PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

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_INHERIT
       PTHREAD_PRIO_NONE
       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.

       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.

       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.

       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.

       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.

       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()

       The Base Definitions volume of POSIX.1‐2017, <pthread.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .