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

CONFORMING TO

POSIX.1-2001.

SEE ALSO

sched_getaffinity(2), sched_getparam(2), sched_getscheduler(2), sched_setaffinity(2), sched_setparam(2), sched_setscheduler(2)

Programming for the real world − POSIX.4 by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.