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311 lines
20 KiB
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Signals (Guile Reference Manual)</title>
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<meta name="description" content="Signals (Guile Reference Manual)">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="POSIX.html" rel="up" title="POSIX">
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<link href="Terminals-and-Ptys.html" rel="next" title="Terminals and Ptys">
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<link href="Processes.html" rel="prev" title="Processes">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Signals">
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<div class="nav-panel">
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<p>
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Next: <a href="Terminals-and-Ptys.html" accesskey="n" rel="next">Terminals and Ptys</a>, Previous: <a href="Processes.html" accesskey="p" rel="prev">Processes</a>, Up: <a href="POSIX.html" accesskey="u" rel="up"><abbr class="acronym">POSIX</abbr> System Calls and Networking</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="Signals-1"><span>7.2.8 Signals<a class="copiable-link" href="#Signals-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-signal"></a>
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<p>The following procedures raise, handle and wait for signals.
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</p>
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<p>Scheme code signal handlers are run via an async (see <a class="pxref" href="Asyncs.html">Asynchronous Interrupts</a>), so
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they’re called in the handler’s thread at the next safe opportunity.
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Generally this is after any currently executing primitive procedure
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finishes (which could be a long time for primitives that wait for an
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external event).
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-kill"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">kill</strong> <var class="def-var-arguments">pid sig</var><a class="copiable-link" href="#index-kill"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fkill"><span class="category-def">C Function: </span><span><strong class="def-name">scm_kill</strong> <var class="def-var-arguments">(pid, sig)</var><a class="copiable-link" href="#index-scm_005fkill"> ¶</a></span></dt>
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<dd><p>Sends a signal to the specified process or group of processes.
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</p>
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<p><var class="var">pid</var> specifies the processes to which the signal is sent:
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</p>
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<dl class="table">
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<dt><var class="var">pid</var> greater than 0</dt>
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<dd><p>The process whose identifier is <var class="var">pid</var>.
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</p></dd>
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<dt><var class="var">pid</var> equal to 0</dt>
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<dd><p>All processes in the current process group.
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</p></dd>
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<dt><var class="var">pid</var> less than -1</dt>
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<dd><p>The process group whose identifier is -<var class="var">pid</var>
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</p></dd>
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<dt><var class="var">pid</var> equal to -1</dt>
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<dd><p>If the process is privileged, all processes except for some special
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system processes. Otherwise, all processes with the current effective
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user ID.
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</p></dd>
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</dl>
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<p><var class="var">sig</var> should be specified using a variable corresponding to
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the Unix symbolic name, e.g.,
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</p>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-SIGHUP"><span class="category-def">Variable: </span><span><strong class="def-name">SIGHUP</strong><a class="copiable-link" href="#index-SIGHUP"> ¶</a></span></dt>
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<dd><p>Hang-up signal.
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</p></dd></dl>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-SIGINT"><span class="category-def">Variable: </span><span><strong class="def-name">SIGINT</strong><a class="copiable-link" href="#index-SIGINT"> ¶</a></span></dt>
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<dd><p>Interrupt signal.
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</p></dd></dl>
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<p>A full list of signals on the GNU system may be found in <a data-manual="libc" href="https://www.gnu.org/software/libc/manual/html_node/Standard-Signals.html#Standard-Signals">Standard
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Signals</a> in <cite class="cite">The GNU C Library Reference Manual</cite>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-raise"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">raise</strong> <var class="def-var-arguments">sig</var><a class="copiable-link" href="#index-raise"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fraise"><span class="category-def">C Function: </span><span><strong class="def-name">scm_raise</strong> <var class="def-var-arguments">(sig)</var><a class="copiable-link" href="#index-scm_005fraise"> ¶</a></span></dt>
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<dd><p>Sends a specified signal <var class="var">sig</var> to the current process, where
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<var class="var">sig</var> is as described for the <code class="code">kill</code> procedure.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-sigaction"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">sigaction</strong> <var class="def-var-arguments">signum [handler [flags [thread]]]</var><a class="copiable-link" href="#index-sigaction"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fsigaction"><span class="category-def">C Function: </span><span><strong class="def-name">scm_sigaction</strong> <var class="def-var-arguments">(signum, handler, flags)</var><a class="copiable-link" href="#index-scm_005fsigaction"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fsigaction_005ffor_005fthread"><span class="category-def">C Function: </span><span><strong class="def-name">scm_sigaction_for_thread</strong> <var class="def-var-arguments">(signum, handler, flags, thread)</var><a class="copiable-link" href="#index-scm_005fsigaction_005ffor_005fthread"> ¶</a></span></dt>
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<dd><p>Install or report the signal handler for a specified signal.
