JAVA线程池重用线程(JAVA Thread pool reusing threads)

 大家。 我对使用Thread Pools有误解。 实际结果与此类的API描述不同。 当我在线程池中使用LinkedBlockedQueue并且它不重用线程时，线程池等待在构造函数中设置的KeepAliveTime，然后终止该线程并创建一个新线程。 当我将KeepAliveTime设置为较小时，例如1秒或更短时间它会删除线程并重新创建它，但如果我设置了一分钟，则不会创建新线程，因为MaxPoolSize不允许它并且队列已经满了所以所有任务都被拒绝，但线程为keepAliveTime这次设置什么都不做。 我很新，不明白为什么它不重用这些线程。 在keepTimeAlive到期后，它会杀死这些线程，如果队列已满，则会创建一个新线程。 为什么这样工作？ 据我所知，如果线程在keepAliveTime期间处于空闲状态，它必须重用它。 它在我使用SynchronousQueue时重用了线程，但没有使用LinkedBlockingQueue 。 
 
public class Main {

    private volatile int remainingTasksCount;
    private volatile static ThreadPoolExecutor consumer = new ThreadPoolExecutor(1, 2, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3));

    private static Runnable task = () -> {
        System.out.println(String.format("consumer %s, id %s, size %s, active count %s, queue %s",
                Thread.currentThread().getName(), Thread.currentThread().getId(),
                consumer.getPoolSize(), consumer.getActiveCount(), 3-consumer.getQueue().remainingCapacity()));
        String s = new String();
        synchronized (s) {
            try {
                s.wait(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    };


    public static void main(String[] args) throws IOException {
        try {
            new Thread(() -> {
                while (true) {
                    try {
                        for (int i = 0; i < 5; i++) {
                            consumer.submit(task);
                        }
                        System.out.println("PUSH TASKS");
                        synchronized (Thread.currentThread()) {
                            Thread.currentThread().wait(10000);
                        }
                    } catch (Throwable th) {
                        System.out.println(th);
                    }
                }
            }).start();
        } catch (Throwable th) {
            System.out.println(th);
        }
    }  
 
 OUTPUT 
 
PUSH TASKS
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 1
consumer pool-1-thread-1, id 15, size 2, active count 1, queue 2
consumer pool-1-thread-1, id 15, size 2, active count 1, queue 0
Disconnected from the target VM, address: '127.0.0.1:64434', transport: 'socket'

Process finished with exit code 1
 
 但是下次生产者提交任务时，我得到了RejectedExecutionException 
 
 如果我将keepAliveTime更改为1 Second 。 一切都运作良好，但创建新的线程。 
 
PUSH TASKS
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 3
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 2
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 1
consumer pool-1-thread-2, id 16, size 2, active count 1, queue 0
PUSH TASKS
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 2
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
consumer pool-1-thread-3, id 17, size 1, active count 1, queue 2
PUSH TASKS
consumer pool-1-thread-4, id 18, size 2, active count 2, queue 3
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-4, id 18, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
PUSH TASKS
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 2
consumer pool-1-thread-5, id 19, size 2, active count 2, queue 3
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-5, id 19, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
 
 如果有人能够解释我的错误，或者我错过了一些基本原则，我将很高兴 

everyone. I have a misunderstanding of working with Thread Pools. The real result differs from API description of this class. When I am using LinkedBlockedQueue in Thread pool with it does not reuse threads, thread pool wait KeepAliveTime that was set in the constructor, then kill this thread and create a new one. When I set KeepAliveTime small, like 1 second or less it deletes thread a recreate it, but if I set for a minute new threads aren't created because MaxPoolSize doesn't allow it and queue already full so all tasks rejected, but threads for which keepAliveTime set minute doing nothing this time. I am quite new and don't understand why it doesn't reuse these threads. after keepTimeAlive expiration it kills these thread and if queue full, it creates a new one. Why it works this way? As far as I understood from API it has to reuse it if threads are idle during keepAliveTime. It reuses threads when I used SynchronousQueue, but not LinkedBlockingQueue.
 
public class Main {

    private volatile int remainingTasksCount;
    private volatile static ThreadPoolExecutor consumer = new ThreadPoolExecutor(1, 2, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3));

    private static Runnable task = () -> {
        System.out.println(String.format("consumer %s, id %s, size %s, active count %s, queue %s",
                Thread.currentThread().getName(), Thread.currentThread().getId(),
                consumer.getPoolSize(), consumer.getActiveCount(), 3-consumer.getQueue().remainingCapacity()));
        String s = new String();
        synchronized (s) {
            try {
                s.wait(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    };


    public static void main(String[] args) throws IOException {
        try {
            new Thread(() -> {
                while (true) {
                    try {
                        for (int i = 0; i < 5; i++) {
                            consumer.submit(task);
                        }
                        System.out.println("PUSH TASKS");
                        synchronized (Thread.currentThread()) {
                            Thread.currentThread().wait(10000);
                        }
                    } catch (Throwable th) {
                        System.out.println(th);
                    }
                }
            }).start();
        } catch (Throwable th) {
            System.out.println(th);
        }
    }  
 
OUTPUT
 
PUSH TASKS
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 1
consumer pool-1-thread-1, id 15, size 2, active count 1, queue 2
consumer pool-1-thread-1, id 15, size 2, active count 1, queue 0
Disconnected from the target VM, address: '127.0.0.1:64434', transport: 'socket'

Process finished with exit code 1
 
But next time producer submit tasks, I get RejectedExecutionException
 
if I change keepAliveTime to 1 Second. Everything is working well, but creates new Threads.
 
PUSH TASKS
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 3
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 2
consumer pool-1-thread-1, id 15, size 2, active count 2, queue 1
consumer pool-1-thread-2, id 16, size 2, active count 1, queue 0
PUSH TASKS
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 3
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 2
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-2, id 16, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
consumer pool-1-thread-3, id 17, size 1, active count 1, queue 2
PUSH TASKS
consumer pool-1-thread-4, id 18, size 2, active count 2, queue 3
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-4, id 18, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
PUSH TASKS
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 2
consumer pool-1-thread-5, id 19, size 2, active count 2, queue 3
consumer pool-1-thread-3, id 17, size 2, active count 2, queue 1
consumer pool-1-thread-5, id 19, size 2, active count 2, queue 1
consumer pool-1-thread-3, id 17, size 2, active count 1, queue 0
 
I will be glad if someone could explain me my fault, or something basic principle that I missed

原文：https://stackoverflow.com/questions/47157431