Semaphore意为信号量，它的使用原理跟操作系统中的PV原语非常相似，所以不再多说。下面是一个使用Semaphore的例子。
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 sp = new Semaphore(3);
for (int i = 0; i < 10; i++) {
Runnable runnable = new Runnable() {
public void run() {
try {
sp.acquire();
} catch (InterruptedException e1) {
e1.printStackTrace();
}
System.out.println("Thread: "
+ Thread.currentThread().getName()
+ " gets in,we now have "
+ (3 - sp.availablePermits()) + " concurrent");
try {
Thread.sleep((long) (Math.random() * 10000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Thread: "
+ Thread.currentThread().getName() + " is leaving");
sp.release();
}
};
service.execute(runnable);
}
service.shutdown();
}
}
