A knowledge of pthreads is necessary to understand osdThread.c and osdSem.c.

The following are good references

Programming with POSIX Threads, David R. Butenhof, Addison-weslet, 1997

Multithreaded Programming with Pthreads, Bil Lewis & Daniel J. Berg,
Sun Microsystems, 1998

Pthreads Programming, Bradford Nichols etc, O'Reilly & Associates, 1996

The implementation of semMutex is based on the example code by Bil Leeis
that os available via the WWW.