java并发包顶层AQS(抽象的队列式的同步器)分析，结合ReentrantLock分析（源码分析）

package com.kailong.lock;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.LockSupport;
import sun.misc.Unsafe;
/**
 * Created by Administrator on 2017/4/20.
 * 抽象的队列式的同步器
 * 不同的自定义同步器争用共享资源的方式也不同。自定义同步器在实现时只需要实现共享资源state的获取与释放方式即可，
 * 至于具体线程等待队列的维护（如获取资源失败入队/唤醒出队等），AQS已经在顶层实现好了。
 * 自定义同步器实现时主要实现以下几种方法：
     isHeldExclusively()：该线程是否正在独占资源。只有用到condition才需要去实现它。
     tryAcquire(int)：独占方式。尝试获取资源，成功则返回true，失败则返回false。
    tryRelease(int)：独占方式。尝试释放资源，成功则返回true，失败则返回false。
    tryAcquireShared(int)：共享方式。尝试获取资源。负数表示失败；0表示成功，但没有剩余可用资源；正数表示成功，且有剩余资源。
    tryReleaseShared(int)：共享方式。尝试释放资源，成功则返回true，失败则返回false。
 同步类在实现时一般都将自定义同步器（sync）定义为内部类，供自己使用；而同步类自己（Mutex）则实现某个接口，对外服务。当然
 ，接口的实现要直接依赖sync，它们在语义上也存在某种对应关系！！
 而sync只用实现资源state的获取-释放方式tryAcquire-tryRelelase，至于线程的排队、等待、唤醒等，
 上层的AQS都已经实现好了，我们不用关心。比如自己实现可重入独占锁 接下来将会分析源码 让大家理解这个过程
 */
public class AbstractQueuedSynchronizer extends AbstractOwnableSynchronizer implements  java.io.Serializable{
    private static final long serialVersionUID = 7373984972572414691L;//序列化id
    protected AbstractQueuedSynchronizer() { }//无参数改造方法
    static final class Node{
        /**
         * 指示节点正在等待共享模式的标记
         */
        static final Node SHARED = new Node();
        /**
         *指示节点正在等待独占模式的标记
         */
        static final Node EXCLUSIVE = null;
        /**
         *waitStatus值指示线程已取消
         */
        static final int CANCELLED =  1;
        /**
         *waitStatus值表示后续线程需要开启
         */
        static final int SIGNAL    = -1;
        /**
         *waitStatus值表示线程正在等待状态
         */
        static final int CONDITION = -2;
        /**
         *值指示下一个acquireShared应无条件地传播
         */
        static final int PROPAGATE = -3;
        /**
         * 等待状态
         */
        volatile int waitStatus;
        //前驱
        volatile Node prev;
        //后继
        volatile Node next;
        //线程
        volatile Thread thread;
        //下一个等待
        Node nextWaiter;

        /**
         * 如果节点在共享模式下等待，则返回true。
         * @return
         */
        final boolean isShared() {
            return nextWaiter == SHARED;
        }

        /**
         * 返回上一个节点，如果为null，则抛出NullPointerException。
         *当前辈不能为null时使用。 空检查可以
         *被淘汰，但目前是为了帮助虚拟机
          * @返回此节点的前身
         * @return
         * @throws NullPointerException
         */
        final Node predecessor() throws NullPointerException {
            Node p = prev;
            if (p == null)
                throw new NullPointerException();
            else
                return p;
        }

        Node() {    // 用于建立初始头或共享标记
        }
        Node(Thread thread, Node mode) {     //Used by addWaiter
            this.nextWaiter = mode;
            this.thread = thread;
        }
        Node(Thread thread, int waitStatus) { // 按条件使用
            this.waitStatus = waitStatus;
            this.thread = thread;
        }
    }
        private transient volatile Node head;
        private transient volatile Node tail;
        private volatile int state;
        protected final int getState() {
            return state;
        }
        protected final void setState(int newState) {
            state = newState;
        }
        protected final boolean compareAndSetState(int expect, int update) {
            return unsafe.compareAndSwapInt(this, stateOffset, expect, update);
        }
        static final long spinForTimeoutThreshold = 1000L;

    /**
     * 　此方法用于将node加入队尾
     * @param node
     * @return
     */
        private Node enq(final Node node) {
            //CAS"自旋"，直到成功加入队尾  链表操作 加入节点 分两种情况 一如果链表为空则设置为头结点 否则添加即可
            //AtomicInteger.getAndIncrement()函数源码,之前分析的cas机制如此，CAS自旋volatile变量
            for (;;) {
                Node t = tail;
                if (t == null) { // 必须初始化
                    if (compareAndSetHead(new Node()))
                        tail = head;
                } else {
                    node.prev = t;
                    if (compareAndSetTail(t, node)) {
                        t.next = node;
                        return t;
                    }
                }
            }
        }

    /**
     * addWaiter()将该线程加入等待队列的尾部，并标记为独占模式；
     * 此方法用于将当前线程加入到等待队列的队尾，并返回当前线程所在的结点
     * @param mode
     * @return
     */
        private Node addWaiter(Node mode) {
            // //以给定模式构造结点。mode有两种：EXCLUSIVE（独占）和SHARED（共享）
            Node node = new Node(Thread.currentThread(), mode);
            // //尝试快速方式直接放到队尾。 这里只是很简单的链表操作只不过多线程 因此需要用cas机制
            Node pred = tail;//头结点
            if (pred != null) {
                node.prev = pred;
                if (compareAndSetTail(pred, node)) {//利用cas机制修改节点 因为多线程操作 所以利用cas保证线程安全
                    pred.next = node;
                    return node;
                }
            }
            //上一步失败则通过enq入队。
            enq(node);
            return node;
        }
        private void setHead(Node node) {
            head = node;
            node.thread = null;
            node.prev = null;
        }

