已同步未同步

Question

synchronized似乎没有像我预期的那样工作。它不应该使括号内的代码相对于由同一对象进行synchronized的单独代码块是原子的吗？

我发现它在我的代码中根本不同步。

private Object movementMutex_ = new Object();    

// Thread
public void run()
{
    while (run_)
    {
        synchronized(movementMutex_)
        {
            if (timeToMove_)
            {
                Log.v("meh", "timeToMove_ was true, moving");
                makeMove();
                Log.v("meh", "Move Complete. Setting timeToMove_ to false");
                timeToMove_ = false;
                Log.v("meh", "timeToMove_ is now false");
            }
        }
    }
}


// Called by a different thread so that this thread knows when to make a move
public void move()
{
    Log.v("meh", "awaiting movementMutex in move()");
    // Synchronizing so that timeToMove_ doesn't get set true while in the middle of moving and thus setting it back false prematurely
    synchronized(movementMutex_)
    {
        Log.v("meh", "move called, setting timeToMove_");
        timeToMove_ = true;
        Log.v("meh", "timeToMove_ is now true");
    }
}

查看Log打印输出，我发现它们的打印顺序出乎意料。根据我对synchronized的理解，粗体的语句应该无法被非粗体的打印输出解释，但事实并非如此，我试图避免的事情正在发生:我错过了下一步，因为我在它仍然为真的时候将其设置为真，并立即将其转换为假。

 08-12 10:47:19.860: V/meh(27639): awaiting movementMutex in move()  
 08-12 10:47:19.985: V/meh(27639): move called, setting timeToMove_  
 08-12 10:47:19.985: V/meh(27639): timeToMove_ is now true  
 08-12 10:47:19.985: V/meh(27639): **timeToMove_ was true, moving**  
 08-12 10:47:20.352: V/meh(27639): awaiting movementMutex in move()  

下一行应该是不可能的。它不是在等待movementMutex！

08-12 10:47:20.352: V/meh(27639): move called, setting timeToMove_  
08-12 10:47:20.360: V/meh(27639): timeToMove_ is now true  
08-12 10:47:20.360: V/meh(27639): **Move Complete. Setting timeToMove_ to false**  
08-12 10:47:20.360: V/meh(27639): **timeToMove_ is now false**  

Answer 1

正如对该问题的注释中所提到的，线程能够重新进入它自己的同步锁。"makeMove()“函数调用实际上是调用"move()”的发起者，这意味着它在同一线程下执行，因此不会被锁定。简而言之，下面的代码不会导致死锁；它会毫无问题地执行，这就是我所经历的。

synchronized(movementMutex_)
{
    synchronized(movementMutex_)
    {
        doSomething();
    }
}