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diff --git a/c_user/message_manager.rst b/c_user/message_manager.rst deleted file mode 100644 index d622cef..0000000 --- a/c_user/message_manager.rst +++ /dev/null @@ -1,757 +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. - -Message Manager -############### - -.. index:: messages -.. index:: message queues - -Introduction -============ - -The message manager provides communication and synchronization capabilities -using RTEMS message queues. The directives provided by the message manager -are: - -- rtems_message_queue_create_ - Create a queue - -- rtems_message_queue_ident_ - Get ID of a queue - -- rtems_message_queue_delete_ - Delete a queue - -- rtems_message_queue_send_ - Put message at rear of a queue - -- rtems_message_queue_urgent_ - Put message at front of a queue - -- rtems_message_queue_broadcast_ - Broadcast N messages to a queue - -- rtems_message_queue_receive_ - Receive message from a queue - -- rtems_message_queue_get_number_pending_ - Get number of messages pending on a queue - -- rtems_message_queue_flush_ - Flush all messages on a queue - -Background -========== - -Messages --------- - -A message is a variable length buffer where information can be stored to -support communication. The length of the message and the information stored in -that message are user-defined and can be actual data, pointer(s), or empty. - -Message Queues --------------- - -A message queue permits the passing of messages among tasks and ISRs. Message -queues can contain a variable number of messages. Normally messages are sent -to and received from the queue in FIFO order using the -``rtems_message_queue_send`` directive. However, the -``rtems_message_queue_urgent`` directive can be used to place messages at the -head of a queue in LIFO order. - -Synchronization can be accomplished when a task can wait for a message to -arrive at a queue. Also, a task may poll a queue for the arrival of a message. - -The maximum length message which can be sent is set on a per message queue -basis. The message content must be copied in general to/from an internal -buffer of the message queue or directly to a peer in certain cases. This copy -operation is performed with interrupts disabled. So it is advisable to keep -the messages as short as possible. - -Building a Message Queue Attribute Set --------------------------------------- -.. index:: message queue attributes - -In general, an attribute set is built by a bitwise OR of the desired attribute -components. The set of valid message queue attributes is provided in the -following table: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_FIFO`` - - tasks wait by FIFO (default) - * - ``RTEMS_PRIORITY`` - - tasks wait by priority - * - ``RTEMS_LOCAL`` - - local message queue (default) - * - ``RTEMS_GLOBAL`` - - global message queue - -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 local -message queue with the task priority waiting queue discipline. The -attribute_set parameter to the ``rtems_message_queue_create`` directive could -be either ``RTEMS_PRIORITY`` or ``RTEMS_LOCAL | RTEMS_PRIORITY``. The -attribute_set parameter can be set to ``RTEMS_PRIORITY`` because -``RTEMS_LOCAL`` is the default for all created message queues. If a similar -message queue were to be known globally, then the attribute_set parameter would -be ``RTEMS_GLOBAL | RTEMS_PRIORITY``. - -Building a MESSAGE_QUEUE_RECEIVE Option Set -------------------------------------------- - -In general, an option is built by a bitwise OR of the desired option -components. The set of valid options for the ``rtems_message_queue_receive`` -directive are listed in the following table: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for a message (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - -An option listed as a default is not required to appear in the option OR list, -although it is a good programming practice to specify default options. If all -defaults are desired, the option ``RTEMS_DEFAULT_OPTIONS`` should be specified -on this call. - -This example demonstrates the option parameter needed to poll for a message to -arrive. The option parameter passed to the ``rtems_message_queue_receive`` -directive should be ``RTEMS_NO_WAIT``. - -Operations -========== - -Creating a Message Queue ------------------------- - -The ``rtems_message_queue_create`` directive creates a message queue with the -user-defined name. The user specifies the maximum message size and maximum -number of messages which can be placed in the message queue at one time. The -user may select FIFO or task priority as the method for placing waiting tasks -in the task wait queue. RTEMS allocates a Queue Control Block (QCB) from the -QCB free list to maintain the newly created queue as well as memory for the -message buffer pool associated with this message queue. RTEMS also generates a -message queue ID which is returned to the calling task. - -For GLOBAL