The unlock method of ReentrantLockd realizes source code analysis

Read the unlock() source code of ReentrantLock:
//This method: delegate to the release implementation of sync.
   public void unlock() {
        sync.release(1);
    }


public final boolean release(int arg) {
        // release the lock successfully
        if (tryRelease(arg)) {
            Node h = head;
	   
            if (h != null && h.waitStatus != 0)
	      
                unparkSuccessor(h);
            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, that is, getState is 1, if c!=0, it means the lock is reentrant.
            if (c == 0) {
                free = true;
                setExclusiveOwnerThread(null);
            }
            setState(c);
            return free;
        }

   
 // wake up the second node
    private void unparkSuccessor(Node node) {
        
        int ws = node.waitStatus;
        if (ws < 0)
	    //Set the first node state to 0
            compareAndSetWaitStatus(node, ws, 0);

       // get the second node
        Node s = node.next;
        if (s == null || s.waitStatus > 0) {
            s = null;
	    //Start the loop from the end of the queue until you get the node with the state < 0 closest to the note
            for (Node t = tail; t != null && t != node; t = t.prev)
                if (t.waitStatus <= 0)
                    s = t;
        }
	//Unlock and wake up a waiting thread
        if (s != null)
            LockSupport.unpark(s.thread);
    }