[getdns-users] PHP Language Bindings and Async Event Management

[Neel Goyal]

As a followup, the iOS bindings also created an event base that worked
native w/ grand central dispatch.  Ideally Android could work the same way
without an additional worker thread.

On Tue, Apr 21, 2015 at 11:11 AM Willem Toorop <willem at nlnetlabs.nl> wrote:

> Hi Scott,
>
> With our getdns implementation, the extensions are wrappers that provide
> a uniform interface for different event bases.  We provide extensions
> for libevent, libev and libuv.  We also have a built in event base
> (mini_event) based on select, that will we the default extension when
> you did not set one explicitly with getdns_extension_set_libevent_base,
> getdns_extension_set_libev_loop and getdns_extension_set_libuv_loop.
>
> All those extension provide their uniform interface through a list of
> function pointers with the same signature (the virtual method table
> (hence vmt)) in another struct which might have extension specific data
> (like the event base itself where the extension provides the uniform
> interface for).  So they are actually objects for the getdns_eventloop
> class...
>
> One of the functions in the VMT is the cleanup function which will
> destroy the extension, but in case of the libevent, libev and libuv
> extension, not the event bases with which the extension was created and
> set.  Only with mini_event there was no event base on which the
> extension was based, so that will destroy the event base with the
> extension.
>
> I think this answers everything you wanted to know about this, but there
> is something else interesting too.
>
> Our implementation provides means to create an event base extension
> yourself.  In fact, the node bindings use this to hook into the node
> native libuv event loop (so it does not use the libuv extension!).
> I do not know how async operation is handled with php normally, but to
> just give an example for its potential (which might event not be
> realistic)... If we could provide python bindings for those methods to
> create your own extension, it might be possible to hook into native
> python event systems, like twisted.
>
> Food for thought ;)
>
> Cheers,
> -- Willem
>
>
>
>
>
> Op 21-04-15 om 13:30 schreef Hollenbeck, Scott:
> >> -----Original Message-----
> >> From: getdns-api [mailto:getdns-api-bounces at vpnc.org] On Behalf Of
> >> Goyal, Neel
> >> Sent: Monday, April 20, 2015 1:58 PM
> >> To: Melinda Shore; getdns-api at vpnc.org
> >> Subject: Re: [getdns-api] PHP Language Bindings and Async Event
> >> Management
> >>
> >> Freeing the context should not clean up the event base.  If the event
> >> base
> >> is shared between other async libs and they are adding to that event
> >> base,
> >> a context destroy should not prevent those libs from still functioning.
> >> The context_destroy makes sure the context is detached from the
> >> event_base, but any structures specific to libevent are not cleaned up.
> >> Much like the user has to create the lib event base explicitly and then
> >> attach it to getdns, the user has to free it.
> >
> > Neel, in a note I sent to this list last week (BTW, it looks like recent
> notes aren't being archived) I described a challenge I found in trying to
> use the PHP libevent extension with getdns. I can create an event base, but
> I don't see an easy way to attach that to a context. Come on down if you
> have a chance and I'll walk you through what I found.
> >
> > So, I took a look at how I could use the functions provided by the
> getdns libevent extension. Looking at the code in context.c, I found that
> getdns_context_create() calls
> getdns_context_create_with_memory_functions(), which calls
> getdns_context_create_with_extended_memory_functions(). That function calls
> getdns_mini_event_init() (in file libmini_event.c), which creates an event
> base and sets an event loop. That base is cleaned up when calling
> getdns_context_destroy(), which calls
> context->extension->vmt->cleanup(context->extension).
> >
> > Scott
> >
> > _______________________________________________
> > getdns-api mailing list
> > getdns-api at vpnc.org
> >
>
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