message queues, the maximum message size is effectively limited to -the longest message which the MPCI is capable of transmitting. - -Obtaining Message Queue IDs ---------------------------- - -When a message queue is created, RTEMS generates a unique message queue ID. -The message queue ID may be obtained by either of two methods. First, as the -result of an invocation of the ``rtems_message_queue_create`` directive, the -queue ID is stored in a user provided location. Second, the queue ID may be -obtained later using the ``rtems_message_queue_ident`` directive. The queue ID -is used by other message manager directives to access this message queue. - -Receiving a Message -------------------- - -The ``rtems_message_queue_receive`` directive attempts to retrieve a message -from the specified message queue. If at least one message is in the queue, -then the message is removed from the queue, copied to the caller's message -buffer, and returned immediately along with the length of the message. When -messages are unavailable, one of the following situations applies: - -- By default, the calling task will wait forever for the message to arrive. - -- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return with an - error status code. - -- Specifying a timeout limits the period the task will wait before returning - with an error status. - -If the task waits for a message, then it is placed in the message queue's task -wait queue in either FIFO or task priority order. All tasks waiting on a -message queue are returned an error code when the message queue is deleted. - -Sending a Message ------------------ - -Messages can be sent to a queue with the ``rtems_message_queue_send`` and -``rtems_message_queue_urgent`` directives. These directives work identically -when tasks are waiting to receive a message. A task is removed from the task -waiting queue, unblocked, and the message is copied to a waiting task's message -buffer. - -When no tasks are waiting at the queue, ``rtems_message_queue_send`` places the -message at the rear of the message queue, while ``rtems_message_queue_urgent`` -places the message at the front of the queue. The message is copied to a -message buffer from this message queue's buffer pool and then placed in the -message queue. Neither directive can successfully send a message to a message -queue which has a full queue of pending messages. - -Broadcasting a Message ----------------------- - -The ``rtems_message_queue_broadcast`` directive sends the same message to every -task waiting on the specified message queue as an atomic operation. The -message is copied to each waiting task's message buffer and each task is -unblocked. The number of tasks which were unblocked is returned to the caller. - -Deleting a Message Queue ------------------------- - -The ``rtems_message_queue_delete`` directive removes a message queue from the -system and frees its control block as well as the memory associated with this -message queue's message buffer pool. A message queue can be deleted by any -local task that knows the message queue's ID. As a result of this directive, -all tasks blocked waiting to receive a message from the message queue will be -readied and returned a status code which indicates that the message queue was -deleted. Any subsequent references to the message queue's name and ID are -invalid. Any messages waiting at the message queue are also deleted and -deallocated. - -Directives -========== - -This section details the message 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_message_queue_create: - -MESSAGE_QUEUE_CREATE - Create a queue -------------------------------------- -.. index:: create a message queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_create - -.. code-block:: c - - rtems_status_code rtems_message_queue_create( - rtems_name name, - uint32_t count, - size_t max_message_size, - rtems_attribute attribute_set, - rtems_id *id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - queue created successfully - * - ``RTEMS_INVALID_NAME`` - - invalid queue name - * - ``RTEMS_INVALID_ADDRESS`` - - ``id`` is NULL - * - ``RTEMS_INVALID_NUMBER`` - - invalid message count - * - ``RTEMS_INVALID_SIZE`` - - invalid message size - * - ``RTEMS_TOO_MANY`` - - too many queues created - * - ``RTEMS_UNSATISFIED`` - - unable to allocate message buffers - * - ``RTEMS_MP_NOT_CONFIGURED`` - - multiprocessing not configured - * - ``RTEMS_TOO_MANY`` - - too many global objects - -**DESCRIPTION:** - -This directive creates a message queue which resides on the local node with the -user-defined name specified in name. For control and maintenance of the queue, -RTEMS allocates and initializes a QCB. Memory is allocated from the RTEMS -Workspace for the specified count of messages, each of max_message_size bytes -in length. The RTEMS-assigned queue id, returned in id, is used to access the -message queue. - -Specifying ``RTEMS_PRIORITY`` in attribute_set causes tasks waiting