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sd-event: add helper for exiting event loop on SIGTERM/SIGINT

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In many (most?) of our event loops we want to exit once SIGTERM/SIGINT
is seen. Add a common helper for that, that does the right things in a
single call.
This commit is contained in:
Lennart Poettering 2022-09-28 11:42:05 +02:00
parent 897448bd37
commit baf3fdec27
5 changed files with 162 additions and 0 deletions
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1
man/rules/meson.build
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@ -583,6 +583,7 @@ manpages = [
''],
['sd_event_now', '3', [], ''],
['sd_event_run', '3', ['sd_event_loop'], ''],
['sd_event_set_signal_exit', '3', [], ''],
['sd_event_set_watchdog', '3', ['sd_event_get_watchdog'], ''],
['sd_event_source_get_event', '3', [], ''],
['sd_event_source_get_pending', '3', [], ''],

101
man/sd_event_set_signal_exit.xml Normal file
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@ -0,0 +1,101 @@
<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_event_set_signal_exit" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_event_set_signal_exit</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_event_set_signal_exit</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_event_set_signal_exit</refname>
<refpurpose>Automatically leave event loop on <constant>SIGINT</constant> and <constant>SIGTERM</constant></refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_event_set_signal_exit</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
<paramdef>int b</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_event_set_signal_exit()</function> may be used to ensure the event loop terminates
once a <constant>SIGINT</constant> or <constant>SIGTERM</constant> signal is received. It is a
convencience wrapper around invocations of
<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for both signals. The two signals are automatically added to the calling thread's signal mask (if a
program is multi-threaded care should be taken to either invoke this function before the first thread is
started or to manually block the two signals process-wide first).</para>
<para>If the parameter <parameter>b</parameter> is specified as true, the event loop will terminate on
<constant>SIGINT</constant> and <constant>SIGTERM</constant>. If specified as false, it will no
longer. When this functionality is turned off the calling thread's signal mask is restored to match the
state before it was turned on, for the two signals. By default the two signals are not handled by the
event loop, and Linux' default signal handling for them is in effect.</para>
<para>It's customary for UNIX programs to exit on either of these two signals, hence it's typically a
good idea to enable this functionality for the main event loop of a program.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para><function>sd_event_set_signal_exit()</function> returns a positive non-zero value when the setting
was successfully changed. It returns a zero when the specified setting was already in effect. On failure,
it returns a negative errno-style error code.</para>
<refsect2>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-ECHILD</constant></term>
<listitem><para>The event loop has been created in a different process.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>The passed event loop object was invalid.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>

2
src/libsystemd/libsystemd.sym
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@ -790,6 +790,8 @@ global:
sd_device_monitor_set_description;
sd_device_monitor_get_description;
sd_event_set_signal_exit;
sd_id128_string_equal;
sd_hwdb_new_from_path;

57
src/libsystemd/sd-event/sd-event.c
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@ -153,6 +153,8 @@ struct sd_event {
LIST_HEAD(sd_event_source, sources);
sd_event_source *sigint_event_source, *sigterm_event_source;
usec_t last_run_usec, last_log_usec;
unsigned delays[sizeof(usec_t) * 8];
};
@ -323,6 +325,9 @@ static sd_event *event_free(sd_event *e) {
assert(e);
e->sigterm_event_source = sd_event_source_unref(e->sigterm_event_source);
e->sigint_event_source = sd_event_source_unref(e->sigint_event_source);
while ((s = e->sources)) {
assert(s->floating);
source_disconnect(s);
@ -4613,3 +4618,55 @@ _public_ int sd_event_source_is_ratelimited(sd_event_source *s) {
return s->ratelimited;
}
_public_ int sd_event_set_signal_exit(sd_event *e, int b) {
bool change = false;
int r;
assert_return(e, -EINVAL);
if (b) {
/* We want to maintain pointers to these event sources, so that we can destroy them when told
* so. But we also don't want them to pin the event loop itself. Hence we mark them as
* floating after creation (and undo this before deleting them again). */
if (!e->sigint_event_source) {
r = sd_event_add_signal(e, &e->sigint_event_source, SIGINT | SD_EVENT_SIGNAL_PROCMASK, NULL, NULL);
if (r < 0)
return r;
assert(sd_event_source_set_floating(e->sigint_event_source, true) >= 0);
change = true;
}
if (!e->sigterm_event_source) {
r = sd_event_add_signal(e, &e->sigterm_event_source, SIGTERM | SD_EVENT_SIGNAL_PROCMASK, NULL, NULL);
if (r < 0) {
if (change) {
assert(sd_event_source_set_floating(e->sigint_event_source, false) >= 0);
e->sigint_event_source = sd_event_source_unref(e->sigint_event_source);
}
return r;
}
assert(sd_event_source_set_floating(e->sigterm_event_source, true) >= 0);
change = true;
}
} else {
if (e->sigint_event_source) {
assert(sd_event_source_set_floating(e->sigint_event_source, false) >= 0);
e->sigint_event_source = sd_event_source_unref(e->sigint_event_source);
change = true;
}
if (e->sigterm_event_source) {
assert(sd_event_source_set_floating(e->sigterm_event_source, false) >= 0);
e->sigterm_event_source = sd_event_source_unref(e->sigterm_event_source);
change = true;
}
}
return change;
}

1
src/systemd/sd-event.h
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@ -116,6 +116,7 @@ int sd_event_get_exit_code(sd_event *e, int *code);
int sd_event_set_watchdog(sd_event *e, int b);
int sd_event_get_watchdog(sd_event *e);
int sd_event_get_iteration(sd_event *e, uint64_t *ret);
int sd_event_set_signal_exit(sd_event *e, int b);
sd_event_source* sd_event_source_ref(sd_event_source *s);
sd_event_source* sd_event_source_unref(sd_event_source *s);