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diff --git a/c_user/barrier_manager.rst b/c_user/barrier_manager.rst deleted file mode 100644 index 7e80879..0000000 --- a/c_user/barrier_manager.rst +++ /dev/null @@ -1,429 +0,0 @@ -.. comment SPDX-License-Identifier: CC-BY-SA-4.0 - -.. COMMENT: COPYRIGHT (c) 1988-2008. -.. COMMENT: On-Line Applications Research Corporation (OAR). -.. COMMENT: All rights reserved. - -Barrier Manager -############### - -.. index:: barrier - -Introduction -============ - -The barrier manager provides a unique synchronization capability which can be -used to have a set of tasks block and be unblocked as a set. The directives -provided by the barrier manager are: - -- rtems_barrier_create_ - Create a barrier - -- rtems_barrier_ident_ - Get ID of a barrier - -- rtems_barrier_delete_ - Delete a barrier - -- rtems_barrier_wait_ - Wait at a barrier - -- rtems_barrier_release_ - Release a barrier - -Background -========== - -A barrier can be viewed as a gate at which tasks wait until the gate is opened. -This has many analogies in the real world. Horses and other farm animals may -approach a closed gate and gather in front of it, waiting for someone to open -the gate so they may proceed. Similarly, cticket holders gather at the gates -of arenas before concerts or sporting events waiting for the arena personnel to -open the gates so they may enter. - -Barriers are useful during application initialization. Each application task -can perform its local initialization before waiting for the application as a -whole to be initialized. Once all tasks have completed their independent -initializations, the "application ready" barrier can be released. - -Automatic Versus Manual Barriers --------------------------------- - -Just as with a real-world gate, barriers may be configured to be manually -opened or automatically opened. All tasks calling the ``rtems_barrier_wait`` -directive will block until a controlling task invokes -the ``rtems_barrier_release`` directive. - -Automatic barriers are created with a limit to the number of tasks which may -simultaneously block at the barrier. Once this limit is reached, all of the -tasks are released. For example, if the automatic limit is ten tasks, then the -first nine tasks calling the ``rtems_barrier_wait`` directive will block. When -the tenth task calls the ``rtems_barrier_wait`` directive, the nine blocked -tasks will be released and the tenth task returns to the caller without -blocking. - -Building a Barrier Attribute Set --------------------------------- - -In general, an attribute set is built by a bitwise OR of the desired attribute -components. The following table lists the set of valid barrier attributes: - -``RTEMS_BARRIER_AUTOMATIC_RELEASE`` - automatically release the barrier when the configured number of tasks are - blocked - -``RTEMS_BARRIER_MANUAL_RELEASE`` - only release the barrier when the application invokes the - ``rtems_barrier_release`` directive. (default) - -.. note:: - - Barriers only support FIFO blocking order because all waiting tasks are - released as a set. Thus the released tasks will all become ready to execute - at the same time and compete for the processor based upon their priority. - -Attribute values are specifically designed to be mutually exclusive, therefore -bitwise OR and addition operations are equivalent as long as each attribute -appears exactly once in the component list. An attribute listed as a default -is not required to appear in the attribute list, although it is a good -programming practice to specify default attributes. If all defaults are -desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` should be specified on this -call. - -This example demonstrates the attribute_set parameter needed to create a -barrier with the automatic release policy. The ``attribute_set`` parameter -passed to the ``rtems_barrier_create`` directive will be -``RTEMS_BARRIER_AUTOMATIC_RELEASE``. In this case, the user must also specify -the ``maximum_waiters`` parameter. - -Operations -========== - -Creating a Barrier ------------------- - -The ``rtems_barrier_create`` directive creates a barrier with a user-specified -name and the desired attributes. RTEMS allocates a Barrier Control Block (BCB) -from the BCB free list. This data structure is used by RTEMS to manage the -newly created barrier. Also, a unique barrier ID is generated and returned to -the calling task. - -Obtaining Barrier IDs ---------------------- - -When a barrier is created, RTEMS generates a unique barrier ID and assigns it -to the created barrier until it is deleted. The barrier ID may be obtained by -either of