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Mutex Manager
#############

Introduction
============

The mutex manager implements the functionality required of the mutex
manager as defined by POSIX 1003.1b-1996. This standard requires that
a compliant operating system provide the facilties to ensure that
threads can operate with mutual exclusion from one another and
defines the API that must be provided.

The services provided by the mutex manager are:

- ``pthread_mutexattr_init`` - Initialize a Mutex Attribute Set

- ``pthread_mutexattr_destroy`` - Destroy a Mutex Attribute Set

- ``pthread_mutexattr_setprotocol`` - Set the Blocking Protocol

- ``pthread_mutexattr_getprotocol`` - Get the Blocking Protocol

- ``pthread_mutexattr_setprioceiling`` - Set the Priority Ceiling

- ``pthread_mutexattr_getprioceiling`` - Get the Priority Ceiling

- ``pthread_mutexattr_setpshared`` - Set the Visibility

- ``pthread_mutexattr_getpshared`` - Get the Visibility

- ``pthread_mutex_init`` - Initialize a Mutex

- ``pthread_mutex_destroy`` - Destroy a Mutex

- ``pthread_mutex_lock`` - Lock a Mutex

- ``pthread_mutex_trylock`` - Poll to Lock a Mutex

- ``pthread_mutex_timedlock`` - Lock a Mutex with Timeout

- ``pthread_mutex_unlock`` - Unlock a Mutex

- ``pthread_mutex_setprioceiling`` - Dynamically Set the Priority Ceiling

- ``pthread_mutex_getprioceiling`` - Dynamically Get the Priority Ceiling

Background
==========

Mutex Attributes
----------------

Mutex attributes are utilized only at mutex creation time. A mutex
attribute structure may be initialized and passed as an argument to
the ``mutex_init`` routine. Note that the priority ceiling of
a mutex may be set at run-time.

*blocking protcol*
    is the XXX

*priority ceiling*
    is the XXX

*pshared*
    is the XXX

PTHREAD_MUTEX_INITIALIZER
-------------------------

This is a special value that a variable of type ``pthread_mutex_t``
may be statically initialized to as shown below:
.. code:: c

    pthread_mutex_t my_mutex = PTHREAD_MUTEX_INITIALIZER;

This indicates that ``my_mutex`` will be automatically initialized
by an implicit call to ``pthread_mutex_init`` the first time
the mutex is used.

Note that the mutex will be initialized with default attributes.

Operations
==========

There is currently no text in this section.

Services
========

This section details the mutex manager’s services.
A subsection is dedicated to each of this manager’s services
and describes the calling sequence, related constants, usage,
and status codes.

pthread_mutexattr_init - Initialize a Mutex Attribute Set
---------------------------------------------------------
.. index:: pthread_mutexattr_init
.. index:: initialize a mutex attribute set

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_init(
    pthread_mutexattr_t \*attr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_mutexattr_init`` routine initializes the mutex attributes
object specified by ``attr`` with the default value for all of the
individual attributes.

**NOTES:**

XXX insert list of default attributes here.

pthread_mutexattr_destroy - Destroy a Mutex Attribute Set
---------------------------------------------------------
.. index:: pthread_mutexattr_destroy
.. index:: destroy a mutex attribute set

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_destroy(
    pthread_mutexattr_t \*attr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

**DESCRIPTION:**

The ``pthread_mutex_attr_destroy`` routine is used to destroy a mutex
attributes object. The behavior of using an attributes object after
it is destroyed is implementation dependent.

**NOTES:**

NONE

pthread_mutexattr_setprotocol - Set the Blocking Protocol
---------------------------------------------------------
.. index:: pthread_mutexattr_setprotocol
.. index:: set the blocking protocol

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_setprotocol(
    pthread_mutexattr_t \*attr,
    int                  protocol
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The protocol argument is invalid.

**DESCRIPTION:**

The ``pthread_mutexattr_setprotocol`` routine is used to set value of the``protocol`` attribute. This attribute controls the order in which
threads waiting on this mutex will receive it.

The ``protocol`` can be one of the following:

*``PTHREAD_PRIO_NONE``*
    in which case blocking order is FIFO.

*``PTHREAD_PRIO_INHERIT``*
    in which case blocking order is priority with the priority inheritance
    protocol in effect.

*``PTHREAD_PRIO_PROTECT``*
    in which case blocking order is priority with the priority ceiling
    protocol in effect.

**NOTES:**

There is currently no way to get simple priority blocking ordering
with POSIX mutexes even though this could easily by supported by RTEMS.

pthread_mutexattr_getprotocol - Get the Blocking Protocol
---------------------------------------------------------
.. index:: pthread_mutexattr_getprotocol
.. index:: get the blocking protocol

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_getprotocol(
    pthread_mutexattr_t \*attr,
    int                 \*protocol
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The protocol pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_mutexattr_getprotocol`` routine is used to obtain
the value of the ``protocol`` attribute. This attribute controls
the order in which threads waiting on this mutex will receive it.

**NOTES:**

NONE

pthread_mutexattr_setprioceiling - Set the Priority Ceiling
-----------------------------------------------------------
.. index:: pthread_mutexattr_setprioceiling
.. index:: set the priority ceiling

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_setprioceiling(
    pthread_mutexattr_t \*attr,
    int                  prioceiling
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The prioceiling argument is invalid.

