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.1‐2008, <pthread.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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       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 .