条件vs对象等待/通知 [英] Conditions vs objects wait/notify

问题描述

我正在阅读关于条件对象以及它们如何为每个对象提供多个等待集，并且区分哪个对象或一组对象/线程获得特定信号。 >
为什么不定期的 Object 这样做？例如。

I was reading about Condition objects and how they offer multiple wait-sets per object and also distinguishing which object or group of objects/threads get a specific signal.
Why doesn't a regular Object do that? E.g.

而不是：

final Condition notFull  = lock.newCondition();   
final Condition notEmpty = lock.newCondition();     

lock.lock();  
try {  
  while (count == items.length)  
     notFull.await();  
  items[putptr] = x;  
  if (++putptr == items.length) putptr = 0;  
      ++count;  
   notEmpty.signal();   

我们这样做：

final Object notFull  = new Object();     
final Object notEmpty = new Object();       

lock.lock();  
try {  
  while (count == items.length)  
     notFull.wait();  
  items[putptr] = x;  
  if (++putptr == items.length) putptr = 0;  
      ++count;  
   notEmpty.notify();   

难道我们还有多个等待集并区分被通知的线程吗？

Don't we still have multiple wait-sets and distinguish among notified threads?

推荐答案

在您的示例中，您在一个锁定上创建了2个条件。这是你不能做的内置同步 - 你不得不使用2对象来获得2个条件。

In your example you created 2 Conditions on one Lock. This is what you can't do with built-in synchronization - you had to use 2 Objects to get 2 conditions.

你的第二个代码被打破了，因为你没有锁在notFull和notEmpty但调用wait / notify - 你会得到IllegalMonitorStateException。但是如果你试图锁定它们，你会看到你不能同时做到。这是区别

And your second code is broken because you did not get lock on notFull and notEmpty but call wait / notify - you'll get IllegalMonitorStateException. But if you tried to lock them both you would see you cannot do that simultaneously. This is the difference

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