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diff --git a/c-user/message/directives.rst b/c-user/message/directives.rst new file mode 100644 index 0000000..7039b2e --- /dev/null +++ b/c-user/message/directives.rst @@ -0,0 +1,1086 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +.. Copyright (C) 2020, 2021 embedded brains GmbH & Co. KG +.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) + +.. This file is part of the RTEMS quality process and was automatically +.. generated. If you find something that needs to be fixed or +.. worded better please post a report or patch to an RTEMS mailing list +.. or raise a bug report: +.. +.. https://www.rtems.org/bugs.html +.. +.. For information on updating and regenerating please refer to the How-To +.. section in the Software Requirements Engineering chapter of the +.. RTEMS Software Engineering manual. The manual is provided as a part of +.. a release. For development sources please refer to the online +.. documentation at: +.. +.. https://docs.rtems.org + +.. _MessageManagerDirectives: + +Directives +========== + +This section details the directives of the Message Manager. A subsection is +dedicated to each of this manager's directives and lists the calling sequence, +parameters, description, return values, and notes of the directive. + +.. Generated from spec:/rtems/message/if/create + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_create() +.. index:: create a message queue + +.. _InterfaceRtemsMessageQueueCreate: + +rtems_message_queue_create() +---------------------------- + +Creates a message queue. + +.. rubric:: CALLING SEQUENCE: + +.. 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 + ); + +.. rubric:: PARAMETERS: + +``name`` + This parameter is the object name of the message queue. + +``count`` + This parameter is the maximum count of pending messages supported by the + message queue. + +``max_message_size`` + This parameter is the maximum size in bytes of a message supported by the + message queue. + +``attribute_set`` + This parameter is the attribute set of the message queue. + +``id`` + This parameter is the pointer to an :ref:`InterfaceRtemsId` object. When + the directive call is successful, the identifier of the created message + queue will be stored in this object. + +.. rubric:: DESCRIPTION: + +This directive creates a message queue which resides on the local node. The +message queue has the user-defined object name specified in ``name``. Memory +is allocated from the RTEMS Workspace for the count of messages specified in +``count``, each of ``max_message_size`` bytes in length. The assigned object +identifier is returned in ``id``. This identifier is used to access the +message queue with other message queue related directives. + +The **attribute set** specified in ``attribute_set`` is built through a +*bitwise or* of the attribute constants described below. Not all combinations +of attributes are allowed. Some attributes are mutually exclusive. If +mutually exclusive attributes are combined, the behaviour is undefined. +Attributes not mentioned below are not evaluated by this directive and have no +effect. Default attributes can be selected by using the +:c:macro:`RTEMS_DEFAULT_ATTRIBUTES` constant. The attribute set defines + +* the scope of the message queue: :c:macro:`RTEMS_LOCAL` (default) or + :c:macro:`RTEMS_GLOBAL` and + +* the task wait queue discipline used by the message queue: + :c:macro:`RTEMS_FIFO` (default) or :c:macro:`RTEMS_PRIORITY`. + +The message queue has a local or global **scope** in a multiprocessing network +(this attribute does not refer to SMP systems). The scope is selected by the +mutually exclusive :c:macro:`RTEMS_LOCAL` and :c:macro:`RTEMS_GLOBAL` +attributes. + +* A **local scope** is the default and can be emphasized through the use of the + :c:macro:`RTEMS_LOCAL` attribute. A local message queue can be only used by + the node which created it. + +* A **global scope** is established if the :c:macro:`RTEMS_GLOBAL` attribute is + set. Setting the global attribute in a single node system has no effect. + +The **task wait queue discipline** is selected by the mutually exclusive +:c:macro:`RTEMS_FIFO` and :c:macro:`RTEMS_PRIORITY` attributes. The discipline +defines the order in which tasks wait for a message to receive on a currently +empty message queue. + +* The **FIFO discipline** is the default and can be emphasized through use of + the :c:macro:`RTEMS_FIFO` attribute. + +* The **priority discipline** is selected by the :c:macro:`RTEMS_PRIORITY` + attribute. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_NAME` + The ``name`` parameter was invalid. