NAME

pthread_getschedparam, pthread_setschedparam — dynamic thread scheduling parameters access (REALTIME THREADS)

SYNOPSIS

[TPS] #include <pthread.h>

int pthread_getschedparam(pthread_t thread, int *restrict policy,
       struct sched_param *restrict param);
int pthread_setschedparam(pthread_t thread, int policy,
       const struct sched_param *param);

DESCRIPTION

The pthread_getschedparam() and pthread_setschedparam() functions shall, respectively, get and set the scheduling policy and parameters of individual threads within a multi-threaded process to be retrieved and set. For SCHED_FIFO and SCHED_RR, the only required member of the sched_param structure is the priority sched_priority. For SCHED_OTHER, the affected scheduling parameters are implementation-defined.

The pthread_getschedparam() function shall retrieve the scheduling policy and scheduling parameters for the thread whose thread ID is given by thread and shall store those values in policy and param, respectively. The priority value returned from pthread_getschedparam() shall be the value specified by the most recent pthread_setschedparam(), pthread_setschedprio(), or pthread_create() call affecting the target thread. It shall not reflect any temporary adjustments to its priority as a result of any priority inheritance or ceiling functions. The pthread_setschedparam() function shall set the scheduling policy and associated scheduling parameters for the thread whose thread ID is given by thread to the policy and associated parameters provided in policy and param, respectively.

The policy parameter may have the value SCHED_OTHER, SCHED_FIFO, or SCHED_RR. The scheduling parameters for the SCHED_OTHER policy are implementation-defined. The SCHED_FIFO and SCHED_RR policies shall have a single scheduling parameter, priority.

^[TSP] If _POSIX_THREAD_SPORADIC_SERVER is defined, then the policy argument may have the value SCHED_SPORADIC, with the exception for the pthread_setschedparam() function that if the scheduling policy was not SCHED_SPORADIC at the time of the call, it is implementation-defined whether the function is supported; in other words, the implementation need not allow the application to dynamically change the scheduling policy to SCHED_SPORADIC. The sporadic server scheduling policy has the associated parameters sched_ss_low_priority, sched_ss_repl_period, sched_ss_init_budget, sched_priority, and sched_ss_max_repl. The specified sched_ss_repl_period shall be greater than or equal to the specified sched_ss_init_budget for the function to succeed; if it is not, then the function shall fail. The value of sched_ss_max_repl shall be within the inclusive range [1,{SS_REPL_MAX}] for the function to succeed; if not, the function shall fail. It is unspecified whether the sched_ss_repl_period and sched_ss_init_budget values are stored as provided by this function or are rounded to align with the resolution of the clock being used.

If the pthread_setschedparam() function fails, the scheduling parameters shall not be changed for the target thread.

RETURN VALUE

If successful, the pthread_getschedparam() and pthread_setschedparam() functions shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The pthread_setschedparam() function shall fail if:

[ENOTSUP]

An attempt was made to set the policy or scheduling parameters to an unsupported value.

[ENOTSUP]

^[TSP] An attempt was made to dynamically change the scheduling policy to SCHED_SPORADIC, and the implementation does not support this change.

The pthread_setschedparam() function may fail if:

[EINVAL]

The value specified by policy or one of the scheduling parameters associated with the scheduling policy policy is invalid.

[EPERM]

The caller does not have appropriate privileges to set either the scheduling parameters or the scheduling policy of the specified thread.

[EPERM]

The implementation does not allow the application to modify one of the parameters to the value specified.

These functions shall not return an error code of [EINTR].

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

If an implementation detects use of a thread ID after the end of its lifetime, it is recommended that the function should fail and report an [ESRCH] error.

FUTURE DIRECTIONS

None.

SEE ALSO

pthread_setschedprio, sched_getparam, sched_getscheduler

XBD <pthread.h>, <sched.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with the POSIX Threads Extension.

Issue 6

The pthread_getschedparam() and pthread_setschedparam() functions are marked as part of the Threads and Thread Execution Scheduling options.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Thread Execution Scheduling option.

The Open Group Corrigendum U026/2 is applied, correcting the prototype for the pthread_setschedparam() function so that its second argument is of type int.

The SCHED_SPORADIC scheduling policy is added for alignment with IEEE Std 1003.1d-1999.

The restrict keyword is added to the pthread_getschedparam() prototype for alignment with the ISO/IEC 9899:1999 standard.

The Open Group Corrigendum U047/1 is applied.

IEEE PASC Interpretation 1003.1 #96 is applied, noting that priority values can also be set by a call to the pthread_setschedprio() function.

Issue 7

The pthread_getschedparam() and pthread_setschedparam() functions are marked only as part of the Thread Execution Scheduling option as the Threads option is now part of the Base.

Austin Group Interpretation 1003.1-2001 #119 is applied, clarifying the accuracy requirements for the sched_ss_repl_period and sched_ss_init_budget values.

Austin Group Interpretation 1003.1-2001 #142 is applied, removing the [ESRCH] error condition.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0459 [314] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0276 [757] is applied.