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897448bd37
So far we expected callers to block the signals manually. Which is usually a good idea, since they should do that before forking off threads and similar. But let's add a mode where we automatically block it for the caller, to simplify things.
208 lines
10 KiB
XML
208 lines
10 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_signal</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_add_signal</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_add_signal</refname>
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<refname>sd_event_source_get_signal</refname>
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<refname>sd_event_signal_handler_t</refname>
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<refname>SD_EVENT_SIGNAL_PROCMASK</refname>
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<refpurpose>Add a UNIX process signal event source to an event
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loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcsynopsisinfo><constant>SD_EVENT_SIGNAL_PROCMASK</constant></funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_signal</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>int <parameter>signal</parameter></paramdef>
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<paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_signal</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_event_add_signal()</function> adds a new UNIX process signal event source to an event
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loop. The event loop object is specified in the <parameter>event</parameter> parameter, and the event
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source object is returned in the <parameter>source</parameter> parameter. The
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<parameter>signal</parameter> parameter specifies the numeric signal to be handled (see <citerefentry
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project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).</para>
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<para>The <parameter>handler</parameter> parameter is a function to call when the signal is received or
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<constant>NULL</constant>. The handler function will be passed the <parameter>userdata</parameter>
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pointer, which may be chosen freely by the caller. The handler also receives a pointer to a
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<structname>signalfd_siginfo</structname> structure containing information about the received signal. See
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<citerefentry
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project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
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further information. The handler may return negative to signal an error (see below), other return values
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are ignored. If <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
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used.</para>
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<para>Only a single handler may be installed for a specific signal. The signal must be blocked in all
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threads before this function is called (using <citerefentry
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project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
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<citerefentry
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project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>). For
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convenience, if the special flag <constant>SD_EVENT_SIGNAL_PROCMASK</constant> is ORed into the specified
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signal the signal will be automatically masked as necessary, for the calling thread. Note that this only
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works reliably if the signal is already masked in all other threads of the process, or if there are no
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other threads at the moment of invocation.</para>
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<para>By default, the event source is enabled permanently (<constant>SD_EVENT_ON</constant>), but this
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may be changed with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If the handler function returns a negative error code, it will either be disabled after the invocation,
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even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to
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terminate, see
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<citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but note that the event source is only removed from the event loop
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when all references to the event source are dropped. To make sure
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an event source does not fire anymore, even if it is still referenced,
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disable the event source using
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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with <constant>SD_EVENT_OFF</constant>.</para>
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<para>If the second parameter of
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<function>sd_event_add_signal()</function> is
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<constant>NULL</constant> no reference to the event source object
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is returned. In this case the event source is considered
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"floating", and will be destroyed implicitly when the event loop
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itself is destroyed.</para>
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<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_signal()</function> is
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<constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
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event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
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the exit code parameter to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para><function>sd_event_source_get_signal()</function> returns
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the configured signal number of an event source created previously
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with <function>sd_event_add_signal()</function>. It takes the
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event source object as the <parameter>source</parameter>
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parameter.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EBUSY</constant></term>
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<listitem><para>A handler is already installed for this
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signal or the signal was not blocked previously.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EDOM</constant></term>
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<listitem><para>The passed event source is not a signal event source.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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