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johnawm：
2012-12-18 wangshibei 写道CountD ...
CountDownLatch的使用
concurrent包里面的CountDownLatch其实可以把它看作一个计数器，只不过这个计数器的操作是原子操作，同时只能有一个线程去操作这个计数器，也就是同时只能有一个线程去减这个计数器里面的值。
CountDownLatch的一个非常典型的应用场景是：有一个任务想要往下执行，但必须要等到其他的任务执行完毕后才可以继续往下执行。假如我们这个想要继续往下执行的任务调用一个CountDownLatch对象的await()方法，其他的任务执行完自己的任务后调用同一个CountDownLatch对象上的countDown()方法，这个调用await()方法的任务将一直阻塞等待，直到这个CountDownLatch对象的计数值减到0为止。
举个例子，有三个工人在为老板干活，这个老板有一个习惯，就是当三个工人把一天的活都干完了的时候，他就来检查所有工人所干的活。记住这个条件：三个工人先全部干完活，老板才检查。所以在这里用Java代码设计两个类，Worker代表工人，Boss代表老板，具体的代码实现如下：
public class Worker implements Runnable{
private CountDownLatch downLatch;
private String name;
public Worker(CountDownLatch downLatch, String name){
this.downLatch = downLatch;
this.name = name;
}
public void run() {
this.doWork();
try
{
TimeUnit.SECONDS.sleep(new Random().nextInt(10));
}catch(InterruptedException ie){
}
System.out.println(this.name + "活干完了！");
this.downLatch.countDown();
}
private void doWork()
{
System.out.println(this.name + "正在干活!");
}
}
==================
public class Boss implements Runnable {
private CountDownLatch downLatch;
public Boss(CountDownLatch downLatch){
this.downLatch = downLatch;
}
public void run() {
System.out.println("老板正在等所有的工人干完活......");
try {
this.downLatch.await();
} catch (InterruptedException e) {
}
System.out.println("工人活都干完了，老板开始检查了！");
}
}
============================
public class CountDownLatchDemo {
public static void main(String[] args) {
ExecutorService executor = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(3);
Worker w1 = new Worker(latch,"张三");
Worker w2 = new Worker(latch,"李四");
Worker w3 = new Worker(latch,"王二");
Boss boss = new Boss(latch);
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
}
}
使用System.nanoTime()试试吧...
System.out.println()是main的线程 不受ExecutorService 管理,他们互补干扰,
使用System.nanoTime()试试吧...
CountDownLatch的一个非常典型的应用场景是：有一个任务想要往下执行，但必须要等到其他的任务执行完毕后才可以继续往下执行。假如我们这个想要继续往下执行的任务调用一个CountDownLatch对象的await()方法，其他的任务执行完自己的任务后调用同一个CountDownLatch对象上的countDown()方法，这个调用await()方法的任务将一直阻塞等待，直到这个CountDownLatch对象的计数值减到0为止。
举个例子，有三个工人在为老板干活，这个老板有一个习惯，就是当三个工人把一天的活都干完了的时候，他就来检查所有工人所干的活。记住这个条件：三个工人先全部干完活，老板才检查。所以在这里用Java代码设计两个类，Worker代表工人，Boss代表老板，具体的代码实现如下：
public class Worker implements Runnable{
private CountDownLatch downLatch;
private String name;
public Worker(CountDownLatch downLatch, String name){
this.downLatch = downLatch;
this.name = name;
}
public void run() {
this.doWork();
try
{
TimeUnit.SECONDS.sleep(new Random().nextInt(10));
}catch(InterruptedException ie){
}
System.out.println(this.name + "活干完了！");
this.downLatch.countDown();
}
private void doWork()
{
System.out.println(this.name + "正在干活!");
}
}
==================
public class Boss implements Runnable {
private CountDownLatch downLatch;
public Boss(CountDownLatch downLatch){
this.downLatch = downLatch;
}
public void run() {
System.out.println("老板正在等所有的工人干完活......");
try {
this.downLatch.await();
} catch (InterruptedException e) {
}
System.out.println("工人活都干完了，老板开始检查了！");
}
}
============================
public class CountDownLatchDemo {
public static void main(String[] args) {
ExecutorService executor = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(3);
Worker w1 = new Worker(latch,"张三");
Worker w2 = new Worker(latch,"李四");
Worker w3 = new Worker(latch,"王二");
Boss boss = new Boss(latch);
