PTHREAD_MUTEXATTR_GETPROTOCOL(P) POSIX Programmer's Manual PTHREAD_MUTEXATTR_GETPROTOCOL(P)
pthread_mutexattr_getprotocol, pthread_mutexattr_setprotocol - get and set the protocol
attribute of the mutex attributes object (REALTIME THREADS)
int pthread_mutexattr_getprotocol(const pthread_mutexattr_t *
restrict attr, int *restrict protocol);
int pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr,
The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions, respec-
tively, 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:
which are defined in the <pthread.h> header.
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.
When a thread is blocking higher priority threads because of owning one or more 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 mutexes
owned by this thread and initialized with this protocol.
When a thread owns one or more 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 mutexes owned by this thread and initialized with this attribute, regardless of
whether other threads are blocked on any of these 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
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 imple-
mentation 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, the same priority inheritance effect shall be propagated to this other
owner thread, in a recursive manner.
Upon successful completion, the pthread_mutexattr_getprotocol() and pthread_mutexattr_set-
protocol() functions shall return zero; otherwise, an error number shall be returned to
indicate the error.
The pthread_mutexattr_setprotocol() function shall fail if:
The value specified by protocol is an unsupported value.
The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions may fail
EINVAL The value specified by attr or 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.
pthread_cond_destroy() , pthread_create() , pthread_mutex_destroy() , the Base Definitions
volume of IEEE Std 1003.1-2001, <pthread.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_MUTEXATTR_GETPROTOCOL(P)