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.TH PTHREAD_MUTEXATTR_GETPROTOCOL "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH 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.

.SH NAME
pthread_mutexattr_getprotocol,
pthread_mutexattr_setprotocol
\(em get and set the protocol attribute of the mutex attributes object
(\fBREALTIME THREADS\fP)
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_mutexattr_getprotocol(const pthread_mutexattr_t
    *restrict \fIattr\fP, int *restrict \fIprotocol\fP);
int pthread_mutexattr_setprotocol(pthread_mutexattr_t *\fIattr\fP,
    int \fIprotocol\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_mutexattr_getprotocol\fR()
and
\fIpthread_mutexattr_setprotocol\fR()
functions, respectively, shall get and set the protocol attribute of
a mutex attributes object pointed to by
.IR attr
which was previously created by the function
\fIpthread_mutexattr_init\fR().
.P
The
.IR protocol
attribute defines the protocol to be followed in utilizing mutexes.
The value of
.IR protocol
may be one of:
.P
.nf
PTHREAD_PRIO_INHERIT
PTHREAD_PRIO_NONE
PTHREAD_PRIO_PROTECT
.fi
.P
which are defined in the
.IR <pthread.h> 
header. The default value of the attribute shall be PTHREAD_PRIO_NONE.
.P
When a thread owns a mutex with the PTHREAD_PRIO_NONE
.IR protocol
attribute, its priority and scheduling shall not be affected by
its mutex ownership.
.P
When a thread is blocking higher priority threads because of owning one
or more robust mutexes with the PTHREAD_PRIO_INHERIT
.IR 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.
.P
When a thread is blocking higher priority threads because of owning one
or more non-robust mutexes with the PTHREAD_PRIO_INHERIT
.IR 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.
.P
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.
.P
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.
.P
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
\fIsched_setparam\fR().
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.
.P
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.
.P
When a thread makes a call to
\fIpthread_mutex_lock\fR(),
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
.IR 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.
.P
The behavior is undefined if the value specified by the
.IR attr
argument to
\fIpthread_mutexattr_getprotocol\fR()
or
\fIpthread_mutexattr_setprotocol\fR()
does not refer to an initialized mutex attributes object.
.SH "RETURN VALUE"
Upon successful completion, the
\fIpthread_mutexattr_getprotocol\fR()
and
\fIpthread_mutexattr_setprotocol\fR()
functions shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_mutexattr_setprotocol\fR()
function shall fail if:
.TP
.BR ENOTSUP
The value specified by
.IR protocol
is an unsupported value.
.P
The
\fIpthread_mutexattr_getprotocol\fR()
and
\fIpthread_mutexattr_setprotocol\fR()
functions may fail if:
.TP
.BR EINVAL
The value specified by
.IR protocol
is invalid.
.TP
.BR EPERM
The caller does not have the privilege to perform the operation.
.P
These functions shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
If an implementation detects that the value specified by the
.IR attr
argument to
\fIpthread_mutexattr_getprotocol\fR()
or
\fIpthread_mutexattr_setprotocol\fR()
does not refer to an initialized mutex attributes object, it is
recommended that the function should fail and report an
.BR [EINVAL] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIpthread_cond_destroy\fR\^(\|)",
.IR "\fIpthread_create\fR\^(\|)",
.IR "\fIpthread_mutex_destroy\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<pthread.h>\fP"
.SH 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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