Re: python threading and timing

Dennis Lee Bieber a écrit :
On Sun, 1 Oct 2006 22:28:10 +0200, "Oeyvind Brandtsegg"
<obrandts@xxxxxxxxx> declaimed the following in comp.lang.python:

Also, I wonder what method I should be using to get a precise timing
in my automation thread (acting as a sequencer).

Use a real-time OS (which neither M$ Windows nor Linux/UNIX claim to
be).

All non-deterministic, multi-tasking, OS's (like Windows, Linux,
Solaris, AmigaOS) only guarantee that, for example, a sleep() call will
not return /before/ the time specified. There is no specification for
how much time /over/ the duration actually takes place.

And setting the task priority into the Windows "real-time" category
is not sufficient -- I had an application that had to put out data on
six pins of the parallel port (acting as three discrete RS-422 style
balanced signals) in time with a (1KHz, as I recall) clock signal coming
in on another pin of the parallel port. The data was still getting
glitches every ~256 clocks as the OS did something in the background.
(the application was written in VC++6, and even disabled the GUI during
the data output operation.


+++

realtime OSes != high level priority threads

And for a sound production using a sequencer, it looks like to need real
realtime.


And dont use Python threads for realtime multithreading, even on a
realtime OS (because of the GIL - Global Interpreter Lock).

May use Python for some -non realtime- parts, but I would not use any
scripting language (not specific to Python) for real-time work (prefer
C, ADA, maybe Java with ad-hoc extensions).

You may go to Python by writing a Python C extension module (doing
realtime work on its own - but never relying on python GIL in critical
times), communicating with normal python scripts (shared memory...
things which dont need the GIL if possible).

A+

Laurent.
.

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