sched.h

The sched.h header file declares functions to manipulate and examine process execution scheduling.

_UNIX03_SOURCE

sched_yield()    
When compiled with SUSV3 thread support (_UNIX03_THREADS or _XOPEN_SOURCE 600), sched.h defines the following symbols:
SCHED_FIFO SCHED_OTHER SCHED_RR

and the sched_param structure.