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[thirdparty/man-pages.git] / man2 / sched_get_priority_max.2

.\" Copyright (C) Tom Bjorkholm & Markus Kuhn, 1996
.\"
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.\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
.\"            First version written
.\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
.\"            revision
.\"
.TH SCHED_GET_PRIORITY_MAX 2 2006-03-23 "Linux" "Linux Programmer's Manual"
.SH NAME
sched_get_priority_max, sched_get_priority_min  \- get static priority range
.SH SYNOPSIS
.B #include <sched.h>
.sp
.BI "int sched_get_priority_max(int " policy );
.sp
.BI "int sched_get_priority_min(int " policy );
.SH DESCRIPTION
.BR sched_get_priority_max ()
returns the maximum priority value that can be used with the
scheduling algorithm identified by \fIpolicy\fP.
.BR sched_get_priority_min ()
returns the minimum priority value that can be used with the
scheduling algorithm identified by \fIpolicy\fP.
Supported \fIpolicy\fP
values are
.BR SCHED_FIFO ,
.BR SCHED_RR ,
.BR SCHED_OTHER ,
and
.BR SCHED_BATCH .
Further details about these policies can be found in
.BR sched_setscheduler (2).

Processes with numerically higher priority values are scheduled before
processes with numerically lower priority values.
Thus, the value
returned by
.BR sched_get_priority_max ()
will be greater than the
value returned by
.BR sched_get_priority_min ().

Linux allows the static priority value range 1 to 99 for
\fBSCHED_FIFO\fP and \fBSCHED_RR\fP and the priority 0 for
\fBSCHED_OTHER\fP and \fBSCHED_BATCH\fP.
Scheduling priority ranges for the various policies
are not alterable.

The range of scheduling priorities may vary on other POSIX systems,
thus it is a good idea for portable applications to use a virtual
priority range and map it to the interval given by
.BR sched_get_priority_max ()
and
.BR sched_get_priority_min ().
POSIX.1-2001 requires a spread of at least 32 between the maximum and the
minimum values for \fBSCHED_FIFO\fP and \fBSCHED_RR\fP.

POSIX systems on which
.BR sched_get_priority_max ()
and
.BR sched_get_priority_min ()
are available define
.B _POSIX_PRIORITY_SCHEDULING
in \fI<unistd.h>\fP.
.SH RETURN VALUE
On success,
.BR sched_get_priority_max ()
and
.BR sched_get_priority_min ()
return the maximum/minimum priority value for the named scheduling
policy.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
The argument \fIpolicy\fP does not identify a defined scheduling policy.
.SH CONFORMING TO
POSIX.1-2001.
.SH SEE ALSO
.ad l
.nh
.BR sched_getaffinity (2),
.BR sched_getparam (2),
.BR sched_getscheduler (2),
.BR sched_setaffinity (2),
.BR sched_setparam (2),
.BR sched_setscheduler (2)
.PP
.I Programming for the real world \- POSIX.4
by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.