Subj : Tjme out in lock
To   : comp.programming.threads
From : Alex
Date : Wed Apr 06 2005 05:15 pm

Hi, continuing with my learning about this (thanks everybody for the great
answers)
I was wondering if is possible to add time supportfor a semaphore (in user
code).
To be more explicit, if I have a simple semaphore that supports basic P V
ops,
is it possible to add a time_out?
Ithought something like this (acquire for at most n secs)

Enter critical section
if sem is not acquired
  acquire
else
  wait(n secs)
  if sem is not acquired
    acquire
  else
    TIMEOUT
Exit critical section

This seems to work, but I see a problem that entering the critical section
creates a bottleneck
if other threads try to enter the code. Ideally all threads should do the
waiting concurrently, and
then try to get the semaphore, but I'm not sure is possible?
And one other problem is that if the semaphore is released while waiting,
the thread will be waiting till
the end of the timeout. Maybe a signal should be added or maybe do busy
wait?
Keep in mind I do this to learn. I know there already is support in
pthreads, but I'm trying to
understand and see it for myself.

Thanks for any comment!

.