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``id`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_NUMBER` + The ``count`` parameter was invalid. + +:c:macro:`RTEMS_INVALID_SIZE` + The ``max_message_size`` parameter was invalid. + +:c:macro:`RTEMS_TOO_MANY` + There was no inactive object available to create a message queue. The + number of message queue available to the application is configured through + the :ref:`CONFIGURE_MAXIMUM_MESSAGE_QUEUES` application configuration + option. + +:c:macro:`RTEMS_TOO_MANY` + In multiprocessing configurations, there was no inactive global object + available to create a global message queue. The number of global objects + available to the application is configured through the + :ref:`CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS` application configuration + option. + +:c:macro:`RTEMS_INVALID_NUMBER` + The product of ``count`` and ``max_message_size`` is greater than the + maximum storage size. + +:c:macro:`RTEMS_UNSATISFIED` + There was not enough memory available in the RTEMS Workspace to allocate + the message buffers for the message queue. + +.. rubric:: NOTES: + +For message queues with a global scope, the maximum message size is effectively +limited to the longest message which the :term:`MPCI` is capable of +transmitting. + +For control and maintenance of the message queue, RTEMS allocates a :term:`QCB` +from the local QCB free pool and initializes it. + +The QCB for a global message queue is allocated on the local node. Message +queues should not be made global unless remote tasks must interact with the +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 identifier must be transmitted to every node in the system for +insertion in the local copy of the global object table. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within device driver initialization context. + +* The directive may be called from within task context. + +* The directive may obtain and release the object allocator mutex. This may + cause the calling task to be preempted. + +* When the directive operates on a global object, the directive sends a message + to remote nodes. This may preempt the calling task. + +* The number of message queues available to the application is configured + through the :ref:`CONFIGURE_MAXIMUM_MESSAGE_QUEUES` application configuration + option. + +* Where the object class corresponding to the directive is configured to use + unlimited objects, the directive may allocate memory from the RTEMS + Workspace. + +* The number of global objects available to the application is configured + through the :ref:`CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS` application + configuration option. + +.. Generated from spec:/rtems/message/if/construct + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_construct() + +.. _InterfaceRtemsMessageQueueConstruct: + +rtems_message_queue_construct() +------------------------------- + +Constructs a message queue from the specified the message queue configuration. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_construct( + const rtems_message_queue_config *config, + rtems_id *id + ); + +.. rubric:: PARAMETERS: + +``config`` + This parameter is the pointer to an :ref:`InterfaceRtemsMessageQueueConfig` + object. It configures the message queue. + +``id`` + This parameter is the pointer to an :ref:`InterfaceRtemsId` object. When + the directive call is successful, the identifier of the constructed message + queue will be stored in this object. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``config`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_NAME` + The message queue name in the configuration was invalid. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``id`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_NUMBER` + The maximum number of pending messages in the configuration was zero. + +:c:macro:`RTEMS_INVALID_SIZE` + The maximum message size in the configuration was zero. + +:c:macro:`RTEMS_TOO_MANY` + There was no inactive message queue object available to construct a message + queue. + +:c:macro:`RTEMS_TOO_MANY` + In multiprocessing configurations, there was no inactive global object + available to construct a global message queue. + +:c:macro:`RTEMS_INVALID_SIZE` + The maximum message size in the configuration was too big and resulted in + integer overflows in calculations carried out to determine the size of the + message buffer area. + +:c:macro:`RTEMS_INVALID_NUMBER` + The maximum number of pending messages in the configuration was too big and + resulted in integer overflows in calculations carried out to determine the + size of the message buffer area. + +:c:macro:`RTEMS_UNSATISFIED` + The message queue storage area begin pointer in the configuration was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_UNSATISFIED` + The message queue storage area size in the configuration was not equal to + the size calculated from the maximum number of pending messages and the + maximum message size. + +.. rubric:: NOTES: + +In contrast to message queues created by +:ref:`InterfaceRtemsMessageQueueCreate`, the message queues constructed by this +directive use a user-provided message buffer storage area. + +This directive is intended for applications which do not want to use the RTEMS +Workspace and instead statically allocate all operating system resources. An +application based solely on static allocation can avoid any runtime memory +allocators. This can simplify the application architecture as well as any +analysis that may be required. + +The value for :ref:`CONFIGURE_MESSAGE_BUFFER_MEMORY` should not include memory +for message queues constructed by :ref:`InterfaceRtemsMessageQueueConstruct`. