From 72a62ad88f82fe1ffee50024db4dd0f3fa5806f7 Mon Sep 17 00:00:00 2001 From: Chris Johns Date: Thu, 3 Nov 2016 16:58:08 +1100 Subject: Rename all manuals with an _ to have a -. It helps released naming of files. --- c-user/message_manager.rst | 757 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 757 insertions(+) create mode 100644 c-user/message_manager.rst (limited to 'c-user/message_manager.rst') diff --git a/c-user/message_manager.rst b/c-user/message_manager.rst new file mode 100644 index 0000000..d622cef --- /dev/null +++ b/c-user/message_manager.rst @@ -0,0 +1,757 @@ +.. 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. -- cgit v1.2.3