实战Java内存泄漏问题分析 -- hazelcast2.0.3使用时内存泄漏 -- 2

hazelcast 提供了3中方法调用startCleanup:

第一种是在ConcuurentMapManager的构造函数中，通过调用node的executorManager中的ScheduledExecutorService来创建每秒运行一次cleanup操作的线程（代码例如以下）。

因为这是ConcuurentMapManager构造函数的代码，所以这样的调用startCleanup的操作是默认就会有的。

node.executorManager.getScheduledExecutorService().scheduleAtFixedRate(new Runnable() {
publicvoid run() {
for (CMap cMap : maps.values()) {
cMap.startCleanup(false);
}
}
}, 1, 1, TimeUnit.SECONDS);

另外一种是通过配置文件来触发startCleanup的运行。配置 PutOperationhandlerif overcapacity policy。我们系统的配置文件没有配置这方面的policy，全部这样的方式在我们系统中没有使用。

第三种是自己直接写代码去调用startCleanup函数（public方法。线程安全的）. 这个没有实如今我们的系统中。

所以我的调查方向放在了第一种调用的情况，hazelcast里面的ScheduledExecutorService是通过java.util.ScheduledThreadPoolExecutor 来实现的.

esScheduled = new ScheduledThreadPoolExecutor(5, new ExecutorThreadFactory(node.threadGroup,
node.getThreadPoolNamePrefix("scheduled"), classLoader), new RejectionHandler()) {
protected void beforeExecute(Thread t, Runnable r) {
threadPoolBeforeExecute(t, r);
}
}

查看ScheduledThreadPoolExecutor的实现，它把线程实现分成了3个部分： runnable tasks可运行任务, workers to execute the tasks运行任务的详细线程 以及 ScheduledThreadPoolExecutor 调度workers依照要求运行runnable tasks。

我们通过scheduleAtFixdRate提交了task，scheduleAtFixedRate先把它打包成反复运行的ScheduleFutureTask

<pre name="code" class="java">    public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
long initialDelay,
long period,
TimeUnit unit) {
if (command == null || unit == null)
throw new NullPointerException();
if (period <= 0)
throw new IllegalArgumentException();
RunnableScheduledFuture<?

> t = decorateTask(command,
new <strong>ScheduledFutureTas</strong>k<Object>(command,
null,
triggerTime(initialDelay, unit),
unit.toNanos(period)));
delayedExecute(t);
return t;
}

ScheduleFutureTask的run方法实现又一次schedule：

public void  run() {
boolean periodic = isPeriodic();
if (!canRunInCurrentRunState(periodic))
cancel(false);
else if (!periodic)
ScheduledFutureTask.super.run();
else if (ScheduledFutureTask.super.runAndReset()) {
setNextRunTime();
<strong> reExecutePeriodic(outerTask);</strong>
}
}

delayedExecute里面假设当前worker的数目小于初始化定义的CorePool的数目，就创建新的worker线程，然后把task放到queue里面

private void delayedExecute(Runnable command) {
if (isShutdown()) {
reject(command);
return;
}
// Prestart a thread if necessary. We cannot prestart it
// running the task because the task (probably) shouldn't be
// run yet, so thread will just idle until delay elapses.
if (getPoolSize() < getCorePoolSize())
prestartCoreThread();

<strong> super.getQueue().add(command);</strong>
}
public boolean prestartCoreThread() {
return addIfUnderCorePoolSize(null);
}
private boolean addIfUnderCorePoolSize(Runnable firstTask) {
Thread t = null;
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
if (poolSize < corePoolSize && runState == RUNNING)
t = addThread(firstTask);
} finally {
mainLock.unlock();
}
return t != null;
}
private Thread addThread(Runnable firstTask) {
Worker w = new Worker(firstTask);
Thread t = threadFactory.newThread(w);
boolean workerStarted = false;
if (t != null) {
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
w.thread = t;
workers.add(w);
int nt = ++poolSize;
if (nt > largestPoolSize)
largestPoolSize = nt;
try {
t.start();
workerStarted = true;
}
finally {
if (!workerStarted)
workers.remove(w);
}
}
return t;
}

