【并发编程】- 线程池使用poll()方法设置等待时间移除已完成的任务

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接着上一篇文章-【并发编程】- ExecutorCompletionService使用poll()方法移除已完成的任务

ExecutorCompletionService使用poll()方法设置等待时间移除已完成的任务

修改运行类执行代码如下：

public class SecondPollRun {
    public static void main(String[] args) {
        PollFirstCallable pollFirstCallable = new PollFirstCallable();
        PollSecondCallable pollSecondCallable = new PollSecondCallable();

        ExecutorService executorService = Executors.newCachedThreadPool();
        ExecutorCompletionService completionService = new ExecutorCompletionService(executorService);
        completionService.submit(pollFirstCallable);
        completionService.submit(pollSecondCallable);

        for (int i = 0; i < 2; i++) {
            try {
                System.out.println("移除已完成任务的结果："+completionService.poll(7, TimeUnit.SECONDS).get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
        System.out.println("主线程输出结果完成！");
    }
}

运行结果如下：

com.ozx.concurrentprogram.executor.service.PollFirstCallable线程执行任务时间：1660285569519

移除已完成任务的结果：com.ozx.concurrentprogram.executor.service.PollFirstCallable

com.ozx.concurrentprogram.executor.service.PollSecondCallable线程执行任务时间：1660285574515

移除已完成任务的结果：com.ozx.concurrentprogram.executor.service.PollSecondCallable

主线程输出结果完成！

从运行结果看出一个线程休眠了5秒，poll()方法等待获取返回值的时间是6s，completionService调用poll()方法能移除第一个线程，但是第二个线程休眠时间是10秒，所以再调用poll()方法移除第二个线程，所以一共等待12秒才能将两个已完成的线程移除。

修改运行类代码如下：

public class SecondPollRun {
    public static void main(String[] args) {
        PollFirstCallable pollFirstCallable = new PollFirstCallable();
        PollSecondCallable pollSecondCallable = new PollSecondCallable();

        ExecutorService executorService = Executors.newCachedThreadPool();
        ExecutorCompletionService completionService = new ExecutorCompletionService(executorService);
        completionService.submit(pollFirstCallable);
        completionService.submit(pollSecondCallable);


            try {
                System.out.println("poll等待4秒");
                System.out.println("移除已完成任务的结果："+completionService.poll(4, TimeUnit.SECONDS));
                System.out.println("----------------");
                System.out.println("poll等待6秒");
                System.out.println("移除已完成任务的结果："+completionService.poll(6, TimeUnit.SECONDS).get());
                System.out.println("----------------");
                System.out.println("poll等待11秒");
                System.out.println("移除已完成任务的结果："+completionService.poll(11, TimeUnit.SECONDS).get());
                System.out.println("----------------");

            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }

        System.out.println("主线程输出结果完成！");
    }
}

运行结果如下：

poll等待4秒

移除已完成任务的结果：null

poll等待6秒

com.ozx.concurrentprogram.executor.service.PollFirstCallable线程执行任务时间：1660286411233

移除已完成任务的结果：com.ozx.concurrentprogram.executor.service.PollFirstCallable

poll等待11秒

com.ozx.concurrentprogram.executor.service.PollSecondCallable线程执行任务时间：1660286416225

移除已完成任务的结果：com.ozx.concurrentprogram.executor.service.PollSecondCallable

主线程输出结果完成！

从运行结果看出ExecutorCompletionService调用poll()方法等待时间小于任务执行的时间，那么返回值为null。