生产环境 java.util.concurrent.RejectedExecutionException: event executor terminated 错误分析

今天运维在执行线上功能时发现服务异常,跟进之后发现Redis出现问题,如下:

[ERROR] [2022-05-26 00:05:01.518] [c.q.d.utils.DataAccessSampleRedisUtil:326][Thread-154] 服务名称:ivdg-data-access-service--> 查询缓存数据出错:Unknown redis exception; nested exception is java.util.concurrent.RejectedExecutionException: event executor terminated
org.springframework.data.redis.RedisSystemException: Unknown redis exception; nested exception is java.util.concurrent.RejectedExecutionException: event executor terminatedat org.springframework.data.redis.FallbackExceptionTranslationStrategy.getFallback(FallbackExceptionTranslationStrategy.java:53)at org.springframework.data.redis.FallbackExceptionTranslationStrategy.translate(FallbackExceptionTranslationStrategy.java:43)at org.springframework.data.redis.connection.lettuce.LettuceConnection.convertLettuceAccessException(LettuceConnection.java:273)at org.springframework.data.redis.connection.lettuce.LettuceScriptingCommands.convertLettuceAccessException(LettuceScriptingCommands.java:236)at org.springframework.data.redis.connection.lettuce.LettuceScriptingCommands.evalSha(LettuceScriptingCommands.java:195)at org.springframework.data.redis.connection.DefaultedRedisConnection.evalSha(DefaultedRedisConnection.java:1502)at org.springframework.data.redis.connection.DefaultStringRedisConnection.evalSha(DefaultStringRedisConnection.java:1757)at sun.reflect.GeneratedMethodAccessor606.invoke(Unknown Source)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at org.springframework.data.redis.core.CloseSuppressingInvocationHandler.invoke(CloseSuppressingInvocationHandler.java:61)at com.sun.proxy.$Proxy258.evalSha(Unknown Source)at org.springframework.data.redis.core.script.DefaultScriptExecutor.eval(DefaultScriptExecutor.java:77)at org.springframework.data.redis.core.script.DefaultScriptExecutor.lambda$execute$0(DefaultScriptExecutor.java:68)at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:228)at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:188)at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:175)at org.springframework.data.redis.core.script.DefaultScriptExecutor.execute(DefaultScriptExecutor.java:58)at org.springframework.data.redis.core.script.DefaultScriptExecutor.execute(DefaultScriptExecutor.java:52)at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:350)at com.qsdi.dataAccess.utils.DataAccessSampleRedisUtil.lambda$scanData$7(DataAccessSampleRedisUtil.java:324)at java.util.stream.Streams$RangeIntSpliterator.forEachRemaining(Streams.java:110)at java.util.stream.IntPipeline$Head.forEach(IntPipeline.java:559)at com.qsdi.dataAccess.utils.DataAccessSampleRedisUtil.scanData(DataAccessSampleRedisUtil.java:318)at com.qsdi.dataAccess.service.impl.DataSamplingInspectionHourStatisticsServiceImpl.handleHourData(DataSamplingInspectionHourStatisticsServiceImpl.java:69)at com.qsdi.dataAccess.service.impl.DataSamplingInspectionHourStatisticsServiceImpl.statisticsDataByTime(DataSamplingInspectionHourStatisticsServiceImpl.java:58)at com.qsdi.dataAccess.job.HourStatisticsByVehicleJobHandler.execute(HourStatisticsByVehicleJobHandler.java:29)at com.xxl.job.core.thread.JobThread.run(JobThread.java:163)
Caused by: java.util.concurrent.RejectedExecutionException: event executor terminatedat io.netty.util.concurrent.SingleThreadEventExecutor.reject(SingleThreadEventExecutor.java:926)at io.netty.util.concurrent.SingleThreadEventExecutor.offerTask(SingleThreadEventExecutor.java:353)at io.netty.util.concurrent.SingleThreadEventExecutor.addTask(SingleThreadEventExecutor.java:346)at io.netty.util.concurrent.SingleThreadEventExecutor.execute(SingleThreadEventExecutor.java:828)at io.netty.util.concurrent.SingleThreadEventExecutor.execute(SingleThreadEventExecutor.java:818)at io.netty.util.concurrent.AbstractScheduledEventExecutor.schedule(AbstractScheduledEventExecutor.java:261)at io.netty.util.concurrent.AbstractScheduledEventExecutor.schedule(AbstractScheduledEventExecutor.java:177)at io.netty.util.concurrent.AbstractEventExecutorGroup.schedule(AbstractEventExecutorGroup.java:50)at io.netty.util.concurrent.AbstractEventExecutorGroup.schedule(AbstractEventExecutorGroup.java:32)at io.lettuce.core.protocol.CommandExpiryWriter.potentiallyExpire(CommandExpiryWriter.java:168)at io.lettuce.core.protocol.CommandExpiryWriter.write(CommandExpiryWriter.java:115)at io.lettuce.core.RedisChannelHandler.dispatch(RedisChannelHandler.java:195)at io.lettuce.core.StatefulRedisConnectionImpl.dispatch(StatefulRedisConnectionImpl.java:176)at io.lettuce.core.AbstractRedisAsyncCommands.dispatch(AbstractRedisAsyncCommands.java:474)at io.lettuce.core.AbstractRedisAsyncCommands.evalsha(AbstractRedisAsyncCommands.java:512)at sun.reflect.GeneratedMethodAccessor608.invoke(Unknown Source)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at io.lettuce.core.FutureSyncInvocationHandler.handleInvocation(FutureSyncInvocationHandler.java:63)at io.lettuce.core.internal.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:79)at com.sun.proxy.$Proxy254.evalsha(Unknown Source)at org.springframework.data.redis.connection.lettuce.LettuceScriptingCommands.evalSha(LettuceScriptingCommands.java:193)... 23 common frames omitted

