coroutine based event bus

thijs · 2015-12-05T07:55:48+00:00

Internal redirection mean nginx invoked location as a internal function call rather than going over tcp/socket.additional two connections: When re...

coroutine based event bus

thijs

Hi,

For an application which is extensible through plugins I'm looking into setting up an event bus. Common Lua practice is to implement this as coroutines.

When initially starting the routine, I can pass the generic data, each event will have its own data. This allows for a clean separation. Something like;

-- generic piece for event dispatching
function myapp.nextEvent(...)
   return coroutine.yield(...)
end

-- each plugin module
return function(my, generic, parameters)
   -- initialize plugin, we now have my-generic-parameters as local upvalues

  while true do
     local event, parameters = myapp.nextEvent()
     -- deal with the event
  end
end

It's the standrad way of doing this with Lua, but is this a sensible approach with OpenResty?

Things that come to mind;

when starting this module from `init_by_lua` can I resume it from other directives?
considering this directive, will I be dragging along globals in the upvalues and have performance penalties when using them?
how resilient is this from the 'yield across c boundary' error?

anything else? any help is appreciated

regards

Thijs

agentzh

Hello!

On Sat, Dec 5, 2015 at 7:55 AM, Thijs Schreijer wrote:
> It's the standrad way of doing this with Lua, but is this a sensible
> approach with OpenResty?
>

You are free to use whatever you see fit. Just please keep in mind
that abstractions like coroutines come with a price. For the best
performance, try your best to avoid unnecessary coroutine API calls on
hot code paths. Having said that, I'm not entirely sure that I do
understand what exactly you are trying to achieve.

> when starting this module from `init_by_lua` can I resume it from other
> directives?

Not really. `init_by_lua` runs in the nginx master process while other
directives run in the nginx workers.

> considering this directive, will I be dragging along globals in the upvalues
> and have performance penalties when using them?

Yes. So better declare your upvalues as locals in the outer scope.

> how resilient is this from the 'yield across c boundary' error?
>

It depends on the Lua function calls on the calling chain. Some
builtin Lua functions like require() are currently implemented as C
functions and may result in such errors. Try your best to avoid them.

Regards,
-agentzh