BlockingQueue和ExecutorService

这是一篇快速而肮脏的文章，但我已承诺将发表我在Playtomic研究的所有内容。

我们正在讨论如何限制ExecutorService可以排队多少个任务。 我们试图 控制服务可以处理多少内存以避免内存不足异常。 该服务接受来自Kafka主题的消息 并通过API。 这些操作以相同的内部逻辑结束，该逻辑是线程化的。

有一种队列BlockingQueue，可以等待直到队列中的某个位置空闲为止。 似乎使用ExecutionService 提交任务时，使用BlockingQueue的对象将等待，直到该队列未满为止。 但不是，ExecutionService拒绝任务。

您知道，反复试验可以节省您阅读手册的时间。 我很自豪地说，这是我第一次阅读本手册。

此测试显示发生了什么：

public class BlockingQueueExecutorServiceTest {

    @Test
    public void submitTest() {
        // Worst case scenario: accept only 1 thread in the queue.
        int nThreads = 1;


        ExecutorService exService = new ThreadPoolExecutor(
            nThreads,
            nThreads,
            0L,
            TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<>(nThreads));


        // Full this with tasks
        for (int i = 0; i < 10000; ++i) {
            WaitingTask t = new WaitingTask(i);
            exService.submit(t);

        }
    }

    private static class WaitingTask implements Runnable {

        int index;
        public WaitingTask(int index) {
            this.index = index;
        }

        @Override
        public void run() {

            try {
                log.info("Running task {}", index);
                Thread.sleep(1000);
            } catch (InterruptedException e) {

            }
        }
    }
}

java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@550dbc7a[Not completed, task = java.util.concurrent.Executors$RunnableAdapter@4dbb42b7[Wrapped task = com.playtomic.anemone.matchmaker.service.BlockingQueueExecutorServiceTest$WaitingTask@66f57048]] rejected from java.util.concurrent.ThreadPoolExecutor@21282ed8[Running, pool size = 1, active threads = 1, queued tasks = 1, completed tasks = 0]

    at java.base/java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2055)
    at java.base/java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:825)
    at java.base/java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1355)
    at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:118)
    at com.playtomic.anemone.matchmaker.service.BlockingQueueExecutorServiceTest.submitTest(BlockingQueueExecutorServiceTest.java:28)
... more boring stacktrace

如果要等到队列未满，则必须提供一个RejectedExecutionHandler来执行此操作。 例如，Spring的CallerBlocksPolicy。

public class BlockingQueueExecutorServiceTest {

    @Test
    public void submitTest() {
        // Worst case scenario: accept only 1 thread in the queue.
        int nThreads = 1;

        CallerBlocksPolicy policy = new CallerBlocksPolicy(10000); // 10secs
        ExecutorService exService = new ThreadPoolExecutor(
            nThreads,
            nThreads,
            0L,
            TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<>(nThreads), 
            policy);


        // Full this with tasks
        for (int i = 0; i < 10000; ++i) {
            WaitingTask t = new WaitingTask(i);
            exService.submit(t);

        }
    }

    private static class WaitingTask implements Runnable {

        int index;
        public WaitingTask(int index) {
            this.index = index;
        }

        @Override
        public void run() {

            try {
                log.info("Running task {}", index);
                Thread.sleep(1000);
            } catch (InterruptedException e) {

            }
        }
    }
}

这次我们得到：

12:21:32.409 [pool-1-thread-1] INFO com.playtomic.anemone.matchmaker.service.BlockingQueueExecutorServiceTest - Running task 0
12:21:32.422 [main] DEBUG org.springframework.integration.util.CallerBlocksPolicy - Attempting to queue task execution for 10000 milliseconds
12:21:33.420 [pool-1-thread-1] INFO com.playtomic.anemone.matchmaker.service.BlockingQueueExecutorServiceTest - Running task 1
12:21:33.420 [main] DEBUG org.springframework.integration.util.CallerBlocksPolicy - Task execution queued
12:21:33.421 [main] DEBUG org.springframework.integration.util.CallerBlocksPolicy - Attempting to queue task execution for 10000 milliseconds
12:21:34.423 [pool-1-thread-1] INFO com.playtomic.anemone.matchmaker.service.BlockingQueueExecutorServiceTest - Running task 2

Header: https://unsplash.com/photos/Kj2SaNHG-hg

from: https://dev.to//playtomic/linkedblockingqueue-and-executorservice-1pc5