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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Xenomai API: Message queues services.</title>
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<h1>Message queues services.<br>
<small>
[<a class="el" href="group__posix.html">POSIX skin.</a>]</small>
</h1>
<p>
<div class="dynheader">
Collaboration diagram for Message queues services.:</div>
<div class="dynsection">
<center><table><tr><td><img src="group__posix__mq.png" border="0" alt="" usemap="#group____posix____mq_map">
<map name="group____posix____mq_map">
<area shape="rect" href="group__posix.html" title="Xenomai POSIX skin is an implementation of a small subset of the Single Unix specification..." alt="" coords="7,5,100,32"></map></td></tr></table></center>
</div>
<hr><a name="_details"></a><h2>Detailed Description</h2>
Message queues services.
<p>
A message queue allow exchanging data between real-time threads. For a POSIX message queue, maximum message length and maximum number of messages are fixed when it is created with <a class="el" href="group__posix__mq.html#g6e6c4881ac0fd3ad18d733b96d088b8b" title="Open a message queue.">mq_open()</a>.
<p>
<table border="0" cellpadding="0" cellspacing="0">
<tr><td></td></tr>
<tr><td colspan="2"><br><h2>Functions</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">mqd_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#g6e6c4881ac0fd3ad18d733b96d088b8b">mq_open</a> (const char *name, int oflags,...)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Open a message queue. <a href="#g6e6c4881ac0fd3ad18d733b96d088b8b"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#g14a1dc0204a7f84bb4e8a1813a70af49">mq_close</a> (mqd_t fd)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Close a message queue. <a href="#g14a1dc0204a7f84bb4e8a1813a70af49"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#gccd8c5ee36e60d990963e1d544ef4140">mq_unlink</a> (const char *name)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Unlink a message queue. <a href="#gccd8c5ee36e60d990963e1d544ef4140"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#ge3d8e022fcc1114c0cd4b30ccd1f15e4">mq_send</a> (mqd_t fd, const char *buffer, size_t len, unsigned prio)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Send a message to a message queue. <a href="#ge3d8e022fcc1114c0cd4b30ccd1f15e4"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#gcf2baf29d0ad8c7c49bc42793c36f0a2">mq_timedsend</a> (mqd_t fd, const char *buffer, size_t len, unsigned prio, const struct timespec *abs_timeout)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Attempt, during a bounded time, to send a message to a message queue. <a href="#gcf2baf29d0ad8c7c49bc42793c36f0a2"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">ssize_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#g6370a6bb8f2b87e52ec4fcf340939128">mq_receive</a> (mqd_t fd, char *buffer, size_t len, unsigned *priop)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Receive a message from a message queue. <a href="#g6370a6bb8f2b87e52ec4fcf340939128"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">ssize_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#g5e82a3bba3003f84bccb615adcba1f57">mq_timedreceive</a> (mqd_t fd, char *__restrict__ buffer, size_t len, unsigned *__restrict__ priop, const struct timespec *__restrict__ abs_timeout)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Attempt, during a bounded time, to receive a message from a message queue. <a href="#g5e82a3bba3003f84bccb615adcba1f57"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#gccb588f0005137d7b4db3cff0fb7f7fe">mq_getattr</a> (mqd_t fd, struct mq_attr *attr)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Get the attributes object of a message queue. <a href="#gccb588f0005137d7b4db3cff0fb7f7fe"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#gb7670280d7cf1753b1448fb3ad61befc">mq_setattr</a> (mqd_t fd, const struct mq_attr *__restrict__ attr, struct mq_attr *__restrict__ oattr)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Set flags of a message queue. <a href="#gb7670280d7cf1753b1448fb3ad61befc"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__mq.html#g346fbeb512b59ecf90be445718724936">mq_notify</a> (mqd_t fd, const struct sigevent *evp)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Register the current thread to be notified of message arrival at an empty message queue. <a href="#g346fbeb512b59ecf90be445718724936"></a><br></td></tr>
</table>
<hr><h2>Function Documentation</h2>
<a class="anchor" name="g14a1dc0204a7f84bb4e8a1813a70af49"></a><!-- doxytag: member="mq.c::mq_close" ref="g14a1dc0204a7f84bb4e8a1813a70af49" args="(mqd_t fd)" -->
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<td class="memname">int mq_close </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em> </td>
<td> ) </td>
<td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Close a message queue.
