The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> pthread_mutexattr_getprotocol, pthread_mutexattr_setprotocol - get and set the protocol attribute of the mutex attributes object (REALTIME THREADS)

#### SYNOPSIS

> ``[MC1] #include <pthread.h>
> int pthread_mutexattr_getprotocol(const pthread_mutexattr_t
> *restrict` attr`, int *restrict` protocol`);
> int pthread_mutexattr_setprotocol(pthread_mutexattr_t *`attr`,
> int` protocol`);``
> `
> `

#### DESCRIPTION

> The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions, respectively, shall get and set the protocol attribute of a mutex attributes object pointed to by attr which was previously created by the function pthread_mutexattr_init().

> The protocol attribute defines the protocol to be followed in utilizing mutexes. The value of protocol may be one of:

> [RPI|TPI]
> PTHREAD_PRIO_INHERIT
> [MC1]
> PTHREAD_PRIO_NONE
> [RPP|TPP]
> PTHREAD_PRIO_PROTECT

> which are defined in the <pthread.h> header. The default value of the attribute shall be PTHREAD_PRIO_NONE.

> When a thread owns a mutex with the PTHREAD_PRIO_NONE protocol attribute, its priority and scheduling shall not be affected by its mutex ownership.

> [RPI] When a thread is blocking higher priority threads because of owning one or more robust mutexes with the PTHREAD_PRIO_INHERIT protocol attribute, it shall execute at the higher of its priority or the priority of the highest priority thread waiting on any of the robust mutexes owned by this thread and initialized with this protocol.

> [TPI] When a thread is blocking higher priority threads because of owning one or more non-robust mutexes with the PTHREAD_PRIO_INHERIT protocol attribute, it shall execute at the higher of its priority or the priority of the highest priority thread waiting on any of the non-robust mutexes owned by this thread and initialized with this protocol.

> [RPP] When a thread owns one or more robust mutexes initialized with the PTHREAD_PRIO_PROTECT protocol, it shall execute at the higher of its priority or the highest of the priority ceilings of all the robust mutexes owned by this thread and initialized with this attribute, regardless of whether other threads are blocked on any of these robust mutexes or not.

> [TPP] When a thread owns one or more non-robust mutexes initialized with the PTHREAD_PRIO_PROTECT protocol, it shall execute at the higher of its priority or the highest of the priority ceilings of all the non-robust mutexes owned by this thread and initialized with this attribute, regardless of whether other threads are blocked on any of these non-robust mutexes or not.

> While a thread is holding a mutex which has been initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attributes, it shall not be subject to being moved to the tail of the scheduling queue at its priority in the event that its original priority is changed, such as by a call to sched_setparam(). Likewise, when a thread unlocks a mutex that has been initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attributes, it shall not be subject to being moved to the tail of the scheduling queue at its priority in the event that its original priority is changed.

> If a thread simultaneously owns several mutexes initialized with different protocols, it shall execute at the highest of the priorities that it would have obtained by each of these protocols.

> [RPI|TPI] When a thread makes a call to pthread_mutex_lock(), the mutex was initialized with the protocol attribute having the value PTHREAD_PRIO_INHERIT, when the calling thread is blocked because the mutex is owned by another thread, that owner thread shall inherit the priority level of the calling thread as long as it continues to own the mutex. The implementation shall update its execution priority to the maximum of its assigned priority and all its inherited priorities. Furthermore, if this owner thread itself becomes blocked on another mutex with the protocol attribute having the value PTHREAD_PRIO_INHERIT, the same priority inheritance effect shall be propagated to this other owner thread, in a recursive manner.

> The behavior is undefined if the value specified by the attr argument to pthread_mutexattr_getprotocol() or pthread_mutexattr_setprotocol() does not refer to an initialized mutex attributes object.

#### RETURN VALUE

> Upon successful completion, the pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions shall return zero; otherwise, an error number shall be returned to indicate the error.

#### ERRORS

> The pthread_mutexattr_setprotocol() function shall fail if:

> [ENOTSUP]
>   The value specified by protocol is an unsupported value.

> The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions may fail if:

> [EINVAL]
>   The value specified by protocol is invalid.
> [EPERM]
>   The caller does not have the privilege to perform the operation.

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

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> None.

#### RATIONALE

> If an implementation detects that the value specified by the attr argument to pthread_mutexattr_getprotocol() or pthread_mutexattr_setprotocol() does not refer to an initialized mutex attributes object, it is recommended that the function should fail and report an [EINVAL] error.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> pthread_cond_destroy, pthread_create, pthread_mutex_destroy

> XBD <pthread.h>

#### CHANGE HISTORY

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

> Marked as part of the Realtime Threads Feature Group.

#### Issue 6

> The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions are marked as part of the Threads option and either the Thread Priority Protection or Thread Priority Inheritance options.

> The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Thread Priority Protection or Thread Priority Inheritance options.

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

#### Issue 7

> SD5-XSH-ERN-135 is applied, updating the DESCRIPTION to define a default value for the protocol attribute.

> SD5-XSH-ERN-188 is applied, updating the DESCRIPTION.

> The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions are moved from the Threads option to require support of either the Non-Robust Mutex Priority Protection option or the Non-Robust Mutex Priority Inheritance option or the Robust Mutex Priority Protection option or the Robust Mutex Priority Inheritance option.

> The [EINVAL] error for an uninitialized mutex attributes object is removed; this condition results in undefined behavior.

End of informative text.

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