Threading Problem
Steve Holden
steve at holdenweb.com
Wed Dec 22 07:41:31 EST 2004
Norbert wrote:
> Hello *,
> i am experimenting with threads and get puzzling results.
> Consider the following example:
> #--------------------
> import threading, time
>
> def threadfunction():
> .....print "threadfunction: entered"
> .....x = 10
> .....while x < 40:
> .........time.sleep(1) # time unit is seconds
> .........print "threadfunction x=%d" % x
> .........x += 10
>
>
>
> print "start"
> th = threading.Thread(target = threadfunction())
> th.start()
> print "start completed"
> #--------------------
> (the dots are inserted becaus Google mangles the lines otherwise)
>
> This program gives the following result :
> ----
> start
> threadfunction: entered
> threadfunction x=10
> threadfunction x=20
> threadfunction x=30
> start completed
> ----
> My aim was that the main program should continue to run while
> threadfunction runs in parallel. That's the point of threads after all,
> isn't it ?
>
> I awaited something like the following :
> start
> threadfunction: entered
> start completed <-------------------
> threadfunction x=10
> threadfunction x=20
> threadfunction x=30
>
> Does anyone know what's going on here ?
>
Well, I don't believe there's any guarantee that a thread will get run
preference over its starter - they're both threads, after all. Try
putting a sleep after th.start() and before the print statement and you
should see that the "worker" thread runs while the main thread sleeps.
The same would be true if each were making OS calls and so on. When
everything is more or les continuous computation, and so short it can be
over in microseconds, there's no motivation for the scheduler to stop
one thread and start another.
regards
Steve
--
Steve Holden http://www.holdenweb.com/
Python Web Programming http://pydish.holdenweb.com/
Holden Web LLC +1 703 861 4237 +1 800 494 3119
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