标签：存储 pass let 中文翻译 应用 内部类 app 实例 cal
CountDownLatch的中文翻译为"闭锁"，在JDK1.5中 CountDownLatch类加入进来。为程序猿进行并发编程提供有利的帮助。
首先我们先看看JDK文档中对于CountDownLatch类的介绍：
A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.
大致意思是CountDownLatch为一个同步辅助工具，让一个或多个线程等待，直到其他的线程执行操作完成。
它的功能可以在绝大部分情况上替代join()方法，甚至在实际运用中比join()方法的用法更灵活。
操作过程：用CountDownLatch类创建实例，指定需要等待完成点个数。await()方法会阻塞当前线程，直到计数器减为零。每次线程执行调用countDown()方法，就会使计数器减1，直到计数器减为0时，等待的线程继续运行。
/** * Constructs a {@code CountDownLatch} initialized with the given count. * * @param count the number of times {@link #countDown} must be invoked * before threads can pass through {@link #await} * @throws IllegalArgumentException if {@code count} is negative
* 构造器用给定计数作为参数进行初始化，若参数为负则抛出非法参数异常。
* */ public CountDownLatch(int count) { if (count < 0) throw new IllegalArgumentException("count < 0"); this.sync = new Sync(count); }
1. await() 方法
/** * Causes the current thread to wait until the latch has counted down to * zero, unless the thread is {@linkplain Thread#interrupt interrupted}. * 使当前线程等待直到闭锁的计数器为0，除非线程由于中断异常中断。 */ public void await() throws InterruptedException { sync.acquireSharedInterruptibly(1); }
2. await(long timeout, TimeUnit unit) 方法
/** * Causes the current thread to wait until the latch has counted down to * zero, unless the thread is {@linkplain Thread#interrupt interrupted}, * or the specified waiting time elapses.
* 使当前线程等待直到闭锁计数器为0，除非线程遇到线程中断异常中断，或者超出指定的等待时间。 * @param timeout the maximum time to wait 超出的最大等待时间 * @param unit the time unit of the {@code timeout} argument 指定最大等待时间的时间单位 * @return {@code true} if the count reached zero and {@code false} * if the waiting time elapsed before the count reached zero * @throws InterruptedException if the current thread is interrupted * while waiting */ public boolean await(long timeout, TimeUnit unit) throws InterruptedException { return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout)); }
3. countDown() 方法
/** * Decrements the count of the latch, releasing all waiting threads if * the count reaches zero. * 减少闭锁的计数，若计数达到0则释放所有等待线程 * <p>If the current count is greater than zero then it is decremented. * If the new count is zero then all waiting threads are re-enabled for * thread scheduling purposes. * * <p>If the current count equals zero then nothing happens. */ public void countDown() { sync.releaseShared(1); }
4. getCount() 方法
/** * Returns the current count. * 返回当前计数器的值 * <p>This method is typically used for debugging and testing purposes. * * @return the current count */ public long getCount() { return sync.getCount(); }
应用：
有这么一道题：用4个线程并发执行从1加到100，每个线程只能加25个数，主线程需要等待子线程结束完成后才能结束。
思想：可以用join()方法，也可以用CountDownLatch对象来暂停主线程。
代码：
import java.util.concurrent.CountDownLatch; public class Compute { public static int sum = 0;// 存储1加到100的数 public static CountDownLatch count = new CountDownLatch(4);// 闭锁，计数器设置为4 static class ComputeThread extends Thread {// 内部类 int start, end;// 起始与结束 public ComputeThread(int start, int end) { this.start = start; this.end = end; } @Override public void run() {// 每个线程都进行累加 for (int i = start; i <= end; i++) { sum += i; } System.out.println(currentThread().getName() + ":" + sum); count.countDown(); } } public static void main(String[] args) throws InterruptedException { // 建立4个线程 ComputeThread c1 = new Compute.ComputeThread(1, 25); ComputeThread c2 = new Compute.ComputeThread(26, 50); ComputeThread c3 = new Compute.ComputeThread(51, 75); ComputeThread c4 = new Compute.ComputeThread(76, 100); // 启动4个线程 c1.start(); c2.start(); c3.start(); c4.start(); // 让调用线程停止，等待计数器为0 count.await(); System.out.println(sum); } }
标签：存储 pass let 中文翻译 应用 内部类 app 实例 cal
原文地址：https://www.cnblogs.com/JimKing/p/8972231.html