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within device driver initialization context. + +* The directive may be called from within task context. + +* The directive may obtain and release the object allocator mutex. This may + cause the calling task to be preempted. + +* When the directive operates on a global object, the directive sends a message + to remote nodes. This may preempt the calling task. + +* The number of message queues available to the application is configured + through the :ref:`CONFIGURE_MAXIMUM_MESSAGE_QUEUES` application configuration + option. + +* Where the object class corresponding to the directive is configured to use + unlimited objects, the directive may allocate memory from the RTEMS + Workspace. + +* The number of global objects available to the application is configured + through the :ref:`CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS` application + configuration option. + +.. Generated from spec:/rtems/message/if/ident + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_ident() + +.. _InterfaceRtemsMessageQueueIdent: + +rtems_message_queue_ident() +--------------------------- + +Identifies a message queue by the object name. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_ident( + rtems_name name, + uint32_t node, + rtems_id *id + ); + +.. rubric:: PARAMETERS: + +``name`` + This parameter is the object name to look up. + +``node`` + This parameter is the node or node set to search for a matching object. + +``id`` + This parameter is the pointer to an :ref:`InterfaceRtemsId` object. When + the directive call is successful, the object identifier of an object with + the specified name will be stored in this object. + +.. rubric:: DESCRIPTION: + +This directive obtains a message queue identifier associated with the message +queue name specified in ``name``. + +The node to search is specified in ``node``. It shall be + +* a valid node number, + +* the constant :c:macro:`RTEMS_SEARCH_ALL_NODES` to search in all nodes, + +* the constant :c:macro:`RTEMS_SEARCH_LOCAL_NODE` to search in the local node + only, or + +* the constant :c:macro:`RTEMS_SEARCH_OTHER_NODES` to search in all nodes + except the local node. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``id`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_NAME` + The ``name`` parameter was 0. + +:c:macro:`RTEMS_INVALID_NAME` + There was no object with the specified name on the specified nodes. + +:c:macro:`RTEMS_INVALID_NODE` + In multiprocessing configurations, the specified node was invalid. + +.. rubric:: NOTES: + +If the message queue name is not unique, then the message queue identifier will +match the first message queue with that name in the search order. However, this +message queue identifier is not guaranteed to correspond to the desired message +queue. + +The objects are searched from lowest to the highest index. If ``node`` is +:c:macro:`RTEMS_SEARCH_ALL_NODES`, all nodes are searched with the local node +being searched first. All other nodes are searched from lowest to the highest +node number. + +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. + +The message queue identifier is used with other message related directives to +access the message queue. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within any runtime context. + +* The directive will not cause the calling task to be preempted. + +.. Generated from spec:/rtems/message/if/delete + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_delete() +.. index:: delete a message queue + +.. _InterfaceRtemsMessageQueueDelete: + +rtems_message_queue_delete() +---------------------------- + +Deletes the message queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_delete( rtems_id id ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the message queue identifier. + +.. rubric:: 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. