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Diffstat (limited to 'man/sd_event_wait.xml')
| -rw-r--r-- | man/sd_event_wait.xml | 275 |
1 files changed, 204 insertions, 71 deletions
diff --git a/man/sd_event_wait.xml b/man/sd_event_wait.xml index 7ca50aedf9..1eefa80700 100644 --- a/man/sd_event_wait.xml +++ b/man/sd_event_wait.xml @@ -21,7 +21,7 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>. --> -<refentry id="sd_event_wait"> +<refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude"> <refentryinfo> <title>sd_event_wait</title> @@ -46,14 +46,32 @@ <refname>sd_event_wait</refname> <refname>sd_event_prepare</refname> <refname>sd_event_dispatch</refname> - - <refpurpose>Run parts of the libsystemd event loop</refpurpose> + <refname>sd_event_get_state</refname> + <refname>SD_EVENT_INITIAL</refname> + <refname>SD_EVENT_PREPARING</refname> + <refname>SD_EVENT_ARMED</refname> + <refname>SD_EVENT_PENDING</refname> + <refname>SD_EVENT_RUNNING</refname> + <refname>SD_EVENT_EXITING</refname> + <refname>SD_EVENT_FINISHED</refname> + + <refpurpose>Low-level event loop operations</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> + <funcsynopsisinfo><token>enum</token> { + <constant>SD_EVENT_INITIAL</constant>, + <constant>SD_EVENT_PREPARING</constant>, + <constant>SD_EVENT_ARMED</constant>, + <constant>SD_EVENT_PENDING</constant>, + <constant>SD_EVENT_RUNNING</constant>, + <constant>SD_EVENT_EXITING</constant>, + <constant>SD_EVENT_FINISHED</constant>, +};</funcsynopsisinfo> + <funcprototype> <funcdef>int <function>sd_event_prepare</function></funcdef> <paramdef>sd_event *<parameter>event</parameter></paramdef> @@ -62,7 +80,7 @@ <funcprototype> <funcdef>int <function>sd_event_wait</function></funcdef> <paramdef>sd_event *<parameter>event</parameter></paramdef> - <paramdef>uint64_t <parameter>timeout</parameter></paramdef> + <paramdef>uint64_t <parameter>usec</parameter></paramdef> </funcprototype> <funcprototype> @@ -70,66 +88,184 @@ <paramdef>sd_event *<parameter>event</parameter></paramdef> </funcprototype> + <funcprototype> + <funcdef>int <function>sd_event_get_state</function></funcdef> + <paramdef>sd_event *<parameter>event</parameter></paramdef> + </funcprototype> + </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> - <para>Functions described here form parts of an event loop.</para> - - <para><function>sd_event_prepare</function> checks for pending + <para>The low-level <function>sd_event_prepare()</function>, + <function>sd_event_wait()</function> and + <function>sd_event_dispatch()</function> functions may be used to + execute specific phases of an event loop. See + <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry> + and + <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry> + for higher-level functions that execute individual but complete + iterations of an event loop or run it continously.</para> + + <para><function>sd_event_prepare()</function> checks for pending events and arms necessary timers. If any events are ready to be - processed, it returns a positive value, and the events should be - processed with <function>sd_event_dispatch</function>. - <function>sd_event_dispatch</function> runs a handler for one of - the events from the sources with the highest priority. On success, - <function>sd_event_dispatch</function> returns either 0, which - means that the loop is finished, or a positive value, which means - that the loop is again in the initial state and - <function>sd_event_prepare</function> should be called again. - </para> + processed ("pending"), it returns a positive, non-zero value, and the caller + should process these events with + <function>sd_event_dispatch()</function>.</para> + + <para><function>sd_event_dispatch()</function> dispatches the + highest priority event source that has a pending event. On + success, <function>sd_event_dispatch()</function> returns either + zero, which indicates that no further event sources may be + dispatched and exiting of the event loop was requested via + <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>; + or a positive non-zero value, which means that an event source was + dispatched and the loop returned to its initial state, and the + caller should initiate the next event loop iteration by invoking + <function>sd_event_prepare()</function> again.</para> + + <para>In case <function>sd_event_prepare()</function> returned + zero, <function>sd_event_wait()</function> should be called to + wait for further events or a timeout. If any events are ready to + be processed, it returns a positive, non-zero value, and the + events should be dispatched with + <function>sd_event_dispatch()</function>. Otherwise, the event + loop returned to its initial state and the next event loop + iteration should be initiated by invoking + <function>sd_event_prepare()</function> again.</para> + + <para><function>sd_event_get_state()</function> may be used to + determine the state the event loop is currently in. It returns one + of the states described below.</para> + + <para>All four functions take, as the first argument, the event + loop object <parameter>event</parameter> that has been created + with <function>sd_event_new()</function>. The timeout for + <function>sd_event_wait()</function> is specified in + <parameter>usec</parameter> in milliseconds. <constant>(uint64_t) + -1</constant> may be used to specify an infinite timeout.</para> +</refsect1> + + <refsect1> + <title>State Machine</title> + + <para>The event loop knows the following states, that may be + queried with <function>sd_event_get_state()</function>.</para> - <para>In case <function>sd_event_prepare</function> returned 0, - <function>sd_event_wait</function> should be called to wait for - events or a timeout. If any events are ready to be processed, it - returns a positive value, and the events should be processed with - <function>sd_event_dispatch</function>. Otherwise, the loop is - back in the initial state and <function>sd_event_prepare</function> - should be called again.</para> + <variablelist> + <varlistentry> + <term><constant>SD_EVENT_INITIAL</constant></term> + + <listitem><para>The initial state the event loop is in, + before each event loop iteration. Use + <function>sd_event_prepare()</function> to transition the + event loop into the <constant>SD_EVENT_ARMED</constant> or + <constant>SD_EVENT_PENDING</constant> states.