<p>
This service closes the message queue descriptor <em>fd</em>. The message queue is destroyed only when all open descriptors are closed, and when unlinked with a call to the <a class="el" href="group__posix__mq.html#gccd8c5ee36e60d990963e1d544ef4140" title="Unlink a message queue.">mq_unlink()</a> service.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor.</td></tr>
</table>
</dl>
<dl compact><dt><b>Return values:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>0</em> </td><td>on success; </td></tr>
<tr><td valign="top"></td><td valign="top"><em>-1</em> </td><td>with <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is an invalid message queue descriptor;</li><li>EPERM, the caller context is invalid.</li></ul>
</td></tr>
</table>
</dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>kernel module initialization or cleanup routine;</li><li>kernel-space cancellation cleanup routine;</li><li>user-space thread (Xenomai threads switch to secondary mode);</li><li>user-space cancellation cleanup routine.</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_close.html">Specification.</a> </dd></dl>
<dl compact><dt><b>Examples: </b></dt><dd>
<a class="el" href="rtcan__rtt_8c-example.html#a8">rtcan_rtt.c</a>.</dl>
</div>
</div><p>
<a class="anchor" name="gccb588f0005137d7b4db3cff0fb7f7fe"></a><!-- doxytag: member="mq.c::mq_getattr" ref="gccb588f0005137d7b4db3cff0fb7f7fe" args="(mqd_t fd, struct mq_attr *attr)" -->
<div class="memitem">
<div class="memproto">
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<td class="memname">int mq_getattr </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">struct mq_attr * </td>
<td class="paramname"> <em>attr</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Get the attributes object of a message queue.
<p>
This service stores, at the address <em>attr</em>, the attributes of the messages queue descriptor <em>fd</em>.<p>
The following attributes are set:<ul>
<li><em>mq_flags</em>, flags of the message queue descriptor <em>fd</em>;</li><li><em>mq_maxmsg</em>, maximum number of messages in the message queue;</li><li><em>mq_msgsize</em>, maximum message size;</li><li><em>mq_curmsgs</em>, number of messages currently in the queue.</li></ul>
<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>attr</em> </td><td>address where the message queue attributes will be stored on success.</td></tr>
</table>
</dl>
<dl compact><dt><b>Return values:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>0</em> </td><td>on success; </td></tr>
<tr><td valign="top"></td><td valign="top"><em>-1</em> </td><td>with <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid descriptor.</li></ul>
</td></tr>
</table>
</dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_getattr.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="g346fbeb512b59ecf90be445718724936"></a><!-- doxytag: member="mq.c::mq_notify" ref="g346fbeb512b59ecf90be445718724936" args="(mqd_t fd, const struct sigevent *evp)" -->
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<td class="memname">int mq_notify </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const struct sigevent * </td>
<td class="paramname"> <em>evp</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Register the current thread to be notified of message arrival at an empty message queue.
<p>
If <em>evp</em> is not <em>NULL</em> and is the address of a <b>sigevent</b> structure with the <em>sigev_notify</em> member set to SIGEV_SIGNAL, the current thread will be notified by a signal when a message is sent to the message queue <em>fd</em>, the queue is empty, and no thread is blocked in call to <a class="el" href="group__posix__mq.html#g6370a6bb8f2b87e52ec4fcf340939128" title="Receive a message from a message queue.">mq_receive()</a> or <a class="el" href="group__posix__mq.html#g5e82a3bba3003f84bccb615adcba1f57" title="Attempt, during a bounded time, to receive a message from a message queue.">mq_timedreceive()</a>. After the notification, the thread is unregistered.<p>
If <em>evp</em> is <em>NULL</em> or the <em>sigev_notify</em> member is SIGEV_NONE, the current thread is unregistered.<p>
Only one thread may be registered at a time.<p>
If the current thread is not a Xenomai POSIX skin thread (created with <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a>), this service fails.<p>
Note that signals sent to user-space Xenomai POSIX skin threads will cause them to switch to secondary mode.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>evp</em> </td><td>pointer to an event notification structure.</td></tr>
</table>
</dl>
<dl compact><dt><b>Return values:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>0</em> </td><td>on success; </td></tr>
<tr><td valign="top"></td><td valign="top"><em>-1</em> </td><td>with <em>errno</em> set if:<ul>
<li>EINVAL, <em>evp</em> is invalid;</li><li>EPERM, the caller context is invalid;</li><li>EBADF, <em>fd</em> is not a valid message queue descriptor;</li><li>EBUSY, another thread is already registered.</li></ul>
</td></tr>
</table>
</dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai kernel-space POSIX skin thread,</li><li>Xenomai user-space POSIX skin thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_notify.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="g6e6c4881ac0fd3ad18d733b96d088b8b"></a><!-- doxytag: member="mq.c::mq_open" ref="g6e6c4881ac0fd3ad18d733b96d088b8b" args="(const char *name, int oflags,...)" -->
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<td class="memname">mqd_t mq_open </td>
<td>(</td>
<td class="paramtype">const char * </td>
<td class="paramname"> <em>name</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>oflags</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype"> </td>
<td class="paramname"> <em>...</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Open a message queue.
