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sd-event: permit a USEC_INFINITY timeout as an alternative to a disabling an event source

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This should simplify handling of time events in clients and is in-line with the USEC_INFINITY macro we already have.
This way setting a timeout to 0 indicates "elapse immediately", and a timeout of USEC_INFINITY "elapse never".
This commit is contained in:
Lennart Poettering 2016-02-01 00:20:18 +01:00
parent 1bce0ffa66
commit 393003e1de
2 changed files with 25 additions and 38 deletions
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57
man/sd_event_add_time.xml
View file

@ -114,41 +114,28 @@
<refsect1>
<title>Description</title>
<para><function>sd_event_add_time()</function> adds a new timer
event source to an event loop. The event loop object is specified
in the <parameter>event</parameter> parameter, the event source
object is returned in the <parameter>source</parameter>
parameter. The <parameter>clock</parameter> parameter takes a
clock identifier, one of <constant>CLOCK_REALTIME</constant>,
<constant>CLOCK_MONOTONIC</constant>,
<constant>CLOCK_BOOTTIME</constant>,
<constant>CLOCK_REALTIME_ALARM</constant>, or
<constant>CLOCK_BOOTTIME_ALARM</constant>. See
<citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details regarding the various types of clocks. The
<parameter>usec</parameter> parameter specifies the earliest time,
in microseconds (µs), relative to the clock's epoch, when
the timer shall be triggered. If a time already in the past is
specified (including <constant>0</constant>), this timer source
"fires" immediately and is ready to be dispatched. The
<parameter>accuracy</parameter> parameter specifies an additional
accuracy value in µs specifying how much the timer event may be
delayed. Use <constant>0</constant> to select the default accuracy
(250ms). Use 1µs for maximum accuracy. Consider specifying
60000000µs (1min) or larger for long-running events that may be
delayed substantially. Picking higher accuracy values allows the
system to coalesce timer events more aggressively, improving
power efficiency. The <parameter>handler</parameter> parameter
shall reference a function to call when the timer elapses. The
handler function will be passed the
<parameter>userdata</parameter> pointer, which may be chosen
freely by the caller. The handler is also passed the configured
trigger time, even if it is actually called
slightly later, subject to the specified accuracy value,
the kernel timer slack (see
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>),
and additional scheduling latencies. To query the actual time the
handler was called use
<para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
<parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
<constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
<citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
dispatched. If the paramater is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
which may be used as an alternative to explicitly disabling a timer event source with
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
<parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
slightly later, subject to the specified accuracy value, the kernel timer slack (see
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
scheduling latencies. To query the actual time the handler was called use
<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>By default, the timer will elapse once

6
src/libsystemd/sd-event/sd-event.c
View file

@ -1070,7 +1070,6 @@ _public_ int sd_event_add_time(
int r;
assert_return(e, -EINVAL);
assert_return(usec != (uint64_t) -1, -EINVAL);
assert_return(accuracy != (uint64_t) -1, -EINVAL);
assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
assert_return(!event_pid_changed(e), -ECHILD);
@ -1760,7 +1759,6 @@ _public_ int sd_event_source_set_time(sd_event_source *s, uint64_t usec) {
struct clock_data *d;
assert_return(s, -EINVAL);
assert_return(usec != (uint64_t) -1, -EINVAL);
assert_return(EVENT_SOURCE_IS_TIME(s->type), -EDOM);
assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
assert_return(!event_pid_changed(s->event), -ECHILD);
@ -1890,6 +1888,8 @@ static usec_t sleep_between(sd_event *e, usec_t a, usec_t b) {
if (a <= 0)
return 0;
if (a >= USEC_INFINITY)
return USEC_INFINITY;
if (b <= a + 1)
return a;
@ -1979,7 +1979,7 @@ static int event_arm_timer(
d->needs_rearm = false;
a = prioq_peek(d->earliest);
if (!a || a->enabled == SD_EVENT_OFF) {
if (!a || a->enabled == SD_EVENT_OFF || a->time.next == USEC_INFINITY) {
if (d->fd < 0)
return 0;