pthread_mutexattr_getprotocol(3C)										 pthread_mutexattr_getprotocol(3C)

NAME

       pthread_mutexattr_getprotocol, pthread_mutexattr_setprotocol - get or set protocol attribute of mutex attribute object

SYNOPSIS

       cc -mt [ flag... ] file... -lpthread [ library... ]
       #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);

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

       The protocol attribute defines the protocol to be followed in utilizing mutexes. The value of protocol may be  one  of	PTHREAD_PRIO_NONE,
       PTHREAD_PRIO_INHERIT, or PTHREAD_PRIO_PROTECT, which are defined by the header <pthread.h>.

       When a thread owns a mutex with the  PTHREAD_PRIO_NONE protocol attribute, its priority and scheduling are not affected by its mutex owner-
       ship.

       When a thread is blocking higher priority threads because of owning one or more mutexes with the  PTHREAD_PRIO_INHERIT protocol	attribute,
       it executes 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 executes 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.

       While a thread is holding a mutex that has been initialized with the PRIO_INHERIT or  PRIO_PROTECT protocol attributes, it will not be sub-
       ject  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 PRIO_INHERIT or PRIO_PROTECT  protocol
       attributes, it will not be subject to being moved to the tail of the scheduling queue at its priority in the event that its original prior-
       ity is changed.

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

       When a thread makes a call to pthread_mutex_lock(), if the symbol  _POSIX_THREAD_PRIO_INHERIT is defined and 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 will inherit the priority level of the calling thread as long as it continues to own the mutex. The implementa-
       tion updates its execution priority to the maximum of its assigned priority and all its inherited priorities. Furthermore,  if  this  owner
       thread  becomes blocked on another mutex, the same priority inheritance effect will be propagated to the other owner thread, in a recursive
       manner.

       If  the	symbol	_POSIX_THREAD_PRIO_INHERIT  is	defined,  when	a  mutex  initialized  with  the  protocol  attribute  having  the   value
       PTHREAD_PRIO_INHERIT dies, the behavior depends on the robustness attribute of the mutex. See pthread_mutexattr_getrobust_np(3C).

       A thread that uses mutexes initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attribute values should have its con-
       tentionscope attribute equal to PTHREAD_SCOPE_SYSTEM (see pthread_attr_getscope(3C)) and its  scheduling  policy  equal	to  SCHED_FIFO	or
       SCHED_RR (see pthread_attr_getschedparam(3C) and pthread_getschedparam(3C)).

       If  a  thread  with contentionscope attribute equal to PTHREAD_SCOPE_PROCESS and/or its scheduling policy equal to SCHED_OTHER uses a mutex
       initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attribute value, the effect on the thread's scheduling and  pri-
       ority is unspecified.

       The  _POSIX_THREAD_PRIO_INHERIT	and _POSIX_THREAD_PRIO_PROTECT options are designed to provide features to solve priority inversion due to
       mutexes. A priority inheritance or priority ceiling mutex is designed to minimize the dispatch latency of a high priority thread when a low
       priority thread is holding a mutex required by the high priority thread.  This is a specific need for the realtime application domain.

       Threads	created  by  realtime  applications  need  to  be  such  that their priorities can influence their access to system resources (CPU
       resources, at least), in competition with all threads running on the system.

       Upon successful completion, the pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol()  functions  return	0.  Otherwise,	an
       error number is returned to indicate the error.

       The  pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions will fail if:

       EINVAL	       The value specified by attr is NULL.

       ENOSYS	       Neither of the options _POSIX_THREAD_PRIO_PROTECT and _POSIX_THREAD_PRIO_INHERIT is defined and the system does not support
		       the function.

       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 attr or protocol is invalid.

       EPERM	       The caller does not have the privilege to perform the operation.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       pthread_create(3C), pthread_mutex_init(3C), pthread_cond_init(3C), pthread_mutexattr_getrobust_np(3C), attributes(5), standards(5)

								    23 Mar 2005 				 pthread_mutexattr_getprotocol(3C)