introduction and first question about multithreading

[Vojtěch Polášek]

Greetings,
My name is Vojta and I am blind student. I am slowly learning Python for
about 4 years and I like it alot, mostly its ability to run on various
platforms.
My primary system is Ubuntu 12.04, but I have Windows XP at hand. I am
using python 2.7. I have learned basics from the book A byte of Python
(for version 2.X) and something from Dive into Python. But most things I
learned by trial and error and thanks to solutions on stackoverflow.com.
I Don't know much about good programming concepts in Python, just in
general, so feel free to educate me about them.

I haven't created anything great yet, but I am working on a game for
blind people. It is a simple game of reaction, but I have to start with
something, my next plan is Sudoku game.
I am using Pygame for handling of sounds and keyboard events, speech
dispatcher under Linux and pyttsx under Windows to provide speech
output, numpy for sound cutting and my two little and simple modules for
providing menu system and unified interface for both speech engines.
During the development, I discovered, that I have to use multithreading
to be able to check for key presses and manage the game at the same
time. I tried threading module but this wasn't enough for me, because
function running in the separate thread needed to access variables in
the main thread at least I couldn't find the way how to do that. So I
switched to multiprocessing and started using pipes for communication
between processes. All is working well, except for one thing.
My menu module uses a loop to check for keyboard events through pygame.
I don't import pygame into my module directly, but rather pass it
through my main module like this:
menu.pygame = pygame
All was working well until I started using multiprocessing. I may have a
probable cause but I need your help.
In my main module I am running a similar loop for checking keyboard
input in separate process. When a player loses, the loop finishes and I
join the process. Then the menu module kicks in and should launch its
own loop checking for pygame keyboard events, but right after doing it
it prints:
[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has
not been called
[xcb] Aborting, sorry about that.
python: ../../src/xcb_io.c:273: poll_for_event: Assertion
`!xcb_xlib_threads_sequence_lost' failed
received SigAbrt - core dumped
Are atachments allowed here? I can send you my whole code.
Please help me, if you can.
Thank you very much,
Vojta

[Roy Smith]

In article <mailman.2011.1341994...@python.org>,

Vojt®ßch Pol®¢‰ek <kre...@gmail.com> wrote:

> Then the menu module kicks in and should launch its
> own loop checking for pygame keyboard events, but right after doing it
> it prints:
> [xcb] Unknown sequence number while processing queue
> [xcb] Most likely this is a multi-threaded client and XInitThreads has
> not been called
> [xcb] Aborting, sorry about that.

I googled for "Unknown sequence number while processing queue" and found:

http://www.gtkforums.com/viewtopic.php?f=3&t=55708

sounds like it addresses your problem.

[Dave Angel]

> join the process. Then the menu module kicks in and should launch its

> own loop checking for pygame keyboard events, but right after doing it
> it prints:
> [xcb] Unknown sequence number while processing queue
> [xcb] Most likely this is a multi-threaded client and XInitThreads has
> not been called
> [xcb] Aborting, sorry about that.

> python: ../../src/xcb_io.c:273: poll_for_event: Assertion
> `!xcb_xlib_threads_sequence_lost' failed
> received SigAbrt - core dumped
> Are atachments allowed here? I can send you my whole code.
> Please help me, if you can.
> Thank you very much,
> Vojta

Welcome to python-list. I'm glad you're enjoying Python.

I haven't used pygame, but I know that (like almost all GUI toolkits) it
uses an event loop for interacting with at least the keyboard. You
should be able to add other code to that event loop in some manner,
without going to the trouble of either multiple threads or multiple
processes.

But I'll ignore that and talk about multithreading. You say

>function running in the separate thread needed to access variables in
>the main thread at least I couldn't find the way how to do that

but there is nothing special about threads. If you can figure out what
namespace a variable is in, you can access it. In fact, one large
reason people switch from multithread to multiple processes is to avoid
the accidental reuse of variables.

As for posting large code, you can upload it to a site like pastebin,
and put a link in your message here. Don't expect too much, however, as
most of us are averse at looking at a large fragment of somebody else's
code.





--

DaveA