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no message queue associated with the identifier specified by + ``id``. + +:c:macro:`RTEMS_ILLEGAL_ON_REMOTE_OBJECT` + The message queue resided on a remote node. + +.. rubric:: NOTES: + +When the message queue is deleted, any messages in the queue are returned to +the free message buffer pool. Any information stored in those messages is +lost. The message buffers allocated for the message queue are reclaimed. + +The :term:`QCB` for the deleted message queue is reclaimed by RTEMS. + +When a global message queue is deleted, the message queue identifier must be +transmitted to every node in the system for deletion from the local copy of the +global object table. + +The message queue must reside on the local node, even if the message queue was +created with the :c:macro:`RTEMS_GLOBAL` attribute. + +Proxies, used to represent remote tasks, are reclaimed when the message queue +is deleted. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within device driver initialization context. + +* The directive may be called from within task context. + +* The directive may obtain and release the object allocator mutex. This may + cause the calling task to be preempted. + +* When the directive operates on a global object, the directive sends a message + to remote nodes. This may preempt the calling task. + +* The calling task does not have to be the task that created the object. Any + local task that knows the object identifier can delete the object. + +* Where the object class corresponding to the directive is configured to use + unlimited objects, the directive may free memory to the RTEMS Workspace. + +.. Generated from spec:/rtems/message/if/send + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_send() +.. index:: send message to a queue + +.. _InterfaceRtemsMessageQueueSend: + +rtems_message_queue_send() +-------------------------- + +Puts the message at the rear of the queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_send( + rtems_id id, + const void *buffer, + size_t size + ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``buffer`` + This parameter is the begin address of the message buffer to send. + +``size`` + This parameter is the size in bytes of the message buffer to send. + +.. rubric:: 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. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``buffer`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_SIZE` + The size of the message exceeded the maximum message size of the queue as + defined by :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct`. + +:c:macro:`RTEMS_TOO_MANY` + The maximum number of pending messages supported by the queue as defined by + :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct` has been reached. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within task context. + +* The directive may be called from within interrupt context. + +* The directive may unblock a task. This may cause the calling task to be + preempted. + +* When the directive operates on a remote object, the directive sends a message + to the remote node and waits for a reply. This will preempt the calling + task. + +.. Generated from spec:/rtems/message/if/urgent + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_urgent() +.. index:: put message at front of queue + +.. _InterfaceRtemsMessageQueueUrgent: + +rtems_message_queue_urgent() +---------------------------- + +Puts the message at the front of the queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_urgent( + rtems_id id, + const void *buffer, + size_t size + ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``buffer`` + This parameter is the begin address of the message buffer to send urgently. + +``size`` + This parameter is the size in bytes of the message buffer to send urgently. + +.. rubric:: 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 front of the queue. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``buffer`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_SIZE` + The size of the message exceeded the maximum message size of the queue as + defined by :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct`. + +:c:macro:`RTEMS_TOO_MANY` + The maximum number of pending messages supported by the queue as defined by + :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct` has been reached. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within task context. + +* The directive may be called from within interrupt context. + +* The directive may unblock a task. This may cause the calling task to be + preempted. + +* When the directive operates on a remote object, the directive sends a message + to the remote node and waits for a reply. This will preempt the calling + task. + +.. Generated from spec:/rtems/message/if/broadcast + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_broadcast() +.. index:: broadcast message to a queue + +.. _InterfaceRtemsMessageQueueBroadcast: + +rtems_message_queue_broadcast() +------------------------------- + +Broadcasts the messages to the tasks waiting at the queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_broadcast( + rtems_id id, + const void *buffer, + size_t size, + uint32_t *count + ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``buffer`` + This parameter is the begin address of the message buffer to broadcast. + +``size`` + This parameter is the size in bytes of the message buffer to broadcast. + +``count`` + This parameter is the pointer to an `uint32_t + <https://en.cppreference.com/w/c/types/integer>`_ object. When the + directive call is successful, the number of unblocked tasks will be stored + in this object. + +.. rubric:: 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`` bytes in length is copied +to that task's message buffer. The number of tasks that were unblocked is +returned in ``count``. