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| <div class="section" id="named-message-queue-interfaces"> |
| <h1>Named Message Queue Interfaces<a class="headerlink" href="#named-message-queue-interfaces" title="Permalink to this headline">¶</a></h1> |
| <p>NuttX supports POSIX named message queues for inter-task communication. |
| Any task may send or receive messages on named message queues. Interrupt |
| handlers may send messages via named message queues.</p> |
| <blockquote> |
| <div><ul class="simple"> |
| <li><p><a class="reference internal" href="#c.mq_open" title="mq_open"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_open()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_close" title="mq_close"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_close()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_unlink" title="mq_unlink"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_unlink()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_send" title="mq_send"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_send()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_timedsend" title="mq_timedsend"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_timedsend()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_receive" title="mq_receive"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_receive()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_timedreceive" title="mq_timedreceive"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_timedreceive()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_notify" title="mq_notify"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_notify()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_setattr" title="mq_setattr"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_setattr()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.mq_getattr" title="mq_getattr"><code class="xref c c-func docutils literal notranslate"><span class="pre">mq_getattr()</span></code></a></p></li> |
| </ul> |
| </div></blockquote> |
| <dl class="c function"> |
| <dt id="c.mq_open"> |
| <a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <code class="sig-name descname"><span class="pre">mq_open</span></code><span class="sig-paren">(</span><em class="property"><span class="pre">const</span></em> <span class="pre">char</span> <span class="pre">*</span><em><span class="pre">mqName</span></em>, <span class="pre">int</span> <em><span class="pre">oflags</span></em>, <span class="pre">...</span><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_open" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Establishes a connection between a named message queue and the calling |
| task. After a successful call of mq_open(), the task can reference the |
| message queue using the address returned by the call. The message queue |
| remains usable until it is closed by a successful call to mq_close().</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqName</strong> – Name of the queue to open</p></li> |
| <li><p><strong>oflags</strong> – <p>Open flags. These may be any combination of:</p> |
| <ul> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_RDONLY</span></code>. Open for read access.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_WRONLY</span></code>. Open for write access.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_RDWR</span></code>. Open for both read & write access.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_CREAT</span></code>. Create message queue if it does not already exist.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_EXCL</span></code>. Name must not exist when opened.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code>. Don’t wait for data.</p></li> |
| </ul> |
| </p></li> |
| <li><p><strong>...</strong> – <p><strong>Optional parameters</strong>. When the O_CREAT flag is specified, |
| POSIX requires that a third and fourth parameter be supplied:</p> |
| <ul> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mode</span></code>. The mode parameter is of type mode_t. In the POSIX |
| specification, this mode value provides file permission bits for |
| the message queue. This parameter is required but not used in the |
| present implementation.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">attr</span></code>. A pointer to an mq_attr that is provided to initialize. |
| the message queue. If attr is NULL, then the messages queue is |
| created with implementation-defined default message queue |
| attributes. If attr is non-NULL, then the message queue mq_maxmsg |
| attribute is set to the corresponding value when the queue is |
| created. The mq_maxmsg attribute determines the maximum number of |
| messages that can be queued before addition attempts to send |
| messages on the message queue fail or cause the sender to block; |
| the mq_msgsize attribute determines the maximum size of a message |
| that can be sent or received. Other elements of attr are ignored |
| (i.e, set to default message queue attributes).</p></li> |
| </ul> |
| </p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p>A message queue descriptor or -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>)</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name. Differences from the full POSIX implementation include:</p> |
| <ul class="simple"> |
| <li><p>The mq_msgsize attributes determines the maximum size of a message |
| that may be sent or received. In the present implementation, this |
| maximum message size is limited at 22 bytes.</p></li> |
| </ul> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_close"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_close</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_close" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Used to indicate that the calling task is finished with the specified |
