HP 3000 Manuals

DCE for the HP 3000

Writing Thread-Safe Code 

The standard C/XL library is not completely thread safe on the HP 3000.
Hewlett-Packard has provided a set of wrapper functions to intercept
calls to the C library and make them thread safe.  The wrapper
definitions reside in the /usr/include/thdwrp.h file.

MPE/iX 5.0 Express III Documentation