pthread_setschedparam Subroutine

Purpose

Sets schedpolicy and schedparam attributes of a thread.

Library

Threads Library (libpthreads.a)

Syntax

#include <pthread.h>
#include <sys/sched.h>

int pthread_setschedparam (thread, schedpolicy, schedparam)
pthread_t thread;
int schedpolicy;
const struct sched_param *schedparam;

Description

The pthread_setschedparam subroutine dynamically sets the schedpolicy and schedparam attributes of the thread thread. The schedpolicy attribute specifies the scheduling policy of the thread. The schedparam attribute specifies the scheduling parameters of a thread created with this attributes object. The sched_priority field of the sched_param structure contains the priority of the thread. It is an integer value.

If the target thread has system contention scope, the process must have root authority to set the scheduling policy to either SCHED_FIFO or SCHED_RR.

Note: The pthread.h header file must be the first included file of each source file using the threads library. Otherwise, the -D_THREAD_SAFE compilation flag should be used, or the cc_r compiler used. In this case, the flag is automatically set.

This subroutine is part of the Base Operating System (BOS) Runtime. The implementation of this subroutine is dependent on the priority scheduling POSIX option. The priority scheduling POSIX option is implemented in the operating system.

Parameters

Item	Description
thread	Specifies the target thread.
schedpolicy	Points to the schedpolicy attribute to set. It must have one of the following values: SCHED_FIFO Denotes first-in first-out scheduling. SCHED_RR Denotes round-robin scheduling. SCHED_OTHER Denotes the default operating system scheduling policy. It is the default value. If schedpolicy is SCHED_OTHER, then sched_priority must be in the range from 40 to 80, where 40 is the least favored priority and 80 is the most favored. Note: Priority of threads with a process contention scope and a SCHED_OTHER policy is controlled by the kernel; thus, setting the priority of such a thread has no effect. However, priority of threads with a system contention scope and a SCHED_OTHER policy can be modified. The modification directly affects the underlying kernel thread nice value.
schedparam	Points to where the scheduling parameters to set are stored. The `sched_priority` field must be in the range from 1 to 127, where 1 is the least favored priority, and 127 the most favored. If schedpolicy is SCHED_OTHER, then sched_priority must be in the range from 40 to 80, where 40 is the least favored priority and 80 is the most favored. Note: Prior to AIX® 5.3, users are not permitted to change the priority of a thread when setting its scheduling policy to SCHED_OTHER. In this case, the priority is managed directly by the kernel, and the only legal value that can be passed to pthread_setschedparam is DEFAULT_PRIO, which is defined in pthread.h as 1. All other passed values are ignored. Beginning with AIX 5.3, users can change the priority of a thread when setting its scheduling policy to SCHED_OTHER. The legal values that can be passed to pthread_setschedparam range from 40 to 80. Only privileged users can set a priority higher than 60. A value ranging from 1 to 39 provides the same priority as 40, and a value ranging from 81 to 127 provides the same priority as 80.

Return Values

Upon successful completion, 0 is returned. Otherwise, an error code is returned.

Error Codes

The pthread_setschedparam subroutine is unsuccessful if the following is true:

Item	Description
EINVAL	The thread or schedparam parameters are not valid.
ENOSYS	The priority scheduling POSIX option is not implemented.
ENOTSUP	The value of the schedpolicy or schedparam attributes are not supported.
EPERM	The target thread has insufficient permission to perform the operation or is already engaged in a mutex protocol.
ESRCH	The thread thread does not exist.