同步对象设置为空 [英] synchronized object set to null

问题描述

我有两个线程 Thread1 和 Thread2

//Within Thread1     
synchronized(obj1)  
{  
    obj1 = null;  
}  

//Within Thread2  
synchronized(obj1)  
{  
    do something  
}   

如果 jvm 首先执行 thread1 并将 obj1 设置为 null，那么 thread2 会立即看到该更改还是需要一些时间，并且 jvm 仍然可以运行 thread2 同步块，因为 obj1 尚未为 null?

If jvm first executes thread1 and sets obj1 to null, then will thread2 see that change immediately or will it take time and jvm could still run the thread2 synchronized block since obj1 is not yet null?

推荐答案

这几乎肯定会破坏同步抽象——我不相信 thread2 会立即看到变化.您永远不应该更改您正在同步的对象的引用，更不用说将其设置为 null，这将在任何进一步尝试对其进行同步时导致 NullPointerException.

This will almost certainly break the synchronization abstraction -- I wouldn't be confident that thread2 will see the change immediately. You should never change the reference of the object you're synchronizing on, much less set it to null, which will cause a NullPointerException on any further attempts to synchronize on it.

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