newbie question on threading

[Gonçalo Rodrigues]

On 13 Oct 2002 02:32:32 -0400, aahz at pythoncraft.com (Aahz) wrote:

>In article <jsngquskdhc0cpg867djcna0cl6u8tlm9l at 4ax.com>,
>Gonçalo Rodrigues  <op73418 at mail.telepac.pt> wrote:
>>
>>#Balancing act: We can't afford a pure busy loop, so we
>>#have to sleep; but if we sleep the whole timeout time,
>>#we'll be unresponsive.
>>
>>My question is: why is a busy loop not affordable (without a sleep
>>call), e.g. something like (in pseudo-code description)
>>
>>while 1:
>>    <acquire lock>
>>    if <acquire sucessfull>:
>>        break
>>    if <timedout?>:
>>        break
>>    <calculate endtime>
>
>Consider this:
>
>    while 1:
>        pass
>
>Given the above loop in a thread, how much useful work is the thread
>doing?  Not much, right?  Well, adding an "if" statement to the loop
>doesn't do any good for producing useful work.

I must be missing something but I am not understanding. Isn't that what
the wait method is supposed to do? Put the thread dormant, waiting until
you get timedout or you can acquire the lock? The only difference
between the pseudo-loop I wrote above and the one in the threading
module is a call to to time.sleep - and that is the core of my question,
why even bother to add the sleep call? Why not just a pure simple busy
loop? Why can't we afford it?

Once again, my ignorance thanks all the banishment it can get,
Gonçalo Rodrigues