在 python 中使用 get_nowait() 而不引发空异常 [英] Use get_nowait() in python without raising empty exception

问题描述

我有一个进程间队列，它通常是空的，并且偶尔会出现一些东西.在我的一个线程中，我想像这样定义一个 while 循环:

I have an inter-process queue that is usually empty and only once in a while does something appear in it. In one of my threads I want to define a while loop like this:

def mythread(queue1):

    while (queue1.get_nowait() != 1):
        #do stuff

这很好用，直到队列为空，这在我的情况下很快发生.当队列为空时，调用 get_nowait() 或 get(False) 会引发空队列异常.有没有什么方法可以在不阻塞和不引发空异常的情况下检查队列?

This works great until the queue is empty which happens quickly in my case. When the queue is empty calling get_nowait() or get(False) raises the empty queue exception. Is there any way to check the queue without blocking AND without raising the empty exception?

推荐答案

使用empty方法

if queue1.empty():
   pass
else:
   # get items from the queue

注意:医生说不可靠"(不是开玩笑).

Note: doc says "not reliable" (no kidding).

我想那是因为它可以在发布消息时返回 True(队列为空)，所以操作不像捕获异常那样原子.好吧，然后是一个 get_nowait() 调用我想除非其他线程也可以使用队列，否则这无关紧要，在这种情况下可能会发生竞争条件并且队列可能为空尝试从中阅读！

I suppose that's because it can return True (queue is empty) while a message is posted, so the operation is not as atomic as catching the exception. Well, followed by a get_nowait() call I suppose it doesn't matter unless some other thread can consume the queue as well, in which case a racing condition could occur and the queue could be empty when you try to read from it!

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