for a -message to be serviced according to task priority. When ``RTEMS_FIFO`` is -specified, waiting tasks are serviced in First In-First Out order. - -**NOTES:** - -This directive will not cause the calling task to be preempted. - -The following message queue attribute constants are defined by RTEMS: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_FIFO`` - - tasks wait by FIFO (default) - * - ``RTEMS_PRIORITY`` - - tasks wait by priority - * - ``RTEMS_LOCAL`` - - local message queue (default) - * - ``RTEMS_GLOBAL`` - - global message queue - -Message queues should not be made global unless remote tasks must interact with -the created message queue. This is to avoid the system overhead incurred by -the creation of a global message queue. When a global message queue is -created, the message queue's name and id must be transmitted to every node in -the system for insertion in the local copy of the global object table. - -For GLOBAL message queues, the maximum message size is effectively limited to -the longest message which the MPCI is capable of transmitting. - -The total number of global objects, including message queues, is limited by the -``maximum_global_objects`` field in the configuration table. - -.. _rtems_message_queue_ident: - -MESSAGE_QUEUE_IDENT - Get ID of a queue ---------------------------------------- -.. index:: get ID of a message queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_ident - -.. code-block:: c - - rtems_status_code rtems_message_queue_ident( - rtems_name name, - uint32_t node, - rtems_id *id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - queue identified successfully - * - ``RTEMS_INVALID_ADDRESS`` - - ``id`` is NULL - * - ``RTEMS_INVALID_NAME`` - - queue name not found - * - ``RTEMS_INVALID_NODE`` - - invalid node id - -**DESCRIPTION:** - -This directive obtains the queue id associated with the queue name specified in -name. If the queue name is not unique, then the queue id will match one of the -queues with that name. However, this queue id is not guaranteed to correspond -to the desired queue. The queue id is used with other message related -directives to access the message queue. - -**NOTES:** - -This directive will not cause the running task to be preempted. - -If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched with the local -node being searched first. All other nodes are searched with the lowest -numbered node searched first. - -If node is a valid node number which does not represent the local node, then -only the message queues exported by the designated node are searched. - -This directive does not generate activity on remote nodes. It accesses only -the local copy of the global object table. - -.. _rtems_message_queue_delete: - -MESSAGE_QUEUE_DELETE - Delete a queue -------------------------------------- -.. index:: delete a message queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_delete - -.. code-block:: c - - rtems_status_code rtems_message_queue_delete( - rtems_id id - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - queue deleted successfully - * - ``RTEMS_INVALID_ID`` - - invalid queue id - * - ``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - - cannot delete remote queue - -**DESCRIPTION:** - -This directive deletes the message queue specified by ``id``. As a result of -this directive, all tasks blocked waiting to receive a message from this queue -will be readied and returned a status code which indicates that the message -queue was deleted. If no tasks are waiting, but the queue contains messages, -then RTEMS returns these message buffers back to the system message buffer -pool. The QCB for this queue as well as the memory for the message buffers is -reclaimed by RTEMS. - -**NOTES:** - -The calling task will be preempted if its preemption mode is enabled and one or -more local tasks with a higher priority than the calling task are waiting on -the deleted queue. The calling task will NOT be preempted if the tasks that -are waiting are remote tasks. - -The calling task does not have to be the task that created the queue, although -the task and queue must reside on the same node. - -When the queue is deleted, any messages in the queue are returned to the free -message buffer pool. Any information stored in those messages is lost. - -When a global message queue is deleted, the message queue id must be -transmitted to every node in the system for deletion from the local copy of the -global object table. - -Proxies, used to represent remote tasks, are reclaimed when the message queue -is deleted. - -.. _rtems_message_queue_send: - -MESSAGE_QUEUE_SEND - Put message at rear of a queue ---------------------------------------------------- -.. index:: send message to a queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_send - -.. code-block:: c - - rtems_status_code rtems_message_queue_send( - rtems_id id, - cons void *buffer, - size_t size - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - message