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Threading in python

Aahz aahz at pythoncraft.com
Tue Dec 13 19:17:21 EST 2005 
In article <mailman.2057.1134517248.18701.python-list at python.org>,
Carl J. Van Arsdall <cvanarsdall at mvista.com> wrote:
>
>I have some questions regarding python's threading.

These answers assume you're using CPython; Jython and IronPython have
different answers.

>1.  Who schedules which threads run and when?  Is this something left up 
>to the operating system or does python provide a mechanism for this?

Strictly OS -- Python provides no control.

>2.  I've read that python threads don't like to allow other threads to 
>run except in certain situations, these would be situations where there 
>is sleep or I/O happening, is this true?  If so, what are the cases in 
>which a python thread would not give up the processor?

There is only a single thread of Python code running at any time.
Calling out to external libraries (e.g. C code) can release the Global
Interpreter Lock.  Python's standard I/O routines do this automatically
for you, but you're free to write your own code that does this (e.g.
mxODBC).

>3.  Is there a way to which thread is running? I mean something a bit 
>more robust than a print statement inside the thread, I want to be able 
>to see when a context switch occurs, is this possible?  The reason for 
>this is I will have threads deadlocked waiting for I/O and I am 
>interested to see how often context switching occurs.

You'd have to write some kind of logging.  You can use the logging
module.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

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