pthread_setschedprio Subroutine

Purpose

Dynamic thread scheduling parameters access (REALTIME THREADS).

Syntax

#include <pthread.h>

int pthread_setschedprio(pthread_t thread, int prio); 

Description

The pthread_setschedprio() function sets the scheduling priority for the thread whose thread ID is given by thread to the value given by prio. If a thread whose policy or priority has been modified by pthread_setschedprio() is a running thread or is runnable, the effect on its position in the tread list depends on the direction of the modification as follows:

• If the priority is raised, the thread becomes the tail of the thread list.
• If the priority is unchanged, the thread does not change position in the thread list.
• If the priority is lowered, the thread becomes the head of the thread list.

Valid priorities are within the range returned by the sched_get_priority_max() and sched_get_priority_min().

If the pthread_setschedprio() function fails, the scheduling priority of the target thread remains unchanged.

Rationale

The pthread_setschedprio() function provides a way for an application to temporarily raise its priority and then lower it again, without having the undesired side-effect of yielding to other threads of the same priority. This is necessary if the application is to implement its own strategies for bounding priority inversion, such as priority inheritance or priority ceilings. This capability is especially important if the implementation does not support the Thread Priority Protection or Thread Priority Inheritance options; but even if those options are supported, this capability is needed if the application is to bound priority inheritance for other resources, such as semaphores.

The standard developers considered that, while it might be preferable conceptually to solve this problem by modifying the specification of pthread_setschedparam(), it was too late to make such a change, because there might be implementations that would need to be changed. Therefore, this new function was introduced.

Return Values

If successful, the pthread_setschedprio() function returns 0; otherwise, an error number is returned to indicate the error.

Error Codes

The pthread_setschedprio() function might fail if:

The pthread_setschedprio function does not return an error code of [EINTR].