Question

synchronized似乎没有像我预期的那样发挥作用。它不应该使括号内的代码相对于同一对象synchronized的单独代码块而言是原子的吗？

我发现它在我的代码中根本没有同步。

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");
    }
}

查看日志打印输出，我看到它们以意想不到的顺序打印。从我对同步的理解来看，粗体语句应该是非粗体打印输出无法解释的，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，因为我设置它如果它仍然是真的并且及时将其变为假，则为真。

 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()

下一行不应该是可能的。它不是在等待运动互动！

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

正如对问题的评论中所提到的，线程能够重新进入自己的同步锁。 “makeMove（）”函数调用实际上是调用“move（）”的发起者，这意味着它在同一个线程下执行，因此没有被锁定。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();
    }
}

同步不同步

1 个答案: