PTHREAD_SETSCHEDPRIO(3P)

NAME
pthread_setschedprio - dynamic thread scheduling parameters access (REALTIME THREADS)

SYNOPSIS

#include <pthread.h>

int pthread_setschedprio(pthread_t thread, int prio);

DESCRIPTION

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.

RETURN VALUE

If successful, the pthread_setschedprio() function shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The pthread_setschedprio() function may fail if:

EINVAL
    The value of prio is invalid for the scheduling policy of the specified thread.

ENOTSUP
    An attempt was made to set the priority to an unsupported value.

EPERM
    The caller does not have the appropriate permission to set the scheduling policy of the specified thread.

EPERM
    The implementation does not allow the application to modify the priority to the value specified.

ESRCH
    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 following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

None.

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 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.

FUTURE DIRECTIONS

None.

SEE ALSO

Scheduling Policies , pthread_getschedparam() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .