Java所提供的Semaphore跟Operating System Concepts上所講的Semaphore一樣。
可以用它來解決：
- Producer and Consumer Problem
- The Readers-Writers Problem
- The Dining-Philosophers Problem
- Pool的實作
- 控制critical region
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40import java.util.concurrent.Semaphore;
public class SemaphoreDemo {
Semaphore pool = new Semaphore(10);
public static void main(String args[]) {
final SemaphoreDemo demo = new SemaphoreDemo();
for (int i = 0; i < 30; i++) {
new Thread(new Runnable() {
public void run() {
demo.mutualExclusion();
}
}, "Thread" + i).start();
}
}
private void mutualExclusion() {
try {
pool.acquire();
System.out.println(Thread.currentThread().getName() + " inside mutual exclusive region");
Thread.sleep(1000);
}
catch (InterruptedException e) {
e.printStackTrace();
}
finally {
pool.release();
System.out.println(Thread.currentThread().getName() + " outside of mutual exclusive region");
}
}
}
當pool為空的時候，想要使用pool資源的thread會進入blocking狀態，直到有其他thread執行release()釋放pool資源，喚醒其中在blocking狀態的thread。