如上代码段所示, 再调用redis执行luna脚本查询时提示异常,具体异常描述是由SingeThreadEventExecutor这个类调用execute方法时出现的异常,源码如下:

private void execute(Runnable task, boolean immediate) {boolean inEventLoop = inEventLoop();addTask(task);if (!inEventLoop) {startThread();if (isShutdown()) {boolean reject = false;try {if (removeTask(task)) {reject = true;}} catch (UnsupportedOperationException e) {// The task queue does not support removal so the best thing we can do is to just move on and// hope we will be able to pick-up the task before its completely terminated.// In worst case we will log on termination.}if (reject) {reject();}}}if (!addTaskWakesUp && immediate) {wakeup(inEventLoop);}}

分析这个方法，大意是将当前写事件提交到 SingleThreadEventExecutor 任务队列中。报错是在 addTask 这个方法：

/*** Add a task to the task queue, or throws a {@link RejectedExecutionException} if this instance was shutdown* before.*/protected void addTask(Runnable task) {ObjectUtil.checkNotNull(task, "task");if (!offerTask(task)) {reject(task);}}

这个方法判断如果没有插入任务队列成功就调用 reject (task) 拒绝任务，reject (task) 里面抛出的异常就是我们看到的最外面的异常。于是看一看 offerTask 方法：

final boolean offerTask(Runnable task) {if (isShutdown()) {reject();}return taskQueue.offer(task);}@Overridepublic boolean isShutdown() {return state >= ST_SHUTDOWN;}private static final int ST_NOT_STARTED = 1;private static final int ST_STARTED = 2;private static final int ST_SHUTTING_DOWN = 3;private static final int ST_SHUTDOWN = 4;private static final int ST_TERMINATED = 5;

这里可以看出 offerTask 的时候校验了当前的 SingleThreadEventExecutor 的状态是否是结束和终止。那么问题来了，是什么导致的 SingleThreadEventExecutor 的状态为终止的勒，通过前面缘由中日志可以看到 SingleThreadEventExecutor 也打印了堆溢出的错误日志，搜索这个日志是哪里打印的，发现：

private void doStartThread() {assert thread == null;executor.execute(new Runnable() {@Overridepublic void run() {thread = Thread.currentThread();if (interrupted) {thread.interrupt();}boolean success = false;updateLastExecutionTime();try {SingleThreadEventExecutor.this.run();success = true;} catch (Throwable t) {logger.warn("Unexpected exception from an event executor: ", t);} finally {for (;;) {int oldState = state;if (oldState >= ST_SHUTTING_DOWN || STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, ST_SHUTTING_DOWN)) {break;}}// Check if confirmShutdown() was called at the end of the loop.if (success && gracefulShutdownStartTime == 0) {if (logger.isErrorEnabled()) {logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must " +"be called before run() implementation terminates.");}}try {// Run all remaining tasks and shutdown hooks. At this point the event loop// is in ST_SHUTTING_DOWN state still accepting tasks which is needed for// graceful shutdown with quietPeriod.for (;;) {if (confirmShutdown()) {break;}}// Now we want to make sure no more tasks can be added from this point. This is// achieved by switching the state. Any new tasks beyond this point will be rejected.for (;;) {int oldState = state;if (oldState >= ST_SHUTDOWN || STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, ST_SHUTDOWN)) {break;}}// We have the final set of tasks in the queue now, no more can be added, run all remaining.// No need to loop here, this is the final pass.confirmShutdown();} finally {try {cleanup();} finally {// Lets remove all FastThreadLocals for the Thread as we are about to terminate and notify// the future. The user may block on the future and once it unblocks the JVM may terminate// and start unloading classes.// See https://github.com/netty/netty/issues/6596.FastThreadLocal.removeAll();STATE_UPDATER.set(SingleThreadEventExecutor.this, ST_TERMINATED);threadLock.countDown();int numUserTasks = drainTasks();if (numUserTasks > 0 && logger.isWarnEnabled()) {logger.warn("An event executor terminated with " +"non-empty task queue (" + numUserTasks + ')');}terminationFuture.setSuccess(null);}}}}});}

这个方法，这个方法里面同时在 finally 设置了状态为 ST_TERMINATED，这个方法大意是启动 eventloop 真正的线程来轮询读写事件，这个方法将在首次执行 excute 方法的时候被调用，注意这里的 executor 变量是一个线程池，于是查阅资料才认识到，eventloopgroup 下的每个 eventloop 实际上都会引用到一个线程池，这个线程池线程数目与 eventloop 总大小相同，是 fork/join 框架创建的，真正执行轮询逻辑实际上是这个线程池去提交的。eventloop 的意义实际上只是为了保存任务队列。真正的去轮询任务队列的逻辑是由其代理的线程池去执行的。

这样也就清楚了，整个事故实际很简单，就是先由于内存溢出的错误导致 eventloop 的状态为终止，这个终止状态据我看到的代码貌似是不可逆的，然后当在调用 chanel.write 的时候提交任务到 eventloop 校验状态为终止所以报了拒绝错误。

解决这个 bug 的重要途径是找到内存溢出的原因，这里就不赘述了，因为在网上没有搜到这个错的原因，所以跟了一下代码，在这里做个记录，后续分析一下到底是哪里有内存溢出问题再贴上解决方案

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