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authorChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
committerChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
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+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+.. COMMENT: All rights reserved.
+
+Key Manager
+###########
+
+Introduction
+============
+
+The key manager allows for the creation and deletion of Data keys
+specific to threads.
+
+The directives provided by the key manager are:
+
+- pthread_key_create_ - Create Thread Specific Data Key
+
+- pthread_key_delete_ - Delete Thread Specific Data Key
+
+- pthread_setspecific_ - Set Thread Specific Key Value
+
+- pthread_getspecific_ - Get Thread Specific Key Value
+
+Background
+==========
+
+There is currently no text in this section.
+
+Operations
+==========
+
+There is currently no text in this section.
+
+Directives
+==========
+
+This section details the key manager's directives. A subsection is dedicated
+to each of this manager's directives and describes the calling sequence,
+related constants, usage, and status codes.
+
+.. _pthread_key_create:
+
+pthread_key_create - Create Thread Specific Data Key
+----------------------------------------------------
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <pthread.h>
+ int pthread_key_create(
+ pthread_key_t *key,
+ void (*destructor)( void )
+ );
+
+**STATUS CODES:**
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EAGAIN``
+ - There were not enough resources available to create another key.
+ * - ``ENOMEM``
+ - Insufficient memory exists to create the key.
+
+**DESCRIPTION**
+
+The ``pthread_key_create()`` function shall create a thread-specific data key
+visible to all threads in the process. Key values provided by
+``pthread_key_create()`` are opaque objects used to locate thread-specific
+data. Although the same key value may be used by different threads, the values
+bound to the key by ``pthread_setspecific()`` are maintained on a per-thread
+basis and persist for the life of the calling thread.
+
+Upon key creation, the value ``NULL`` shall be associated with the new key in
+all active threads. Upon thread creation, the value ``NULL`` shall be
+associated with all defined keys in the new thread.
+
+**NOTES**
+
+An optional destructor function may be associated with each key value. At
+thread exit, if a key value has a non-``NULL`` destructor pointer, and the
+thread has a non-``NULL`` value associated with that key, the value of the key
+is set to NULL, and then the function pointed to is called with the previously
+associated value as its sole argument. The order of destructor calls is
+unspecified if more than one destructor exists for a thread when it exits.
+
+.. _pthread_key_delete:
+
+pthread_key_delete - Delete Thread Specific Data Key
+----------------------------------------------------
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <pthread.h>
+ int pthread_key_delete(
+ pthread_key_t key
+ );
+
+**STATUS CODES:**
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+ - The key was invalid
+
+**DESCRIPTION:**
+
+The ``pthread_key_delete()`` function shall delete a thread-specific data key
+previously returned by ``pthread_key_create()``. The thread-specific data
+values associated with key need not be NULL at the time
+``pthread_key_delete()`` is called. It is the responsibility of the application
+to free any application storage or perform any cleanup actions for data
+structures related to the deleted key or associated thread-specific data in any
+threads; this cleanup can be done either before or after
+``pthread_key_delete()`` is called. Any attempt to use key following the call
+to ``pthread_key_delete()`` results in undefined behavior.
+
+**NOTES:**
+
+The ``pthread_key_delete()`` function shall be callable from within destructor
+functions. No destructor functions shall be invoked by
+``pthread_key_delete()``. Any destructor function that may have been associated
+with key shall no longer be called upon thread exit.
+
+.. _pthread_setspecific:
+
+pthread_setspecific - Set Thread Specific Key Value
+---------------------------------------------------
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <pthread.h>
+ int pthread_setspecific(
+ pthread_key_t key,
+ const void *value
+ );
+
+**STATUS CODES:**
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+ - The specified key is invalid.
+
+**DESCRIPTION:**
+
+The ``pthread_setspecific()`` function shall associate a thread-specific value
+with a key obtained via a previous call to ``pthread_key_create()``. Different
+threads may bind different values to the same key. These values are typically
+pointers to blocks of dynamically allocated memory that have been reserved for
+use by the calling thread.
+
+**NOTES:**
+
+The effect of calling ``pthread_setspecific()`` with a key value not obtained
+from ``pthread_key_create()`` or after key has been deleted with
+``pthread_key_delete()`` is undefined.
+
+``pthread_setspecific()`` may be called from a thread-specific data destructor
+function. Calling ``pthread_setspecific()`` from a thread-specific data
+destructor routine may result either in lost storage (after at least
+``PTHREAD_DESTRUCTOR_ITERATIONS`` attempts at destruction) or in an infinite
+loop.
+
+.. _pthread_getspecific:
+
+pthread_getspecific - Get Thread Specific Key Value
+---------------------------------------------------
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <pthread.h>
+ void *pthread_getspecific(
+ pthread_key_t key
+ );
+
+**STATUS CODES:**
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``NULL``
+ - There is no thread-specific data associated with the specified key.
+ * - ``non-NULL``
+ - The data associated with the specified key.
+
+**DESCRIPTION:**
+
+The ``pthread_getspecific()`` function shall return the value currently bound
+to the specified key on behalf of the calling thread.
+
+**NOTES:**
+
+The effect of calling ``pthread_getspecific()`` with a key value not obtained
+from ``pthread_key_create()`` or after key has been deleted with
+``pthread_key_delete()`` is undefined.
+
+``pthread_getspecific()`` may be called from a thread-specific data destructor
+function. A call to ``pthread_getspecific()`` for the thread-specific data key
+being destroyed shall return the value ``NULL``, unless the value is changed
+(after the destructor starts) by a call to ``pthread_setspecific()``.