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sched_get_priority_max() - Unix, Linux System Call
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NAME
sched_get_priority_max, sched_get_priority_min - get static priority range
SYNOPSIS
#include <sched.h>
int sched_get_priority_max(int policy);
int sched_get_priority_min(int policy);
DESCRIPTION
sched_get_priority_max() returns the maximum priority value that can be used with the
scheduling algorithm identified by policy.
sched_get_priority_min() returns the minimum priority value that can be used with the
scheduling algorithm identified by policy. Supported policy
values are
SCHED_FIFO, SCHED_RR, SCHED_OTHER, and
SCHED_BATCH. Further details about these policies can be found in
sched_setscheduler(2).
Processes with numerically higher priority values are scheduled before
processes with numerically lower priority values. Thus, the value
returned by sched_get_priority_max() will be greater than the
value returned by sched_get_priority_min().
Linux allows the static priority value range 1 to 99 for
SCHED_FIFO and SCHED_RR and the priority 0 for
SCHED_OTHER and SCHED_BATCH.
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
sched_get_priority_max() and sched_get_priority_min().
POSIX.1-2001 requires a spread of at least 32 between the maximum and the
minimum values for SCHED_FIFO and SCHED_RR.
POSIX systems on which
sched_get_priority_max() and
sched_get_priority_min() are available define
_POSIX_PRIORITY_SCHEDULING in <unistd.h>.
RETURN VALUE
On success,
sched_get_priority_max() and
sched_get_priority_min() return the maximum/minimum priority value for the named scheduling
policy.
On error, -1 is returned, and
errno is set appropriately.
ERRORS
Tag | Description |
EINVAL |
The parameter policy does not identify a defined scheduling policy.
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CONFORMING TO
POSIX.1-2001.
SEE ALSO
Programming for the real world - POSIX.4 by Bill O. Gallmeister, OReilly & Associates, Inc., ISBN 1-56592-074-0
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