话说 ReentrantLock_ 源码

Lock lock  =  new ReentrantLock(false);lock.lock();
/**     * 申请锁     *     * <p>Acquires the lock if it is not held by another thread and returns     * immediately, setting the lock hold count to one.     *  如果没有其他线程持有这个锁，就马上返回，并设置锁持有数为1     * <p>If the current thread already holds the lock then the hold     * count is incremented by one and the method returns immediately.     * 如果当前线程持有锁，就吧持有数量+1（可重入） 然后立即返回      * <p>If the lock is held by another thread then the     * current thread becomes disabled for thread scheduling     * purposes and lies dormant until the lock has been acquired,     * at which time the lock hold count is set to one.     * 如果锁被其他线程持有，当前线程对于调度就不可用，然后睡着， 直到获取锁，然后把锁持有数改为1      */// ReentrantLock.classpublic void lock() {    sync.lock();}// NonfairSync.classfinal void lock() {    // 先抢一下（上一篇说的 ：小强二话不说先看看能不能跟老板选饼）    if (compareAndSetState(0, 1))        setExclusiveOwnerThread(Thread.currentThread());    else        // 如果没有抢到 再去申请        acquire(1);}// AbstractQueuedSynchronizer.class public final void acquire(int arg) {        // 这个tryAcquire会再抢一次（小强还抱着插队的幻想）        if (!tryAcquire(arg) &&            // 抢不到 就后边排队吧            acquireQueued(addWaiter(Node.EXCLUSIVE), arg))            selfInterrupt(); }
 // ReentrantLock.class protected final boolean tryAcquire(int acquires) {            return nonfairTryAcquire(acquires); }
// ReentrantLock.class // 这里需要了解AQS 我其他文章有写 可以去看final boolean nonfairTryAcquire(int acquires) {    // 获取当前线程    final Thread current = Thread.currentThread();    // 获取state标志位    int c = getState();    if (c == 0) {        // 如果没有线程持有尝试获取锁（小强看见没人跟老板说话 直接插队买饼）        if (compareAndSetState(0, acquires)) {            setExclusiveOwnerThread(current);            return true;        }    }    // 如果有线程持有  看一下是不是自己    else if (current == getExclusiveOwnerThread()) {        // 如果是自己就修改持有数        int nextc = c + acquires;        // 超过最大锁数         if (nextc < 0) // overflow            throw new Error("Maximum lock count exceeded");        setState(nextc);        return true;    }    return false;}