    /**
     * 此方法用于唤醒等待队列中下一个线程。下面是源码：
     * @param node
     */
        private void unparkSuccessor(Node node) {
            int ws = node.waitStatus;//这里，node一般为当前线程所在的结点。
            if (ws < 0)
                compareAndSetWaitStatus(node, ws, 0);//置零当前线程所在的结点状态，允许失败。
            Node s = node.next;
            if (s == null || s.waitStatus > 0) {//如果为空或已取消
                s = null;
                for (Node t = tail; t != null && t != node; t = t.prev)
                    if (t.waitStatus <= 0)//从这里可以看出，<=0的结点，都是还有效的结点。
                        s = t;
            }
            if (s != null)
                LockSupport.unpark(s.thread);//唤醒
        }

    /**
     * 释放   还是cas机制 一个大的自旋 然后修改即可
     */
        private void doReleaseShared() {
            for (;;) {
                Node h = head;
                if (h != null && h != tail) {
                    int ws = h.waitStatus;
                    if (ws == Node.SIGNAL) {
                        if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))
                            continue;            // loop to recheck cases
                        unparkSuccessor(h);//唤醒后继
                    }
                    else if (ws == 0 &&
                            !compareAndSetWaitStatus(h, 0, Node.PROPAGATE))
                        continue;                // loop on failed CAS
                }
                if (h == head)                   // loop if head changed
                    break;
            }
        }

    /**
     * 此方法在setHead()的基础上多了一步，就是自己苏醒的同时，如果条件符合（
     * 比如还有剩余资源），还会去唤醒后继结点，毕竟是共享模式！
     　　doReleaseShared()我们留着下一小节的releaseShared()里来讲。
     * @param node
     * @param propagate
     */
        private void setHeadAndPropagate(Node node, int propagate) {
            Node h = head;
            setHead(node);//head指向自己
            //如果还有剩余量，继续唤醒下一个邻居线程
            if (propagate > 0 || h == null || h.waitStatus < 0 ||
                    (h = head) == null || h.waitStatus < 0) {
                Node s = node.next;
                if (s == null || s.isShared())
                    doReleaseShared();
            }
        }
        private void cancelAcquire(Node node) {
            if (node == null)
                return;
            node.thread = null;
            Node pred = node.prev;
            while (pred.waitStatus > 0)
                node.prev = pred = pred.prev;
            Node predNext = pred.next;
            node.waitStatus = Node.CANCELLED;
            if (node == tail && compareAndSetTail(node, pred)) {
                compareAndSetNext(pred, predNext, null);
            } else {
                int ws;
                if (pred != head &&
                        ((ws = pred.waitStatus) == Node.SIGNAL ||
                                (ws <= 0 && compareAndSetWaitStatus(pred, ws, Node.SIGNAL))) &&
                        pred.thread != null) {
                    Node next = node.next;
                    if (next != null && next.waitStatus <= 0)
                        compareAndSetNext(pred, predNext, next);
                } else {
                    unparkSuccessor(node);
                }

                node.next = node; // help GC
            }
        }
        private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
            int ws = pred.waitStatus;//拿到前驱的状态
            if (ws == Node.SIGNAL)
                return true;// //如果已经告诉前驱拿完号后通知自己一下，那就可以安心休息了
            if (ws > 0) {
                /*
 8             * 如果前驱放弃了，那就一直往前找，直到找到最近一个正常等待的状态，并排在它的后边。
 9            * 注意：那些放弃的结点，由于被自己“加塞”到它们前边，它们相当于形成一个无引用链，注意垃圾回收
              会进行可达性分析，稍后就会被保安大叔赶走了(GC回收)！
10            */
                do {
                    node.prev = pred = pred.prev;
                } while (pred.waitStatus > 0);
                pred.next = node;
            } else {
                //如果前驱正常，那就把前驱的状态设置成SIGNAL，告诉它拿完号后通知自己一下。有可能失败，
                compareAndSetWaitStatus(pred, ws, Node.SIGNAL);
            }
            return false;
        }
        static void selfInterrupt() {
            Thread.currentThread().interrupt();
        }

    /**
     * 如果线程找好安全休息点后，那就可以安心去休息了。此方法就是让线程去休息，真正进入等待状态。
     * @return
     */
        private final boolean parkAndCheckInterrupt() {
            LockSupport.park(this);
            return Thread.interrupted();
        }

