RTPRIO(2) | FreeBSD System Calls Manual | RTPRIO(2) |
NAME
rtprio, rtprio_thread — examine or modify realtime or idle priorityLIBRARY
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 system call reports the highest priority in the process, or sets all threads' priority in the process, depending on value of the function argument.
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 priority.
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.
AUTHORS
The original author was <hvd@terry.ping.dk>. This implementation in FreeBSD was substantially rewritten by . The rtprio_thread() system call was implemented by .December 27, 2011 | FreeBSD |