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
}
}
分享到：
评论
6 楼
johnawm
2013-01-05
2012-12-18
有道理！！
wangshibei 写道
CountDownLatch这个东西还有点用，当计数器减为0时调用的应该是“notifyall”，而不是“notify”，所以只需要“latch”就可以了，不用“doneLatch ”
johnawm 写道
要统计时间你可以再加一个CountDownLatch变量用来表示老板检查结束，如
package methodtest;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class CountDonwLatchTest {
public static void main(String[] a) {
long startTime = System.currentTimeMillis();
ExecutorService executor = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(3);
CountDownLatch doneLatch = new CountDownLatch(1);
Worker w1 = new Worker(latch, "张三");
Worker w2 = new Worker(latch, "李四");
Worker w3 = new Worker(latch, "王二");
Boss boss = new Boss(latch, doneLatch);
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
try {
doneLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(System.currentTimeMillis() - startTime);
}
}
class Worker implements Runnable {
private CountDownLatch downLatch;
private String name;
public Worker(CountDownLatch downLatch, String name) {
this.downLatch = downLatch;
this.name = name;
}
public void run() {
this.doWork();
try {
TimeUnit.SECONDS.sleep(new Random().nextInt(10));
} catch (InterruptedException ie) {
}
System.out.println(this.name + "活干完了！");
this.downLatch.countDown();
}
private void doWork() {
System.out.println(this.name + "正在干活!");
}
}
class Boss implements Runnable {
private CountDownLatch downLatch;
private CountDownLatch doneLatch;
public Boss(CountDownLatch downLatch,CountDownLatch doneLatch) {
this.downLatch = downLatch;
this.doneLatch = doneLatch;
}
public void run() {
System.out.println("老板正在等所有的工人干完活...");
try {
this.downLatch.await();
} catch (InterruptedException e) {
}
System.out.println("工人活都干完了，老板开始检查了！");
doneLatch.countDown();
}
}
有道理！！
5 楼
wangshibei
2012-12-18
CountDownLatch这个东西还有点用，当计数器减为0时调用的应该是“notifyall”，而不是“notify”，所以只需要“latch”就可以了，不用“doneLatch ”
johnawm 写道
要统计时间你可以再加一个CountDownLatch变量用来表示老板检查结束，如
package methodtest;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class CountDonwLatchTest {
public static void main(String[] a) {
long startTime = System.currentTimeMillis();
ExecutorService executor = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(3);
CountDownLatch doneLatch = new CountDownLatch(1);
Worker w1 = new Worker(latch, "张三");
Worker w2 = new Worker(latch, "李四");
Worker w3 = new Worker(latch, "王二");
Boss boss = new Boss(latch, doneLatch);
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
try {
doneLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(System.currentTimeMillis() - startTime);
}
}
class Worker implements Runnable {
private CountDownLatch downLatch;
private String name;
public Worker(CountDownLatch downLatch, String name) {
this.downLatch = downLatch;
this.name = name;
}
public void run() {
this.doWork();
try {
TimeUnit.SECONDS.sleep(new Random().nextInt(10));
} catch (InterruptedException ie) {
}
System.out.println(this.name + "活干完了！");
this.downLatch.countDown();
}
private void doWork() {
System.out.println(this.name + "正在干活!");
}
}
class Boss implements Runnable {
private CountDownLatch downLatch;
private CountDownLatch doneLatch;
public Boss(CountDownLatch downLatch,CountDownLatch doneLatch) {
this.downLatch = downLatch;
this.doneLatch = doneLatch;
}
public void run() {
System.out.println("老板正在等所有的工人干完活...");
