Java多种方法实现等待所有子线程完成再继续执行(java主线程等待子线程结束)

  本篇文章为你整理了Java多种方法实现等待所有子线程完成再继续执行(java主线程等待子线程结束)的详细内容,包含有java主线程等待子线程结束再返回 java主线程等待子线程结束 java主线程等待子线程 java等待多线程执行完成汇合结果 Java多种方法实现等待所有子线程完成再继续执行,希望能帮助你了解 Java多种方法实现等待所有子线程完成再继续执行。

  在现实世界中,我们常常需要等待其它任务完成,才能继续执行下一步。Java实现等待子线程完成再继续执行的方式很多。我们来一一查看一下。

  Thread的join方法

  该方法是Thread提供的方法,调用join()时,会阻塞主线程,等该Thread完成才会继续执行,代码如下:

  

private static void threadJoin() {

 

   List Thread threads = new ArrayList ();

   for (int i = 0; i NUM; i++) {

   Thread t = new Thread(new PkslowTask("Task " + i));

   t.start();

   threads.add(t);

   threads.forEach(t - {

   try {

   t.join();

   } catch (InterruptedException e) {

   throw new RuntimeException(e);

   System.out.println("threadJoin Finished All Tasks...");

  

 

  结果:

  

Task 6 is running

 

  Task 9 is running

  Task 3 is running

  Task 4 is running

  Task 7 is running

  Task 0 is running

  Task 2 is running

  Task 1 is running

  Task 5 is running

  Task 8 is running

  Task 1 is completed

  Task 8 is completed

  Task 6 is completed

  Task 4 is completed

  Task 3 is completed

  Task 0 is completed

  Task 7 is completed

  Task 9 is completed

  Task 2 is completed

  Task 5 is completed

  threadJoin Finished All Tasks...

  

 

  CountDownLatch

  CountDownLatch是一个很好用的并发工具,初始化时要指定线程数,如10。在子线程调用countDown()时计数减1。直到为0时,await()方法才不会阻塞。代码如下:

  

private static void countDownLatch() {

 

   CountDownLatch latch = new CountDownLatch(NUM);

   for (int i = 0; i NUM; i++) {

   Thread t = new Thread(() - {

   System.out.println("countDownLatch running...");

   try {

   Thread.sleep(1000);

   System.out.println("countDownLatch Finished...");

   latch.countDown();

   } catch (InterruptedException e) {

   throw new RuntimeException(e);

   t.start();

   try {

   latch.await();

   } catch (InterruptedException e) {

   throw new RuntimeException(e);

   System.out.println("countDownLatch Finished All Tasks...");

  

 

  结果:

  

countDownLatch running...

 

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch running...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished...

  countDownLatch Finished All Tasks...

  

 

  CyclicBarrier

  CyclicBarrier与CountDownLatch类似,但CyclicBarrier可重置,可重用。代码如下:

  

private static void cyclicBarrier() {

 

   CyclicBarrier barrier = new CyclicBarrier(NUM + 1);

   for (int i = 0; i NUM; i++) {

   Thread t = new Thread(() - {

   System.out.println("cyclicBarrier running...");

   try {

   Thread.sleep(1000);

   System.out.println("cyclicBarrier Finished...");

   barrier.await();

   } catch (InterruptedException BrokenBarrierException e) {

   throw new RuntimeException(e);

   t.start();

   try {

   barrier.await();

   } catch (InterruptedException BrokenBarrierException e) {

   throw new RuntimeException(e);

   System.out.println("cyclicBarrier Finished All Tasks...");

  

 

  结果:

  

cyclicBarrier running...

 

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier running...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished...

  cyclicBarrier Finished All Tasks...

  

 

  executorService.isTerminated()

  ExecutorService调用shutdown()方法后,可以通过方法isTerminated()来判断任务是否完成。代码如下:

  

private static void executeServiceIsTerminated() {

 

   ExecutorService executorService = Executors.newFixedThreadPool(THREADS);

   IntStream.range(0, NUM)

   .forEach(i - executorService.execute(new PkslowTask("Task " + i)));

   executorService.shutdown();

   while (!executorService.isTerminated()) {

   //waiting...

   System.out.println("executeServiceIsTerminated Finished All Tasks...");

  

 

  结果:

  

Task 0 is running

 

  Task 2 is running

  Task 1 is running

  Task 3 is running

  Task 4 is running

  Task 0 is completed

  Task 2 is completed

  Task 5 is running

  Task 4 is completed

  Task 7 is running

  Task 3 is completed

  Task 1 is completed

  Task 8 is running

  Task 6 is running

  Task 9 is running

  Task 5 is completed

  Task 9 is completed

  Task 7 is completed

  Task 6 is completed

  Task 8 is completed

  executeServiceIsTerminated Finished All Tasks...