<p>
This service establishes a connection between the message queue named <em>name</em> and the calling context (kernel-space as a whole, or user-space process).<p>
One of the following values should be set in <em>oflags:</em> <ul>
<li>O_RDONLY, meaning that the returned queue descriptor may only be used for receiving messages;</li><li>O_WRONLY, meaning that the returned queue descriptor may only be used for sending messages;</li><li>O_RDWR, meaning that the returned queue descriptor may be used for both sending and receiving messages.</li></ul>
<p>
If no message queue named <em>name</em> exists, and <em>oflags</em> has the <em>O_CREAT</em> bit set, the message queue is created by this function, taking two more arguments:<ul>
<li>a <em>mode</em> argument, of type <b>mode_t</b>, currently ignored;</li><li>an <em>attr</em> argument, pointer to an <b>mq_attr</b> structure, specifying the attributes of the new message queue.</li></ul>
<p>
If <em>oflags</em> has the two bits <em>O_CREAT</em> and <em>O_EXCL</em> set and the message queue alread exists, this service fails.<p>
If the O_NONBLOCK bit is set in <em>oflags</em>, the <a class="el" href="group__posix__mq.html#ge3d8e022fcc1114c0cd4b30ccd1f15e4" title="Send a message to a message queue.">mq_send()</a>, <a class="el" href="group__posix__mq.html#g6370a6bb8f2b87e52ec4fcf340939128" title="Receive a message from a message queue.">mq_receive()</a>, <a class="el" href="group__posix__mq.html#gcf2baf29d0ad8c7c49bc42793c36f0a2" title="Attempt, during a bounded time, to send a message to a message queue.">mq_timedsend()</a> and <a class="el" href="group__posix__mq.html#g5e82a3bba3003f84bccb615adcba1f57" title="Attempt, during a bounded time, to receive a message from a message queue.">mq_timedreceive()</a> services return <em>-1</em> with <em>errno</em> set to EAGAIN instead of blocking their caller.<p>
The following arguments of the <b>mq_attr</b> structure at the address <em>attr</em> are used when creating a message queue:<ul>
<li><em>mq_maxmsg</em> is the maximum number of messages in the queue (128 by default);</li><li><em>mq_msgsize</em> is the maximum size of each message (128 by default).</li></ul>
<p>
<em>name</em> may be any arbitrary string, in which slashes have no particular meaning. However, for portability, using a name which starts with a slash and contains no other slash is recommended.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>name</em> </td><td>name of the message queue to open;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>oflags</em> </td><td>flags.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>a message queue descriptor on success; <p>
-1 with <em>errno</em> set if:<ul>
<li>ENAMETOOLONG, the length of the <em>name</em> argument exceeds 64 characters;</li><li>EEXIST, the bits <em>O_CREAT</em> and <em>O_EXCL</em> were set in <em>oflags</em> and the message queue already exists;</li><li>ENOENT, the bit <em>O_CREAT</em> is not set in <em>oflags</em> and the message queue does not exist;</li><li>ENOSPC, allocation of system memory failed, or insufficient memory exists in the system heap to create the queue, try increasing CONFIG_XENO_OPT_SYS_HEAPSZ;</li><li>EPERM, attempting to create a message queue from an invalid context;</li><li>EINVAL, the <em>attr</em> argument is invalid;</li><li>EMFILE, too many descriptors are currently open.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd>When creating a message queue, only the following contexts are valid:<ul>
<li>kernel module initialization or cleanup routine;</li><li>user-space thread (Xenomai threads switch to secondary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_open.html">Specification.</a> </dd></dl>
<dl compact><dt><b>Examples: </b></dt><dd>
<a class="el" href="rtcan__rtt_8c-example.html#a17">rtcan_rtt.c</a>.</dl>
</div>
</div><p>
<a class="anchor" name="g6370a6bb8f2b87e52ec4fcf340939128"></a><!-- doxytag: member="mq.c::mq_receive" ref="g6370a6bb8f2b87e52ec4fcf340939128" args="(mqd_t fd, char *buffer, size_t len, unsigned *priop)" -->
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<td class="memname">ssize_t mq_receive </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">char * </td>
<td class="paramname"> <em>buffer</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">size_t </td>
<td class="paramname"> <em>len</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned * </td>
<td class="paramname"> <em>priop</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Receive a message from a message queue.