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_PREPARING</constant></term> + + <listitem><para>An event source is currently being prepared, + i.e. the preparation handler is currently being excuted, as + set with + <citerefentry><refentrytitle>sd_event_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This + state is only seen in the event source preparation handler + that is invoked from the + <function>sd_event_prepare()</function> call and is + immediately followed by <constant>SD_EVENT_ARMED</constant> or + <constant>SD_EVENT_PENDING</constant>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_ARMED</constant></term> + + <listitem><para><function>sd_event_prepare()</function> has + been called and no event sources were ready to be + dispatched. Use <function>sd_event_wait()</function> to wait + for new events, and transition into + <constant>SD_EVENT_PENDING</constant> or back into + <constant>SD_EVENT_INITIAL</constant>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_PENDING</constant></term> + + <listitem><para><function>sd_event_prepare()</function> or + <function>sd_event_wait()</function> have been called and + there were event sources with events pending. Use + <function>sd_event_dispatch()</function> to dispatch the + highest priority event source and transition back to + <constant>SD_EVENT_INITIAL</constant>, or + <constant>SD_EVENT_FINISHED</constant>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_RUNNING</constant></term> + + <listitem><para>A regular event source is currently being + dispatched. This state is only seen in the event source + handler that is invoked from the + <function>sd_event_dispatch()</function> call, and is + immediately followed by <constant>SD_EVENT_INITIAL</constant> + or <constant>SD_EVENT_FINISHED</constant> as soon the event + source handler returns. Note that during dispatching of exit + event sources the <constant>SD_EVENT_EXITING</constant> state + is seen instead.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_EXITING</constant></term> + + <listitem><para>Similar to + <constant>SD_EVENT_RUNNING</constant> but is the state in + effect while dispatching exit event sources. It is followed by + <constant>SD_EVENT_INITIAL</constant> or + <constant>SD_EVENT_FINISHED</constant> as soon as the event + handler returns.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SD_EVENT_FINISHED</constant></term> + + <listitem><para>The event loop has exited. All exit event + sources have run. If the event loop is in this state it serves + no purpose anymore, and should be freed.</para></listitem> + </varlistentry> + + </variablelist> + + <para>A simplified flow chart of the states and the calls to + transition between them is shown below. Note that + <constant>SD_EVENT_PREPARING</constant>, + <constant>SD_EVENT_RUNNING</constant> and + <constant>SD_EVENT_EXITING</constant> are not shown here.</para> <programlisting> - ┌──────────┐ - │ initial ├──←←←←←←←←←←←←←←←←←←←─┐ - └───┬──────┘ ↑ - │ ↑ - sd_event_prepare ┌─────────┐ ↑ - ├ 0 →→→→→→→──┤ armed │ ↑ - 1 └───┬─────┘ ↑ - ↓ │ ↑ - ↓ sd_event_wait ↑ - ├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘ - ┌───┴──────┐ ↑ - │ pending │ ↑ - └───┬──────┘ ↑ - │ ↑ - sd_event_dispatch ↑ - ↓ ↑ - ├ 1 ──────────→→→→→→→─────────┘ - 0 - ↓ - ┌───┴──────┐ - │ finished │ - └──────────┘ + INITIAL -<---<---<---<---<---<---<---<---<---<---<---<---\ + | | + | ^ + | | + v ret == 0 | + sd_event_prepare() >--->--->--->--->- ARMED | + | | ^ + | ret > 0 | | + | | | + v v ret == 0 | + PENDING <---<---<---<---<---< sd_event_wait() >--->--->--+ + | ret > 0 ^ + | | + | | + v | + sd_event_dispatch() >--->--->--->--->--->--->--->--->--->--->/ + | ret > 0 + | ret == 0 + | + v + FINISHED </programlisting> - - <para>All three functions take, as the first argument, the event - loop object <parameter>event</parameter> that is created with - <function>sd_event_new</function>. The timeout for - <function>sd_event_wait</function> is specified with - <parameter>timeout</parameter> in milliseconds. - <constant>(uint64_t) -1</constant> may be used to specify an - infinite timeout.</para> </refsect1> <refsect1> @@ -137,13 +273,15 @@ <para>On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code. In case - of <function>sd_event_prepare</function> and - <function>sd_event_wait</function>, a positive value means that - events are ready to be processed and 0 means that no events are - ready. In case of <function>sd_event_dispatch</function>, a - positive value means that the loop is again in the initial state - and 0 means the loop is finished. For any of these functions, a - negative return value means the loop must be aborted.</para> + of <function>sd_event_prepare()</function> and + <function>sd_event_wait()</function>, a positive, non-zero return + code indicates that events are ready to be processed and zero + indicates that no events are ready. In case of + <function>sd_event_dispatch()</function>, a positive, non-zero + return code indicates that the event loop returned to its initial + state and zero indicates the event loop has + exited. <function>sd_event_get_state()</function> returns a + positive or zero state on success.</para> </refsect1> <refsect1> @@ -156,7 +294,7 @@ <term><constant>-EINVAL</constant></term> <listitem><para>The <parameter>event</parameter> parameter is - <constant>NULL</constant>.</para></listitem> + invalid or <constant>NULL</constant>.</para></listitem> </varlistentry> <varlistentry> @@ -185,14 +323,7 @@ <para>Other errors are possible, too.</para> </refsect1> - <refsect1> - <title>Notes</title> - - <para>Functions described here are available - as a shared library, which can be compiled and linked to with the - <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> - file.</para> - </refsect1> + <xi:include href="libsystemd-pkgconfig.xml" /> <refsect1> <title>See Also</title> @@ -200,13 +331,15 @@ <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, - <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, - <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>. + <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> |