Java ThreadPoolExecutor 在使用 ArrayBlockingQueue 时卡住

Java ThreadPoolExecutor getting stuck while using ArrayBlockingQueue

提问by Ravi Rao

I'm working on some application and using ThreadPoolExecutor for handling various tasks. ThreadPoolExecutor is getting stuck after some duration. To simulate this in a simpler environment, I've written a simple code where I'm able to simulate the issue.

我正在开发一些应用程序并使用 ThreadPoolExecutor 来处理各种任务。ThreadPoolExecutor 在一段时间后卡住了。为了在更简单的环境中模拟这一点，我编写了一个简单的代码，我可以在其中模拟问题。

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class MyThreadPoolExecutor {
    private int poolSize = 10;
    private int maxPoolSize = 50;
    private long keepAliveTime = 10;
    private ThreadPoolExecutor threadPool = null;
    private final ArrayBlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(
            100000);

    public MyThreadPoolExecutor() {
        threadPool = new ThreadPoolExecutor(poolSize, maxPoolSize,
                keepAliveTime, TimeUnit.SECONDS, queue);
        threadPool.setRejectedExecutionHandler(new RejectedExecutionHandler() {

            @Override
            public void rejectedExecution(Runnable runnable,
                    ThreadPoolExecutor threadPoolExecutor) {
                System.out
                        .println("Execution rejected. Please try restarting the application.");
            }

        });
    }

    public void runTask(Runnable task) {
        threadPool.execute(task);
    }

    public void shutDown() {
        threadPool.shutdownNow();
    }
    public ThreadPoolExecutor getThreadPool() {
        return threadPool;
    }

    public void setThreadPool(ThreadPoolExecutor threadPool) {
        this.threadPool = threadPool;
    }

    public static void main(String[] args) {
        MyThreadPoolExecutor mtpe = new MyThreadPoolExecutor();
        for (int i = 0; i < 1000; i++) {
            final int j = i;
            mtpe.runTask(new Runnable() {

                @Override
                public void run() {
                    System.out.println(j);
                }

            });
        }
    }
}

Try executing this code a few times. It normally print outs the number on console and when all threads end, it exists. But at times, it finished all task and then is not getting terminated. The thread dump is as follows:

尝试多次执行此代码。它通常在控制台上打印出数字，当所有线程结束时，它就存在。但有时，它完成了所有任务，然后没有被终止。线程转储如下：

MyThreadPoolExecutor [Java Application] 
    MyThreadPoolExecutor at localhost:2619 (Suspended)  
        Daemon System Thread [Attach Listener] (Suspended)  
        Daemon System Thread [Signal Dispatcher] (Suspended)    
        Daemon System Thread [Finalizer] (Suspended)    
            Object.wait(long) line: not available [native method]   
            ReferenceQueue<T>.remove(long) line: not available    
            ReferenceQueue<T>.remove() line: not available    
            Finalizer$FinalizerThread.run() line: not available 
        Daemon System Thread [Reference Handler] (Suspended)    
            Object.wait(long) line: not available [native method]   
            Reference$Lock(Object).wait() line: 485 
            Reference$ReferenceHandler.run() line: not available    
        Thread [pool-1-thread-1] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-2] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-3] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-4] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-6] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-8] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-5] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-10] (Suspended)   
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-9] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [pool-1-thread-7] (Suspended)    
            Unsafe.park(boolean, long) line: not available [native method]  
            LockSupport.park(Object) line: not available    
            AbstractQueuedSynchronizer$ConditionObject.await() line: not available  
            ArrayBlockingQueue<E>.take() line: not available  
            ThreadPoolExecutor.getTask() line: not available    
            ThreadPoolExecutor$Worker.run() line: not available 
            Thread.run() line: not available    
        Thread [DestroyJavaVM] (Suspended)  
    C:\Program Files\Java\jre1.6.0_07\bin\javaw.exe (Jun 17, 2010 10:42:33 AM)  

In my actual application,ThreadPoolExecutor threads go in this state and then it stops responding.

在我的实际应用程序中，ThreadPoolExecutor 线程进入此状态，然后停止响应。

Regards, Ravi Rao

问候， 拉维·拉奥

采纳答案by Tim Bender

In your mainmethod, you never call mtpe.shutdown(). A ThreadPoolExecutorwill attempt to keep its corePoolSizealive indefinitely. Sometimes, you get lucky and you have more than corePoolSizethreads alive, so every worker thread will go into a conditional logic branch that allows it to terminate after your specified timeout period of 10 seconds. However, as you have noticed, sometimes this is not the case so every thread in the executor will block on ArrayBlockingQueue.take()and wait for a new task.

在您的main方法中，您从不调用mtpe.shutdown(). 一个的ThreadPoolExecutor将试图保持其corePoolSize存活下去。有时，您很幸运，并且您有多个corePoolSize线程处于活动状态，因此每个工作线程都会进入一个条件逻辑分支，允许它在您指定的 10 秒超时时间后终止。但是，正如您所注意到的，有时情况并非如此，因此执行程序中的每个线程都会在ArrayBlockingQueue.take()上阻塞并等待新任务。

Also, please note, there is a significant difference between ExecutorService.shutdown()and ExecutorService.shutdownNow(). If you call ExecutorService.shutdownNow() as your wrapper implementation indicates, you will on occasion drop some tasks which have not been assigned for execution.

另外，请注意，ExecutorService.shutdown()和ExecutorService.shutdownNow()之间存在显着差异。如果您按照包装器实现的指示调用 ExecutorService.shutdownNow()，您有时会删除一些尚未分配执行的任务。

Update:Since my original answer, the ThreadPoolExecutorimplementation has changed such that the program in the original post should never exit.

更新：自从我最初的回答以来，ThreadPoolExecutor实现已经发生了变化，原始帖子中的程序永远不会退出。