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 .