpcMessage消息；
-> ServerOnRequestProcessor.process()处理RpcMessage消息；
-> TransactionMessageHandler.onRequest()处理RpcMessage消息；
-> RemotingServer.sendAsyncResponse()返回包含xid的响应给客户端；

复制代码

6.Client获取Server的响应与处理的源码

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);
}
}
...
}

复制代码

-> TransactionMessageHandler.onRequest()处理RpcMessage消息；
-> DefaultCoordinator.onRequest()处理RpcMessage消息；
-> GlobalBeginRequest.handle()处理开启全局事务请求；
-> AbstractTCInboundHandler.handle()开启全局事务返回全局事务；
-> DefaultCoordinator.doGlobalBegin()开启全局事务；
-> DefaultCore.begin()创建全局事务会话并开启；
-> GlobalSession.createGlobalSession()创建全局事务会话；
-> GlobalSession.begin()开启全局事务会话；
-> AbstractSessionManager.onBegin()
-> AbstractSessionManager.addGlobalSession()
-> AbstractSessionManager.writeSession()
-> TransactionStoreManager.writeSession()持久化全局事务会话；

复制代码

由于Seata Client发送开启全局事务的请求给Seata Server时，会通过MessageFuture的get()方法同步等待Seata Server返回响应。所以当Seata Client获取Seata Server的响应并通过complete()方法设置MessageFuture已经完成后，原来同步等待Seata Server响应的线程便会继续往下处理。

即某线程执行CompletableFuture.complete()方法后，执行CompletableFuture.get()方法的线程就不会被阻塞而会被唤醒。

public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
...
@Override
public AbstractResultMessage onRequest(AbstractMessage request, RpcContext context) {
if (!(request instanceof AbstractTransactionRequestToTC)) {
throw new IllegalArgumentException();
}
AbstractTransactionRequestToTC transactionRequest = (AbstractTransactionRequestToTC) request;
transactionRequest.setTCInboundHandler(this);
return transactionRequest.handle(context);
}
...
}
public class GlobalBeginRequest extends AbstractTransactionRequestToTC {
...
@Override
public AbstractTransactionResponse handle(RpcContext rpcContext) {
return handler.handle(this, rpcContext);
}
...
}
public abstract class AbstractTCInboundHandler extends AbstractExceptionHandler implements TCInboundHandler {
private static final Logger LOGGER = LoggerFactory.getLogger(AbstractTCInboundHandler.class);
@Override
public GlobalBeginResponse handle(GlobalBeginRequest request, final RpcContext rpcContext) {
GlobalBeginResponse response = new GlobalBeginResponse();
exceptionHandleTemplate(new AbstractCallback<GlobalBeginRequest, GlobalBeginResponse>() {
@Override
public void execute(GlobalBeginRequest request, GlobalBeginResponse response) throws TransactionException {
try {
//开启全局事务
doGlobalBegin(request, response, rpcContext);
} catch (StoreException e) {
throw new TransactionException(TransactionExceptionCode.FailedStore, String.format("begin global request failed. xid=%s, msg=%s", response.getXid(), e.getMessage()), e);
}
}
}, request, response);
return response;
}
...
}
public class DefaultCoordinator extends AbstractTCInboundHandler implements TransactionMessageHandler, Disposable {
private final DefaultCore core;
...
@Override
protected void doGlobalBegin(GlobalBeginRequest request, GlobalBeginResponse response, RpcContext rpcContext) throws TransactionException {
//接下来才真正处理开启全局事务的业务逻辑
//其中会调用DefaultCore来真正开启一个全局事务，即拿到xid并设置到响应里去
response.setXid(core.begin(
rpcContext.getApplicationId(),//应用程序id
rpcContext.getTransactionServiceGroup(),//事务服务分组
request.getTransactionName(),//事务名称
request.getTimeout())//超时时间
);
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Begin new global transaction applicationId: {},transactionServiceGroup: {}, transactionName: {},timeout:{},xid:{}", rpcContext.getApplicationId(), rpcContext.getTransactionServiceGroup(), request.getTransactionName(), request.getTimeout(), response.getXid());
}
}
...
}
public class DefaultCore implements Core {
...
@Override
public String begin(String applicationId, String transactionServiceGroup, String name, int timeout) throws TransactionException {
//创建一个全局事务会话
GlobalSession session = GlobalSession.createGlobalSession(applicationId, transactionServiceGroup, name, timeout);
//通过slf4j的MDC把xid放入线程本地变量副本里去
MDC.put(RootContext.MDC_KEY_XID, session.getXid());
//添加一个全局事务会话的生命周期监听器
session.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
//打开Session，其中会对全局事务会话进行持久化
session.begin();
//transaction start event，发布会话开启事件
MetricsPublisher.postSessionDoingEvent(session, false);
//返回全局事务会话的xid
return session.getXid();
}
...
}
public class GlobalSession implements SessionLifecycle, SessionStorable {
...
public static GlobalSession createGlobalSession(String applicationId, String txServiceGroup, String txName, int timeout) {
GlobalSession session = new GlobalSession(applicationId, txServiceGroup, txName, timeout, false);
return session;
}
public GlobalSession(String applicationId, String transactionServiceGroup, String transactionName, int timeout, boolean lazyLoadBranch) {
//全局事务id是通过UUIDGenerator来生成的
this.transactionId = UUIDGenerator.generateUUID();
this.status = GlobalStatus.Begin;
this.lazyLoadBranch = lazyLoadBranch;
if (!lazyLoadBranch) {
this.branchSessions = new ArrayList<>();
}
this.applicationId = applicationId;
this.transactionServiceGroup = transactionServiceGroup;
this.transactionName = transactionName;
this.timeout = timeout;
//根据UUIDGenerator生成的transactionId + XID工具生成最终的xid
this.xid = XID.generateXID(transactionId);
}
@Override
public void begin() throws TransactionException {
this.status = GlobalStatus.Begin;
this.beginTime = System.currentTimeMillis();
this.active = true;
for (SessionLifecycleListener lifecycleListener : lifecycleListeners) {
lifecycleListener.onBegin(this);
}
}
...
}
public abstract class AbstractSessionManager implements SessionManager, SessionLifecycleListener {
...
@Override
public void onBegin(GlobalSession globalSession) throws TransactionException {
addGlobalSession(globalSession);
}
@Override
public void addGlobalSession(GlobalSession session) throws TransactionException {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("MANAGER[{}] SESSION[{}] {}", name, session, LogOperation.GLOBAL_ADD);
}
writeSession(LogOperation.GLOBAL_ADD, session);
}
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)) {
...
}
}
...
}