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``buffer`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``count`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_SIZE` + The size of the message exceeded the maximum message size of the queue as + defined by :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct`. + +.. rubric:: NOTES: + +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 :ref:`InterfaceRtemsMessageQueueSend`. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within task context. + +* The directive may be called from within interrupt context. + +* The directive may unblock a task. This may cause the calling task to be + preempted. + +* When the directive operates on a remote object, the directive sends a message + to the remote node and waits for a reply. This will preempt the calling + task. + +.. Generated from spec:/rtems/message/if/receive + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_receive() +.. index:: receive message from a queue + +.. _InterfaceRtemsMessageQueueReceive: + +rtems_message_queue_receive() +----------------------------- + +Receives a message from the queue. + +.. rubric:: CALLING SEQUENCE: + +.. 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 + ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``buffer`` + This parameter is the begin address of the buffer to receive the message. + The buffer shall be large enough to receive a message of the maximum length + of the queue as defined by :ref:`InterfaceRtemsMessageQueueCreate` or + :ref:`InterfaceRtemsMessageQueueConstruct`. The ``size`` parameter cannot + be used to specify the size of the buffer. + +``size`` + This parameter is the pointer to a `size_t + <https://en.cppreference.com/w/c/types/size_t>`_ object. When the + directive call is successful, the size in bytes of the received messages + will be stored in this object. This parameter cannot be used to specify + the size of the buffer. + +``option_set`` + This parameter is the option set. + +``timeout`` + This parameter is the timeout in :term:`clock ticks <clock tick>` if the + :c:macro:`RTEMS_WAIT` option is set. Use :c:macro:`RTEMS_NO_TIMEOUT` to + wait potentially forever. + +.. rubric:: DESCRIPTION: + +This directive receives a message from the queue specified by ``id``. + +The **option set** specified in ``option_set`` is built through a *bitwise or* +of the option constants described below. Not all combinations of options are +allowed. Some options are mutually exclusive. If mutually exclusive options +are combined, the behaviour is undefined. Options not mentioned below are not +evaluated by this directive and have no effect. Default options can be selected +by using the :c:macro:`RTEMS_DEFAULT_OPTIONS` constant. + +The calling task can **wait** or **try to receive** a message from the queue +according to the mutually exclusive :c:macro:`RTEMS_WAIT` and +:c:macro:`RTEMS_NO_WAIT` options. + +* **Waiting to receive** a message from the queue is the default and can be + emphasized through the use of the :c:macro:`RTEMS_WAIT` option. The + ``timeout`` parameter defines how long the calling task is willing to wait. + Use :c:macro:`RTEMS_NO_TIMEOUT` to wait potentially forever, otherwise set a + timeout interval in clock ticks. + +* **Trying to receive** a message from the queue is selected by the + :c:macro:`RTEMS_NO_WAIT` option. If this option is defined, then the + ``timeout`` parameter is ignored. When a message from the queue cannot be + immediately received, then the :c:macro:`RTEMS_UNSATISFIED` status is + returned. + +With either :c:macro:`RTEMS_WAIT` or :c:macro:`RTEMS_NO_WAIT` if there is at +least one message in the queue, then it is copied to the buffer, the size is +set to return the length of the message in bytes, and this directive returns +immediately with the :c:macro:`RTEMS_SUCCESSFUL` status 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 +the directive returns immediately with the :c:macro:`RTEMS_UNSATISFIED` status +code. 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 :c:macro:`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 :c:macro:`RTEMS_FIFO` +option specified, then the calling task is placed at the rear of the wait +queue. