i'm using java theadpool ,but i got a error i can't understand

Question

<bean id="threadPoolTaskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
    <property name="corePoolSize" value="6"/>
    <property name="maxPoolSize" value="6"/>
    <property name="queueCapacity" value="5"/>
    <property name="keepAliveSeconds" value="120"/>
    <property name="threadNamePrefix" value="myThread_"/>
</bean>

---

    public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

    ThreadPoolTaskExecutor executor = (ThreadPoolTaskExecutor) context.getBean("threadPoolTaskExecutor");
    List<Integer> list = new ArrayList<Integer>();

    for(int i=0;i<1000;i++){
        list.add(i);
        if(6 == list.size()){
            doWork(list,executor);
            list.clear();
        }
    }

    if(list.size() > 0)
        doWork(list,executor);

    System.out.println("all work finished");

}

static void doWork(List<Integer> list,ThreadPoolTaskExecutor executor){
    final CountDownLatch latch = new CountDownLatch(list.size());
    for(final int i:list){
        executor.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(200);
                    latch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
    try {
        latch.await();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

}

Above is my code. When I set queueCapacity 6 or larger than 6 it works well, but when queueCapacity is less than 6 the program will produce an error:

> Exception in thread "main"
> org.springframework.core.task.TaskRejectedException: Executor
> [java.util.concurrent.ThreadPoolExecutor@1f7911b[Running, pool size =
> 6, active threads = 0, queued tasks = 5, completed tasks = 18]] did
> not accept task: com.my.service.test.Test$1@1de8526; nested exception
> is java.util.concurrent.RejectedExecutionException: Task
> com.my.service.test.Test$1@1de8526 rejected from
> java.util.concurrent.ThreadPoolExecutor@1f7911b[Running, pool size =
> 6, active threads = 0, queued tasks = 5, completed tasks = 18]    at
> org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:305)
>   at com.my.service.test.Test.doWork(Test.java:42)    at
> com.my.service.test.Test.main(Test.java:27)   at
> sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)   at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
>   at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>   at java.lang.reflect.Method.invoke(Method.java:606)     at
> com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
> Caused by: java.util.concurrent.RejectedExecutionException: Task
> com.my.service.test.Test$1@1de8526 rejected from
> java.util.concurrent.ThreadPoolExecutor@1f7911b[Running, pool size =
> 6, active threads = 0, queued tasks = 5, completed tasks = 18]    at
> java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
>   at
> java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
>   at
> java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
>   at
> org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:302)
>   ... 7 more

Who can tell me why, when I put a task to the thread pool, the poll first puts the task to workQueue?

Answer 1

Rules for creating threads internally by Sun:

1. If the number of threads is less than the corePoolSize, create a new thread to run a new task.

2. If the number of threads is equal (or greater than) the corePoolSize, put the task into the queue.

3. If the queue is full, and the number of threads is less than the maxPoolSize, create a new thread to run tasks in.

4. If the queue is full, and the number of threads is greater than or equal to maxPoolSize, reject the task.

Your case is the last one where number of thread has reached to maxPoolSize i.e 6 and the queue is also full (number of task in queue is 5) so the task comes is rejected and gives TaskRejectedException.

Answer 2

<property name="queueCapacity" value="5"/>

So the maximum ammount of "waiting" tasks to be executed is 5. Any futher submit performed before previous tasks are complete, will result in TaskRejectException

This information is also stored in exception itself

[java.util.concurrent.ThreadPoolExecutor@1f7911b[Running, pool size = 6, active threads = 0, queued tasks = 5, completed tasks = 18]