    /**
     * acquireQueued()使线程在等待队列中获取资源，一直获取到资源后才返回。
     * 如果在整个等待过程中被中断过，则返回true，否则返回false。
     * 进入等待状态休息，直到其他线程彻底释放资源后唤醒自己，自己再拿到资源，然后就可以去干自己想干的事了
     * 在等待队列中排队拿号
     * @param node
     * @param arg
     * @return
     */
        final boolean acquireQueued(final Node node, int arg) {
            boolean failed = true;//标记是否成功拿到资源
            try {
                boolean interrupted = false;//标记等待过程中是否被中断过
                for (;;) {//加入自旋  不断操作
                    final Node p = node.predecessor();//拿到前驱
                    if (p == head && tryAcquire(arg)) {////拿到资源后，将head指向该结点。所以head所指的标杆结点，就是当前获取到资源的那个结点或null。
                        setHead(node);
                        p.next = null; // help GC 这里帮助垃圾回收器回收节点
                        failed = false;//返回等待过程中是否被中断过
                        return interrupted;
                    }
                    // //如果自己可以休息了，就进入waiting状态，直到被unpark()
                    /**
                     * 结点进入队尾后，检查状态，找到安全休息点；
                     调用park()进入waiting状态，等待unpark()或interrupt()唤醒自己；
                     被唤醒后，看自己是不是有资格能拿到号。如果拿到，head指向当前结点，
                     并返回从入队到拿到号的整个过程中是否被中断过；如果没拿到，继续流程1。
                     */
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            parkAndCheckInterrupt())//检查状态 接下来将会进行检查状态分析 看看线程是否进入waiting状态
                        interrupted = true;////如果等待过程中被中断过，哪怕只有那么一次，就将interrupted标记为true
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }
        private void doAcquireInterruptibly(int arg)
                throws InterruptedException {
            final Node node = addWaiter(Node.EXCLUSIVE);
            boolean failed = true;
            try {
                for (;;) {
                    final Node p = node.predecessor();
                    if (p == head && tryAcquire(arg)) {
                        setHead(node);
                        p.next = null; // help GC
                        failed = false;
                        return;
                    }
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            parkAndCheckInterrupt())
                        throw new InterruptedException();
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }
        private boolean doAcquireNanos(int arg, long nanosTimeout)
                throws InterruptedException {
            if (nanosTimeout <= 0L)
                return false;
            final long deadline = System.nanoTime() + nanosTimeout;
            final Node node = addWaiter(Node.EXCLUSIVE);
            boolean failed = true;
            try {
                for (;;) {
                    final Node p = node.predecessor();
                    if (p == head && tryAcquire(arg)) {
                        setHead(node);
                        p.next = null; // help GC
                        failed = false;
                        return true;
                    }
                    nanosTimeout = deadline - System.nanoTime();
                    if (nanosTimeout <= 0L)
                        return false;
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            nanosTimeout > spinForTimeoutThreshold)
                        LockSupport.parkNanos(this, nanosTimeout);
                    if (Thread.interrupted())
                        throw new InterruptedException();
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }

    /**
     * 此方法用于将当前线程加入等待队列尾部休息，直到其他线程释放资源唤醒自己，
     * 自己成功拿到相应量的资源后才返回。下面是doAcquireShared()的源码：　　
     * 有木有觉得跟acquireQueued()很相似？对，其实流程并没有太大区别。
     * 只不过这里将补中断的selfInterrupt()放到doAcquireShared()里了，
     * 而独占模式是放到acquireQueued()之外，其实都一样.　跟独占模式比，
     * 还有一点需要注意的是，这里只有线程是head.next时（“老二”），
     * 才会去尝试获取资源，有剩余的话还会唤醒之后的队友。那么问题就来了，
     * 假如老大用完后释放了5个资源，而老二需要6个，老三需要1个，老四需要2个。
     * 因为老大先唤醒老二，老二一看资源不够自己用继续park()，也更不会去唤醒老三和老四了。
     * 独占模式，同一时刻只有一个线程去执行，这样做未尝不可；但共享模式下，
     * 多个线程是可以同时执行的，现在因为老二的资源需求量大，
     * 而把后面量小的老三和老四也都卡住了。
     * @param arg
     */
        private void doAcquireShared(int arg) {
            final Node node = addWaiter(Node.SHARED);//加入队列尾部
            boolean failed = true;//是否成功标志
            try {
                boolean interrupted = false;//等待过程中是否被中断过的标志
                for (;;) {
                    final Node p = node.predecessor();//前驱
                    if (p == head) {
                        int r = tryAcquireShared(arg);//如果到head的下一个，因为head是拿到资源的线程，此时node被唤醒，
                        // 很可能是head用完资源来唤醒自己的,尝试获取资源
                        if (r >= 0) {
                            setHeadAndPropagate(node, r);//将head指向自己，还有剩余资源可以再唤醒之后的线程
                            p.next = null; // help GC
                            if (interrupted)
                                selfInterrupt();//如果等待过程中被打断过，此时将中断补上。
                            failed = false;
                            return;
                        }
                    }
                    //判断状态，寻找安全点，进入waiting状态，等着被unpark()或interrupt()
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            parkAndCheckInterrupt())
                        interrupted = true;
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }
        private void doAcquireSharedInterruptibly(int arg)
                throws InterruptedException {
            final Node node = addWaiter(Node.SHARED);
            boolean failed = true;
            try {
                for (;;) {
                    final Node p = node.predecessor();
                    if (p == head) {
                        int r = tryAcquireShared(arg);
                        if (r >= 0) {
                            setHeadAndPropagate(node, r);
                            p.next = null; // help GC
                            failed = false;
                            return;
                        }
                    }
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            parkAndCheckInterrupt())
                        throw new InterruptedException();
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }
        private boolean doAcquireSharedNanos(int arg, long nanosTimeout)
                throws InterruptedException {
            if (nanosTimeout <= 0L)
                return false;
            final long deadline = System.nanoTime() + nanosTimeout;
            final Node node = addWaiter(Node.SHARED);
            boolean failed = true;
            try {
                for (;;) {
                    final Node p = node.predecessor();
                    if (p == head) {
                        int r = tryAcquireShared(arg);
                        if (r >= 0) {
                            setHeadAndPropagate(node, r);
                            p.next = null; // help GC
                            failed = false;
                            return true;
                        }
                    }
                    nanosTimeout = deadline - System.nanoTime();
                    if (nanosTimeout <= 0L)
                        return false;
                    if (shouldParkAfterFailedAcquire(p, node) &&
                            nanosTimeout > spinForTimeoutThreshold)
                        LockSupport.parkNanos(this, nanosTimeout);
                    if (Thread.interrupted())
                        throw new InterruptedException();
                }
            } finally {
                if (failed)
                    cancelAcquire(node);
            }
        }

