[erlang-patches] allow use of proplists in supervisor start specs

[Daniel Luna]

I have to mention that I think brutal_kill is a really bad choice for a
default.

It breaks the expectation in Erlang that supervisors can never crash. An
expectation that is in the core of what makes Erlang the great language
that it is.

Dangling process trees are not fun to deal with (and don't happen on a VM
crash).

To preserve the correctness and trust of supervision trees the default
should be either infinity or depend on the child type.

For worker children brutal_kill is fine. For supervisor children infinity
is the only sensible choice.
On Jul 1, 2014 7:06 AM, "Loïc Hoguin" <essen@REDACTED> wrote:

> Just wanted to say I agree with everything José said, except 3. the
> different defaults for different process types. It makes things too hard to
> keep track of.
>
> I think brutal_kill is a great choice because it makes it easier for the
> user to stumble upon cold-start issues when restarting their
> application/release. The VM may crash so there's never a guarantee to run
> shutdown functions anyway, and too few people forget to test cases when
> these didn't run, leading to potential production disasters.
>
> On 06/30/2014 04:37 PM, José Valim wrote:
>
>> I have some feedback based on my experience in writing and teaching
>> Erlang/Elixir.
>>
>> 1. I would always require the supervision strategy. When I am
>> prototyping, it is usually hard for me to reason about the intensity and
>> restarts, but I can always reason about the supervision strategy. All
>> teaching materials I know of also discuss the supervision right away, so
>> having it explicit shouldn't hurt those cases.
>>
>> For such cases, maybe we should use the format of {{strategy(), map()},
>> [children()]} (which is similar to what we have today).
>>
>> 2. I also agree with Richard. Having a default of 0 restarts may cause
>> confusion and forcing people to define them won't help when they still
>> have no idea of what values they should use (because it is prototyping /
>> early deploys). I usually fine tune those values based on the production
>> system reports so having saner defaults, like Ulf's, may make more sense.
>>
>> 3. The child_spec defaults are great and similar to the ones we use in
>> Elixir with the only difference being the shutdown value. We have a
>> default of 5000, which is the one usually recommended, but we set it to
>> "infinity" if the type is a "supervisor" (which is the OTP docs
>> recommendation if I remember correctly).
>>
>> Regarding 3., if the recommendation and the consensus in actual systems
>> is to use brutal_kill for shutdown, I will gladly change Elixir to make
>> it consistent with OTP defaults.
>>
>> Thanks for opening the changes for discussion!
>>
>> *José Valim*
>> www.plataformatec.com.br <http://www.plataformatec.com.br/>
>> Skype: jv.ptec
>> Founder and Lead Developer
>>
>>
>>
>>
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>>
> --
> Loïc Hoguin
> http://ninenines.eu
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