sent successfully - * - ``RTEMS_INVALID_ID`` - - invalid queue id - * - ``RTEMS_INVALID_SIZE`` - - invalid message size - * - ``RTEMS_INVALID_ADDRESS`` - - ``buffer`` is NULL - * - ``RTEMS_UNSATISFIED`` - - out of message buffers - * - ``RTEMS_TOO_MANY`` - - queue's limit has been reached - -**DESCRIPTION:** - -This directive sends the message buffer of size bytes in length to the queue -specified by id. If a task is waiting at the queue, then the message is copied -to the waiting task's buffer and the task is unblocked. If no tasks are waiting -at the queue, then the message is copied to a message buffer which is obtained -from this message queue's message buffer pool. The message buffer is then -placed at the rear of the queue. - -**NOTES:** - -The calling task will be preempted if it has preemption enabled and a higher -priority task is unblocked as the result of this directive. - -Sending a message to a global message queue which does not reside on the local -node will generate a request to the remote node to post the message on the -specified message queue. - -If the task to be unblocked resides on a different node from the message queue, -then the message is forwarded to the appropriate node, the waiting task is -unblocked, and the proxy used to represent the task is reclaimed. - -.. _rtems_message_queue_urgent: - -MESSAGE_QUEUE_URGENT - Put message at front of a queue ------------------------------------------------------- -.. index:: put message at front of queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_urgent - -.. code-block:: c - - rtems_status_code rtems_message_queue_urgent( - rtems_id id, - const void *buffer, - size_t size - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - message sent successfully - * - ``RTEMS_INVALID_ID`` - - invalid queue id - * - ``RTEMS_INVALID_SIZE`` - - invalid message size - * - ``RTEMS_INVALID_ADDRESS`` - - ``buffer`` is NULL - * - ``RTEMS_UNSATISFIED`` - - out of message buffers - * - ``RTEMS_TOO_MANY`` - - queue's limit has been reached - -**DESCRIPTION:** - -This directive sends the message buffer of size bytes in length to the queue -specified by id. If a task is waiting on the queue, then the message is copied -to the task's buffer and the task is unblocked. If no tasks are waiting on the -queue, then the message is copied to a message buffer which is obtained from -this message queue's message buffer pool. The message buffer is then placed at -the front of the queue. - -**NOTES:** - -The calling task will be preempted if it has preemption enabled and a higher -priority task is unblocked as the result of this directive. - -Sending a message to a global message queue which does not reside on the local -node will generate a request telling the remote node to post the message on the -specified message queue. - -If the task to be unblocked resides on a different node from the message queue, -then the message is forwarded to the appropriate node, the waiting task is -unblocked, and the proxy used to represent the task is reclaimed. - -.. _rtems_message_queue_broadcast: - -MESSAGE_QUEUE_BROADCAST - Broadcast N messages to a queue ---------------------------------------------------------- -.. index:: broadcast message to a queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_broadcast - -.. code-block:: c - - rtems_status_code rtems_message_queue_broadcast( - rtems_id id, - const void *buffer, - size_t size, - uint32_t *count - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - message broadcasted successfully - * - ``RTEMS_INVALID_ID`` - - invalid queue id - * - ``RTEMS_INVALID_ADDRESS`` - - ``buffer`` is NULL - * - ``RTEMS_INVALID_ADDRESS`` - - ``count`` is NULL - * - ``RTEMS_INVALID_SIZE`` - - invalid message size - -**DESCRIPTION:** - -This directive causes all tasks that are waiting at the queue specified by id -to be unblocked and sent the message contained in buffer. Before a task is -unblocked, the message buffer of size byes in length is copied to that task's -message buffer. The number of tasks that were unblocked is returned in count. - -**NOTES:** - -The calling task will be preempted if it has preemption enabled and a higher -priority task is unblocked as the result of this directive. - -The execution time of this directive is directly related to the number of tasks -waiting on the message queue, although it is more efficient than the equivalent -number of invocations of ``rtems_message_queue_send``. - -Broadcasting a message to a global message queue which does not reside on the -local node will generate a request telling the remote node to broadcast the -message to the specified message queue. - -When a task is unblocked which resides on a different node from the message -queue, a copy of the message is forwarded to the appropriate node, the waiting -task is unblocked, and the proxy used to represent the task is reclaimed. - -.. _rtems_message_queue_receive: - -MESSAGE_QUEUE_RECEIVE - Receive