opendarwin man page for rtprio

RTPRIO(2)						      BSD System Calls Manual							 RTPRIO(2)

NAME
     rtprio -- examine or modify a process realtime or idle priority

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/rtprio.h>

     int
     rtprio(int function, pid_t pid, struct rtprio *rtp);

DESCRIPTION
     The rtprio() system call is used to lookup or change the realtime or idle priority of a process.

     The function argument specifies the operation to be performed.  RTP_LOOKUP to lookup the current priority, and RTP_SET to set the priority.
     The pid argument specifies the process to be used, 0 for the current process.

     The *rtp argument is a pointer to a struct rtprio which is used to specify the priority and priority type.  This structure has the following
     form:

     struct rtprio {
	     u_short type;
	     u_short prio;
     };

     The value of the type field may be RTP_PRIO_REALTIME for realtime priorities, RTP_PRIO_NORMAL for normal priorities, and RTP_PRIO_IDLE for
     idle priorities.  The priority specified by the prio field ranges between 0 and RTP_PRIO_MAX (usually 31).  0 is the highest possible prior-
     ity.

     Realtime and idle priority is inherited through fork() and exec().

     A realtime process can only be preempted by a process of equal or higher priority, or by an interrupt; idle priority processes will run only
     when no other real/normal priority process is runnable.  Higher real/idle priority processes preempt lower real/idle priority processes.
     Processes of equal real/idle priority are run round-robin.

RETURN VALUES
     The rtprio() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS
     The rtprio() system call will fail if

     [EINVAL]		The specified prio was out of range.

     [EPERM]		The calling process is not allowed to set the realtime priority.  Only root is allowed to change the realtime priority of
			any process, and non-root may only change the idle priority of the current process.

     [ESRCH]		The specified process was not found.

SEE ALSO
     nice(1), ps(1), rtprio(1), setpriority(2), nice(3), renice(8)

AUTHORS
     The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>.  This implementation in FreeBSD was substantially rewritten by David
     Greenman.

BSD
								   July 23, 1994							       BSD