two methods. First, as the result of an invocation of the -``rtems_barrier_create`` directive, the barrier ID is stored in a user provided -location. Second, the barrier ID may be obtained later using the -``rtems_barrier_ident`` directive. The barrier ID is used by other barrier -manager directives to access this barrier. - -Waiting at a Barrier --------------------- - -The ``rtems_barrier_wait`` directive is used to wait at -the specified barrier. Since a barrier is, by definition, never immediately, -the task may wait forever for the barrier to be released or it may -specify a timeout. Specifying a timeout limits the interval the task will -wait before returning with an error status code. - -If the barrier is configured as automatic and there are already one less then -the maximum number of waiters, then the call will unblock all tasks waiting at -the barrier and the caller will return immediately. - -When the task does wait to acquire the barrier, then it is placed in the -barrier's task wait queue in FIFO order. All tasks waiting on a barrier are -returned an error code when the barrier is deleted. - -Releasing a Barrier -------------------- - -The ``rtems_barrier_release`` directive is used to release the specified -barrier. When the ``rtems_barrier_release`` is invoked, all tasks waiting at -the barrier are immediately made ready to execute and begin to compete for the -processor to execute. - -Deleting a Barrier ------------------- - -The ``rtems_barrier_delete`` directive removes a barrier from the system and -frees its control block. A barrier can be deleted by any local task that knows -the barrier's ID. As a result of this directive, all tasks blocked waiting for -the barrier to be released, will be readied and returned a status code which -indicates that the barrier was deleted. Any subsequent references to the -barrier's name and ID are invalid. - -Directives -========== - -This section details the barrier 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. - -.. _rtems_barrier_create: - -BARRIER_CREATE - Create a barrier ---------------------------------- -.. index:: create a barrier - -**CALLING SEQUENCE:** - -.. index:: rtems_barrier_create - -.. code-block:: c - - rtems_status_code rtems_barrier_create( - rtems_name name, - rtems_attribute attribute_set, - uint32_t maximum_waiters, - rtems_id *id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - barrier created successfully - * - ``RTEMS_INVALID_NAME`` - - invalid barrier name - * - ``RTEMS_INVALID_ADDRESS`` - - ``id`` is NULL - * - ``RTEMS_TOO_MANY`` - - too many barriers created - -**DESCRIPTION:** - -This directive creates a barrier which resides on the local node. The created -barrier has the user-defined name specified in ``name`` and the initial count -specified in ``count``. For control and maintenance of the barrier, RTEMS -allocates and initializes a BCB. The RTEMS-assigned barrier id is returned in -``id``. This barrier id is used with other barrier related directives to -access the barrier. - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_BARRIER_MANUAL_RELEASE`` - - only release - -Specifying ``RTEMS_BARRIER_AUTOMATIC_RELEASE`` in ``attribute_set`` causes -tasks calling the ``rtems_barrier_wait`` directive to block until there are -``maximum_waiters - 1`` tasks waiting at the barrier. When the -``maximum_waiters`` task invokes the ``rtems_barrier_wait`` directive, the -previous ``maximum_waiters - 1`` tasks are automatically released and the -caller returns. - -In contrast, when the ``RTEMS_BARRIER_MANUAL_RELEASE`` attribute is specified, -there is no limit on the number of tasks that will block at the barrier. Only -when the ``rtems_barrier_release`` directive is invoked, are the tasks waiting -at the barrier unblocked. - -**NOTES:** - -This directive will not cause the calling task to be preempted. - -The following barrier attribute constants are defined by RTEMS: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_BARRIER_AUTOMATIC_RELEASE`` - - automatically release the barrier when the configured number of tasks are - blocked - * - ``RTEMS_BARRIER_MANUAL_RELEASE`` - - only release the barrier when the application invokes - the ``rtems_barrier_release`` directive. (default) - -.. _rtems_barrier_ident: - -BARRIER_IDENT - Get ID of a barrier ------------------------------------ -.. index:: get ID of a barrier -.. index:: obtain ID of a barrier - -**CALLING SEQUENCE:** - -.. index:: rtems_barrier_ident - -.. code-block:: c - - rtems_status_code rtems_barrier_ident( - rtems_name name, - rtems_id *id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - barrier identified successfully - * - ``RTEMS_INVALID_NAME`` - - barrier name not found - * - ``RTEMS_INVALID_NODE`` - - invalid node id - -**DESCRIPTION:** - -This directive obtains the barrier id associated with the barrier name. If the -barrier name is not unique, then the barrier id will match one of the barriers -with that name. However, this barrier id is not guaranteed to correspond to -the desired barrier. The barrier id is used by other barrier related -directives to access the barrier. - -**NOTES:** - -This directive will not cause the running task to be preempted. - -.. _rtems_barrier_delete: - -BARRIER_DELETE - Delete a barrier ---------------------------------- -.. index:: delete a barrier - -**CALLING SEQUENCE:** - -.. index:: rtems_barrier_delete - -.. code-block:: c - - rtems_status_code rtems_barrier_delete( - rtems_id id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - barrier deleted successfully - * - ``RTEMS_INVALID_ID`` - - invalid barrier id - -**DESCRIPTION:** - -This directive deletes the barrier specified by ``id``. All tasks blocked -waiting for the barrier to be released will be readied and returned a status -code which indicates that the barrier was deleted. The BCB for this barrier is -reclaimed by RTEMS. - -**NOTES:** - -The calling task will be preempted if it is enabled by the task's execution -mode and a higher priority local task is waiting on the deleted barrier. The -calling task will NOT be preempted if all of the tasks that are waiting on the -barrier are remote tasks. - -The calling task does not have to be the task that created the barrier. Any -local task that knows the barrier id can delete the barrier. - -.. _rtems_barrier_wait: - -BARRIER_OBTAIN - Acquire a barrier ----------------------------------- -.. index:: obtain a barrier -.. index:: lock a barrier - -**CALLING SEQUENCE:** - -.. index:: rtems_barrier_wait - -.. code-block:: c - - rtems_status_code rtems_barrier_wait( - rtems_id id, - rtems_interval timeout - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - barrier released and task unblocked - * - ``RTEMS_UNSATISFIED`` - - barrier not available - * - ``RTEMS_TIMEOUT`` - - timed out waiting for barrier - * - ``RTEMS_OBJECT_WAS_DELETED`` - - barrier deleted while waiting - * - ``RTEMS_INVALID_ID`` - - invalid barrier id - -**DESCRIPTION:** - -This directive acquires the barrier specified by ``id``. The ``RTEMS_WAIT`` -and ``RTEMS_NO_WAIT`` components of the options parameter indicate whether the -calling task wants to wait for the barrier to become available or return -immediately if the barrier is not currently available. With either -``RTEMS_WAIT`` or ``RTEMS_NO_WAIT``, if the current barrier count is positive, -then it is decremented by one and the barrier is successfully acquired by -returning immediately with a successful return code. - -Conceptually, the calling task should always be thought of as blocking when it -makes this call and being unblocked when the barrier is released. If the -barrier is configured for manual release, this rule of thumb will always be -valid. If the barrier is configured for automatic release, all callers will -block except for the one which is the Nth task which trips the automatic -release condition. - -The timeout parameter specifies the maximum interval the calling task is -willing to be blocked waiting for the barrier. If it is set to -``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. If the barrier -is available or the ``RTEMS_NO_WAIT`` option component is set, then timeout is -ignored. - -**NOTES:** - -The following barrier acquisition option constants are defined by RTEMS: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for barrier (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - -A clock tick is required to support the timeout functionality of this -directive. - -.. _rtems_barrier_release: - -BARRIER_RELEASE - Release a barrier ------------------------------------ -.. index:: wait at a barrier -.. index:: release a barrier - -**CALLING SEQUENCE:** - -.. index:: rtems_barrier_release - -.. code-block:: c - - rtems_status_code rtems_barrier_release( - rtems_id id, - uint32_t *released - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - barrier released successfully - * - ``RTEMS_INVALID_ID`` - - invalid barrier id - -**DESCRIPTION:** - -This directive releases the barrier specified by id. All tasks waiting at the -barrier will be unblocked. If the running task's preemption mode is enabled -and one of the unblocked tasks has a higher priority than the running task. - -**NOTES:** - -The calling task may be preempted if it causes a higher priority task to be -made ready for execution. |