pthread_mutex_getprioceiling

Synopsis

#include <pthread.h>

int pthread_mutex_getprioceiling(const pthread_mutex_t *restrict mutex,
                                 int *restrict prioceiling);

int pthread_mutex_setprioceiling(pthread_mutex_t *restrict mutex,
                                 int prioceiling, int *restrict old_ceiling);

Status

Implemented

Conformance

IEEE Std 1003.1-2017

Description

The pthread_mutex_getprioceiling() function shall return the current priority ceiling of the mutex.

The pthread_mutex_setprioceiling() function shall attempt to lock the mutex as if by a call to pthread_mutex_lock(), except that the process of locking the mutex need not adhere to the priority protect protocol. On acquiring the mutex it shall change the mutex’s priority ceiling and then release the mutex as if by a call to pthread_mutex_unlock(). When the change is successful, the previous value of the priority ceiling shall be returned in old_ceiling.

If the pthread_mutex_setprioceiling() function fails, the mutex priority ceiling shall not be changed.

The values of prioceiling and old_ceiling are POSIX priorities, as described in Scheduling priorities. A mutex has a priority ceiling only if its protocol attribute is PTHREAD_PRIO_PROTECT; for a mutex with the PTHREAD_PRIO_NONE or PTHREAD_PRIO_INHERIT protocol both functions fail with EINVAL.

Return value

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

Errors

These functions shall fail if:

  • EINVAL - The protocol attribute of mutex is PTHREAD_PRIO_NONE.

  • EPERM - The implementation requires appropriate privileges to perform the operation and the caller does not have appropriate privileges.

The pthread_mutex_setprioceiling() function shall fail if:

  • EAGAIN - The mutex could not be acquired because the maximum number of recursive locks for mutex has been exceeded.

  • EDEADLK - The mutex type is PTHREAD_MUTEX_ERRORCHECK and the current thread already owns the mutex.

  • EINVAL - The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread’s priority is higher than the mutex’s current priority ceiling, and the implementation adheres to the priority protect protocol in the process of locking the mutex.

  • ENOTRECOVERABLE - The mutex is a robust mutex and the state protected by the mutex is not recoverable.

  • EOWNERDEAD - The mutex is a robust mutex and the process containing the previous owning thread terminated while holding the mutex lock. The mutex lock shall be acquired by the calling thread, and it is up to the new owner to make the state consistent (see pthread_mutex_lock()).

The pthread_mutex_setprioceiling() function may fail if:

  • EDEADLK - A deadlock condition was detected.

  • EINVAL - The priority requested by prioceiling is out of range.

  • EOWNERDEAD - The mutex is a robust mutex and the previous owning thread terminated while holding the mutex lock. The mutex lock shall be acquired by the calling thread, and it is up to the new owner to make the state consistent (see pthread_mutex_lock()).

These functions shall not return an error code of EINTR.

POSIX deviations

IEEE Std 1003.1-2017 defines the values of the priority ceiling within the range of priorities of the SCHED_FIFO scheduling policy. Phoenix-RTOS supports only the SCHED_RR policy, so prioceiling is checked against the range of SCHED_RR priorities, returned by sched_get_priority_min(SCHED_RR) and sched_get_priority_max(SCHED_RR), and pthread_mutex_setprioceiling() fails with EINVAL for a value outside of it. The Phoenix-RTOS kernel schedules all threads with a single priority-based round-robin policy, which keeps the scheduler small and its behaviour predictable on resource-constrained real-time targets.