Mac OS X (10.3) does not support POSIX semaphores but implements its own set of semaphores. This can be a problem with portability therefor I created POSIX compliant wrappers using the underlying native Mac OS X semaphores.

Sememu includes funtions that emulate POSIX semaphores on a Mac OS X system
using the "native" Carbon semaphores. Named semaphores are currently not
implemented (i.e. sem_open() and sem_close() always fails with errno set
to ENOSYS).

You can get the sources for sememu, or read about its functionality.