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</p>
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<p><var class="var">signum</var> is the signal number, which can be specified using the value
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of variables such as <code class="code">SIGINT</code>.
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</p>
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<p>If <var class="var">handler</var> is omitted, <code class="code">sigaction</code> returns a pair: the
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<abbr class="acronym">CAR</abbr> is the current signal handler, which will be either an
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integer with the value <code class="code">SIG_DFL</code> (default action) or
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<code class="code">SIG_IGN</code> (ignore), or the Scheme procedure which handles the
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signal, or <code class="code">#f</code> if a non-Scheme procedure handles the signal.
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The <abbr class="acronym">CDR</abbr> contains the current <code class="code">sigaction</code> flags for the
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handler.
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</p>
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<p>If <var class="var">handler</var> is provided, it is installed as the new handler for
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<var class="var">signum</var>. <var class="var">handler</var> can be a Scheme procedure taking one
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argument, or the value of <code class="code">SIG_DFL</code> (default action) or
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<code class="code">SIG_IGN</code> (ignore), or <code class="code">#f</code> to restore whatever signal handler
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was installed before <code class="code">sigaction</code> was first used. When a scheme
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procedure has been specified, that procedure will run in the given
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<var class="var">thread</var>. When no thread has been given, the thread that made this
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call to <code class="code">sigaction</code> is used.
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</p>
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<p><var class="var">flags</var> is a <code class="code">logior</code> (see <a class="pxref" href="Bitwise-Operations.html">Bitwise Operations</a>) of the
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following (where provided by the system), or <code class="code">0</code> for none.
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</p>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-SA_005fNOCLDSTOP"><span class="category-def">Variable: </span><span><strong class="def-name">SA_NOCLDSTOP</strong><a class="copiable-link" href="#index-SA_005fNOCLDSTOP"> ¶</a></span></dt>
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<dd><p>By default, <code class="code">SIGCHLD</code> is signaled when a child process stops
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(ie. receives <code class="code">SIGSTOP</code>), and when a child process terminates.
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With the <code class="code">SA_NOCLDSTOP</code> flag, <code class="code">SIGCHLD</code> is only signaled
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for termination, not stopping.
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</p>
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<p><code class="code">SA_NOCLDSTOP</code> has no effect on signals other than
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<code class="code">SIGCHLD</code>.
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</p></dd></dl>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-SA_005fRESTART"><span class="category-def">Variable: </span><span><strong class="def-name">SA_RESTART</strong><a class="copiable-link" href="#index-SA_005fRESTART"> ¶</a></span></dt>
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<dd><p>If a signal occurs while in a system call, deliver the signal then
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restart the system call (as opposed to returning an <code class="code">EINTR</code> error
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from that call).
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</p></dd></dl>
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<p>Guile handles signals asynchronously. When it receives a signal, the
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synchronous signal handler just records the fact that a signal was
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received and sets a flag to tell the relevant Guile thread that it has a
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pending signal. When the Guile thread checks the pending-interrupt
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flag, it will arrange to run the asynchronous part of the signal
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handler, which is the handler attached by <code class="code">sigaction</code>.
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</p>
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<p>This strategy has some perhaps-unexpected interactions with the
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<code class="code">SA_RESTART</code> flag, though: because the synchronous handler doesn’t
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do very much, and notably it doesn’t run the Guile handler, it’s
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impossible to interrupt a thread stuck in a long-running system call via
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a signal handler that is installed with <code class="code">SA_RESTART</code>: the
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synchronous handler just records the pending interrupt, but then the
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system call resumes and Guile doesn’t have a chance to actually check
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the flag and run the asynchronous handler. That’s just how it is.
