That article does not take into account that the QThread logic is in python. That is the problem
The problem is the processing function is in Python. Moving it to be C++ only would work fine. Python would invoke a compiled function that would start the multithreaded processing and complete immediately, then the Qt event loop could be used via signals/slots to inform completion.
Sent: Monday, December 09, 2019 at 1:05 PM
From: "Ognyan Moore" <ognyan.mo...@gmail.com>
To: pyside@qt-project.org
Subject: Re: [PySide] PySide Digest, Vol 83, Issue 13
From: "Ognyan Moore" <ognyan.mo...@gmail.com>
To: pyside@qt-project.org
Subject: Re: [PySide] PySide Digest, Vol 83, Issue 13
I think it would be great if we can have some guidance regarding multi-threading with CPU heavy tasks, not just IO bound tasks. Say I wanted to multi-thread a function
def cpu_intensive_function(a: int, b: int, c: int) -> np.ndarray:return some_numpy_function_calls(a, b, c)
How would I run this function in such a way that the computation does not hang the GUI thread? I have attempted to follow the guidance on this blog post here: https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/ . Where I utilize QObject.moveToThread(some_thread) as that article suggests, the function still executes in the GUI thread.
Some caveats here being that I am making an attempt to have no references to mutable objects in the GUI thread and the thread doing the computation.
Thanks!
Ogi
On Mon, Dec 9, 2019 at 3:00 AM <pyside-requ...@qt-project.org> wrote:
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Today's Topics:
1. Re: Keeping GUI responsive (Sivan Greenberg)
----------------------------------------------------------------------
Message: 1
Date: Sun, 8 Dec 2019 17:54:10 +0200
From: Sivan Greenberg <si...@omniqueue.com>
To: Israel Brewster <ijbrews...@alaska.edu>
Cc: pyside@qt-project.org
Subject: Re: [PySide] Keeping GUI responsive
Message-ID:
<cajncf-av+xygpo6gv+kr-neifnedtiwg3gyylyg16njqjbr...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi Israel,
If your non main function is mostly IO bound, you could try implement your
processing function with an interface that allows for polling of results
using co-routines which is very slim and very robust (I used that in the
past for several PyQt & PySide small apps but also for a full blown project
for Ubuntu back in 2006[0] , though with PyGTK - but principle is same) and
will allow your GUI main loop to be in charge, even if you ever need to use
a spawned shell command or program! (see links below)
It seems that nowadays, there are even ready made libs for that (this one
seems very interesting): https://github.com/reclosedev/async_gui and also
supports abstraction over multiprocessing which would support you even if
the the subtask is indeed CPU intensive (like data cleansing , validation
etc).
If you're using python 3 , the whole coroutines interface has been greatly
simplified, and could be easier to use, however the first guide will
explain in deep and show how to achieve cooperative multitasking using
plain Python 2.x interface:
-
http://masnun.com/2015/11/13/python-generators-coroutines-native-coroutines-and-async-await.html
-
https://medium.com/velotio-perspectives/an-introduction-to-asynchronous-programming-in-python-af0189a88bbb
HTH,
-Sivan
[0]:
http://www.ubuntugeek.com/hubackup-backup-application-for-ubuntu-home-users.html
On Thu, Dec 5, 2019 at 1:41 AM Israel Brewster <ijbrews...@alaska.edu>
wrote:
> I know this is a FAQ, however I haven’t been able to make any of the
> standard answers work for me. Here’s the situation:
>
> - using PySide2 5.12.2
> - I have an object (QMainWindow subclass) that contains most of the code
> for my application
> - One of the functions that runs in response to user input takes around 2
> seconds to run. The GUI obviously freezes during this time (BAD!)
> - Said function needs to access and modify several large variables (pandas
> data frames) from the main object
>
> So here’s the problem: If I run this function as a separate (python)
> thread, that doesn’t help - the GUI is still frozen. I’m thinking this is
> due to the GIL, but I could be wrong about that. Running under the
> multiprocessing module, however, doesn’t appear to be an option due to the
> number and size of the data structures that the function needs to modify,
> and if I try just to see what happens, the process actually crashes.
>
> So what are my options here? How can I keep the GUI responsive while this
> function runs, without being able to spin it off as a separate process? Or
> is the only option going to be to completely rip apart the function and try
> to re-build it in such a way that it can, somehow, still access the memory
> from the main thread, while doing the processing in a separate function?
> ---
> Israel Brewster
> Software Engineer
> Alaska Volcano Observatory
> Geophysical Institute - UAF
> 2156 Koyukuk Drive
> Fairbanks AK 99775-7320
> Work: 907-474-5172
> cell: 907-328-9145
>
> _______________________________________________
> PySide mailing list
> PySide@qt-project.org
> https://lists.qt-project.org/listinfo/pyside
>
--
-Sivan
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