死磕Java并发之CountDownLatch与CyclicBarrier、Semaphore
等待多线程完成的CountDownLatch
CountDownLatch一般用于某个线程A等待若干个其他线程执行完任务之后，它才执行
public class CountDownLatchCase {
public static void main(String[] args) {
final CountDownLatch latch = new CountDownLatch(2);
threadStart(latch);
threadStart(latch);
try {
System.out.println("等待2个子线程执行完毕...");
latch.await();
System.out.println("2个子线程已经执行完毕");
System.out.println("继续执行主线程");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
static void threadStart(final CountDownLatch latch) {
new Thread() {
@Override
public void run() {
try {
System.out.println("子线程" + Thread.currentThread().getName() + "正在执行");
Thread.sleep(3000);
System.out.println("子线程" + Thread.currentThread().getName() + "执行完毕");
latch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
}
同步屏障CyclicBarrier
CyclicBarrier一般用于一组线程互相等待至某个状态，然后这一组线程再同时执行
public class CyclicBarrierCase {
public static void main(String[] args) {
int N = 4;
CyclicBarrier barrier = new CyclicBarrier(N, new Runnable() {
@Override
public void run() {
System.out.println("当前线程" + Thread.currentThread().getName());
}
});
for (int i = 0; i < N; i++) {
new Writer(barrier).start();
}
try {
Thread.sleep(25000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("CyclicBarrier重用");
for (int i = 0; i < N; i++) {
new Writer(barrier).start();
}
}
static class Writer extends Thread {
private CyclicBarrier cyclicBarrier;
public Writer(CyclicBarrier cyclicBarrier) {
this.cyclicBarrier = cyclicBarrier;
}
@Override
public void run() {
System.out.println("线程" + Thread.currentThread().getName() + "正在写入数据...");
try {
Thread.sleep(5000); //以睡眠来模拟写入数据操作
System.out.println("线程" + Thread.currentThread().getName() + "写入数据完毕，等待其他线程写入完毕");
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
System.out.println("所有线程写入完毕，继续处理其他任务...");
}
}
}
CyclicBarrier与CountDownLatch的区别
CountDownLatch的计数器只能使用一次，而CyclicBarrier的计数器可以使用reset()方法重置。
控制并发线程数的Semaphore(信号量)
Semaphore是用来控制同时访问特定资源的线程数量，它通过协调各个线程，以保证合理的使用公共资源。
public class SemaphoreCase {
public static void main(String[] args) {
// 工人数
int N = 8;
// 机器数目
Semaphore semaphore = new Semaphore(5);
for (int i = 1; i <= N; i++) {
new Worker(i, semaphore).start();
}
}
static class Worker extends Thread {
private int num;
private Semaphore semaphore;
public Worker(int num, Semaphore semaphore) {
this.num = num;
this.semaphore = semaphore;
}
@Override
public void run() {
try {
semaphore.acquire();
System.out.println("工人" + this.num + "占用一个机器在生产...");
Thread.sleep(2000);
System.out.println("工人" + this.num + "释放出机器");
semaphore.release();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}