try {
this.downLatch.await();
} catch (InterruptedException e) {
}
System.out.println("工人活都干完了，老板开始检查了！");
doneLatch.countDown();
}
}
4 楼
johnawm
2012-08-28
要统计时间你可以再加一个CountDownLatch变量用来表示老板检查结束，如
package methodtest;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class CountDonwLatchTest {
public static void main(String[] a) {
long startTime = System.currentTimeMillis();
ExecutorService executor = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(3);
CountDownLatch doneLatch = new CountDownLatch(1);
Worker w1 = new Worker(latch, "张三");
Worker w2 = new Worker(latch, "李四");
Worker w3 = new Worker(latch, "王二");
Boss boss = new Boss(latch, doneLatch);
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
try {
doneLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(System.currentTimeMillis() - startTime);
}
}
class Worker implements Runnable {
private CountDownLatch downLatch;
private String name;
public Worker(CountDownLatch downLatch, String name) {
this.downLatch = downLatch;
this.name = name;
}
public void run() {
this.doWork();
try {
TimeUnit.SECONDS.sleep(new Random().nextInt(10));
} catch (InterruptedException ie) {
}
System.out.println(this.name + "活干完了！");
this.downLatch.countDown();
}
private void doWork() {
System.out.println(this.name + "正在干活!");
}
}
class Boss implements Runnable {
private CountDownLatch downLatch;
private CountDownLatch doneLatch;
public Boss(CountDownLatch downLatch,CountDownLatch doneLatch) {
this.downLatch = downLatch;
this.doneLatch = doneLatch;
}
public void run() {
System.out.println("老板正在等所有的工人干完活...");
try {
this.downLatch.await();
} catch (InterruptedException e) {
}
System.out.println("工人活都干完了，老板开始检查了！");
doneLatch.countDown();
}
}
3 楼
bubiaiyou
2012-08-27
javac_xinyun 写道
somefuture 写道
如果想统计时间，我这样做
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
使用System.nanoTime()试试吧...
System.out.println()是main的线程 不受ExecutorService 管理,他们互补干扰,
2 楼
javac_xinyun
2012-08-09
somefuture 写道
如果想统计时间，我这样做
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
使用System.nanoTime()试试吧...
1 楼
somefuture
2012-08-03
如果想统计时间，我这样做
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
long start871456 = System.currentTimeMillis();
executor.execute(w3);
executor.execute(w2);
executor.execute(w1);
executor.execute(boss);
executor.shutdown();
long end84654856 = System.currentTimeMillis();
System.out.println("运行时间是" + (end84654856 - start871456) + "毫秒");
为什么不行呢？
发表评论
-
线程中断
2012-11-15 16:04 3196线程的中断"interrupt& ... -
任务间使用管道输入输出
2011-10-17 10:42 1118管道流PipedReader和PipedWriter,它不同于 ... -
使用同步队列解决任务协作问题
2011-10-17 10:17 1393Java API里面提供了许多同步队列，你可以使用它来解决任务 ... -
简单生产者-消费者
2011-10-16 22:46 982考虑一个场景：一个饭店有一个厨师和一个服务员。菜做好之后，厨师 ... -
NIO响应中断
2012-11-30 15:59 1048不同于IO，NIO通道会自动地相应中断，代码如下： publi ... -
关闭底层资源强行中断
2011-10-11 10:26 1252对于IO这种资源无法通过interrupt()方法中断，但是在 ... -
线程中断
2011-10-11 10:09 909线程类的interrupt()方法可对某一线程进行中断，例子如 ... -
多线程中的原子类
2011-10-11 09:47 2046JAVA提供了AtomicInteger，AtomicLong ... -
多个任务运行终止以及资源共享例子
2011-10-11 09:27 929场景： 公园的管理人员 ... -
不正确的访问共享资源
2011-10-10 22:06 873看下面一段代码，这段 ... -
从任务中产生返回值
2011-10-10 21:44 929Runnable接口不返回任何值，如果希望任务完成时能返回一个 ... -
学会显示地使用Lock
2011-10-10 19:41 975Lock对象在使用的时候必须被显示地创建、锁定和释放。它和sy ... -
Daemon的使用
2011-10-10 19:12 1016后台线程是程序在运行的时候在后台提供一种通用服务的线程，当所有 ...
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