<p>
If the message queue <em>fd</em> is not empty and if <em>len</em> is greater than the <em>mq_msgsize</em> of the message queue, this service copies, at the address <em>buffer</em>, the queued message with the highest priority.<p>
If the queue is empty and the flag <em>O_NONBLOCK</em> is not set for the descriptor <em>fd</em>, the calling thread is suspended until some message is sent to the queue. If the queue is empty and the flag <em>O_NONBLOCK</em> is set for the descriptor <em>fd</em>, this service returns immediately a value of -1 with <em>errno</em> set to EAGAIN.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>the queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>buffer</em> </td><td>the address where the received message will be stored on success;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>len</em> </td><td><em>buffer</em> length;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>priop</em> </td><td>address where the priority of the received message will be stored on success.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>the message length, and copy a message at the address <em>buffer</em> on success; <p>
-1 with no message unqueued and <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid descriptor open for reading;</li><li>EMSGSIZE, the length <em>len</em> is lesser than the message queue <em>mq_msgsize</em> attribute;</li><li>EAGAIN, the queue is empty, and the flag <em>O_NONBLOCK</em> is set for the descriptor <em>fd</em>;</li><li>EPERM, the caller context is invalid;</li><li>EINTR, the service was interrupted by a signal.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai kernel-space thread,</li><li>Xenomai user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_receive.html">Specification.</a> </dd></dl>
<dl compact><dt><b>Examples: </b></dt><dd>
<a class="el" href="rtcan__rtt_8c-example.html#a22">rtcan_rtt.c</a>.</dl>
</div>
</div><p>
<a class="anchor" name="ge3d8e022fcc1114c0cd4b30ccd1f15e4"></a><!-- doxytag: member="mq.c::mq_send" ref="ge3d8e022fcc1114c0cd4b30ccd1f15e4" args="(mqd_t fd, const char *buffer, size_t len, unsigned prio)" -->
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<td class="memname">int mq_send </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const char * </td>
<td class="paramname"> <em>buffer</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">size_t </td>
<td class="paramname"> <em>len</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned </td>
<td class="paramname"> <em>prio</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Send a message to a message queue.