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``buffer`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``size`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +:c:macro:`RTEMS_UNSATISFIED` + The queue was empty. + +:c:macro:`RTEMS_TIMEOUT` + The timeout happened while the calling task was waiting to receive a + message + +:c:macro:`RTEMS_OBJECT_WAS_DELETED` + The queue was deleted while the calling task was waiting to receive a + message. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* When a local queue is accessed and the :c:macro:`RTEMS_NO_WAIT` option is + set, the directive may be called from within interrupt context. + +* The directive may be called from within task context. + +* When the request cannot be immediately satisfied and the + :c:macro:`RTEMS_WAIT` option is set, the calling task blocks at some point + during the directive call. + +* The timeout functionality of the directive requires a :term:`clock tick`. + +* When the directive operates on a remote object, the directive sends a message + to the remote node and waits for a reply. This will preempt the calling + task. + +.. Generated from spec:/rtems/message/if/get-number-pending + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_get_number_pending() +.. index:: get number of pending messages + +.. _InterfaceRtemsMessageQueueGetNumberPending: + +rtems_message_queue_get_number_pending() +---------------------------------------- + +Gets the number of messages pending on the queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_get_number_pending( + rtems_id id, + uint32_t *count + ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``count`` + This parameter is the pointer to an `uint32_t + <https://en.cppreference.com/w/c/types/integer>`_ object. When the + directive call is successful, the number of pending messages will be stored + in this object. + +.. rubric:: DESCRIPTION: + +This directive returns the number of messages pending on the queue specified by +``id`` in ``count``. If no messages are present on the queue, count is set to +zero. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``count`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within task context. + +* The directive may be called from within interrupt context. + +* When the directive operates on a remote object, the directive sends a message + to the remote node and waits for a reply. This will preempt the calling + task. + +.. Generated from spec:/rtems/message/if/flush + +.. raw:: latex + + \clearpage + +.. index:: rtems_message_queue_flush() +.. index:: flush messages on a queue + +.. _InterfaceRtemsMessageQueueFlush: + +rtems_message_queue_flush() +--------------------------- + +Flushes all messages on the queue. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + rtems_status_code rtems_message_queue_flush( rtems_id id, uint32_t *count ); + +.. rubric:: PARAMETERS: + +``id`` + This parameter is the queue identifier. + +``count`` + This parameter is the pointer to an `uint32_t + <https://en.cppreference.com/w/c/types/integer>`_ object. When the + directive call is successful, the number of pending messages removed from + the queue will be stored in this object. + +.. rubric:: DESCRIPTION: + +This directive removes all pending messages from the queue specified by ``id``. +The number of messages removed is returned in ``count``. If no messages are +present on the queue, count is set to zero. + +.. rubric:: RETURN VALUES: + +:c:macro:`RTEMS_SUCCESSFUL` + The requested operation was successful. + +:c:macro:`RTEMS_INVALID_ID` + There was no queue associated with the identifier specified by ``id``. + +:c:macro:`RTEMS_INVALID_ADDRESS` + The ``count`` parameter was `NULL + <https://en.cppreference.com/w/c/types/NULL>`_. + +.. rubric:: NOTES: + +The directive does not flush tasks waiting to receive a message from the +:term:`wait queue` of the message queue. + +.. rubric:: CONSTRAINTS: + +The following constraints apply to this directive: + +* The directive may be called from within interrupt context. + +* The directive may be called from within device driver initialization context. + +* The directive may be called from within task context. + +* The directive will not cause the calling task to be preempted. + +.. Generated from spec:/rtems/message/if/buffer + +.. raw:: latex + + \clearpage + +.. index:: RTEMS_MESSAGE_QUEUE_BUFFER() + +.. _InterfaceRTEMSMESSAGEQUEUEBUFFER: + +RTEMS_MESSAGE_QUEUE_BUFFER() +---------------------------- + +Defines a structure which can be used as a message queue buffer for messages of +the specified maximum size. + +.. rubric:: CALLING SEQUENCE: + +.. code-block:: c + + RTEMS_MESSAGE_QUEUE_BUFFER( size_t maximum_message_size ); + +.. rubric:: PARAMETERS: + +``maximum_message_size`` + This parameter is the maximum message size in bytes. + +.. rubric:: NOTES: + +Use this macro to define the message buffer storage area for +:ref:`InterfaceRtemsMessageQueueConstruct`. |