如何在 Executor Service 上完成任務直到一段時間？

Question

我想檢索已完成任務的線程的結果並檢索結果並忽略其他線程。 我的目標是做這樣的事情。

public class Main {
    public static void main(String[] args) {
        ExecutorService service = Executors.newFixedThreadPool(16);

        for(int i = 0 ; i < 100 ; i++) {
            service.submit(threadClass);
            // some thread that generates result in 5 seconds say
        }
        
        // Main thread does some work here that takes time


        /*
        The task that has finished till this point should be taken
        Let's say 7 results are generated till this point,
        So get the 7 results and stop other threads
        Want result like a List<Integer>
        */

        

        service.shutdownNow(); // stop all other threads
          

    }

}

Answer 1

您可以使用CompletionService ，內部使用阻塞隊列，“已完成”的Future將放入此隊列，因此您可以調用queue#poll來獲取所有完成Future 。 ：

        ExecutorService service = Executors.newFixedThreadPool(16);
        CompletionService<Integer> completionService = new ExecutorCompletionService<>(service);
        for(int i = 0 ; i < 100 ; i++) {
            completionService.submit(new Callable<Integer>() {
                @Override
                public Integer call() throws Exception {
                    Random random = new Random();
                    int nextInt = random.nextInt(10000);
                    System.out.println("I will take " + nextInt + " ms to finish");
                    try {
                        Thread.sleep(nextInt);
                    } catch (InterruptedException e) {
                        System.out.println("I am interrupt");
                        return -1;
                    }
                    System.out.println("I am finish");
                    return nextInt;
                }
            });
        }
        // do other work
        Thread.sleep(5000);
        List<Integer> completeResult = new ArrayList<>();
        Future<Integer> future;
        while ((future = completionService.poll()) != null) {
            try {
                completeResult.add(future.get());
            } catch (Exception exception) {
                // exception
            }
        }
        service.shutdownNow();
        System.out.println(completeResult);

Answer 2

ExecutorService.submit返回一個Future ，可以用來等待完成並get結果。

有一個版本的get有超時，這對於輪詢完成很有用。

您應該收集期貨並使用它們。 保留 100 個 Futures 的數組，然后在需要時循環它們收集結果，直到有足夠的結果滿足您的需要。