    /**
     * tryAcquire()尝试直接去获取资源，如果成功则直接返回；
     * 此方法尝试去获取独占资源。如果获取成功，则直接返回true，否则直接返回false。
     * 这也正是tryLock()的语义，当然不仅仅只限于tryLock()。如下是tryAcquire()的源码：
     * 至于为甚这里直接抛出异常因为AQS只是一个框架，具体资源的获取/释放方式交由自定义同步器去实现，之所以没有抽象是因为
     * 只是抢占锁 该框架还有共享锁的定义 所以写成抽象不方便开发者书写。
     * @param arg
     * @return
     */
        protected boolean tryAcquire(int arg) {
            throw new UnsupportedOperationException();
        }

    /**
     *
     * @param arg
     * @return
     * 跟tryAcquire()一样，这个方法是需要独占模式的自定义同步器去实现的。正常来说，tryRelease()都会成功的，因为这是独占模式，该线程来释放资源，那么它肯定已经拿到独占资源了，直接减掉相应量的资源即可(state-=arg)，也不需要考虑线程安全的问题。但要注意它的返回值，上面已经提到了，release()是根据tryRelease()的返回值来判断该线程是否已经完成释放掉资源了！所以自义定同步器在实现时，
     * 如果已经彻底释放资源(state=0)，要返回true，否则返回false  和上面的设计理念一样
     * 这个函数并不复杂。一句话概括：用unpark()唤醒等待队列中最前边的那个未放弃线程，这里我们也用s来表示吧。此时，再和acquireQueued()联系起来，s被唤醒后，进入if (p == head && tryAcquire(arg))的判断（即使p!=head也没关系，它会再进入shouldParkAfterFailedAcquire()寻找一个安全点。这里既然s已经是等待队列中最前边的那个未放弃线程了，那么通过shouldParkAfterFailedAcquire()的调整，s也必然会跑到head的next结点，下一次自旋p==head就成立啦），然后s把自己设置成head标杆结点，表示自己已经获取到资源了，
     * acquire()也返回了！！release()是独占模式下线程释放共享资源的顶层入口。它会释放指定量的资源，如果彻底释放了（即state=0）,它会唤醒等待队列里的其他线程来获取资源。
     */
        protected boolean tryRelease(int arg) {
            throw new UnsupportedOperationException();
        }

    /**
     * @param arg
     * @return
     */
        protected int tryAcquireShared(int arg) {
            throw new UnsupportedOperationException();
        }
        protected boolean tryReleaseShared(int arg) {
            throw new UnsupportedOperationException();
        }
        protected boolean isHeldExclusively() {
            throw new UnsupportedOperationException();
        }

    /**
     * 此方法是独占模式下线程获取共享资源的顶层入口。如果获取到资源，线程直接返回，否则进入等待队列，直到获取到资源为止，且整个过程忽略中断的影响。这也正是lock()的语义，
     * 当然不仅仅只限于lock()。获取到资源后，线程就可以去执行其临界区代码了.调用自定义同步器的tryAcquire()尝试直接去获取资源，如果成功则直接返回；
     没成功，则addWaiter()将该线程加入等待队列的尾部，并标记为独占模式；acquireQueued()使线程在等待队列中休息，有机会时（轮到自己，会被unpark()）会去尝试获取资源。获取到资源后才返回。如果在整个等待过程中被中断过，则返回true，否则返回false。
     如果线程在等待过程中被中断过，它是不响应的。只是获取资源后才再进行自我中断selfInterrupt()，将中断补上。
     * @param arg
     */
        public final void acquire(int arg) {
            if (!tryAcquire(arg) &&
                    acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
                selfInterrupt();
        }
        public final void acquireInterruptibly(int arg)
                throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            if (!tryAcquire(arg))
                doAcquireInterruptibly(arg);
        }
        public final boolean tryAcquireNanos(int arg, long nanosTimeout)
                throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            return tryAcquire(arg) ||
                    doAcquireNanos(arg, nanosTimeout);
        }

    /**
     * 释放
     * @param arg
     * @return
     */
        public final boolean release(int arg) {
            if (tryRelease(arg)) {//它调用tryRelease()来释放资源。有一点需要注意的是，它是根据tryRelease()的返回值来判断该线程是否已经完成释放掉资源了！所以自定义同步器在设计tryRelease()的时候要明确这一点！！
                Node h = head;//找到头结点
                if (h != null && h.waitStatus != 0)
                    unparkSuccessor(h);//唤醒等待队列里的下一个线程
                return true;
            }
            return false;
        }

    /**
     * 此方法是共享模式下线程获取共享资源的顶层入口。它会获取指定量的资源，获取成功则直接返回，获取失败则进入等待队列，
     * 直到获取到资源为止，整个过程忽略中断。下面是acquireShared()的源码：tryAcquireShared()尝试获取资源，成功则直接返回；
     失败则通过doAcquireShared()进入等待队列park()，直到被unpark()/interrupt()并成功获取到资源才返回。整个等待过程也是忽略中断的。
     其实跟acquire()的流程大同小异，只不过多了个自己拿到资源后，还会去唤醒后继队友的操作（这才是共享嘛）。
     * @param arg
     */
        public final void acquireShared(int arg) {
            /**
             * 这里tryAcquireShared()依然需要自定义同步器去实现。但是AQS已经把其返回值的语义定义好了：
             * 负值代表获取失败；0代表获取成功，但没有剩余资源；正数表示获取成功，还有剩余资源，其他线程还可以去获取。
             * 所以这里acquireShared()的流程就是：tryAcquireShared()尝试获取资源，成功则直接返回；
              失败则通过doAcquireShared()进入等待队列，直到获取到资源为止才返回。
             */
            if (tryAcquireShared(arg) < 0)
                doAcquireShared(arg);
        }
        public final void acquireSharedInterruptibly(int arg)
                throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            if (tryAcquireShared(arg) < 0)
                doAcquireSharedInterruptibly(arg);
        }
        public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout)
                throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            return tryAcquireShared(arg) >= 0 ||
                    doAcquireSharedNanos(arg, nanosTimeout);
        }

