On 2022-10-08 00:40, Cameron Simpson wrote:
On 07Oct2022 20:16, Robin van der veer <robinvdv...@gmail.com> wrote:
If I have two processes communicating through a JoinableQueue, and I do the
following:
process 1:
queue.put(1) #unfished tasks = 1
queue.join() #block until unfished tasks = 0
print('hello')[/python]
process 2:
queue.get()
queue.task_done() #unfished tasks = 0
queue.put(1) #unfinished tasks 1[/python]
the unfished tasks refers to what is written in the documentation (
https://docs.python.org/3/library/multiprocessing.html#multiprocessing.JoinableQueue.join
)
will 'hello' always be printed? Or is there a chance that the put in
process 2 executes before process 1 noticed that it should unblock?
I had to read this closely. Yes, the second `put(1)` could execute
before the `join()` commences (or tests), and the `hello` would be
blocked still.
It seems that the whole point of join() is that 'hello' should always be
printed, but I just want to make sure that I understand it correctly.
That's the purpose of using `join`, but you need to use it correctly.
The "some tasks are not completed" condition which `join` supports
doesn't fit what you're doing.
So yes, you're correct in your concern.
Maybe 2 queues would suit you better? Maybe not if they are common.
I would go with 2 queues: 1 for input and 1 for output. The outputted
item would be either a result or an indication of an error.
[snip]
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