| message queued <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>. The <code class="docutils literal notranslate"><span class="pre">mq_close()</span></code> deallocates any system |
| resources allocated by the system for use by this task for its message |
| queue.</p> |
| <p>If the calling task has attached a notification request to the message |
| queue via this <code class="docutils literal notranslate"><span class="pre">mqdes</span></code> (see <code class="docutils literal notranslate"><span class="pre">mq_notify()</span></code>), this attachment will be |
| removed and the message queue is available for another task to attach |
| for notification.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p>0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>) if the message queue is closed successfully, otherwise, -1 |
| (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>).</p> |
| </dd> |
| </dl> |
| <p><strong>Assumptions/Limitations:</strong></p> |
| <blockquote> |
| <div><ul class="simple"> |
| <li><p>The behavior of a task that is blocked on either a <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> or |
| <code class="docutils literal notranslate"><span class="pre">mq_receive()</span></code> is undefined when <code class="docutils literal notranslate"><span class="pre">mq_close()</span></code> is called.</p></li> |
| <li><p>The result of using this message queue descriptor after successful |
| return from <code class="docutils literal notranslate"><span class="pre">mq_close()</span></code> is undefined.</p></li> |
| </ul> |
| </div></blockquote> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_unlink"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_unlink</span></code><span class="sig-paren">(</span><em class="property"><span class="pre">const</span></em> <span class="pre">char</span> <span class="pre">*</span><em><span class="pre">mqName</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_unlink" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Removes the message queue named by |
| “mqName.” If one or more tasks have the message queue open when |
| <code class="docutils literal notranslate"><span class="pre">mq_unlink()</span></code> is called, removal of the message queue is postponed |
| until all references to the message queue have been closed.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqName</strong> – Name of the message queue</p></li> |
| </ul> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_send"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_send</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <em class="property"><span class="pre">const</span></em> <span class="pre">void</span> <span class="pre">*</span><em><span class="pre">msg</span></em>, <a class="reference internal" href="structures.html#c.size_t" title="size_t"><span class="pre">size_t</span></a> <em><span class="pre">msglen</span></em>, <span class="pre">int</span> <em><span class="pre">prio</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_send" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Adds the specified message, <code class="docutils literal notranslate"><span class="pre">msg</span></code>, to the message queue, <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>. |
| The <code class="docutils literal notranslate"><span class="pre">msglen</span></code> parameter specifies the length of the message in bytes |
| pointed to by <code class="docutils literal notranslate"><span class="pre">msg</span></code>. This length must not exceed the maximum message |
| length from the <code class="docutils literal notranslate"><span class="pre">mq_getattr()</span></code>.</p> |
| <p>If the message queue is not full, <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> will place the <code class="docutils literal notranslate"><span class="pre">msg</span></code> |
| in the message queue at the position indicated by the <code class="docutils literal notranslate"><span class="pre">prio</span></code> argument. |
| Messages with higher priority will be inserted before lower priority |
| messages The value of <code class="docutils literal notranslate"><span class="pre">prio</span></code> must not exceed <code class="docutils literal notranslate"><span class="pre">MQ_PRIO_MAX</span></code>.</p> |
| <p>If the specified message queue is full and <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> is not set in |
| the message queue, then <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> will block until space becomes |
| available to the queue the message.</p> |
| <p>If the message queue is full and <code class="docutils literal notranslate"><span class="pre">NON_BLOCK</span></code> is set, the message is |
| not queued and <code class="docutils literal notranslate"><span class="pre">ERROR</span></code> is returned.</p> |
| <p><strong>NOTE</strong>: <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> may be called from an interrupt handler. |
| However, it behaves differently when called from the interrupt level:</p> |
| <ul class="simple"> |
| <li><p>It does not check the size of the queue. It will always post the |
| message, even if there are already too many messages in queue. This is |
| because the interrupt handler does not have the option of waiting for |
| the message queue to become non-full.</p></li> |
| <li><p>It doesn’t allocate new memory (because you cannot allocate memory |
| from an interrupt handler). Instead, there is a pool of pre-allocated |
| message structures that may be used just for sending messages from |
| interrupt handlers. The number of such pre-allocated messages is set |
| by the <code class="docutils literal notranslate"><span class="pre">PREALLOC_MQ_IRQ_MSGS</span></code> configuration parameter.</p></li> |
