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https://github.com/matrix-construct/construct
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83 lines
2.4 KiB
Text
83 lines
2.4 KiB
Text
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Overview of the event subsystem
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Adrian Chadd <adrian@creative.net.au>
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One of the things that immediately struck me whilst first looking at the
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code was that the ircd periodically scheduled things in io_loop() but
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it did them manually. This is very wasteful and very tedious.
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Therefore, an event system was added to hybrid. src/event.c contains an
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event system ported from the squid web cache. It is pretty self contained,
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and only a few things (debugging, time resolution) needed changing.
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An event is scheduled through eventAdd() or eventAddIsh() :
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eventAdd(const char *name, EVH * func, void *arg, time_t when, int weight)
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eventAddIsh(const char *name, EVH * func, void *arg, time_t delta_ish,
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int weight)
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after 'when' (or delta_ish) seconds has elapsed from the time the above
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functions are called, the 'func' is called with the given data 'arg'. The
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event is then deleted.
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To delete an event, use eventDelete() :
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eventDelete(EVH * func, void *arg)
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An event is identified by its callback function and data pair.
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Events are run through eventRun(). This is designed to be called *BEFORE*
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your IO handlers, to let events scheduled immediately (ie a time of 0)
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to initiate IO before the IO handlers are called.
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(Believe me, its useful.)
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Example:
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Say you have something which must be called every 15 seconds.
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* You would first define the callback in your module:
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static EVH foo_periodic_event;
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static int initialised = 0;
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* You would then add the event in your initialization function:
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void foo_init(void)
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{
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if (!initialised) {
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eventAdd("foo_periodic_event", foo_periodic_event, NULL, 0, 0);
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initialised = 1;
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}
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}
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This will force the event to be called the next time eventRun() is called,
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rather than waiting 15 seconds.
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* You then define your event callback:
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static void
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foo_periodic_event(void *data)
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{
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/* We'd do our work here */
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/* Then we'd finish */
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eventAdd("foo_periodic_event", foo_periodic_event, NULL, 15, 0);
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}
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Notes:
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* I really should change the timeout value to be in milliseconds. Squid used
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a double, but Dianora had something against floating point code in the main
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loop (which is understandable). If someone wants a fun task .. :-)
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* Note that the 'name' parameter to eventAdd() / eventAddIsh() is a const
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char *, and is *not copied* but *referenced*. Therefore, it is in your
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best interest to use string constants.
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* /stats E for an oper shows pending events. Thanks Diane!
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