    /**
     * releaseShared()吧。此方法是共享模式下线程释放共享资源的顶层入口。它会释放指定量的资源，
     * 如果彻底释放了（即state=0）,它会唤醒等待队列里的其他线程来获取资源。下面是releaseShared()的源码：
     * 释放掉资源后，唤醒后继。跟独占模式下的release()相似，但有一点稍微需要注意：
     * 独占模式下的tryRelease()在完全释放掉资源（state=0）后，才会返回true去唤醒其他线程，
     * 这主要是基于可重入的考量；而共享模式下的releaseShared()则没有这种要求，
     * 一是共享的实质--多线程可并发执行；二是共享模式基本也不会重入，
     * 所以自定义同步器可以根据需要决定返回值。
     * @param arg
     * @return
     */
        public final boolean releaseShared(int arg) {
            if (tryReleaseShared(arg)) {//尝试释放资源
                doReleaseShared();//唤醒后继结点
                return true;
            }
            return false;
        }
        public final boolean hasQueuedThreads() {
            return head != tail;
        }
        public final boolean hasContended() {
            return head != null;
        }
        public final Thread getFirstQueuedThread() {
            return (head == tail) ? null : fullGetFirstQueuedThread();
        }
        private Thread fullGetFirstQueuedThread() {
            Node h, s;
            Thread st;
            if (((h = head) != null && (s = h.next) != null &&
                    s.prev == head && (st = s.thread) != null) ||
                    ((h = head) != null && (s = h.next) != null &&
                            s.prev == head && (st = s.thread) != null))
                return st;
            Node t = tail;
            Thread firstThread = null;
            while (t != null && t != head) {
                Thread tt = t.thread;
                if (tt != null)
                    firstThread = tt;
                t = t.prev;
            }
            return firstThread;
        }
        public final boolean isQueued(Thread thread) {
            if (thread == null)
                throw new NullPointerException();
            for (Node p = tail; p != null; p = p.prev)
                if (p.thread == thread)
                    return true;
            return false;
        }
        final boolean apparentlyFirstQueuedIsExclusive() {
            Node h, s;
            return (h = head) != null &&
                    (s = h.next)  != null &&
                    !s.isShared()         &&
                    s.thread != null;
        }
        public final boolean hasQueuedPredecessors() {
            Node t = tail; // Read fields in reverse initialization order
            Node h = head;
            Node s;
            return h != t &&
                    ((s = h.next) == null || s.thread != Thread.currentThread());
        }
        public final int getQueueLength() {
            int n = 0;
            for (Node p = tail; p != null; p = p.prev) {
                if (p.thread != null)
                    ++n;
            }
            return n;
        }
        public final Collection getQueuedThreads() {
            ArrayList list = new ArrayList();
            for (Node p = tail; p != null; p = p.prev) {
                Thread t = p.thread;
                if (t != null)
                    list.add(t);
            }
            return list;
        }
        public final Collection getExclusiveQueuedThreads() {
            ArrayList list = new ArrayList();
            for (Node p = tail; p != null; p = p.prev) {
                if (!p.isShared()) {
                    Thread t = p.thread;
                    if (t != null)
                        list.add(t);
                }
            }
            return list;
        }
        public final Collection getSharedQueuedThreads() {
            ArrayList list = new ArrayList();
            for (Node p = tail; p != null; p = p.prev) {
                if (p.isShared()) {
                    Thread t = p.thread;
                    if (t != null)
                        list.add(t);
                }
            }
            return list;
        }
        public String toString() {
            int s = getState();
            String q  = hasQueuedThreads() ? "non" : "";
            return super.toString() +
                    "[State = " + s + ", " + q + "empty queue]";
        }
        final boolean isOnSyncQueue(Node node) {
            if (node.waitStatus == Node.CONDITION || node.prev == null)
                return false;
            if (node.next != null) // If has successor, it must be on queue
                return true;
            return findNodeFromTail(node);
        }
        private boolean findNodeFromTail(Node node) {
            Node t = tail;
            for (;;) {
                if (t == node)
                    return true;
                if (t == null)
                    return false;
                t = t.prev;
            }
        }
        final boolean transferForSignal(Node node) {
            if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
                return false;
            Node p = enq(node);
            int ws = p.waitStatus;
            if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
                LockSupport.unpark(node.thread);
            return true;
        }
        final boolean transferAfterCancelledWait(Node node) {
            if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
                enq(node);
                return true;}
            while (!isOnSyncQueue(node))
                Thread.yield();
            return false;
        }
         final int fullyRelease(Node node) {
            boolean failed = true;
            try {
                int savedState = getState();
                if (release(savedState)) {
                    failed = false;
                    return savedState;
                } else {
                    throw new IllegalMonitorStateException();
                }
            } finally {
                if (failed)
                    node.waitStatus = Node.CANCELLED;
            }
        }
        public final boolean owns(ConditionObject condition) {
            return condition.isOwnedBy(this);
        }
        public final boolean hasWaiters(ConditionObject condition) {
            if (!owns(condition))
                throw new IllegalArgumentException("Not owner");
            return condition.hasWaiters();
        }
        public final int getWaitQueueLength(ConditionObject condition) {
            if (!owns(condition))
                throw new IllegalArgumentException("Not owner");
            return condition.getWaitQueueLength();
        }
        public final Collection getWaitingThreads(ConditionObject condition) {
            if (!owns(condition))
                throw new IllegalArgumentException("Not owner");
            return condition.getWaitingThreads();
        }
        public class ConditionObject implements Condition, java.io.Serializable {
            private static final long serialVersionUID = 1173984872572414699L;
            /** First node of condition queue. */
            private transient Node firstWaiter;
            /** Last node of condition queue. */
            private transient Node lastWaiter;
            public ConditionObject() { }
            private Node addConditionWaiter() {
                Node t = lastWaiter;
                // If lastWaiter is cancelled, clean out.
                if (t != null && t.waitStatus != Node.CONDITION) {
                    unlinkCancelledWaiters();
                    t = lastWaiter;
                }
                Node node = new Node(Thread.currentThread(), Node.CONDITION);
                if (t == null)
                    firstWaiter = node;
                else
                    t.nextWaiter = node;
                lastWaiter = node;
                return node;
            }
            private void doSignal(Node first) {
                do {
                    if ( (firstWaiter = first.nextWaiter) == null)
                        lastWaiter = null;
                    first.nextWaiter = null;
                } while (!transferForSignal(first) &&
                        (first = firstWaiter) != null);
            }
            private void doSignalAll(Node first) {
                lastWaiter = firstWaiter = null;
                do {
                    Node next = first.nextWaiter;
                    first.nextWaiter = null;
                    transferForSignal(first);
                    first = next;
                } while (first != null);
            }
            private void unlinkCancelledWaiters() {
                Node t = firstWaiter;
                Node trail = null;
                while (t != null) {
                    Node next = t.nextWaiter;
                    if (t.waitStatus != Node.CONDITION) {
                        t.nextWaiter = null;
                        if (trail == null)
                            firstWaiter = next;
                        else
                            trail.nextWaiter = next;
                        if (next == null)
                            lastWaiter = trail;
                    }
                    else
                        trail = t;
                    t = next;
                }
            }
            public final void signal() {
                if (!isHeldExclusively())
                    throw new IllegalMonitorStateException();
                Node first = firstWaiter;
                if (first != null)
                    doSignal(first);
            }
            public final void signalAll() {
                if (!isHeldExclusively())
                    throw new IllegalMonitorStateException();
                Node first = firstWaiter;
                if (first != null)
                    doSignalAll(first);
            }
            public final void awaitUninterruptibly() {
                Node node = addConditionWaiter();
                int savedState = fullyRelease(node);
                boolean interrupted = false;
                while (!isOnSyncQueue(node)) {
                    LockSupport.park(this);
                    if (Thread.interrupted())
                        interrupted = true;
                }
                if (acquireQueued(node, savedState) || interrupted)
                    selfInterrupt();
            }
            private static final int REINTERRUPT =  1;
            private static final int THROW_IE    = -1;
            private int checkInterruptWhileWaiting(Node node) {
                return Thread.interrupted() ?
                        (transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
                        0;
            }
            private void reportInterruptAfterWait(int interruptMode)
                    throws InterruptedException {
                if (interruptMode == THROW_IE)
                    throw new InterruptedException();
                else if (interruptMode == REINTERRUPT)
                    selfInterrupt();
            }
            public final void await() throws InterruptedException {
                if (Thread.interrupted())
                    throw new InterruptedException();
                Node node = addConditionWaiter();
                int savedState = fullyRelease(node);
                int interruptMode = 0;
                while (!isOnSyncQueue(node)) {
                    LockSupport.park(this);
                    if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                        break;
                }
                if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                    interruptMode = REINTERRUPT;
                if (node.nextWaiter != null) // clean up if cancelled
                    unlinkCancelledWaiters();
                if (interruptMode != 0)
                    reportInterruptAfterWait(interruptMode);
            }
            public final long awaitNanos(long nanosTimeout)
                    throws InterruptedException {
                if (Thread.interrupted())
                    throw new InterruptedException();
                Node node = addConditionWaiter();
                int savedState = fullyRelease(node);
                final long deadline = System.nanoTime() + nanosTimeout;
                int interruptMode = 0;
                while (!isOnSyncQueue(node)) {
                    if (nanosTimeout <= 0L) {
                        transferAfterCancelledWait(node);
                        break;
                    }
                    if (nanosTimeout >= spinForTimeoutThreshold)
                        LockSupport.parkNanos(this, nanosTimeout);
                    if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                        break;
                    nanosTimeout = deadline - System.nanoTime();
                }
                if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                    interruptMode = REINTERRUPT;
                if (node.nextWaiter != null)
                    unlinkCancelledWaiters();
                if (interruptMode != 0)
                    reportInterruptAfterWait(interruptMode);
                return deadline - System.nanoTime();
            }
            public final boolean awaitUntil(Date deadline)
                    throws InterruptedException {
                long abstime = deadline.getTime();
                if (Thread.interrupted())
                    throw new InterruptedException();
                Node node = addConditionWaiter();
                int savedState = fullyRelease(node);
                boolean timedout = false;
                int interruptMode = 0;
                while (!isOnSyncQueue(node)) {
                    if (System.currentTimeMillis() > abstime) {
                        timedout = transferAfterCancelledWait(node);
                        break;
                    }
                    LockSupport.parkUntil(this, abstime);
                    if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                        break;
                }
                if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                    interruptMode = REINTERRUPT;
                if (node.nextWaiter != null)
                    unlinkCancelledWaiters();
                if (interruptMode != 0)
                    reportInterruptAfterWait(interruptMode);
                return !timedout;
            }
            public final boolean await(long time, TimeUnit unit)
                    throws InterruptedException {
                long nanosTimeout = unit.toNanos(time);
                if (Thread.interrupted())
                    throw new InterruptedException();
                Node node = addConditionWaiter();
                int savedState = fullyRelease(node);
                final long deadline = System.nanoTime() + nanosTimeout;
                boolean timedout = false;
                int interruptMode = 0;
                while (!isOnSyncQueue(node)) {
                    if (nanosTimeout <= 0L) {
                        timedout = transferAfterCancelledWait(node);
                        break;
                    }
                    if (nanosTimeout >= spinForTimeoutThreshold)
                        LockSupport.parkNanos(this, nanosTimeout);
                    if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                        break;
                    nanosTimeout = deadline - System.nanoTime();
                }
                if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                    interruptMode = REINTERRUPT;
                if (node.nextWaiter != null)
                    unlinkCancelledWaiters();
                if (interruptMode != 0)
                    reportInterruptAfterWait(interruptMode);
                return !timedout;
            }
            final boolean isOwnedBy(AbstractQueuedSynchronizer sync) {
                return sync == AbstractQueuedSynchronizer.this;
            }
            protected final boolean hasWaiters() {
                if (!isHeldExclusively())
                    throw new IllegalMonitorStateException();
                for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
                    if (w.waitStatus == Node.CONDITION)
                        return true;
                }
                return false;
            }
            protected final int getWaitQueueLength() {
                if (!isHeldExclusively())
                    throw new IllegalMonitorStateException();
                int n = 0;
                for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
                    if (w.waitStatus == Node.CONDITION)
                        ++n;
                }
                return n;
            }