| </ul> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor.</p></li> |
| <li><p><strong>msg</strong> – Message to send.</p></li> |
| <li><p><strong>msglen</strong> – The length of the message in bytes.</p></li> |
| <li><p><strong>prio</strong> – The priority of the message.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><p>On success, <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> returns 0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>); on |
| error, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) is returned, with <code class="docutils literal notranslate"><span class="pre">`errno</span></code> <#ErrnoAccess>`__ set |
| to indicate the error:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EAGAIN</span></code>. The queue was empty, and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag was set |
| for the message queue description referred to by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>. Either <code class="docutils literal notranslate"><span class="pre">msg</span></code> or <code class="docutils literal notranslate"><span class="pre">mqdes</span></code> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code> or the value of |
| <code class="docutils literal notranslate"><span class="pre">prio</span></code> is invalid.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EPERM</span></code>. Message queue opened not opened for writing.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EMSGSIZE</span></code>. <code class="docutils literal notranslate"><span class="pre">msglen</span></code> was greater than the <code class="docutils literal notranslate"><span class="pre">maxmsgsize</span></code> |
| attribute of the message queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINTR</span></code>. The call was interrupted by a signal handler.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_timedsend"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_timedsend</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <em class="property"><span class="pre">const</span></em> <span class="pre">char</span> <span class="pre">*</span><em><span class="pre">msg</span></em>, <a class="reference internal" href="structures.html#c.size_t" title="size_t"><span class="pre">size_t</span></a> <em><span class="pre">msglen</span></em>, <span class="pre">int</span> <em><span class="pre">prio</span></em>, <em class="property"><span class="pre">const</span></em> <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.timespec" title="timespec"><span class="pre">timespec</span></a> <span class="pre">*</span><em><span class="pre">abstime</span></em><span class="sig-paren">)</span><span class="pre">;</span><a class="headerlink" href="#c.mq_timedsend" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Adds the specified message, <code class="docutils literal notranslate"><span class="pre">msg</span></code>, to the message queue, <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>. |
| The <code class="docutils literal notranslate"><span class="pre">msglen</span></code> parameter specifies the length of the message in bytes |
| pointed to by <code class="docutils literal notranslate"><span class="pre">msg</span></code>. This length must not exceed the maximum message |
| length from the <code class="docutils literal notranslate"><span class="pre">mq_getattr()</span></code>.</p> |
| <p>If the message queue is not full, <code class="docutils literal notranslate"><span class="pre">mq_timedsend()</span></code> will place the |
| <code class="docutils literal notranslate"><span class="pre">msg</span></code> in the message queue at the position indicated by the <code class="docutils literal notranslate"><span class="pre">prio</span></code> |
| argument. Messages with higher priority will be inserted before lower |
| priority messages The value of <code class="docutils literal notranslate"><span class="pre">prio</span></code> must not exceed <code class="docutils literal notranslate"><span class="pre">MQ_PRIO_MAX</span></code>.</p> |
| <p>If the specified message queue is full and <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> is not set in |
| the message queue, then <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> will block until space becomes |
| available to the queue the message or until a timeout occurs.</p> |
| <p><code class="docutils literal notranslate"><span class="pre">mq_timedsend()</span></code> behaves just like <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code>, except that if the |
| queue is full and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag is not enabled for the message |
| queue description, then <code class="docutils literal notranslate"><span class="pre">abstime</span></code> points to a structure which |
| specifies a ceiling on the time for which the call will block. This |
| ceiling is an absolute timeout in seconds and nanoseconds since the |
| Epoch (midnight on the morning of 1 January 1970).</p> |
| <p>If the message queue is full, and the timeout has already expired by the |
| time of the call, <code class="docutils literal notranslate"><span class="pre">mq_timedsend()</span></code> returns immediately.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor.</p></li> |
| <li><p><strong>msg</strong> – Message to send.</p></li> |
| <li><p><strong>msglen</strong> – The length of the message in bytes.</p></li> |
| <li><p><strong>prio</strong> – The priority of the message.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><p>On success, <code class="docutils literal notranslate"><span class="pre">mq_send()</span></code> returns 0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>); on |
