[erlang-questions] valid use for gen_server?

Scott Lystig Fritchie <>
Tue Oct 5 00:36:14 CEST 2010


Pablo Platt <> wrote:

pp> I see two options to implement the above, gen_event or custom event
pp> module.  What bothers me in gen_event is that it executes handlers
pp> in its own context.  If events are rare that shouldn't be a problem
pp> but if each IM message will fire several events wouldn't this flood
pp> the gen_event server?

Using gen_event, if you want to apply backpressure, you have the option
of sending the events synchronously.

pp> I can use a custom event module that saves events and handlers in
pp> ETS table and call functions dynamically with Module:Function(Args).
pp> This also doesn't feel right because each IM message will require
pp> several ETS lookups and dynamic functions calls which according to
pp> the efficiency guide are are 6 times slower than normal calls.

Er, sorry, but this sounds like premature worrying.  If handling an
event requires N reductions and therefore N units of time(*), then the
cost of handling the same event using the dynamic functions calls would
be (N - several) + (6 * several) ... which is likely to be really,
*really* close to N.

-Scott

(*) Which isn't exactly true, but it's a good approximation.


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