黑马程序员——线程同步的几种方式

 

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1、CountDownLatch一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。

public class CountdownLatchTest {


public static void main(String[] args) {


ExecutorService service = Executors.newCachedThreadPool();
final CountDownLatch cdOrder = new CountDownLatch(1);
final CountDownLatch cdAnswer = new CountDownLatch(3);
for(int i=0;i<3;i++){
Runnable runnable = new Runnable(){
public void run(){
try {
System.out.println("线程" + Thread.currentThread().getName() + 
"正准备接受命令");
cdOrder.await();
System.out.println("线程" + Thread.currentThread().getName() + 
"已接受命令");
Thread.sleep((long)(Math.random()*10000));
System.out.println("线程" + Thread.currentThread().getName() + 
"回应命令处理结果");
cdAnswer.countDown();
} catch (Exception e) {
e.printStackTrace();
}
}
};
service.execute(runnable);
}
try {
Thread.sleep((long)(Math.random()*10000));

System.out.println("线程" + Thread.currentThread().getName() + 
"即将发布命令");
cdOrder.countDown();
System.out.println("线程" + Thread.currentThread().getName() + 
"已发送命令，正在等待结果");
cdAnswer.await();
System.out.println("线程" + Thread.currentThread().getName() + 
"已收到所有响应结果");
} catch (Exception e) {
e.printStackTrace();
}
service.shutdown();


}
}

2、CyclicBarrier

一个同步辅助类，它允许一组线程互相等待，直到到达某个公共屏障点 (common barrier point)。在涉及一组固定大小的线程的程序中，这些线程必须不时地互相等待，此时 CyclicBarrier 很有用。因为该 barrier 在释放等待线程后可以重用，所以称它为循环 的 barrier。 

public class CyclicBarrierTest {


public static void main(String[] args) {
//创建一个线程池对象
ExecutorService service = Executors.newCachedThreadPool();
final  CyclicBarrier cb = new CyclicBarrier(3);
for(int i=0;i<3;i++){
Runnable runnable = new Runnable(){
public void run(){
try {
Thread.sleep((long)(Math.random()*10000));
System.out.println("线程" + Thread.currentThread().getName() + 
"即将到达集合地点1，当前已有" + (cb.getNumberWaiting()+1) + "个已经到达，" + 
(cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候"));
cb.await();

Thread.sleep((long)(Math.random()*10000));
System.out.println("线程" + Thread.currentThread().getName() + 
"即将到达集合地点2，当前已有" + (cb.getNumberWaiting()+1) + "个已经

到达，" + 
(cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候"));
cb.await();
Thread.sleep((long)(Math.random()*10000));
System.out.println("线程" + Thread.currentThread().getName() + 
"即将到达集合地点3，当前已有" + (cb.getNumberWaiting() + 1) + "个已经到达，" +
(cb.getNumberWaiting()==2?"都到齐了，继续走啊":"正在等候"));
cb.await();
} catch (Exception e) {
e.printStackTrace();
}
}
};
service.execute(runnable);
}
service.shutdown();
}
}

3、Exchanger

可以在对中对元素进行配对和交换的线程的同步点。每个线程将条目上的某个方法呈现给 exchange 方法，与伙伴线程进行匹配，并且在返回时接收其伙伴的对象。Exchanger 可能被视为SynchronousQueue 的双向形式。Exchanger 可能在应用程序（比如遗传算法和管道设计）中很有用

public class ExchangerTest {


public static void main(String[] args) {
ExecutorService service = Executors.newCachedThreadPool();
final Exchanger<String> exchanger = new Exchanger<String>();
service.execute(new Runnable(){
public void run() {
try {


String data1 = "wangxujie";
System.out.println("线程" + Thread.currentThread().getName() + 
"正在把数据" + data1 +"换出去");
Thread.sleep((long)(Math.random()*10000));
String data2 = (String)exchanger.exchange(data1);
System.out.println("线程" + Thread.currentThread().getName() + 
"换回的数据为" + data2);
}catch(Exception e){

}
}
});
service.execute(new Runnable(){
public void run() {
try {


String data1 = "wangzhiming";
System.out.println("线程" + Thread.currentThread().getName() + 
"正在把数据" + data1 +"换出去");
Thread.sleep((long)(Math.random()*10000));
String data2 = (String)exchanger.exchange(data1);
System.out.println("线程" + Thread.currentThread().getName() + 
"换回的数据为" + data2);
}catch(Exception e){

}
}
});
service.shutdown();
}
}