pthread_cond_wait does not relock mutex on release

Thu Apr 18 00:26:00 GMT 2002

> -----Original Message-----
> From: Michael Labhard [mailto:ince@pacifier.com] 
> Sent: Wednesday, April 17, 2002 10:51 PM
> To: cygwin@cygwin.com
> Subject: Re: pthread_cond_wait does not relock mutex on release
>>> Robert and Gerald:
>>          Both quite right.  Although adding the SAFE_PRINTF made no 
> difference in the 
> output, checking a condition value in a loop made all the 
> difference.  
> Putting a printf in the loop revealed to my surprise that 
> "spurious wakeups" 
> were occurring thousands of times per second.  I had naively 
> assumed that a 
> condition would stay set until signalled.  Now I'm led to wonder if a 
> condition variable is any performance improvement over a 
> simple loop and 
> short sleep.  Any thoughts?

Without knowing what you are trying to achieve, I can't comment. However: in multi-threaded programs, a condition variable will almost invariably be more efficient than a loop + sleep.
As for conditions staying set, that isn't the purpose of condition variables: they are designed to allow signalling between threads, to allow efficient use of cpu resources - and to avoid that loop+sleep approach.
Rob
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