protected final boolean tryRelease(int releases) {
    int c = getState() - releases; // 从锁状态减去释放的锁量
    if (Thread.currentThread() != getExclusiveOwnerThread())
        throw new IllegalMonitorStateException();
    boolean free = false;
    if (c == 0) { // 状态为0表示锁被完全释放，成为可用状态
        free = true;
        setExclusiveOwnerThread(null); // 重置锁的拥有者线程
    }
    setState(c);
    return free;
}