| error, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) is returned, with <code class="docutils literal notranslate"><span class="pre">`errno</span></code> <#ErrnoAccess>`__ set |
| to indicate the error:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EAGAIN</span></code>. The queue was empty, and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag was set |
| for the message queue description referred to by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>. Either <code class="docutils literal notranslate"><span class="pre">msg</span></code> or <code class="docutils literal notranslate"><span class="pre">mqdes</span></code> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code> or the value of |
| <code class="docutils literal notranslate"><span class="pre">prio</span></code> is invalid.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EPERM</span></code>. Message queue opened not opened for writing.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EMSGSIZE</span></code>. <code class="docutils literal notranslate"><span class="pre">msglen</span></code> was greater than the <code class="docutils literal notranslate"><span class="pre">maxmsgsize</span></code> |
| attribute of the message queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINTR</span></code>. The call was interrupted by a signal handler.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_receive"> |
| <span class="pre">ssize_t</span> <code class="sig-name descname"><span class="pre">mq_receive</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <span class="pre">void</span> <span class="pre">*</span><em><span class="pre">msg</span></em>, <a class="reference internal" href="structures.html#c.size_t" title="size_t"><span class="pre">size_t</span></a> <em><span class="pre">msglen</span></em>, <span class="pre">int</span> <span class="pre">*</span><em><span class="pre">prio</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_receive" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Receives the oldest of the highest priority messages from the message |
| queue specified by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>. If the size of the buffer in bytes, |
| <code class="docutils literal notranslate"><span class="pre">msgLen</span></code>, is less than the <code class="docutils literal notranslate"><span class="pre">mq_msgsize</span></code> attribute of the message |
| queue, <code class="docutils literal notranslate"><span class="pre">mq_receive()</span></code> will return an error. Otherwise, the selected |
| message is removed from the queue and copied to <code class="docutils literal notranslate"><span class="pre">msg</span></code>.</p> |
| <p>If the message queue is empty and <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> was not set, |
| <code class="docutils literal notranslate"><span class="pre">mq_receive()</span></code> will block until a message is added to the message |
| queue. If more than one task is waiting to receive a message, only the |
| task with the highest priority that has waited the longest will be |
| unblocked.</p> |
| <p>If the queue is empty and <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> is set, <code class="docutils literal notranslate"><span class="pre">ERROR</span></code> will be |
| returned.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message Queue Descriptor.</p></li> |
| <li><p><strong>msg</strong> – Buffer to receive the message.</p></li> |
| <li><p><strong>msglen</strong> – Size of the buffer in bytes.</p></li> |
| <li><p><strong>prio</strong> – If not NULL, the location to store message priority.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><p>On success, the length of the selected message in bytes is |
| returned. On failure, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) is returned and the |
| <code class="docutils literal notranslate"><span class="pre">`errno</span></code> <#ErrnoAccess>`__ is set appropriately:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EAGAIN</span></code> The queue was empty and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag was set |
| for the message queue description referred to by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EPERM</span></code> Message queue opened not opened for reading.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EMSGSIZE</span></code> <code class="docutils literal notranslate"><span class="pre">msglen</span></code> was less than the <code class="docutils literal notranslate"><span class="pre">maxmsgsize</span></code> attribute of |
| the message queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINTR</span></code> The call was interrupted by a signal handler.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code> Invalid <code class="docutils literal notranslate"><span class="pre">msg</span></code> or <code class="docutils literal notranslate"><span class="pre">mqdes</span></code></p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_timedreceive"> |
| <span class="pre">ssize_t</span> <code class="sig-name descname"><span class="pre">mq_timedreceive</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <span class="pre">void</span> <span class="pre">*</span><em><span class="pre">msg</span></em>, <a class="reference internal" href="structures.html#c.size_t" title="size_t"><span class="pre">size_t</span></a> <em><span class="pre">msglen</span></em>, <span class="pre">int</span> <span class="pre">*</span><em><span class="pre">prio</span></em>, <em class="property"><span class="pre">const</span></em> <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.timespec" title="timespec"><span class="pre">timespec</span></a> <span class="pre">*</span><em><span class="pre">abstime</span></em><span class="sig-paren">)</span><span class="pre">;</span><a class="headerlink" href="#c.mq_timedreceive" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Receives the oldest of the highest priority messages from the message |
