pthread_setschedprio - dynamic thread scheduling parameters access (REALTIME THREADS)
The pthread_setschedprio() function shall set the scheduling priority for the thread whose thread ID is given by thread to the value given by prio. See Scheduling Policies for a description on how this function call affects the ordering of the thread in the thread list for its new priority.
If the pthread_setschedprio() function fails, the scheduling priority of the target thread shall not be changed.
If successful, the pthread_setschedprio() function shall return zero; otherwise, an error number shall be returned to indicate the error.
The pthread_setschedprio() function may fail if:
- The value of prio is invalid for the scheduling policy of the specified thread.
- An attempt was made to set the priority to an unsupported value.
- The caller does not have the appropriate permission to set the scheduling policy of the specified thread.
- The implementation does not allow the application to modify the priority to the value specified.
- The value specified by thread does not refer to an existing thread.
The pthread_setschedprio() function shall not return an error code of [EINTR].
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 it 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, as there may be implementations that would need to be changed. Therefore, this new function was introduced.
Scheduling Policies, pthread_getschedparam(), the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
First released in Issue 6. Included as a response to IEEE PASC Interpretation 1003.1 #96.