Lock和Condition在JDK中LinkedBlockingQueue的应用

Lock和Condition在JDK中LinkedBlockingQueue的应用，核心源码注释解析如下：

import java.util.concurrent.LinkedBlockingQueue.Node;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * LinkedBlockingQueue核心方法源码分析
 *
 *
 */
public class LinkedBlockingQueue {

    /** Current number of elements */
    //使用AtomicInteger的原因是：LinkedBlockingQueue的take和put使用的是两把锁。所以需要对count进行同步。
    //同时count使用AtomicInteger可以解决take和put的冲突操作
    private final AtomicInteger count = new AtomicInteger(0); 

    /** Lock held by take, poll, etc */
    private final ReentrantLock takeLock = new ReentrantLock();

    /** Wait queue for waiting takes */
    private final Condition notEmpty = takeLock.newCondition(); //绑定takeLock

    /** Lock held by put, offer, etc */
    private final ReentrantLock putLock = new ReentrantLock();

    /** Wait queue for waiting puts */
    private final Condition notFull = putLock.newCondition();//绑定putLock

    /**
     * Inserts the specified element at the tail of this queue, waiting if
     * necessary for space to become available.
     *
     * @throws InterruptedException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             {@inheritDoc}
     */
    public void put(E e) throws InterruptedException {
        if (e == null)
            throw new NullPointerException();
        // Note: convention in all put/take/etc is to preset local var
        // holding count negative to indicate failure unless set.
        int c = -1;
        Node<E> node = new Node(e);
        final ReentrantLock putLock = this.putLock;
        final AtomicInteger count = this.count;
        putLock.lockInterruptibly();
        try {
            /*
             * Note that count is used in wait guard even though it is not
             * protected by lock. This works because count can only decrease at
             * this point (all other puts are shut out by lock), and we (or some
             * other waiting put) are signalled if it ever changes from
             * capacity. Similarly for all other uses of count in other wait
             * guards.
             */
            while (count.get() == capacity) {
                notFull.await(); //绑定putLock
            }
            enqueue(node);
            // 此处 c =size - 1（size为容器实际大小）
            c = count.getAndIncrement();
            if (c + 1 < capacity) //c+1 =size-1+1 =size ，如果c + 1 =size < capacity 的话
                notFull.signal(); //唤醒其他生产者生产数据
        } finally {
            putLock.unlock();
        }
        if (c == 0) //c=size-1==0，就是size==1？如果size=1代表还有元素，通知消费者生产数据
            signalNotEmpty(); //notEmpty.signal();
    }

    /**
     * Signals a waiting take. Called only from put/offer (which do not
     * otherwise ordinarily lock takeLock.)
     */
    private void signalNotEmpty() {
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lock();
        try {
            notEmpty.signal(); //绑定takeLock
        } finally {
            takeLock.unlock();
        }
    }

    public E take() throws InterruptedException {
        E x;
        int c = -1;
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lockInterruptibly();
        try {
            while (count.get() == 0) {
                notEmpty.await();  //绑定takeLock
            }
            x = dequeue();
            // 有点绕：获取当前count的值，然后减1。
            c = count.getAndDecrement();
            //而此时由于x = dequeue()代码消费了一个数据，所以c=size+1
            if (c > 1)//当前c=size+1>1的话，则就是size>0.所以此时就是有元素的，唤醒其他消费者消费数据
                notEmpty.signal();  //绑定takeLock
        } finally {
            takeLock.unlock();
        }
        if (c == capacity) //c = size +1 ==capacity 所以size =capacity-1，则容器还没有满，所以通知生产者生产数据
            signalNotFull();  // 调用notFull.signal();
        return x;
    }

    /**
     * Signals a waiting put. Called only from take/poll.
     */
    private void signalNotFull() {
        final ReentrantLock putLock = this.putLock;
        putLock.lock();
        try {
            notFull.signal(); //绑定putLock
        } finally {
            putLock.unlock();
        }
    }
}