            protected final Collection getWaitingThreads() {
                if (!isHeldExclusively())
                    throw new IllegalMonitorStateException();
                ArrayList list = new ArrayList();
                for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
                    if (w.waitStatus == Node.CONDITION) {
                        Thread t = w.thread;
                        if (t != null)
                            list.add(t);
                    }
                }
                return list;
            }
        }
        private static final Unsafe unsafe = Unsafe.getUnsafe();
        private static final long stateOffset;
        private static final long headOffset;
        private static final long tailOffset;
        private static final long waitStatusOffset;
        private static final long nextOffset;
        static {
            try {
                /**
                 * 利用静态代码块  实现得到对象的偏移量 那么就可一利用cas机制了
                 */
                stateOffset = unsafe.objectFieldOffset
                        (AbstractQueuedSynchronizer.class.getDeclaredField("state"));
                headOffset = unsafe.objectFieldOffset
                        (AbstractQueuedSynchronizer.class.getDeclaredField("head"));
                tailOffset = unsafe.objectFieldOffset
                        (AbstractQueuedSynchronizer.class.getDeclaredField("tail"));
                waitStatusOffset = unsafe.objectFieldOffset
                        (Node.class.getDeclaredField("waitStatus"));
                nextOffset = unsafe.objectFieldOffset
                        (Node.class.getDeclaredField("next"));

