方案(一)CountDownLatch:
使用CountDownLatch+Semaphore方式实现:
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Semaphore;public class TestABC {
public static void main(String[] args) throws InterruptedException {
CountDownLatch countDownLatch=new CountDownLatch(2);
Semaphore semaphoreC = new Semaphore(1); Thread threadA = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(newjava.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
countDownLatch.countDown();
}
}, "Thread-A"); Thread threadB = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(newjava.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
countDownLatch.countDown();
}
}, "Thread-B"); Thread threadC = new Thread(new Runnable() {
@Override
public void run() {
try {
semaphoreC.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
semaphoreC.release();
}
}, "Thread-C"); // 占用C锁,直到A/B线程完成后,才释放C锁。
semaphoreC.acquire(); threadA.start();
threadB.start();
threadC.start(); countDownLatch.await();
// 释放C锁,让C线程有获取锁的可能
semaphoreC.release(); }
}
上边使用CountDownLatch+Semaphore方式实现,但是缺点:上边这种方式会导致线程阻塞情况。下边这种方案是可以实现不阻塞线程的用法:
import java.util.concurrent.CountDownLatch;public class TestABC {
public static void main(String[] args) throws InterruptedException {
CountDownLatch countDownLatch=new CountDownLatch(2); Thread threadA = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(new java.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
countDownLatch.countDown();
}
}, "Thread-A"); Thread threadB = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(new java.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName());
countDownLatch.countDown();
}
}, "Thread-B"); Thread threadC = new Thread(new Runnable() {
@Override
public void run() {
// 在C中等待A/B運算結束
try {
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
throw new RuntimeException("CountDownLatch等待失败。。。",e);
} System.out.println(Thread.currentThread().getName());
}
}, "Thread-C"); threadA.start();
threadB.start();
threadC.start();
}
}
方案(二):CyclicBarrier
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;public class TestABC {
public static void main(String[] args) throws InterruptedException {
CyclicBarrier cyclicBarrier=new CyclicBarrier(3); Thread threadA = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(new java.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()); // 冲破栅栏代表A线程结束
try {
cyclicBarrier.await();
} catch (InterruptedException | BrokenBarrierException e) {
e.printStackTrace();
throw new RuntimeException("cylicBarrier.await()拋出異常:",e);
}
}
}, "Thread-A"); Thread threadB = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(new java.util.Random().nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()); // 冲破栅栏代表B线程结束
try {
cyclicBarrier.await();
} catch (InterruptedException | BrokenBarrierException e) {
e.printStackTrace();
throw new RuntimeException("cylicBarrier.await()拋出異常:",e);
}
}
}, "Thread-B"); Thread threadC = new Thread(new Runnable() {
@Override
public void run() {
// 等待前两个(A/B)线程结束,只有前两个(A/B)线程结束了才能满足3个线程都冲破栅栏,
try {
// 等待栅栏被冲破,冲破栅栏的条件是:A/B/C三个线程都到达await()。
// 只有栅栏冲破,才能向下执行,否则先到达的线程等待。
cyclicBarrier.await();
} catch (InterruptedException | BrokenBarrierException e) {
e.printStackTrace();
throw new RuntimeException("cylicBarrier.await()拋出異常:",e);
}
// 满足了三个线程都冲破栅栏才向下执行
System.out.println(Thread.currentThread().getName());
}
}, "Thread-C"); threadA.start();
threadB.start();
threadC.start();
}
}