[erlang-questions] What I dislike about Erlang
Sun Sep 2 16:55:47 CEST 2012
On Aug 31, 2012, at 20:57 , Evan Miller wrote:
> A few more comments specific to TinyMQ:
> On Fri, Aug 31, 2012 at 1:20 AM, Richard O'Keefe <ok@REDACTED> wrote:
>> Another documentation failure is that we fail to document what
>> is not there. In TinyMQ, a channel automatically comes into
>> existence when you try to use it. Perhaps as a consequence of
>> this, there is no way to shut a channel down. In TinyMQ, old
>> messages are not removed from a channel when they expire, but
>> the next time someone does a 'subscribe' (waves hands) or a 'poll'
>> or a 'push' *after* they expire. So if processes stop sending
>> and requesting messages to some channel, the last few messages,
>> no matter how large, may hang around forever. I'm sure there
>> is a reason, but because it's a reason for something *not* being
>> there, there's no obvious place to hang the comment, and there
>> isn't one. (Except for the dead 'expire' clause mentioned above.)
>> IT'S HARD TO SPOT SALIENT DETAIL IN A SEA OF GLUE CODE.
> This probably proves your point, but just to be clear old messages
> will only "hang around forever" if 1. there are no new messages on a
> channel and 2. the channel continues to receive requests. If there is
> no activity on a channel for max_age, the gen_server timeout is
> invoked here:
There must be a bug there. You only specify a timeout in the return of init, but that does not persist beyond the first message received. I can't see how that timeout would ever be invoked.
> That calls "expire" (erasing the reference to the channel) and then
> exits the supervisor (eliminating the channel and all of its
If you by that mean that it kills the supervisor, it does not. It kills itself, with the supervisor pid as its exit message.
Either way, why do you create a new supervisor for each channel, and why do you create it outside the supervisor tree (i.e from a gen_server and not another supervisor)? What purpose does it serve?
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