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</p>
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<p>The return value is a pair with information about the old handler as
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described above.
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</p>
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<p>This interface does not provide access to the “signal blocking”
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facility. Maybe this is not needed, since the thread support may
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provide solutions to the problem of consistent access to data
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structures.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-restore_002dsignals"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">restore-signals</strong><a class="copiable-link" href="#index-restore_002dsignals"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frestore_005fsignals"><span class="category-def">C Function: </span><span><strong class="def-name">scm_restore_signals</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005frestore_005fsignals"> ¶</a></span></dt>
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<dd><p>Return all signal handlers to the values they had before any call to
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<code class="code">sigaction</code> was made. The return value is unspecified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-alarm"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">alarm</strong> <var class="def-var-arguments">i</var><a class="copiable-link" href="#index-alarm"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005falarm"><span class="category-def">C Function: </span><span><strong class="def-name">scm_alarm</strong> <var class="def-var-arguments">(i)</var><a class="copiable-link" href="#index-scm_005falarm"> ¶</a></span></dt>
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<dd><p>Set a timer to raise a <code class="code">SIGALRM</code> signal after the specified
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number of seconds (an integer). It’s advisable to install a signal
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handler for
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<code class="code">SIGALRM</code> beforehand, since the default action is to terminate
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the process.
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</p>
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<p>The return value indicates the time remaining for the previous alarm,
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if any. The new value replaces the previous alarm. If there was
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no previous alarm, the return value is zero.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-pause"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">pause</strong><a class="copiable-link" href="#index-pause"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fpause"><span class="category-def">C Function: </span><span><strong class="def-name">scm_pause</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005fpause"> ¶</a></span></dt>
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<dd><p>Pause the current process (thread?) until a signal arrives whose
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action is to either terminate the current process or invoke a
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handler procedure. The return value is unspecified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-sleep"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">sleep</strong> <var class="def-var-arguments">secs</var><a class="copiable-link" href="#index-sleep"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-usleep"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">usleep</strong> <var class="def-var-arguments">usecs</var><a class="copiable-link" href="#index-usleep"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fsleep"><span class="category-def">C Function: </span><span><strong class="def-name">scm_sleep</strong> <var class="def-var-arguments">(secs)</var><a class="copiable-link" href="#index-scm_005fsleep"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fusleep"><span class="category-def">C Function: </span><span><strong class="def-name">scm_usleep</strong> <var class="def-var-arguments">(usecs)</var><a class="copiable-link" href="#index-scm_005fusleep"> ¶</a></span></dt>
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<dd><p>Wait the given period <var class="var">secs</var> seconds or <var class="var">usecs</var> microseconds
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(both integers). If a signal arrives the wait stops and the return
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value is the time remaining, in seconds or microseconds respectively.
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If the period elapses with no signal the return is zero.
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</p>
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<p>On most systems the process scheduler is not microsecond accurate and
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the actual period slept by <code class="code">usleep</code> might be rounded to a system
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clock tick boundary, which might be 10 milliseconds for instance.
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</p>
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<p>See <code class="code">scm_std_sleep</code> and <code class="code">scm_std_usleep</code> for equivalents at
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the C level (see <a class="pxref" href="Blocking.html">Blocking in Guile Mode</a>).
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-getitimer"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">getitimer</strong> <var class="def-var-arguments">which_timer</var><a class="copiable-link" href="#index-getitimer"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-setitimer"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">setitimer</strong> <var class="def-var-arguments">which_timer interval_seconds interval_microseconds value_seconds value_microseconds</var><a class="copiable-link" href="#index-setitimer"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fgetitimer"><span class="category-def">C Function: </span><span><strong class="def-name">scm_getitimer</strong> <var class="def-var-arguments">(which_timer)</var><a class="copiable-link" href="#index-scm_005fgetitimer"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fsetitimer"><span class="category-def">C Function: </span><span><strong class="def-name">scm_setitimer</strong> <var class="def-var-arguments">(which_timer, interval_seconds, interval_microseconds, value_seconds, value_microseconds)</var><a class="copiable-link" href="#index-scm_005fsetitimer"> ¶</a></span></dt>
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<dd><p>Get or set the periods programmed in certain system timers.