<p>
If the message queue <em>fd</em> is not full, this service sends the message of length <em>len</em> pointed to by the argument <em>buffer</em>, with priority <em>prio</em>. A message with greater priority is inserted in the queue before a message with lower priority.<p>
If the message queue is full and the flag <em>O_NONBLOCK</em> is not set, the calling thread is suspended until the queue is not full. If the message queue is full and the flag <em>O_NONBLOCK</em> is set, the message is not sent and the service returns immediately a value of -1 with <em>errno</em> set to EAGAIN.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>buffer</em> </td><td>pointer to the message to be sent;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>len</em> </td><td>length of the message;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>prio</em> </td><td>priority of the message.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 and send a message on success; <p>
-1 with no message sent and <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid message queue descriptor open for writing;</li><li>EMSGSIZE, the message length <em>len</em> exceeds the <em>mq_msgsize</em> attribute of the message queue;</li><li>EAGAIN, the flag O_NONBLOCK is set for the descriptor <em>fd</em> and the message queue is full;</li><li>EPERM, the caller context is invalid;</li><li>EINTR, the service was interrupted by a signal.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai kernel-space thread,</li><li>Xenomai user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_send.html">Specification.</a> </dd></dl>
<dl compact><dt><b>Examples: </b></dt><dd>
<a class="el" href="rtcan__rtt_8c-example.html#a7">rtcan_rtt.c</a>.</dl>
</div>
</div><p>
<a class="anchor" name="gb7670280d7cf1753b1448fb3ad61befc"></a><!-- doxytag: member="mq.c::mq_setattr" ref="gb7670280d7cf1753b1448fb3ad61befc" args="(mqd_t fd, const struct mq_attr *__restrict__ attr, struct mq_attr *__restrict__ oattr)" -->
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<td class="memname">int mq_setattr </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const struct mq_attr *__restrict__ </td>
<td class="paramname"> <em>attr</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">struct mq_attr *__restrict__ </td>
<td class="paramname"> <em>oattr</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Set flags of a message queue.
<p>
This service sets the flags of the <em>fd</em> descriptor to the value of the member <em>mq_flags</em> of the <b>mq_attr</b> structure pointed to by <em>attr</em>.<p>
The previous value of the message queue attributes are stored at the address <em>oattr</em> if it is not <em>NULL</em>.<p>
Only setting or clearing the O_NONBLOCK flag has an effect.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>attr</em> </td><td>pointer to new attributes (only <em>mq_flags</em> is used);</td></tr>
<tr><td valign="top"></td><td valign="top"><em>oattr</em> </td><td>if not <em>NULL</em>, address where previous message queue attributes will be stored on success.</td></tr>
</table>
</dl>
<dl compact><dt><b>Return values:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>0</em> </td><td>on success; </td></tr>
<tr><td valign="top"></td><td valign="top"><em>-1</em> </td><td>with <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid message queue descriptor.</li></ul>
</td></tr>
</table>
</dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_setattr.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="g5e82a3bba3003f84bccb615adcba1f57"></a><!-- doxytag: member="mq.c::mq_timedreceive" ref="g5e82a3bba3003f84bccb615adcba1f57" args="(mqd_t fd, char *__restrict__ buffer, size_t len, unsigned *__restrict__ priop, const struct timespec *__restrict__ abs_timeout)" -->
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<td class="memname">ssize_t mq_timedreceive </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">char *__restrict__ </td>
<td class="paramname"> <em>buffer</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">size_t </td>
<td class="paramname"> <em>len</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned *__restrict__ </td>
<td class="paramname"> <em>priop</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const struct timespec *__restrict__ </td>
<td class="paramname"> <em>abs_timeout</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Attempt, during a bounded time, to receive a message from a message queue.
<p>
This service is equivalent to <a class="el" href="group__posix__mq.html#g6370a6bb8f2b87e52ec4fcf340939128" title="Receive a message from a message queue.">mq_receive()</a>, except that if the flag <em>O_NONBLOCK</em> is not set for the descriptor <em>fd</em> and the message queue is empty, the calling thread is only suspended until the timeout <em>abs_timeout</em> expires.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>the queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>buffer</em> </td><td>the address where the received message will be stored on success;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>len</em> </td><td><em>buffer</em> length;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>priop</em> </td><td>address where the priority of the received message will be stored on success.</td></tr>
<tr><td valign="top"></td><td valign="top"><em>abs_timeout</em> </td><td>the timeout, expressed as an absolute value of the CLOCK_REALTIME clock.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>the message length, and copy a message at the address <em>buffer</em> on success; <p>
-1 with no message unqueued and <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid descriptor open for reading;</li><li>EMSGSIZE, the length <em>len</em> is lesser than the message queue <em>mq_msgsize</em> attribute;</li><li>EAGAIN, the queue is empty, and the flag <em>O_NONBLOCK</em> is set for the descriptor <em>fd</em>;</li><li>EPERM, the caller context is invalid;</li><li>EINTR, the service was interrupted by a signal;</li><li>ETIMEDOUT, the specified timeout expired.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai kernel-space thread,</li><li>Xenomai user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_timedreceive.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="gcf2baf29d0ad8c7c49bc42793c36f0a2"></a><!-- doxytag: member="mq.c::mq_timedsend" ref="gcf2baf29d0ad8c7c49bc42793c36f0a2" args="(mqd_t fd, const char *buffer, size_t len, unsigned prio, const struct timespec *abs_timeout)" -->
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<td class="memname">int mq_timedsend </td>
<td>(</td>
<td class="paramtype">mqd_t </td>
<td class="paramname"> <em>fd</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const char * </td>
<td class="paramname"> <em>buffer</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">size_t </td>
<td class="paramname"> <em>len</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned </td>
<td class="paramname"> <em>prio</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const struct timespec * </td>
<td class="paramname"> <em>abs_timeout</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Attempt, during a bounded time, to send a message to a message queue.