复制代码

-> RemotingServer.sendAsyncResponse()返回包含xid的响应给客户端；
-> AbstractNettyRemotingServer.sendAsyncResponse()异步发送响应；
-> AbstractNettyRemoting.buildResponseMessage()构造包含xid响应；
-> AbstractNettyRemoting.sendAsync()异步发送响应；
-> Netty的Channel.writeAndFlush()发送响应给客户端；

复制代码

7.Seata与Dubbo整合的过滤器源码
(1)调用Dubbo过滤器的入口
(2)Seata与Dubbo整合的过滤器

(1)调用Dubbo过滤器的入口

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 {
...
protected RpcMessage buildResponseMessage(RpcMessage rpcMessage, Object msg, byte messageType) {
RpcMessage rpcMsg = new RpcMessage();
rpcMsg.setMessageType(messageType);
rpcMsg.setCodec(rpcMessage.getCodec()); // same with request
rpcMsg.setCompressor(rpcMessage.getCompressor());
rpcMsg.setBody(msg);
rpcMsg.setId(rpcMessage.getId());
return rpcMsg;
}
//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());
}
});
}
...
}

复制代码

-> ClientHandler.channelRead()接收Seata Server返回的响应；
-> AbstractNettyRemoting.processMessage()处理RpcMessage消息；
-> ClientOnResponseProcessor.process()会设置MessageFuture结果；
-> MessageFuture.setResultMessage()设置MessageFuture结果;
-> CompletableFuture.complete()唤醒阻塞的线程；

复制代码

(2)Seata与Dubbo整合的过滤器
如果线程本地变量副本里的xid不为null，对应于发起RPC调用的情形。如果线程本地变量副本里的xid为null，则对应于接收RPC调用的情形。

当RootContext的xid不为null时，需要设置RpcContext的xid。当RootContext的xid为null + RpcContext的xid不为null时，需要设置RootContext的xid。

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
//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 ClientOnResponseProcessor implements RemotingProcessor {
...
@Override
public void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {
if (rpcMessage.getBody() instanceof MergeResultMessage) {
...
} else if (rpcMessage.getBody() instanceof BatchResultMessage) {
...
} else {
//这里是对普通消息的处理
MessageFuture messageFuture = futures.remove(rpcMessage.getId());
if (messageFuture != null) {
messageFuture.setResultMessage(rpcMessage.getBody());
} else {
if (rpcMessage.getBody() instanceof AbstractResultMessage) {
if (transactionMessageHandler != null) {
transactionMessageHandler.onResponse((AbstractResultMessage) rpcMessage.getBody(), null);
}
}
}
}
}
...
}
public class MessageFuture {
private transient CompletableFuture<Object> origin = new CompletableFuture<>();
...
//Sets result message.
public void setResultMessage(Object obj) {
origin.complete(obj);
}
...
}

复制代码

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