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

NAME

     rtprio, rtprio_thread -- examine or modify 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);

     int
     rtprio_thread(int function, lwpid_t lwpid, struct rtprio *rtp);

DESCRIPTION

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

     The function argument specifies the operation to be performed.  RTP_LOOKUP to lookup the current priority, and RTP_SET to set the priority.

     For the rtprio() system call, the pid argument specifies the process to operate on, 0 for the calling thread.  When pid is non-zero, the sys-
     tem call reports the highest priority in the process, or sets all threads' priority in the process, depending on value of the function argu-
     ment.

     For the rtprio_thread() system call, the lwpid specifies the thread to operate on, 0 for the calling thread.

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

RETURN VALUES

     The rtprio() and rtprio_thread() functions return 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() and rtprio_thread() system calls will fail if:

     [EFAULT]		The rtp pointer passed to rtprio() or rtprio_thread() was invalid.

     [EINVAL]		The specified prio was out of range.

     [EPERM]		The calling thread is not allowed to set the realtime priority.  Only root is allowed to change the realtime priority of
			any thread, and non-root may only change the idle priority of threads the user owns, when the sysctl(8) variable
			security.bsd.unprivileged_idprio is set to non-zero.

     [ESRCH]		The specified process or thread was not found or visible.

SEE ALSO

     nice(1), ps(1), rtprio(1), setpriority(2), nice(3), renice(8), p_cansee(9)

AUTHORS

     The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>.  This implementation in FreeBSD was substantially rewritten by David
     Greenman.	The rtprio_thread() system call was implemented by David Xu.

BSD
								 December 27, 2011							       BSD