| queue specified by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>. If the size of the buffer in bytes, |
| <code class="docutils literal notranslate"><span class="pre">msgLen</span></code>, is less than the <code class="docutils literal notranslate"><span class="pre">mq_msgsize</span></code> attribute of the message |
| queue, <code class="docutils literal notranslate"><span class="pre">mq_timedreceive()</span></code> will return an error. Otherwise, the |
| selected message is removed from the queue and copied to <code class="docutils literal notranslate"><span class="pre">msg</span></code>.</p> |
| <p>If the message queue is empty and <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> was not set, |
| <code class="docutils literal notranslate"><span class="pre">mq_timedreceive()</span></code> will block until a message is added to the message |
| queue (or until a timeout occurs). If more than one task is waiting to |
| receive a message, only the task with the highest priority that has |
| waited the longest will be unblocked.</p> |
| <p><code class="docutils literal notranslate"><span class="pre">mq_timedreceive()</span></code> behaves just like <code class="docutils literal notranslate"><span class="pre">mq_receive()</span></code>, except that if |
| the queue is empty and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag is not enabled for the |
| message queue description, then <code class="docutils literal notranslate"><span class="pre">abstime</span></code> points to a structure which |
| specifies a ceiling on the time for which the call will block. This |
| ceiling is an absolute timeout in seconds and nanoseconds since the |
| Epoch (midnight on the morning of 1 January 1970).</p> |
| <p>If no message is available, and the timeout has already expired by the |
| time of the call, <code class="docutils literal notranslate"><span class="pre">mq_timedreceive()</span></code> returns immediately.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message Queue Descriptor.</p></li> |
| <li><p><strong>msg</strong> – Buffer to receive the message.</p></li> |
| <li><p><strong>msglen</strong> – Size of the buffer in bytes.</p></li> |
| <li><p><strong>prio</strong> – If not NULL, the location to store message priority.</p></li> |
| <li><p><strong>abstime</strong> – The absolute time to wait until a timeout is declared.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><p>On success, the length of the selected message in bytes is |
| returned. On failure, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) is returned and the |
| <code class="docutils literal notranslate"><span class="pre">`errno</span></code> <#ErrnoAccess>`__ is set appropriately:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EAGAIN</span></code>: The queue was empty and the <code class="docutils literal notranslate"><span class="pre">O_NONBLOCK</span></code> flag was set |
| for the message queue description referred to by <code class="docutils literal notranslate"><span class="pre">mqdes</span></code>.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EPERM</span></code>: Message queue opened not opened for reading.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EMSGSIZE</span></code>: <code class="docutils literal notranslate"><span class="pre">msglen</span></code> was less than the <code class="docutils literal notranslate"><span class="pre">maxmsgsize</span></code> attribute |
| of the message queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINTR</span></code>: The call was interrupted by a signal handler.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>: Invalid <code class="docutils literal notranslate"><span class="pre">msg</span></code> or <code class="docutils literal notranslate"><span class="pre">mqdes</span></code> or <code class="docutils literal notranslate"><span class="pre">abstime</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ETIMEDOUT</span></code>: The call timed out before a message could be |
| transferred.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_notify"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_notify</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <span class="pre">FAR</span> <em class="property"><span class="pre">const</span></em> <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.sigevent" title="sigevent"><span class="pre">sigevent</span></a> <span class="pre">*</span><em><span class="pre">notification</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_notify" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>If the <code class="docutils literal notranslate"><span class="pre">notification</span></code> input parameter is not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, this function |
| connects the task with the message queue such that the specified signal |
| will be sent to the task whenever the message queue changes from empty |
| to non-empty. One notification can be attached to a message queue.</p> |
| <p>If <code class="docutils literal notranslate"><span class="pre">notification</span></code>; is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the attached notification is detached |
| (if it was held by the calling task) and the queue is available to |
| attach another notification.</p> |
| <p>When the notification is sent to the registered task, its registration |
| will be removed. The message queue will then be available for |
| registration.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor</p></li> |
| <li><p><strong>notification</strong> – <p>Real-time signal structure containing:</p> |
| <ul> |