全部启动的worker就做一件事情，从queue中取task运行

try {
hasRun = true;
Runnable task = firstTask;
firstTask = null;
while (task != null || (task = <strong>getTask</strong>()) != null) {
<strong>runTask(task);</strong>
task = null;
}
} finally {
workerDone(this);
}
}
}
Runnable getTask() {
<strong> for (;;) {</strong>
try {
int state = runState;
if (state > SHUTDOWN)
return null;
Runnable r;
if (state == SHUTDOWN)  // Help drain queue
r = workQueue.poll();
else if (poolSize > corePoolSize || allowCoreThreadTimeOut)
r = workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS);
else
<strong> r = workQueue.take();</strong>
if (r != null)
return r;
if (workerCanExit()) {
if (runState >= SHUTDOWN) // Wake up others
interruptIdleWorkers();
return null;
}
// Else retry
} catch (InterruptedException ie) {
// On interruption, re-check runState
}
}
}
private void runTask(Runnable task) {
final ReentrantLock runLock = this.runLock;
runLock.lock();
try {
if ((runState >= STOP ||
(Thread.interrupted() && runState >= STOP)) &&
hasRun)
thread.interrupt();
boolean ran = false;
beforeExecute(thread, task);
<strong> try {
task.run();
ran = true;
afterExecute(task, null);
++completedTasks;
} catch (RuntimeException ex) {
if (!ran)
afterExecute(task, ex);
throw ex;
}</strong>
} finally {
runLock.unlock();
}
}

了解了java threadpool的工作原理之后。我们能够知道。startCleanup是代码pass给ScheduledThreadPoolExecutor的runnable task，它不被运行，可能的原因有：

1. ScheduledThreadPoolExecutor初始化时候出错，task全然没有提交成功。因为lastCleanup并非系统应用的启动时间，已经过了几个月了，所以。非常明显在系统初始化的时候，esScheduled(ScheduledThreadPoolExecutor)还是正常工作的，仅仅是突然在2月4号停止了工作，所以这样的可能性能够排除。

2. Worker 没有正常工作。不在从ScheduledThreadPoolExecutor的queue里面取数据，这个非常快就被我排除了：

首先heap dump中有5个pending workers in esScheduled (0/2/3/5/9)：



其次从thread dump中能够看出，这五个线程都是在等着从queue里面取数据：

……
<strong> at java/util/concurrent/locks/AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2025)[optimiz</strong>ed]
at java/util/concurrent/DelayQueue.take(DelayQueue.java:164)[optimized]
at java/util/concurrent/ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:609)[inlined]
at java/util/concurrent/ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:602)[optimized]
at java/util/concurrent/ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)[optimized]
at java/util/concurrent/ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java/lang/Thread.run(Thread.java:662)
at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
-- end of trace
hz._hzInstance_1_com.ericsson.ngin.session.ra.hazelcast.scheduled.thread-2" id=51 idx=0xd8 tid=32639 prio=5 alive, parked, native_blocked
hz._hzInstance_1_com.ericsson.ngin.session.ra.hazelcast.scheduled.thread-3" id=52 idx=0xdc tid=32640 prio=5 alive, parked, native_blocked
hz._hzInstance_1_com.ericsson.ngin.session.ra.hazelcast.scheduled.thread-4" id=53 idx=0xe0 tid=32641 prio=5 alive, parked, native_blocked
hz._hzInstance_1_com.ericsson.ngin.session.ra.hazelcast.scheduled.thread-5" id=75590 idx=0x3cc tid=3308 prio=5 alive, parked, native_blocked

所以worker不正常也被排除了。

3. 我们提交给系统的runner task自己主动从queue里面消失了，从memory dump中确实发现queue没有tasks了



而没有task的原因非常明显是由于当前task运行完之后没有又一次reschedule，至于原因，由于scheduledFutrueTask已经不存在，无法从memory dump和thread dump中分析出结果，成为了一个谜。。

。

。

。。

public void  run() {
boolean periodic = isPeriodic();
if (!canRunInCurrentRunState(periodic))
cancel(false);
else if (!periodic)
ScheduledFutureTask.super.run();
else if (ScheduledFutureTask.super.runAndReset()) {
setNextRunTime();
<strong> reExecutePeriodic(outerTask);</strong>
}
}