            } catch (Exception ex) { throw new Error(ex); }
        }
        private final boolean compareAndSetHead(Node update) {
            return unsafe.compareAndSwapObject(this, headOffset, null, update);
        }
        private final boolean compareAndSetTail(Node expect, Node update) {
            return unsafe.compareAndSwapObject(this, tailOffset, expect, update);
        }
        private static final boolean compareAndSetWaitStatus(Node node,
                                                             int expect,
                                                             int update) {
            return unsafe.compareAndSwapInt(node, waitStatusOffset,
                    expect, update);
        }
        private static final boolean compareAndSetNext(Node node,
                                                       Node expect,
                                                       Node update) {
            return unsafe.compareAndSwapObject(node, nextOffset, expect, update);
        }
    }

package com.kailong.lock;

/**
 * Created by Administrator on 2017/4/20.
 */
public class AbstractOwnableSynchronizer implements java.io.Serializable {

    /** 序列化id */
    private static final long serialVersionUID = 3737899427754241961L;

    /**
     * 空构造器供子类使用。
     */
    protected AbstractOwnableSynchronizer() { }

    /**
     * 当前所有者的排他模式同步。
     */
    private transient Thread exclusiveOwnerThread;

    /**
     * 设置当前拥有独占访问权限的线程。
      {@code null}参数表示没有线程拥有访问权限。
      这种方法不会强加任何同步或
      {@code volatile}字段访问。
      @param线程所有者线程
     */
    protected final void setExclusiveOwnerThread(Thread thread) {
        exclusiveOwnerThread = thread;
    }

    /**
     *返回由{@code setExclusiveOwnerThread}最后设置的线程，
     *或{@code null}如果从未设置。 此方法不另行
     *强制执行任何同步或{@code易失性}字段访问。
     *返回所有者线程
     */
    protected final Thread getExclusiveOwnerThread() {
        return exclusiveOwnerThread;
    }
}

package com.kailong.lock;
import java.util.Collection;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Created by Administrator on 2017/4/20.
 */
public class MyLock {
    private final Sync sync;//同步策略
    /**
     * 抽象的同步  用模板方法设计模式  提供两种策略 公平锁和非公平锁
     */
    static abstract class Sync extends AbstractQueuedSynchronizer{
        private static final long serialVersionUID = -5179523762034025860L;
        abstract void lock();//抽象加锁方法

