标签：实现 ini 通讯 waiting nbsp ++ res interrupt 线程
一般而言，如果没有干预的话，线程在启动之后会一直运行到结束，但有时候我们又需要很多线程来共同完成一个任务，这就牵扯到线程间的通讯。
如何让两个线程先后执行？Thread.join方法
private static void demo2() { Thread A = new Thread(new Runnable() { @Override public void run() { printNumber("A"); } }); Thread B = new Thread(new Runnable() { @Override public void run() { System.out.println("B starts waiting for A"); try { A.join(); } catch (InterruptedException e) { e.printStackTrace(); } printNumber("B"); } }); B.start(); A.start(); }
其中A.join()的意思即是等待A线程执行完毕。
如何让两个线程交互执行？object.wait和object.notify方法
1 /** 2 * A 1, B 1, B 2, B 3, A 2, A 3 3 */ 4 private static void demo3() { 5 Object lock = new Object(); 6 Thread A = new Thread(new Runnable() { 7 @Override 8 public void run() { 9 synchronized (lock) { 10 System.out.println("A 1"); 11 try { 12 lock.wait(); 13 } catch (InterruptedException e) { 14 e.printStackTrace(); 15 } 16 System.out.println("A 2"); 17 System.out.println("A 3"); 18 } 19 } 20 }); 21 Thread B = new Thread(new Runnable() { 22 @Override 23 public void run() { 24 synchronized (lock) { 25 System.out.println("B 1"); 26 System.out.println("B 2"); 27 System.out.println("B 3"); 28 lock.notify(); 29 } 30 } 31 }); 32 A.start(); 33 B.start(); 34 }
A在输出完1之后等待B的notify才会去执行其他的操作。
如何让四个线程的其中一个等待其他三个执行完毕？CountdownLatch就是干这个的。
CountdownLatch的基本用法
CountdownLatch countDownLatch = new CountDownLatch(3;countDownLatch.await() 进入等待状态;countDownLatch.countDown() ，会使内部否计数值减一;countDown()导致count值为 0, 则处于等待态的线程开始执行。1 private static void runDAfterABC() { 2 int worker = 3; 3 CountDownLatch countDownLatch = new CountDownLatch(worker); 4 new Thread(new Runnable() { 5 @Override 6 public void run() { 7 System.out.println("D is waiting for other three threads"); 8 try { 9 countDownLatch.await(); 10 System.out.println("All done, D starts working"); 11 } catch (InterruptedException e) { 12 e.printStackTrace(); 13 } 14 } 15 }).start(); 16 for (char threadName=‘A‘; threadName <= ‘C‘; threadName++) { 17 final String tN = String.valueOf(threadName); 18 new Thread(new Runnable() { 19 @Override 20 public void run() { 21 System.out.println(tN + "is working"); 22 try { 23 Thread.sleep(100); 24 } catch (Exception e) { 25 e.printStackTrace(); 26 } 27 System.out.println(tN + "finished"); 28 countDownLatch.countDown(); 29 } 30 }).start(); 31 } 32 }
如何让三个线程的各自开始做一些事情，然后在某个时间点上进行同步？CyclicBarrier 是干这个的。
CyclicBarrier 的用法：
CyclicBarrier对象，设置初始值，CyclicBarrier cyclicBarrier = new CyclicBarrier(3)；cyclicBarrier.await()开始等待；cyclicBarrier.await() 之后，每个线程都可以执行之后的逻辑。1 private static void runABCWhenAllReady() { 2 int runner = 3; 3 CyclicBarrier cyclicBarrier = new CyclicBarrier(runner); 4 final Random random = new Random(); 5 for (char runnerName=‘A‘; runnerName <= ‘C‘; runnerName++) { 6 final String rN = String.valueOf(runnerName); 7 new Thread(new Runnable() { 8 @Override 9 public void run() { 10 long prepareTime = random.nextInt(10000) + 100; 11 System.out.println(rN + "is preparing for time:" + prepareTime); 12 try { 13 Thread.sleep(prepareTime); 14 } catch (Exception e) { 15 e.printStackTrace(); 16 } 17 try { 18 System.out.println(rN + "is prepared, waiting for others"); 19 cyclicBarrier.await(); // The current runner is ready, waiting for others to be ready 20 } catch (InterruptedException e) { 21 e.printStackTrace(); 22 } catch (BrokenBarrierException e) { 23 e.printStackTrace(); 24 } 25 System.out.println(rN + "starts running"); // All the runners are ready to start running together 26 } 27 }).start(); 28 } 29 }
如何取回某个线程的返回值了？Callable 是干这个的。
先看下定义：
@FunctionalInterface public interface Callable<V> { /** * Computes a result, or throws an exception if unable to do so. * * @return computed result * @throws Exception if unable to compute a result */ V call() throws Exception; }
然后直接给个例子：
1 private static void doTaskWithResultInWorker() { 2 Callable<Integer> callable = new Callable<Integer>() { 3 @Override 4 public Integer call() throws Exception { 5 System.out.println("Task starts"); 6 Thread.sleep(1000); 7 int result = 0; 8 for (int i=0; i<=100; i++) { 9 result += i; 10 } 11 System.out.println("Task finished and return result"); 12 return result; 13 } 14 }; 15 FutureTask<Integer> futureTask = new FutureTask<>(callable); 16 new Thread(futureTask).start(); 17 try { 18 System.out.println("Before futureTask.get()"); 19 System.out.println("Result:" + futureTask.get()); 20 System.out.println("After futureTask.get()"); 21 } catch (InterruptedException e) { 22 e.printStackTrace(); 23 } catch (ExecutionException e) { 24 e.printStackTrace(); 25 } 26 }
注意，其中futureTask.get()方法是阻塞调用。
以上都是一些很基本的应用，在新版本的CompleteFuture中其实提供了更多的链式操作，不过写起来比较复杂，看起来也不清晰。
标签：实现 ini 通讯 waiting nbsp ++ res interrupt 线程
原文地址：https://www.cnblogs.com/029zz010buct/p/10440520.html