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</p>
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<p>These timers have two settings. The first setting, the interval, is the
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value at which the timer will be reset when the current timer expires.
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The second is the current value of the timer, indicating when the next
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expiry will be signaled.
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</p>
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<p><var class="var">which_timer</var> is one of the following values:
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</p>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-ITIMER_005fREAL"><span class="category-def">Variable: </span><span><strong class="def-name">ITIMER_REAL</strong><a class="copiable-link" href="#index-ITIMER_005fREAL"> ¶</a></span></dt>
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<dd><p>A real-time timer, counting down elapsed real time. At zero it raises
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<code class="code">SIGALRM</code>. This is like <code class="code">alarm</code> above, but with a higher
|
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resolution period.
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</p></dd></dl>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-ITIMER_005fVIRTUAL"><span class="category-def">Variable: </span><span><strong class="def-name">ITIMER_VIRTUAL</strong><a class="copiable-link" href="#index-ITIMER_005fVIRTUAL"> ¶</a></span></dt>
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<dd><p>A virtual-time timer, counting down while the current process is
|
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actually using CPU. At zero it raises <code class="code">SIGVTALRM</code>.
|
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</p></dd></dl>
|
||
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|
||
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<dl class="first-defvr first-defvar-alias-first-defvr">
|
||
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<dt class="defvr defvar-alias-defvr" id="index-ITIMER_005fPROF"><span class="category-def">Variable: </span><span><strong class="def-name">ITIMER_PROF</strong><a class="copiable-link" href="#index-ITIMER_005fPROF"> ¶</a></span></dt>
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<dd><p>A profiling timer, counting down while the process is running (like
|
||
|
|
<code class="code">ITIMER_VIRTUAL</code>) and also while system calls are running on the
|
||
|
|
process’s behalf. At zero it raises a <code class="code">SIGPROF</code>.
|
||
|
|
</p>
|
||
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<p>This timer is intended for profiling where a program is spending its
|
||
|
|
time (by looking where it is when the timer goes off).
|
||
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</p></dd></dl>
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||
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<p><code class="code">getitimer</code> returns the restart timer value and its current value,
|
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|
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as a list containing two pairs. Each pair is a time in seconds and
|
||
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microseconds: <code class="code">((<var class="var">interval_secs</var> . <var class="var">interval_usecs</var>)
|
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(<var class="var">value_secs</var> . <var class="var">value_usecs</var>))</code>.
|
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</p>
|
||
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<p><code class="code">setitimer</code> sets the timer values similarly, in seconds and
|
||
|
|
microseconds (which must be integers). The interval value can be zero
|
||
|
|
to have the timer run down just once. The return value is the timer’s
|
||
|
|
previous setting, in the same form as <code class="code">getitimer</code> returns.
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">(setitimer ITIMER_REAL
|
||
|
|
5 500000 ;; Raise SIGALRM every 5.5 seconds
|
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|
|
2 0) ;; with the first SIGALRM in 2 seconds
|
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|
</pre></div>
|
||
|
|
|
||
|
|
<p>Although the timers are programmed in microseconds, the actual
|
||
|
|
accuracy might not be that high.
|
||
|
|
</p>
|
||
|
|
<p>Note that <code class="code">ITIMER_PROF</code> and <code class="code">ITIMER_VIRTUAL</code> are not
|
||
|
|
functional on all platforms and may always error when called.
|
||
|
|
<code class="code">(provided? 'ITIMER_PROF)</code> and <code class="code">(provided? 'ITIMER_VIRTUAL)</code>
|
||
|
|
can be used to test if the those itimers are supported on the given
|
||
|
|
host. <code class="code">ITIMER_REAL</code> is supported on all platforms that support
|
||
|
|
<code class="code">setitimer</code>.
|
||
|
|
</p></dd></dl>
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</div>
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<hr>
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<p>
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Next: <a href="Terminals-and-Ptys.html">Terminals and Ptys</a>, Previous: <a href="Processes.html">Processes</a>, Up: <a href="POSIX.html"><abbr class="acronym">POSIX</abbr> System Calls and Networking</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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