Re: Will "hello" always be printed?
On 2022-10-08 00:40, Cameron Simpson wrote: On 07Oct2022 20:16, Robin van der veer 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] -- https://mail.python.org/mailman/listinfo/python-list
Re: Will "hello" always be printed?
On 07Oct2022 20:16, Robin van der veer 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. Maybe some kind of blocking counter, so that you could track task counts? You'd need to make one, but something which allowed: count = queue.put(1) queue.wait_for(count) print('hello') and at the other end: queue.get() queue.task_done() # bumps the counter count2 = queue.put(1) Here, the counter would not be the internal "unfinished tasks" counter but instead a distinct counter which always went up. Probably a pair: tasks submitted by `put` and tasks completed by `task_done`. You could subclass `JoinableQueue` and add implementations of these counters and add a `wait_for(count)` method. This amounts to assigning each "task" a unique id (the counter) and a means to wait for that id. Cheers, Cameron Simpson -- https://mail.python.org/mailman/listinfo/python-list
Will "hello" always be printed?
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? 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. -- https://mail.python.org/mailman/listinfo/python-list