阻塞与唤醒方式的区别
CountDownLatch计数方式
CountDownLatch是减计数。调用await()后线程阻塞。调用countDown()方法后计数减一，当计数为零时，调用await()的线程被唤醒。
CountDownLatch应用场景为:
一个或一组线程等待另一组线程完成操作后恢复执行
CountDownLatch例子: 模拟赛跑
开始时一组运动员线程等待begin计数器(初始值为1)，当主线程调用begin.countDown()后begin减1，计数器为0,这一组运动员线程同时起跑。主线程等待end计数器(初始值为10)。一个运动员线程到达终点后，调用end.countDown()，end计数器减1。当所有运动员都到达终点后，end计数器为0，主线程恢复执行。
package CountDownLatch;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class RaceSimulation {
public static void main(String args[]){
//比赛开始的倒数锁
CountDownLatch begin=new CountDownLatch(1);
//比赛结束的倒数锁
CountDownLatch end=new CountDownLatch(10);
//十个选手跑步线程
final ExecutorService exec = Executors.newFixedThreadPool(10);
for(int index= 0;index<10;++index){
final int NO=index+1;
Runnable run = new Runnable(){
@Override
public void run() {
try{
//如果计数不为0,则一直等待
//如果当前计数为0,此线程立即执行
begin.await();
Thread.sleep((long)(Math.random()*10000));
System.out.println("No."+NO+" arrived");
}catch(InterruptedException e){
e.printStackTrace();
}finally{
//每个选手到达终点时,end就减1
end.countDown();
}
}
};
exec.submit(run);
}
System.out.println("游戏开始:");
//begin减1,开始游戏
begin.countDown();
//等待end变为0,即所有选手到达终点
try {
end.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("游戏结束");
exec.shutdown();
}
}
CyclicBarrier计数方式
CyclicBarrier是加计数。调用await()后线程阻塞计数器加1，当所有线程都到达屏障被阻塞后，这一组线程才一起恢复执行。
CyclicBarrier的应用场景
一组线程到达一个屏障（即执行CyclicBarrier.await()）时被阻塞，直到最后一个线程到达屏障时，屏障才会开门，所有被屏障拦截的线程才会继续干活。CyclicBarrier默认的构造方法是CyclicBarrier(int parties)，其参数表示屏障拦截的线程数量，每个线程调用await方法告诉CyclicBarrier我已经到达了屏障，然后当前线程被阻塞。
CyclicBarier的例子
package cyclicBarrier;
import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CyclicBarrierDemo {
public static void main(String[] args) {
int N=4;
CyclicBarrier cyclicBarrier=new CyclicBarrier(N,new Runnable() {
@Override
public void run() {
System.out.println("线程"+Thread.currentThread().getName()+"正在执行所有线程到达屏障后执行的操作");
}
});
ExecutorService exec=Executors.newFixedThreadPool(4);
for(int i=0;i<N;++i) {
Runnable r=()->{
try {
System.out.println("线程"+Thread.currentThread().getName()+"正在执行线程的操作");
//用睡眠代替线程的操作
Thread.sleep(new Random().nextInt(1000));
System.out.println("线程"+Thread.currentThread().getName()+"到达屏障");
cyclicBarrier.await();
System.out.println("线程"+Thread.currentThread().getName()+"越过屏障,线程执行完毕");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
};
exec.submit(r);
}
exec.shutdown();
}
}
是否可以重用
CountDownLatch不可以重用
CyclicBarrier可以重用
package cyclicBarrier;
import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CyclicBarrierDemo {
public static void main(String[] args) {
int N=4;
CyclicBarrier cyclicBarrier=new CyclicBarrier(N,new Runnable() {
@Override
public void run() {
System.out.println("线程"+Thread.currentThread().getName()+"正在执行所有线程到达屏障后执行的操作");
}
});
ExecutorService exec1=Executors.newFixedThreadPool(4);
for(int i=0;i<N;++i) {
Runnable r=()->{
try {
System.out.println("线程"+Thread.currentThread().getName()+"正在执行线程的操作");
//用睡眠代替线程的操作
Thread.sleep(new Random().nextInt(1000));
System.out.println("线程"+Thread.currentThread().getName()+"到达屏障");
cyclicBarrier.await();
System.out.println("线程"+Thread.currentThread().getName()+"越过屏障,线程执行完毕");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
};
exec1.submit(r);
}
exec1.shutdown();
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("CyclicBarrier重用");
ExecutorService exec2=Executors.newFixedThreadPool(4);
for(int i=0;i<N;++i) {
Runnable r=()->{
try {
System.out.println("线程"+Thread.currentThread().getName()+"正在执行线程的操作");
//用睡眠代替线程的操作
Thread.sleep(new Random().nextInt(1000));
System.out.println("线程"+Thread.currentThread().getName()+"到达屏障");
cyclicBarrier.await();
System.out.println("线程"+Thread.currentThread().getName()+"越过屏障,线程执行完毕");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
};
exec2.submit(r);
}
exec2.shutdown();
}
}