RTPRIO(2) BSD System Calls Manual RTPRIO(2)NAME
rtprio, lwp_rtprio — examine or modify a process/lwp 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
lwp_rtprio(int function, pid_t pid, lwpid_t tid, struct rtprio *rtp);
DESCRIPTIONrtprio() is used to lookup or change the realtime or idle priority of a
process.
function specifies the operation to be performed. RTP_LOOKUP to lookup
the current priority, and RTP_SET to set the priority. pid specifies the
process to be used, 0 for the current process.
*rtp is a pointer to a struct rtprio which is used to specify the prior‐
ity 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 priori‐
ties, 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 priority.
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 pri‐
ority processes preempt lower real/idle priority processes. Processes of
equal real/idle priority are run round-robin.
The lwp_rtprio() function is the lwp counterpart of rtprio(). It takes
one additional argument, tid, specifying the lwp to be used, -1 for the
current lwp.
RETURN VALUES
The rtprio() and lwp_rtprio() functions return the value 0 if successful;
otherwise the value -1 is returned and the global variable errno is set
to indicate the error.
ERRORSrtprio() and lwp_rtprio() 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 ALSOnice(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 was substantially rewritten by David Greenman.
BSD December 14, 2007 BSD
