180 lines
8.2 KiB
HTML
180 lines
8.2 KiB
HTML
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<title>sigqueue</title>
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<basefont size="3"> <a name="sigqueue"></a> <a name="tag_03_695"></a><!-- sigqueue -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_695_01"></a>NAME</h4>
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<blockquote>sigqueue - queue a signal to a process (<b>REALTIME</b>)</blockquote>
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<h4><a name="tag_03_695_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('RTS')">RTS</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/signal.h.html">signal.h</a>><br>
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<br>
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int sigqueue(pid_t</tt> <i>pid</i><tt>, int</tt> <i>signo</i><tt>, const union sigval</tt> <i>value</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_695_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sigqueue</i>() function shall cause the signal specified by <i>signo</i> to be sent with the value specified by
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<i>value</i> to the process specified by <i>pid</i>. If <i>signo</i> is zero (the null signal), error checking is performed but no
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signal is actually sent. The null signal can be used to check the validity of <i>pid</i>.</p>
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<p>The conditions required for a process to have permission to queue a signal to another process are the same as for the <a href=
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"../functions/kill.html"><i>kill</i>()</a> function.</p>
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<p>The <i>sigqueue</i>() function shall return immediately. If SA_SIGINFO is set for <i>signo</i> and if the resources were
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available to queue the signal, the signal shall be queued and sent to the receiving process. If SA_SIGINFO is not set for
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<i>signo</i>, then <i>signo</i> shall be sent at least once to the receiving process; it is unspecified whether <i>value</i> shall
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be sent to the receiving process as a result of this call.</p>
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<p>If the value of <i>pid</i> causes <i>signo</i> to be generated for the sending process, and if <i>signo</i> is not blocked for
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the calling thread and if no other thread has <i>signo</i> unblocked or is waiting in a <a href=
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"../functions/sigwait.html"><i>sigwait</i>()</a> function for <i>signo</i>, either <i>signo</i> or at least the pending, unblocked
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signal shall be delivered to the calling thread before the <i>sigqueue</i>() function returns. Should any multiple pending signals
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in the range SIGRTMIN to SIGRTMAX be selected for delivery, it shall be the lowest numbered one. The selection order between
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realtime and non-realtime signals, or between multiple pending non-realtime signals, is unspecified.</p>
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</blockquote>
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<h4><a name="tag_03_695_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, the specified signal shall have been queued, and the <i>sigqueue</i>() function shall return a value
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of zero. Otherwise, the function shall return a value of -1 and set <i>errno</i> to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_695_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>sigqueue</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EAGAIN]</dt>
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<dd>No resources are available to queue the signal. The process has already queued {SIGQUEUE_MAX} signals that are still pending at
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the receiver(s), or a system-wide resource limit has been exceeded.</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of the <i>signo</i> argument is an invalid or unsupported signal number.</dd>
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<dt>[EPERM]</dt>
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<dd>The process does not have the appropriate privilege to send the signal to the receiving process.</dd>
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<dt>[ESRCH]</dt>
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<dd>The process <i>pid</i> does not exist.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_695_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_695_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_695_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>sigqueue</i>() function allows an application to queue a realtime signal to itself or to another process, specifying the
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application-defined value. This is common practice in realtime applications on existing realtime systems. It was felt that
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specifying another function in the <i>sig</i>... name space already carved out for signals was preferable to extending the
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interface to <a href="../functions/kill.html"><i>kill</i>()</a>.</p>
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<p>Such a function became necessary when the put/get event function of the message queues was removed. It should be noted that the
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<i>sigqueue</i>() function implies reduced performance in a security-conscious implementation as the access permissions between the
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sender and receiver have to be checked on each send when the <i>pid</i> is resolved into a target process. Such access checks were
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necessary only at message queue open in the previous interface.</p>
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<p>The standard developers required that <i>sigqueue</i>() have the same semantics with respect to the null signal as <a href=
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"../functions/kill.html"><i>kill</i>()</a>, and that the same permission checking be used. But because of the difficulty of
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implementing the "broadcast" semantic of <a href="../functions/kill.html"><i>kill</i>()</a> (for example, to process groups) and
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the interaction with resource allocation, this semantic was not adopted. The <i>sigqueue</i>() function queues a signal to a single
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process specified by the <i>pid</i> argument.</p>
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<p>The <i>sigqueue</i>() function can fail if the system has insufficient resources to queue the signal. An explicit limit on the
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number of queued signals that a process could send was introduced. While the limit is "per-sender", this volume of
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IEEE Std 1003.1-2001 does not specify that the resources be part of the state of the sender. This would require either
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that the sender be maintained after exit until all signals that it had sent to other processes were handled or that all such
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signals that had not yet been acted upon be removed from the queue(s) of the receivers. This volume of
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IEEE Std 1003.1-2001 does not preclude this behavior, but an implementation that allocated queuing resources from a
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system-wide pool (with per-sender limits) and that leaves queued signals pending after the sender exits is also permitted.</p>
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</blockquote>
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<h4><a name="tag_03_695_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_695_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_08.html#tag_02_08_01"><i>Realtime Signals</i></a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/signal.h.html"><i><signal.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_695_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 5. Included for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.</p>
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</blockquote>
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<h4><a name="tag_03_695_12"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>sigqueue</i>() function is marked as part of the Realtime Signals Extension option.</p>
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<p>The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Realtime
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Signals Extension option.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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