ReentrantLock

代码层面分析可重入原理

 final boolean nonfairTryAcquire(int acquires) {
     //获取当前的线程
     final Thread current = Thread.currentThread();
     //获取状态  0 代表当前线程可以获得这把锁
     int c = getState();
     if (c == 0) {
         if (compareAndSetState(0, acquires)) {//CAS
             //设置独占
             setExclusiveOwnerThread(current);
             return true;
         }
     }
     //如果当前状态不为0，则判断当前线程是否是正独占这把锁的线程
     else if (current == getExclusiveOwnerThread()) {
         int nextc = c + acquires;
         if (nextc < 0) // overflow
             //线程状态小于-1
             throw new Error("Maximum lock count exceeded");
         //设置状态
         setState(nextc);
         return true;
     }
     return false;
}