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並發包中關於CountDownLatch類的使用
一個非常有用的類，CountDownLatch， 可以用來在一個線程中等待多個線程完成任務的類；
通常的使用場景是，某個主線程接到一個任務，起了n個子線程去完成，但是主線程需要等待這n個子線程都完成任務了以後才開始執行某個操作；
測試代碼如下：
package test;
import java.util.concurrent.CountDownLatch;
public class TestThread {
/**
*
* @author Administrator/2012-3-1/上午09:19:02
*/
public static void main(String[] args) {
TestThread t=new TestThread();
t.demoCountDown();
}
public void demoCountDown()
{
int count = 10;
final CountDownLatch l = new CountDownLatch(count);
for(int i = 0; i < count; ++i)
{
final int index = i;
new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.currentThread().sleep(20 * 1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("thread " + index + " has finished...");
l.countDown();
}
}).start();
}
try {
l.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("now all threads have finished");
}
}
運行結果：
thread 1 has finished...
thread 3 has finished...
thread 0 has finished...
thread 7 has finished...
thread 4 has finished...
thread 9 has finished...
thread 8 has finished...
thread 2 has finished...
thread 6 has finished...
thread 5 has finished...
now all threads have finished
前麵10個線程的執行完成順序會變化，但是最後一句始終會等待前麵10個線程都完成之後才會執行.
最後更新：2017-04-02 22:16:29