Java执行器没有排队任务的能力 [英] Java executor with no ability to queue tasks

问题描述

我需要一个Java执行器，如果其他任务正在处理，它会拒绝任务。我想不可能操作工作队列大小。

I need an Java executor that rejects tasks if some other task is processing. I guess it's not possible to get manipulating the working queue size.

有人可能会想知道为什么我需要一个具有这样的特性的执行器。我需要一个能够轻松更改策略并允许非零队列大小的功能。

Someone might wonder why I need an executor with such characteristic in the first place. I need an ability to easily change the policy and allow non-zero queue size.

任何想法？

推荐答案

使用 ThreadPoolExecutor 与 SynchronousQueue （复制自此答案）。

工作：

import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.Semaphore;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class SingleTaskExecutor {

public static void main(String[] args) {

    try {
        new SingleTaskExecutor().runTest();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

public void runTest() throws Exception {

    ThreadPoolExecutor tp = new ThreadPoolExecutor(1, 1,
            60L, TimeUnit.SECONDS,
            new SynchronousQueue<Runnable>());

    tp.setRejectedExecutionHandler(new RejectedTaskHandler());

    final Semaphore oneTaskDone = new Semaphore(0);
    tp.execute(new Runnable() {
        @Override public void run() { 
            System.out.println("Sleeping");
            try { Thread.sleep(300); } catch (Exception e) { e.printStackTrace();} 
            System.out.println("Done sleeping");
            oneTaskDone.release();
        }
    });
    tp.execute(new Runnable() {
        @Override public void run() { System.out.println("Never happends"); }
        @Override public String toString() { return "Rejected Runnable"; }
    });
    oneTaskDone.acquire();
    tp.execute(new Runnable() {
        @Override public void run() { System.out.println("Running"); }
    });
    tp.shutdown();
    tp.awaitTermination(100, TimeUnit.MILLISECONDS);
    System.out.println("Finished");
}

static class RejectedTaskHandler implements RejectedExecutionHandler {

    @Override public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        System.out.println("Task rejected: " + r);
    }

}

}

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