java并发编程（7）构建自定义同步工具及条件队列

public void put(V v) throws InterruptedException {
        while (true) {                          //轮询
            synchronized (this) {               //加锁等待
                if (!isFull()) {                //如果缓存没满 则执行插入
                    doPut(v);
                    return;
                }
            }
            Thread.sleep(SLEEP_GRANULARITY);    //如果缓存满了 线程等待一段时间后继续轮询
        }
    }

    public V take() throws InterruptedException {//同理 相反
        while (true) {
            synchronized (this) {
                if (!isEmpty())
                    return doTake();
            }
            Thread.sleep(SLEEP_GRANULARITY);
        }
    }

    // BLOCKS-UNTIL: not-full
    public synchronized void put(V v) throws InterruptedException {
        while (isFull()) {
            wait();             //等待：释放锁且等待；等待通知后获取锁 并继续判断条件谓词
        }
        doPut(v);
        notifyAll();            //通知：通知释放所有等待
    }
　
    // 问题，不好分析，在put 和 take操作后，通知了所有等待条件队列
    // 而且让所有 等待都要去判断 条件谓词；
    // 如我put完成，只需要通知take正在等待的，而无需通知put正在等待的（反之亦然），因为只有take后，缓存才有可能不是满的，才要去判断条件谓词
    public synchronized V take() throws InterruptedException {
        while (isEmpty()) {
            wait();
        }
        V v = doTake();
        notifyAll();
        return v;
    }

public class ConditionBoundedBuffer  {
    protected final Lock lock = new ReentrantLock();
    // 条件谓词 未满
    private final Condition notFull = lock.newCondition();
    // 条件谓词 非空
    private final Condition notEmpty = lock.newCondition();
    private static final int BUFFER_SIZE = 100;
    private final T[] items = (T[]) new Object[BUFFER_SIZE];
    private int tail, head, count;

    // BLOCKS-UNTIL: notFull
    public void put(T x) throws InterruptedException {
        lock.lock();
        try {
            while (count == items.length)
                notFull.await();    //当缓存满了，等待有线程取出缓存；等待未满谓词通知（只有take才有可能让缓存不满）
            items[tail] = x;
            if (++tail == items.length)
                tail = 0;
            ++count;
            notEmpty.signal();      //当插入成功，通知释放非空谓词
        } finally {
            lock.unlock();
        }
    }

    // BLOCKS-UNTIL: notEmpty
    public T take() throws InterruptedException {
        lock.lock();
        try {
            while (count == 0)
                notEmpty.await();   //当缓存为空，等待插入；等待非空谓词通知
            T x = items[head];
            items[head] = null;
            if (++head == items.length)
                head = 0;
            --count;
            notFull.signal();               //当取出一个，通知释放未满谓词
            return x;
        } finally {
            lock.unlock();
        }
    }
}

//通过 lock+条件队列实现信号量Semaphore 许可
public class SemaphoreOnLock {
    private final Lock lock = new ReentrantLock();
    // CONDITION PREDICATE: permitsAvailable (permits > 0)
    private final Condition permitsAvailable = lock.newCondition();
    private int permits;

    SemaphoreOnLock(int initialPermits) {
        lock.lock();
        try {
            permits = initialPermits;
        } finally {
            lock.unlock();
        }
    }

    // BLOCKS-UNTIL: permitsAvailable
    public void acquire() throws InterruptedException {
        lock.lock();
        try {
            while (permits <= 0)            //当许可<0时 等待 许可释放
                permitsAvailable.await();
            --permits;
        } finally {
            lock.unlock();
        }
    }

    public void release() {
        lock.lock();
        try {
            ++permits;                      //释放许可
            permitsAvailable.signal();
        } finally {
            lock.unlock();
        }
    }
}

public class OneShotLatch {
    private final Sync sync = new Sync();

    public void signal() {
        sync.releaseShared(0);
    }

    public void await() throws InterruptedException {
        sync.acquireSharedInterruptibly(0); 
    }

    private class Sync extends AbstractQueuedSynchronizer { //继承AQS
        protected int tryAcquireShared(int ignored) {
            // 判断状态
            return (getState() == 1) ? 1 : -1;
        }

        protected boolean tryReleaseShared(int ignored) {
            //释放状态
            setState(1); // 打开闭锁
            return true; // 其他线程可以获取该闭锁

        }
    }
}