Re: LibEvent binding to Lua? Mix w/ HelperThreads?

[Javier Guerra <javier@...>]

On Friday 31 March 2006 1:52 am, Thomas Harning Jr. wrote:
> Just wondering, how does a LibEvent binding into Lua sound?  Right now
> it seems to be a good option/addition to the HelperThreads library for
> my MoonLog application (syslog/metalog replacement).

it wouldn't be hard to do a thin binding library; the main hurdle i see is 
that any other library you'd want to produce those events would have to give 
you a file descriptor (fd) to wait on.

that's not hard for 'real' file based I/O and sockets; but what about 
databases?  these could block for significant time, and i don't know of 
anyone that gives you an fd telling "call me when this fd is writeable and i 
won't block"

my goal with HelperThreads is to make it easy to write libraries binding any 
kind of blocking C libraries; since several of them doesn't provide any 
non-blocking interface; and those that do might use any of a number of ways 
to signal completion.... the most general mechanism is to spawn a thread and 
let it block.

> ... Another idea I thought of at this later hour is to have
> HelperThreads be the core... and setup a task/thread as the LibEvent
> dispatch loop... and whenever there's events, either signal_task and
> wait, or queue up the data in a threadsafe queue and
> signal_task(0).  When the update handler gets called, the queue gets
> transferred somehow (either by returning an object w/ a CClosure that
> can access the latest queue objects and then free the data via __gc
> and/or :free())

maybe the nicest way to do it would be to add either a Lua object to be 
returned by the update handler.  just set up a hidden Lua table indexed by a 
lightuserdata that holds the pointer given to event_set().  when the event is 
signalled, just get the associated content and return it.

the same mechanism could be used to associate a Lua function to an event, and 
call it when the event is ready.

also, it wouldn't be too hard to do it both as an independent library, and 
provide a 'task-able' event_loop() if Helper-Threads is present.

-- 
Javier

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