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Re: POSIX Semaphores support.
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Re: POSIX Semaphores support.

On Dec 6, 2005, at 12:30 PM, Miguel Filipe wrote:

On 12/6/05, Eric Welch <email@hidden> wrote: Miguel,

For some time OSX has had Posix thread support including semaphores.

In that case, my app has a very strange behaviour on OSX, I make use of sem_init(), sem_wait() & sem_post(), and in OSX my threads never wait on sem_wait().

MacOS X supports named POSIX semaphores, but not unnamed POSIX semaphores.

I expect you must be trapping SIGSYS to prevent your program exiting because of an unsupported system call on the call to sem_init(), since it's implementation is a return of the error ENOSYS.

I googled after that problem and saw a lot of "OSX doesn't support POSIX Semaphores", after which I irresponsibly stopped looking for the cause of the problem. Apparently that could be the case in OSX 10.3, but I'm using 10.4.

Is there any kind of peculiarity in how I should use posix semaphores? (header files, semaphore inicialization or linker flags...)

The first thing you should do is #include <unistd.h> and conditionalize your use of POSIX semaphores on the manifest constant _POSIX_SEMAPHORES, e.g.:

#if ((_POSIX_SEMAPHORES - 200112L) >= 0)
/* This platform fully supports POSIX semaphores */
#if defined(__APPLE__)
/* This platform can support POSIX named semaphores, but not unnamed semaphores */
/* this platform requires that I Google code for P/V semaphores and include it here */

The proper list was more likely "unix-porting", but that's OK; this question comes up from time to time.

-- Terry
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