多线程编程入门(15):线程同步工具之Semaphore(信号量)

package cn.itcast.heima2;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

public class SemaphoreTest {
public static void main(String[] args) {
ExecutorService service = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(3);
for (int i = 0; i < 10; i++) {
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
semaphore.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("线程" + Thread.currentThread().getName() + "进入,当前已有" + (3-semaphore.availablePermits())+"个并发");
try {
Thread.sleep((long)(Math.random()*10000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("线程"+ Thread.currentThread().getName() + "即将离开");
semaphore.release();
//下面的代码有时候不准确,因为其没有和上面的代码合成原子单元
System.out.println("线程"+ Thread.currentThread().getName() + "已离开,当前已有" + (3-semaphore.availablePermits())+"个并发");
}
};
service.execute(runnable);
}
}

}