message from a queue ----------------------------------------------------- -.. index:: receive message from a queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_receive - -.. code-block:: c - - rtems_status_code rtems_message_queue_receive( - rtems_id id, - void *buffer, - size_t *size, - rtems_option option_set, - rtems_interval timeout - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - message received successfully - * - ``RTEMS_INVALID_ID`` - - invalid queue id - * - ``RTEMS_INVALID_ADDRESS`` - - ``buffer`` is NULL - * - ``RTEMS_INVALID_ADDRESS`` - - ``size`` is NULL - * - ``RTEMS_UNSATISFIED`` - - queue is empty - * - ``RTEMS_TIMEOUT`` - - timed out waiting for message - * - ``RTEMS_OBJECT_WAS_DELETED`` - - queue deleted while waiting - -**DESCRIPTION:** - -This directive receives a message from the message queue specified in id. The -``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` options of the options parameter allow the -calling task to specify whether to wait for a message to become available or -return immediately. For either option, if there is at least one message in the -queue, then it is copied to buffer, size is set to return the length of the -message in bytes, and this directive returns immediately with a successful -return code. The buffer has to be big enough to receive a message of the -maximum length with respect to this message queue. - -If the calling task chooses to return immediately and the queue is empty, then -a status code indicating this condition is returned. If the calling task -chooses to wait at the message queue and the queue is empty, then the calling -task is placed on the message wait queue and blocked. If the queue was created -with the ``RTEMS_PRIORITY`` option specified, then the calling task is inserted -into the wait queue according to its priority. But, if the queue was created -with the ``RTEMS_FIFO`` option specified, then the calling task is placed at -the rear of the wait queue. - -A task choosing to wait at the queue can optionally specify a timeout value in -the timeout parameter. The timeout parameter specifies the maximum interval to -wait before the calling task desires to be unblocked. If it is set to -``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. - -**NOTES:** - -The following message receive option constants are defined by RTEMS: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for a message (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - -Receiving a message from a global message queue which does not reside on the -local node will generate a request to the remote node to obtain a message from -the specified message queue. If no message is available and ``RTEMS_WAIT`` was -specified, then the task must be blocked until a message is posted. A proxy is -allocated on the remote node to represent the task until the message is posted. - -A clock tick is required to support the timeout functionality of this -directive. - -.. _rtems_message_queue_get_number_pending: - -MESSAGE_QUEUE_GET_NUMBER_PENDING - Get number of messages pending on a queue ----------------------------------------------------------------------------- -.. index:: get number of pending messages - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_get_number_pending - -.. code-block:: c - - rtems_status_code rtems_message_queue_get_number_pending( - rtems_id id, - uint32_t *count - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - number of messages pending returned successfully - * - ``RTEMS_INVALID_ADDRESS`` - - ``count`` is NULL - * - ``RTEMS_INVALID_ID`` - - invalid queue id - -**DESCRIPTION:** - -This directive returns the number of messages pending on this message queue in -count. If no messages are present on the queue, count is set to zero. - -**NOTES:** - -Getting the number of pending messages on a global message queue which does not -reside on the local node will generate a request to the remote node to actually -obtain the pending message count for the specified message queue. - -.. _rtems_message_queue_flush: - -MESSAGE_QUEUE_FLUSH - Flush all messages on a queue ---------------------------------------------------- -.. index:: flush messages on a queue - -**CALLING SEQUENCE:** - -.. index:: rtems_message_queue_flush - -.. code-block:: c - - rtems_status_code rtems_message_queue_flush( - rtems_id id, - uint32_t *count - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - message queue flushed successfully - * - ``RTEMS_INVALID_ADDRESS`` - - ``count`` is NULL - * - ``RTEMS_INVALID_ID`` - - invalid queue id - -**DESCRIPTION:** - -This directive removes all pending messages from the specified queue id. The -number of messages removed is returned in count. If no messages are present on -the queue, count is set to zero. - -**NOTES:** - -Flushing all messages on a global message queue which does not reside on the -local node will generate a request to the remote node to actually flush the -specified message queue. |