Why queue.empty() returns False even after put() is called?

[Peng Yu]

Hi,

The empty() returns True even after put() has been called. Why it is
empty when there some items in it? Could anybody help me understand
it? Thanks!

~/linux/test/python/man/library/multiprocessing/Queue/empty$ cat
main.py
#!/usr/bin/env python

import multiprocessing

queue = multiprocessing.Queue()
print queue.empty()
queue.put(['a', 'b'])
queue.put(['c', 'd'])
print queue.empty()


Regards,
Peng

 

[Ian Kelly]

Hi,

The empty() returns True even after put() has been called. Why it is
empty when there some items in it? Could anybody help me understand
it? Thanks!

~/linux/test/python/man/library/multiprocessing/Queue/empty$ cat
main.py
#!/usr/bin/env python

import multiprocessing

queue = multiprocessing.Queue()
print queue.empty()
queue.put(['a', 'b'])
queue.put(['c', 'd'])
print queue.empty()

According to the docs, the Queue uses a background thread to load data into it:

When a process first puts an item on the queue a feeder thread is
started which transfers objects from a buffer into the pipe.

Most likely it still appears to be empty because this thread has not
had a chance to run yet. If you try inserting a time.sleep() call,
you should see the queue become non-empty once the background thread
has run.

 

[MRAB]

Hi,

The empty() returns True even after put() has been called. Why it is
empty when there some items in it? Could anybody help me understand
it? Thanks!

~/linux/test/python/man/library/multiprocessing/Queue/empty$ cat
main.py
#!/usr/bin/env python

import multiprocessing

queue = multiprocessing.Queue()
print queue.empty()
queue.put(['a', 'b'])
queue.put(['c', 'd'])
print queue.empty()

It works correctly for me.