  

 

  executorService.awaitTermination

  executorService.awaitTermination方法会等待任务完成,并给一个超时时间,代码如下:

  

private static void executeServiceAwaitTermination() {

 

   ExecutorService executorService = Executors.newFixedThreadPool(THREADS);

   IntStream.range(0, NUM)

   .forEach(i - executorService.execute(new PkslowTask("Task " + i)));

   executorService.shutdown();

   try {

   if (!executorService.awaitTermination(1, TimeUnit.MINUTES)) {

   executorService.shutdownNow();

   } catch (InterruptedException e) {

   throw new RuntimeException(e);

   System.out.println("executeServiceAwaitTermination Finished All Tasks...");

  

 

  结果:

  

Task 0 is running

 

  Task 1 is running

  Task 2 is running

  Task 3 is running

  Task 4 is running

  Task 0 is completed

  Task 5 is running

  Task 1 is completed

  Task 4 is completed

  Task 7 is running

  Task 3 is completed

  Task 8 is running

  Task 2 is completed

  Task 9 is running

  Task 6 is running

  Task 5 is completed

  Task 7 is completed

  Task 9 is completed

  Task 8 is completed

  Task 6 is completed

  executeServiceAwaitTermination Finished All Tasks...

  

 

  executorService.invokeAll

  使用invokeAll提交所有任务,代码如下:

  

private static void executeServiceInvokeAll() {

 

   ExecutorService executorService = Executors.newFixedThreadPool(THREADS);

   List Callable Void tasks = new ArrayList ();

   IntStream.range(0, NUM)

   .forEach(i - tasks.add(new PkslowTask("Task " + i)));

   try {

   executorService.invokeAll(tasks);

   } catch (InterruptedException e) {

   throw new RuntimeException(e);

   executorService.shutdown();

   System.out.println("executeServiceInvokeAll Finished All Tasks...");

  

 

  结果:

  

Task 1 is running

 

  Task 2 is running

  Task 0 is running

  Task 3 is running

  Task 4 is running

  Task 1 is completed

  Task 3 is completed

  Task 0 is completed

  Task 2 is completed

  Task 4 is completed

  Task 8 is running

  Task 5 is running

  Task 6 is running

  Task 9 is running

  Task 7 is running

  Task 8 is completed

  Task 5 is completed

  Task 6 is completed

  Task 9 is completed

  Task 7 is completed

  executeServiceInvokeAll Finished All Tasks...

  

 

  ExecutorCompletionService

  ExecutorCompletionService通过take()方法,会返回最早完成的任务,代码如下:

  

private static void executorCompletionService() {

 

   ExecutorService executorService = Executors.newFixedThreadPool(10);

   CompletionService String service = new ExecutorCompletionService (executorService);

   List Callable String callables = new ArrayList ();

   callables.add(new DelayedCallable(2000, "2000ms"));

   callables.add(new DelayedCallable(1500, "1500ms"));

   callables.add(new DelayedCallable(6000, "6000ms"));

   callables.add(new DelayedCallable(2500, "2500ms"));

   callables.add(new DelayedCallable(300, "300ms"));

   callables.add(new DelayedCallable(3000, "3000ms"));

   callables.add(new DelayedCallable(1100, "1100ms"));

   callables.add(new DelayedCallable(100, "100ms"));

   callables.add(new DelayedCallable(100, "100ms"));

   callables.add(new DelayedCallable(100, "100ms"));

   callables.forEach(service::submit);

   for (int i = 0; i NUM; i++) {

   try {

   Future String future = service.take();

   System.out.println(future.get() + " task is completed");

   } catch (InterruptedException ExecutionException e) {

   throw new RuntimeException(e);

   System.out.println("executorCompletionService Finished All Tasks...");

   executorService.shutdown();

   awaitTerminationAfterShutdown(executorService);

  

 

  这里不同任务的时长是不一样的,但会先返回最早完成的任务:

  

2000ms is running

 

  2500ms is running

  300ms is running

  1500ms is running

  6000ms is running

  3000ms is running

  1100ms is running

  100ms is running

  100ms is running

  100ms is running

  100ms is completed

  100ms is completed

  100ms task is completed

  100ms task is completed

  100ms is completed

  100ms task is completed

  300ms is completed

  300ms task is completed

  1100ms is completed

  1100ms task is completed

  1500ms is completed

  1500ms task is completed

  2000ms is completed

  2000ms task is completed

  2500ms is completed

  2500ms task is completed

  3000ms is completed

  3000ms task is completed

  6000ms is completed

  6000ms task is completed

  executorCompletionService Finished All Tasks...

  

 

  代码请看GitHub: https://github.com/LarryDpk/pkslow-samples

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