**DESCRIPTION:**

The ``pthread_mutexattr_setprioceiling`` routine is used to set value of the``prioceiling`` attribute. This attribute specifies the priority that
is the ceiling for threads obtaining this mutex. Any task obtaining this
mutex may not be of greater priority that the ceiling. If it is of lower
priority, then its priority will be elevated to ``prioceiling``.

**NOTES:**

NONE

pthread_mutexattr_getprioceiling - Get the Priority Ceiling
-----------------------------------------------------------
.. index:: pthread_mutexattr_getprioceiling
.. index:: get the priority ceiling

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_getprioceiling(
    const pthread_mutexattr_t \*attr,
    int                       \*prioceiling
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The prioceiling pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_mutexattr_getprioceiling`` routine is used to obtain the
value of the ``prioceiling`` attribute. This attribute specifies the
priority ceiling for this mutex.

**NOTES:**

NONE

pthread_mutexattr_setpshared - Set the Visibility
-------------------------------------------------
.. index:: pthread_mutexattr_setpshared
.. index:: set the visibility

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_setpshared(
    pthread_mutexattr_t \*attr,
    int                  pshared
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The pshared argument is invalid.

**DESCRIPTION:**

**NOTES:**

pthread_mutexattr_getpshared - Get the Visibility
-------------------------------------------------
.. index:: pthread_mutexattr_getpshared
.. index:: get the visibility

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutexattr_getpshared(
    const pthread_mutexattr_t \*attr,
    int                       \*pshared
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The pshared pointer argument is invalid.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_init - Initialize a Mutex
---------------------------------------
.. index:: pthread_mutex_init
.. index:: initialize a mutex

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_init(
    pthread_mutex_t           \*mutex,
    const pthread_mutexattr_t \*attr
    );

**STATUS CODES:**

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The specified protocol is invalid.

*EAGAIN*
    The system lacked the necessary resources to initialize another mutex.

*ENOMEM*
    Insufficient memory exists to initialize the mutex.

*EBUSY*
    Attempted to reinialize the object reference by mutex, a previously
    initialized, but not yet destroyed.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_destroy - Destroy a Mutex
---------------------------------------
.. index:: pthread_mutex_destroy
.. index:: destroy a mutex

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_destroy(
    pthread_mutex_t \*mutex
    );

**STATUS CODES:**

*EINVAL*
    The specified mutex is invalid.

*EBUSY*
    Attempted to destroy the object reference by mutex, while it is locked or
    referenced by another thread.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_lock - Lock a Mutex
---------------------------------
.. index:: pthread_mutex_lock
.. index:: lock a mutex

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_lock(
    pthread_mutex_t \*mutex
    );

**STATUS CODES:**

*EINVAL*
    The specified mutex is invalid.

*EINVAL*
    The mutex has the protocol attribute of PTHREAD_PRIO_PROTECT and the
    priority of the calling thread is higher than the current priority
    ceiling.

*EDEADLK*
    The current thread already owns the mutex.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_trylock - Poll to Lock a Mutex
--------------------------------------------
.. index:: pthread_mutex_trylock
.. index:: poll to lock a mutex

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_trylock(
    pthread_mutex_t \*mutex
    );

**STATUS CODES:**

*EINVAL*
    The specified mutex is invalid.

*EINVAL*
    The mutex has the protocol attribute of PTHREAD_PRIO_PROTECT and the
    priority of the calling thread is higher than the current priority
    ceiling.

*EBUSY*
    The mutex is already locked.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_timedlock - Lock a Mutex with Timeout
---------------------------------------------------
.. index:: pthread_mutex_timedlock
.. index:: lock a mutex with timeout

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    #include <time.h>
    int pthread_mutex_timedlock(
    pthread_mutex_t       \*mutex,
    const struct timespec \*timeout
    );

**STATUS CODES:**

*EINVAL*
    The specified mutex is invalid.

*EINVAL*
    The nanoseconds field of timeout is invalid.

*EINVAL*
    The mutex has the protocol attribute of PTHREAD_PRIO_PROTECT and the
    priority of the calling thread is higher than the current priority
    ceiling.

*EDEADLK*
    The current thread already owns the mutex.

*ETIMEDOUT*
    The calling thread was unable to obtain the mutex within the specified
    timeout period.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_unlock - Unlock a Mutex
-------------------------------------
.. index:: pthread_mutex_unlock
.. index:: unlock a mutex

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_unlock(
    pthread_mutex_t \*mutex
    );

**STATUS CODES:**

*EINVAL*
    The specified mutex is invalid.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_setprioceiling - Dynamically Set the Priority Ceiling
-------------------------------------------------------------------
.. index:: pthread_mutex_setprioceiling
.. index:: dynamically set the priority ceiling

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_setprioceiling(
    pthread_mutex_t \*mutex,
    int              prioceiling,
    int             \*oldceiling
    );

**STATUS CODES:**

*EINVAL*
    The oldceiling pointer parameter is invalid.

*EINVAL*
    The prioceiling parameter is an invalid priority.

*EINVAL*
    The specified mutex is invalid.

**DESCRIPTION:**

**NOTES:**

pthread_mutex_getprioceiling - Get the Current Priority Ceiling
---------------------------------------------------------------
.. index:: pthread_mutex_getprioceiling
.. index:: get the current priority ceiling

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_mutex_getprioceiling(
    pthread_mutex_t \*mutex,
    int             \*prioceiling
    );

**STATUS CODES:**

*EINVAL*
    The prioceiling pointer parameter is invalid.

*EINVAL*
    The specified mutex is invalid.

**DESCRIPTION:**

**NOTES:**

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.