为什么这个队列会这样？

Question

我正在编写一个从多处理队列中提取的对象，我发现当我运行这段代码时，我得到 data = []。而如果我告诉程序在指定的地方休眠一会儿，我会得到 data = [1,2]，因为它应该。

from multiprocessing import Queue
import time

q = Queue()
taken = 0
data = []

for i in [1,2]:
  q.put(i)
# time.sleep(1) making this call causes the correct output 
while not q.empty() and taken < 2:
   try:
     data.append(q.get(timeout=1))
     taken+=1
   except Empty:
     continue

**编辑：**如果 while 循环之前有打印语句，也会发生这种情况。这向我表明，正在发生对 q.put() 的调用，但我找不到关于此问题的任何文档。

Answer 1

在 docs 中提到了 multiprocessing.Queue

Note When an object is put on a queue, the object is pickled and a background thread later flushes the pickled data to an underlying pipe. This has some consequences which are a little surprising, but should not cause any practical difficulties – if they really bother you then you can instead use a queue created with a manager.

After putting an object on an empty queue there may be an infinitesimal delay before the queue’s empty() method returns False and get_nowait() can return without raising Queue.Empty. ...

为什么这个队列会这样？

Why does this queue behave like this?

python-2.7

python-multiprocessing