Question

I am trying to port a project (from linux) that uses Semaphores to Mac OS X however some of the posix semaphores are not implemented on Mac OS X

The one that I hit in this port is sem_timedwait()

I don’t know much about semaphores but from the man pages sem_wait() seems to be close to sem_timedwait and it is implemented

From the man pages

sem_timedwait() function shall
lock the semaphore referenced by
sem as in the sem_wait() function.
However, if the semaphore cannot be
locked without waiting for another
process or thread to unlock the
semaphore by performing a sem_post()
function, this wait shall be ter-
minated when the specified timeout
expires

From my limited understanding of how semphores work I can see that sem_timedwait() is safer, but I still should be able to use sem_wait()

Is this correct? If not what other alternatives do I have…

Thanks

Answer 1

It’s likely that the timeout is important to the operation of the algorithm. Therefore just using sem_wait() might not work.

You could use sem_trywait(), which returns right away in all cases. You can then loop, and use a sleep interval that you choose, each time decrementing the total timeout until you either run out of timeout or the semaphore is acquired.

A much better solution is to rewrite the algorithm to use a condition variable, and then you can use pthread_cond_timedwait() to get the appropriate timeout.