NAME

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

SYNOPSIS

       #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:

       PTHREAD_PRIO_NONE

       PTHREAD_PRIO_INHERIT

       PTHREAD_PRIO_PROTECT

       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 these protocols.

       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, the same priority inheritance effect shall be propagated to this other owner
       thread, in a recursive manner.

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 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.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_cond_destroy()  ,  pthread_create()  ,  pthread_mutex_destroy()  , the Base Definitions volume of
       IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT

       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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .