java非公平锁如何理解

/**

 * Sync object for non-fair locks

 */

static final class NonfairSync extends Sync {

    private static final long serialVersionUID = 7316153563782823691L;

    /**

     * Performs lock.  Try immediate barge, backing up to normal

     * acquire on failure.

     */

    final void lock() {

        if (compareAndSetState(0, 1))

            setExclusiveOwnerThread(Thread.currentThread());

        else

            acquire(1);

    }

    protected final boolean tryAcquire(int acquires) {

        return nonfairTryAcquire(acquires);

    }

}

/**

 * Sync object for fair locks

 */

static final class FairSync extends Sync {

    private static final long serialVersionUID = -3000897897090466540L;

    final void lock() {

        acquire(1);

    }

    /**

     * Fair version of tryAcquire.  Don't grant access unless

     * recursive call or no waiters or is first.

     */

    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;

    }

}