深谈多并发计数器CountDownLatch(一)
2017-09-08 13:33
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概述
CountDownLatch是JAVA提供在java.util.concurrent包下的一个工具辅助类,也可以把它看成是一个计数器,其内部维护着一个count计数,只不过对这个计数器的操作都是原子操作,同时只能有一个线程去操作这个计数器,CountDownLatch通过构造函数传入一个初始计数值,调用者可以通过调用CounDownLatch对象的cutDown()方法,来使计数减1;如果调用对象上的await()方法,那么调用者就会一直阻塞在这里,直到别人通过cutDown方法,将计数减到0,才可以继续执行。
案列分析
package org.apache.commons.lang3;
import java.util.concurrent.CountDownLatch;
/**
/**
* @author xiefg
* @create 2017-09-08 11:16
* @desc
**/
public class CountDownLatchDemo {
/**
* 参数数2,表示计数器计数为2
*/
private final static CountDownLatch countDownLatch = new CountDownLatch(2);
/**
* 示例demo线程类
*/
private static class DemoThread extends Thread {
private final String demoThreadName;
private final int demoSleepTime;
public DemoThread(String name, int sleepTime) {
demoThreadName = name;
demoSleepTime = sleepTime;
}
@Override
public void run() {
System.out.println("[" + demoThreadName + "] started!");
try {
Thread.sleep(demoSleepTime);
} catch (InterruptedException e) {
e.printStackTrace();
}
countDownLatch.countDown();
System.out.println("[" + demoThreadName + "] end!");
}
}
/**
* 示例线程类
*/
private static class CountDownLatchThread extends Thread {
@Override
public void run() {
System.out.println("[CountDownLatchThread] started!");
try {
// 线程挂起
countDownLatch.await();
} catch (InterruptedException e) {
}
System.out.println("[CountDownLatchThread] end!");
}
}
public static void main(String[] args) throws Exception {
// 执行 CountDownLatchThread
new CountDownLatchThread().start();
// 运行两个工作线程
new DemoThread("DemoThread1", 5000).start();
// 工作线程2运行2秒
new DemoThread("DemoThread2", 2000).start();
}
}
这里只是知道如何使用,接下来看看原理。
CountDownLatch是JAVA提供在java.util.concurrent包下的一个工具辅助类,也可以把它看成是一个计数器,其内部维护着一个count计数,只不过对这个计数器的操作都是原子操作,同时只能有一个线程去操作这个计数器,CountDownLatch通过构造函数传入一个初始计数值,调用者可以通过调用CounDownLatch对象的cutDown()方法,来使计数减1;如果调用对象上的await()方法,那么调用者就会一直阻塞在这里,直到别人通过cutDown方法,将计数减到0,才可以继续执行。
案列分析
package org.apache.commons.lang3;
import java.util.concurrent.CountDownLatch;
/**
/**
* @author xiefg
* @create 2017-09-08 11:16
* @desc
**/
public class CountDownLatchDemo {
/**
* 参数数2,表示计数器计数为2
*/
private final static CountDownLatch countDownLatch = new CountDownLatch(2);
/**
* 示例demo线程类
*/
private static class DemoThread extends Thread {
private final String demoThreadName;
private final int demoSleepTime;
public DemoThread(String name, int sleepTime) {
demoThreadName = name;
demoSleepTime = sleepTime;
}
@Override
public void run() {
System.out.println("[" + demoThreadName + "] started!");
try {
Thread.sleep(demoSleepTime);
} catch (InterruptedException e) {
e.printStackTrace();
}
countDownLatch.countDown();
System.out.println("[" + demoThreadName + "] end!");
}
}
/**
* 示例线程类
*/
private static class CountDownLatchThread extends Thread {
@Override
public void run() {
System.out.println("[CountDownLatchThread] started!");
try {
// 线程挂起
countDownLatch.await();
} catch (InterruptedException e) {
}
System.out.println("[CountDownLatchThread] end!");
}
}
public static void main(String[] args) throws Exception {
// 执行 CountDownLatchThread
new CountDownLatchThread().start();
// 运行两个工作线程
new DemoThread("DemoThread1", 5000).start();
// 工作线程2运行2秒
new DemoThread("DemoThread2", 2000).start();
}
}
这里只是知道如何使用,接下来看看原理。
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