110 lines
5 KiB
HTML
110 lines
5 KiB
HTML
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<!DOCTYPE html>
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<html>
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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>Asynchronous Signals (Guile Reference Manual)</title>
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<meta name="description" content="Asynchronous Signals (Guile Reference Manual)">
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<meta name="keywords" content="Asynchronous Signals (Guile Reference Manual)">
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<meta name="Generator" content=".texi2any-real">
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<link href="index.html" rel="start" title="Top">
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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="General-Libguile-Concepts.html" rel="up" title="General Libguile Concepts">
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<link href="Multi_002dThreading.html" rel="next" title="Multi-Threading">
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<link href="Control-Flow.html" rel="prev" title="Control Flow">
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<style type="text/css">
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a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
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</style>
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Asynchronous-Signals">
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<div class="nav-panel">
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<p>
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Next: <a href="Multi_002dThreading.html" accesskey="n" rel="next">Multi-Threading</a>, Previous: <a href="Control-Flow.html" accesskey="p" rel="prev">Control Flow</a>, Up: <a href="General-Libguile-Concepts.html" accesskey="u" rel="up">General concepts for using libguile</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="Asynchronous-Signals-1"><span>5.4.4 Asynchronous Signals<a class="copiable-link" href="#Asynchronous-Signals-1"> ¶</a></span></h4>
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<p>You can not call libguile functions from handlers for POSIX signals, but
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you can register Scheme handlers for POSIX signals such as
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<code class="code">SIGINT</code>. These handlers do not run during the actual signal
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delivery. Instead, they are run when the program (more precisely, the
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thread that the handler has been registered for) reaches the next
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<em class="emph">safe point</em>.
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</p>
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<p>The libguile functions themselves have many such safe points.
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Consequently, you must be prepared for arbitrary actions anytime you
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call a libguile function. For example, even <code class="code">scm_cons</code> can contain
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a safe point and when a signal handler is pending for your thread,
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calling <code class="code">scm_cons</code> will run this handler and anything might happen,
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including a non-local exit although <code class="code">scm_cons</code> would not ordinarily
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do such a thing on its own.
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</p>
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<p>If you do not want to allow the running of asynchronous signal handlers,
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you can block them temporarily with <code class="code">scm_dynwind_block_asyncs</code>, for
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example. See <a class="xref" href="Asyncs.html">Asynchronous Interrupts</a>.
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</p>
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<p>Since signal handling in Guile relies on safe points, you need to make
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sure that your functions do offer enough of them. Normally, calling
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libguile functions in the normal course of action is all that is needed.
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But when a thread might spent a long time in a code section that calls
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no libguile function, it is good to include explicit safe points. This
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can allow the user to interrupt your code with <kbd class="key">C-c</kbd>, for example.
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</p>
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<p>You can do this with the macro <code class="code">SCM_TICK</code>. This macro is
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syntactically a statement. That is, you could use it like this:
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</p>
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<div class="example">
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<pre class="example-preformatted">while (1)
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{
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SCM_TICK;
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do_some_work ();
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}
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</pre></div>
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<p>Frequent execution of a safe point is even more important in multi
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threaded programs, See <a class="xref" href="Multi_002dThreading.html">Multi-Threading</a>.
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</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Multi_002dThreading.html">Multi-Threading</a>, Previous: <a href="Control-Flow.html">Control Flow</a>, Up: <a href="General-Libguile-Concepts.html">General concepts for using libguile</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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</body>
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</html>
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