Semaphore的使用

Semaphore主要的作用時限制併發的線程數，過多的線程會導致cpu資源耗盡，使線程執行任務變緩慢
 *         Semaphore可用於pool池技術 Semaphore(1,false);非公平鎖，若第二個參數爲true則使公平鎖(與線程啓動有關)
 *         permits.acquire();獲取信號量 permits.release();釋放信號量
 *         permits.acquireUninterruptibly();當前線程不可中斷
 *         permits.availablePermits();獲取當前可用的信號量
 *         permits.drainPermits();立即獲取當前可用的信號量，並將可用信號量置零
 *         permits.tryAcquire();嘗試獲取信號量，失敗返回false，成功返回true
 *         permits.tryAcquire(long time,TimeUnit timeUnit);指定時間嘗試獲取一個信號量
 *         permits.tryAcquire(int n,long time,TimeUnit timeUnit);指定時間嘗試獲取n個信號量

 

public class Container {
	private Object[] container = new Object[5];
	private final int size = container.length;
	private final Semaphore set = new Semaphore(5);// 生產者
	private final Semaphore get = new Semaphore(5);// 消費者
	private final ReentrantLock lock = new ReentrantLock();
	private final Condition setCondition = lock.newCondition();// 生產條件
	private final Condition getCondition = lock.newCondition();// 消費條件

	public boolean isEmpty() {
		boolean empty = true;
		for (int i = 0; i < size; i++) {
			if (container[i] != null) {
				empty = false;
				break;
			}
		}
		return empty;
	}

	public boolean isFull() {
		boolean full = true;
		for (int i = 0; i < size; i++) {
			if (container[i] == null) {
				full = false;
				break;
			}
		}
		return full;
	}

	public void get() {
		get.acquireUninterruptibly();
		lock.lock();
		while (isEmpty()) {
			try {
				getCondition.await();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		for (int i = 0; i < size; i++) {
			if (container[i] != null) {
				System.out.println(Thread.currentThread().getName()+" consume " + container[i]);
				container[i] = null;
				break;
			}
		}
		setCondition.signalAll();
		lock.unlock();
		get.release();
	}

	public void set(String str) {
		set.acquireUninterruptibly();
		lock.lock();
		while(isFull()){
			try {
				setCondition.await();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		for (int i = 0; i < size; i++) {
			if (container[i] == null) {
				System.out.println(Thread.currentThread().getName()+" product " + str);
				container[i] = str;
				break;
			}
		}
		getCondition.signalAll();
		lock.unlock();
		set.release();
	}
}



public class Consumer extends Thread {
	Container c;

	Consumer(Container c) {
		this.c = c;
	}
	@Override
	public void run() {
		while(true){
		c.get();
		}
	}
}


public class Productor extends Thread {
	Container c;

	Productor(Container c) {
		this.c = c;
	}

	@Override
	public void run() {
		while (true) {
			c.set("data");
		}
	}
}

public class SemaphoreTest {
	public static void main(String[] args) {
		Container c = new Container();
		for (int i = 0; i < 5; i++) {
            new Consumer(c).start();
            new Productor(c).start();
		}
	}

	}