简介
在事实世界中，咱们经常须要期待其它工作实现，能力继续执行下一步。Java实现期待子线程实现再继续执行的形式很多。咱们来一一查看一下。
Thread的join办法
该办法是Thread提供的办法，调用join()时，会阻塞主线程，等该Thread实现才会继续执行，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...");}后果：
Task 6 is runningTask 9 is runningTask 3 is runningTask 4 is runningTask 7 is runningTask 0 is runningTask 2 is runningTask 1 is runningTask 5 is runningTask 8 is runningTask 1 is completedTask 8 is completedTask 6 is completedTask 4 is completedTask 3 is completedTask 0 is completedTask 7 is completedTask 9 is completedTask 2 is completedTask 5 is completedthreadJoin 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()办法才不会阻塞。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...");}后果：
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相似，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...");}后果：
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()办法后，能够通过办法isTerminated()来判断工作是否实现。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...");}后果：
Task 0 is runningTask 2 is runningTask 1 is runningTask 3 is runningTask 4 is runningTask 0 is completedTask 2 is completedTask 5 is runningTask 4 is completedTask 7 is runningTask 3 is completedTask 1 is completedTask 8 is runningTask 6 is runningTask 9 is runningTask 5 is completedTask 9 is completedTask 7 is completedTask 6 is completedTask 8 is completedexecuteServiceIsTerminated Finished All Tasks...executorService.awaitTermination
executorService.awaitTermination办法会期待工作实现，并给一个超时工夫，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...");}后果：
Task 0 is runningTask 1 is runningTask 2 is runningTask 3 is runningTask 4 is runningTask 0 is completedTask 5 is runningTask 1 is completedTask 4 is completedTask 7 is runningTask 3 is completedTask 8 is runningTask 2 is completedTask 9 is runningTask 6 is runningTask 5 is completedTask 7 is completedTask 9 is completedTask 8 is completedTask 6 is completedexecuteServiceAwaitTermination Finished All Tasks...executorService.invokeAll
应用invokeAll提交所有工作，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...");}后果：
Task 1 is runningTask 2 is runningTask 0 is runningTask 3 is runningTask 4 is runningTask 1 is completedTask 3 is completedTask 0 is completedTask 2 is completedTask 4 is completedTask 8 is runningTask 5 is runningTask 6 is runningTask 9 is runningTask 7 is runningTask 8 is completedTask 5 is completedTask 6 is completedTask 9 is completedTask 7 is completedexecuteServiceInvokeAll Finished All Tasks...ExecutorCompletionService
ExecutorCompletionService通过take()办法，会返回最早实现的工作，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);}这里不同工作的时长是不一样的，但会先返回最早实现的工作：
2000ms is running2500ms is running300ms is running1500ms is running6000ms is running3000ms is running1100ms is running100ms is running100ms is running100ms is running100ms is completed100ms is completed100ms task is completed100ms task is completed100ms is completed100ms task is completed300ms is completed300ms task is completed1100ms is completed1100ms task is completed1500ms is completed1500ms task is completed2000ms is completed2000ms task is completed2500ms is completed2500ms task is completed3000ms is completed3000ms task is completed6000ms is completed6000ms task is completedexecutorCompletionService Finished All Tasks...代码
代码请看GitHub: https://github.com/LarryDpk/pkslow-samples