<p>
This service is equivalent to <a class="el" href="group__posix__mq.html#ge3d8e022fcc1114c0cd4b30ccd1f15e4" title="Send a message to a message queue.">mq_send()</a>, except that if the message queue is full and the flag <em>O_NONBLOCK</em> is not set for the descriptor <em>fd</em>, the calling thread is only suspended until the timeout specified by <em>abs_timeout</em> expires.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>fd</em> </td><td>message queue descriptor;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>buffer</em> </td><td>pointer to the message to be sent;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>len</em> </td><td>length of the message;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>prio</em> </td><td>priority of the message;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>abs_timeout</em> </td><td>the timeout, expressed as an absolute value of the CLOCK_REALTIME clock.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 and send a message on success; <p>
-1 with no message sent and <em>errno</em> set if:<ul>
<li>EBADF, <em>fd</em> is not a valid message queue descriptor open for writing;</li><li>EMSGSIZE, the message length exceeds the <em>mq_msgsize</em> attribute of the message queue;</li><li>EAGAIN, the flag O_NONBLOCK is set for the descriptor <em>fd</em> and the message queue is full;</li><li>EPERM, the caller context is invalid;</li><li>ETIMEDOUT, the specified timeout expired;</li><li>EINTR, the service was interrupted by a signal.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai kernel-space thread,</li><li>Xenomai user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_timedsend.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="gccd8c5ee36e60d990963e1d544ef4140"></a><!-- doxytag: member="mq.c::mq_unlink" ref="gccd8c5ee36e60d990963e1d544ef4140" args="(const char *name)" -->
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<td class="memname">int mq_unlink </td>
<td>(</td>
<td class="paramtype">const char * </td>
<td class="paramname"> <em>name</em> </td>
<td> ) </td>
<td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Unlink a message queue.
<p>
This service unlinks the message queue named <em>name</em>. The message queue is not destroyed until all queue descriptors obtained with the <a class="el" href="group__posix__mq.html#g6e6c4881ac0fd3ad18d733b96d088b8b" title="Open a message queue.">mq_open()</a> service are closed with the <a class="el" href="group__posix__mq.html#g14a1dc0204a7f84bb4e8a1813a70af49" title="Close a message queue.">mq_close()</a> service. However, after a call to this service, the unlinked queue may no longer be reached with the <a class="el" href="group__posix__mq.html#g6e6c4881ac0fd3ad18d733b96d088b8b" title="Open a message queue.">mq_open()</a> service.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>name</em> </td><td>name of the message queue to be unlinked.</td></tr>
</table>
</dl>
<dl compact><dt><b>Return values:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>0</em> </td><td>on success; </td></tr>
<tr><td valign="top"></td><td valign="top"><em>-1</em> </td><td>with <em>errno</em> set if:<ul>
<li>EPERM, the caller context is invalid;</li><li>ENAMETOOLONG, the length of the <em>name</em> argument exceeds 64 characters;</li><li>ENOENT, the message queue does not exist.</li></ul>
</td></tr>
</table>
</dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>kernel module initialization or cleanup routine;</li><li>kernel-space cancellation cleanup routine;</li><li>user-space thread (Xenomai threads switch to secondary mode);</li><li>user-space cancellation cleanup routine.</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/mq_unlink.html">Specification.</a> </dd></dl>
</div>
</div><p>
</div>
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