        /**
         *  这个方法相当于AQS的ryAcquire，为什么非公平版的TryAcquire代码需要写在父类Sync 这里？
          注意tryLock，它是只调用非公平版的tryLock。而ReentrantLock 是代理了
          Sync ，根据多态机制。所以非公平版的TryAcquire只能写在父类Sync这里了。
         * @param acquires
         * @return
         */
        final boolean nonfairTryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0) // overflow
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
        }

        protected final boolean tryRelease(int releases) {
            int c = getState() - releases;
            if (Thread.currentThread() != getExclusiveOwnerThread())
                throw new IllegalMonitorStateException();
            boolean free = false;
            if (c == 0) {
                free = true;
                setExclusiveOwnerThread(null);
            }
            setState(c);
            return free;
        }

        protected final boolean isHeldExclusively() {
            return getExclusiveOwnerThread() == Thread.currentThread();
        }

        final ConditionObject newCondition() {
            return new ConditionObject();
        }

        final Thread getOwner() {
            return getState() == 0 ? null : getExclusiveOwnerThread();
        }

        final int getHoldCount() {
            return isHeldExclusively() ? getState() : 0;
        }

        final boolean isLocked() {
            return getState() != 0;
        }
        private void readObject(java.io.ObjectInputStream s)
                throws java.io.IOException, ClassNotFoundException {
            s.defaultReadObject();
            setState(0); // reset to unlocked state
        }
    }

    /**
     * 静态内部类  实现非公平锁
     */
    static  final  class  NonfairSync extends Sync{

        @Override
        void lock() {
            if (compareAndSetState(0, 1))
                setExclusiveOwnerThread(Thread.currentThread());
            else
                acquire(1);
        }
        protected final boolean tryAcquire(int acquires) {
            return nonfairTryAcquire(acquires);
        }
    }

    /**
     * 静态内部类实现公平锁
     */
    static final class FairSync extends Sync{
        @Override
        void lock() {
            acquire(1);
        }
        protected final boolean tryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (!hasQueuedPredecessors() &&
                        compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0)
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
        }
    }
    /**
     * 无参构造方法默认是非公平锁
     */
    public MyLock() {
        sync = new NonfairSync();
    }

    /**
     * 传递boolean值 判断公平锁还是非公平锁
     * @param fair
     */
    public MyLock(boolean fair) {
        sync = fair ? new FairSync() : new NonfairSync();
    }
    /**
     * 加锁方法 调用sync的lock方法 他会根据子类的模板方法来加锁 实现公平锁或者非公平锁
     */
    public void lock() {
        sync.lock();
    }

    /**
     *
     * @throws InterruptedException
     */
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    /**
     *
     * @return
     */
    public boolean tryLock() {
        return sync.nonfairTryAcquire(1);
    }

    /**
     *
     * @param timeout
     * @param unit
     * @return
     * @throws InterruptedException
     */
    public boolean tryLock(long timeout, TimeUnit unit)
            throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }

    /**
     *
     */
    public void unlock() {
        sync.release(1);
    }

    /**
     *
     * @return
     */
    public Condition newCondition() {
        return sync.newCondition();
    }

    /**
     *
     * @return
     */
    public int getHoldCount() {
        return sync.getHoldCount();
    }

    /**
     *
     * @return
     */
    public boolean isHeldByCurrentThread() {
        return sync.isHeldExclusively();
    }

    /**
     *
     * @return
     */
    public boolean isLocked() {
        return sync.isLocked();
    }

    /**
     *
     * @return
     */
    public final boolean isFair() {
        return sync instanceof FairSync;
    }

    /**
     *
     * @return
     */
    protected Thread getOwner() {
        return sync.getOwner();
    }

    /**
     *
     * @return
     */
    public final boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    /**
     *
     * @param thread
     * @return
     */
    public final boolean hasQueuedThread(Thread thread) {
        return sync.isQueued(thread);
    }

    /**
     *
     * @return
     */
    public final int getQueueLength() {
        return sync.getQueueLength();
    }

    /**
     *
     * @return
     */
    protected Collection getQueuedThreads() {
        return sync.getQueuedThreads();
    }

    /**
     *
     * @param condition
     * @return
     */
    public boolean hasWaiters(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     *
     * @param condition
     * @return
     */
    public int getWaitQueueLength(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     *
     * @param condition
     * @return
     */
    protected Collection getWaitingThreads(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     * toString 方法覆盖
     * @return
     */
    public String toString() {
        Thread o = sync.getOwner();
        return super.toString() + ((o == null) ?
                "[Unlocked]" :
                "[Locked by thread " + o.getName() + "]");
    }
    public  static void main(String[]args){
        Lock lock=new ReentrantLock();
    }
}

package com.kailong.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;

/**
 * Created by Administrator on 2017/4/20.
 * 自定义顶层接口 实现锁的基本功能
 */
public interface MysLock {
    /**
     * 加锁  如果锁已经被占用那么等待
     */
    void lock();

    /**
     *获得锁但优先响应中断
     * @throws InterruptedException
     */
    void lockInterruptibly() throws InterruptedException;

    /**
     * 尝试获得锁 如果成功 返回true 失败返回false 此方法不等待，立即返回
     * @return
     */
    boolean tryLock();

    /**
     *给定时间尝试获得锁
     * @param time
     * @param unit
     * @return
     * @throws InterruptedException
     */
    boolean tryLock(long time, TimeUnit unit) throws InterruptedException;

    /**
     * 释放锁
     */
    void unlock();

    /**
     *条件
     * @return
     */
    Condition newCondition();
}