Original from  Gerard Gerritsen  to Peter Fitzsimmons on 04-01-1996
Original Subject: Threads

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  GG>> But how much difference will it make for a two threaded program ?

  PF> A lot.  DosEnterCritSec() _ALWAYS_ forces all other threads to stop.

GG> But since there are only two threads that should not make any difference.

 It certainly does. With DosEnterCritSec, the second thread will be 
stopped no matter what it is doing. Even if it is nowhere near 
anything that might be a resource conflict. 

  PF> A semaphore will only cause another thread (or the thread asking for
  PF> the semaphore) to stop if and only if there has been a collision with
  PF> that semaphore.
  PF> Big difference.

GG> I do not know for sure but I think using DosEnterCritSec 
GG> takes less overhead then using semaphores ?

 Nope.. 

 The "intent" of Semaphores and CritSec is quite a bit different. 
Semaphores are intended to prevent resource collisions or sycronize
threads. CritSec is meant to make sure one thread is given ALL the cycles
within a single 
process. 
 Sure you can use CritSec in place of a Semaphore, just as you could 
use a Crop Duster in place of a Flyswatter. But the side effects might
be more than you intended..  


   Denis       

 Certified OS/2 Engineer, Certified OS/2 Instructor, Certifiable....
 All opinions are my very own, IBM has no claim upon them

.
--- Maximus/2 3.01