| <li><p><code class="docutils literal notranslate"><span class="pre">sigev_notify</span></code>. Should be SIGEV_SIGNAL (but actually ignored)</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">sigev_signo</span></code>. The signo to use for the notification</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">sigev_value</span></code>. Value associated with the signal</p></li> |
| </ul> |
| </p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><p>On success <code class="docutils literal notranslate"><span class="pre">mq_notify()</span></code> returns 0; on error, -1 |
| is returned, with <code class="docutils literal notranslate"><span class="pre">errno</span></code> set to indicate the error:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EBADF</span></code>. The descriptor specified in <code class="docutils literal notranslate"><span class="pre">mqdes</span></code> is invalid.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EBUSY</span></code>. Another process has already registered to receive |
| notification for this message queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>. <code class="docutils literal notranslate"><span class="pre">sevp->sigev_notify</span></code> is not one of the permitted |
| values; or <code class="docutils literal notranslate"><span class="pre">sevp->sigev_notify</span></code> is <code class="docutils literal notranslate"><span class="pre">SIGEV_SIGNAL</span></code> and |
| <code class="docutils literal notranslate"><span class="pre">sevp->sigev_signo</span></code> is not a valid signal number.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ENOMEM</span></code>. Insufficient memory.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name. Differences from the full POSIX implementation include:</p> |
| <ul class="simple"> |
| <li><p>The notification signal will be sent to the registered task even if |
| another task is waiting for the message queue to become non-empty. |
| This is inconsistent with the POSIX specification which states, “If a |
| process has registered for notification of message arrival at a |
| message queue and some process is blocked in <code class="docutils literal notranslate"><span class="pre">mq_receive</span></code> waiting |
| to receive a message when a message arrives at the queue, the |
| arriving message will satisfy the appropriate <code class="docutils literal notranslate"><span class="pre">mq_receive()</span></code> … |
| The resulting behavior is as if the message queue remains empty, and |
| no notification will be sent.”</p></li> |
| </ul> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_setattr"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_setattr</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <em class="property"><span class="pre">const</span></em> <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.mq_attr" title="mq_attr"><span class="pre">mq_attr</span></a> <span class="pre">*</span><em><span class="pre">mqStat</span></em>, <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.mq_attr" title="mq_attr"><span class="pre">mq_attr</span></a> <span class="pre">*</span><em><span class="pre">oldMqStat</span></em><span class="sig-paren">)</span><span class="pre">;</span><a class="headerlink" href="#c.mq_setattr" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Sets the attributes associated with the specified message queue “mqdes.” |
| Only the “O_NONBLOCK” bit of the “mq_flags” can be changed.</p> |
| <p>If <code class="docutils literal notranslate"><span class="pre">oldMqStat</span></code> is non-null, mq_setattr() will store the previous message |
| queue attributes at that location (just as would have been returned by |
| mq_getattr()).</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor</p></li> |
| <li><p><strong>mqStat</strong> – New attributes</p></li> |
| <li><p><strong>oldMqState</strong> – Old attributes</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p>0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>) if attributes are set successfully, otherwise -1 |
| (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>).</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.mq_getattr"> |
| <span class="pre">int</span> <code class="sig-name descname"><span class="pre">mq_getattr</span></code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.mqd_t" title="mqd_t"><span class="pre">mqd_t</span></a> <em><span class="pre">mqdes</span></em>, <em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="structures.html#c.mq_attr" title="mq_attr"><span class="pre">mq_attr</span></a> <span class="pre">*</span><em><span class="pre">mqStat</span></em><span class="sig-paren">)</span><a class="headerlink" href="#c.mq_getattr" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Gets status information and attributes associated with the specified |
| message queue.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>mqdes</strong> – Message queue descriptor</p></li> |
| <li><p><strong>mqStat</strong> – <p>Buffer in which to return attributes. The returned |
| attributes include:</p> |
| <ul> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mq_maxmsg</span></code>. Max number of messages in queue.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mq_msgsize</span></code>. Max message size.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mq_flags</span></code>. Queue flags.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mq_curmsgs</span></code>. Number of messages currently in queue.</p></li> |
| </ul> |
| </p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p>0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>) if attributes provided, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) otherwise.</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
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