On 3/4/21 7:45 AM, José Valim wrote:
Thanks for sharing. I have read the proposal and I think it describes
the problem well!
I have only one minor comment on the proposed solution, which is this:
> The new supervisor flag is named |shutdown| with possible values
|normal|, |any_significant|and |all_significant|, with |normal| being
the default.
I don't like "normal" being the default because now I have to remember
to change two places, the supervisor specification and the child spec,
when configuring a significant child. The argument for this choice was:
> With the supervisor |shutdown| flag set to |normal|, the child spec
flag |significant| is ignored, even if present and set to |true|. This
is intended as a safety means to defend against unwanted breaking of
old code.
I don't think it is possible for old code to break because there is no
old code using significant in a child spec. :)
Therefore I would propose for the default to be either any_significant
or all_significant (if we want to be conversative, the latter). If we
really think a default of normal is necessary, then I would propose to
at least warn if the supervisor is normal and a significant child is
given, as that will eventually save someone from debugging why the
significant flag is not working as expected. :)
I also think #{shutdown => normal} in a supervisor spec can be
confusing, because someone may think it is customizing the exit reason
of the supervisor, which is typically shutdown (and not normal). If
normal is no longer the default, you could remove the normal option
altogether, but if you want to keep it, perhaps something like
ignore_significant is clearer?
I would prefer the normal option remain, but with a different name. I
agree using the name "normal" would be confusing. However, the option
should exist to mark a supervisor as part of a static supervision
hierarchy. There should also be error checking to ensure child specs
with significant set to true cause an error (the value doesn't get
silently ignored). The error can be used as a return value for
supervisor:start_child/2 and would block significant use where it is
considered inappropriate (some supervisor processes would want to always
exist as part of a static hierarchy).
I am not sure about a name instead of "normal" for the option.
Alternative name ideas for the option are "default", "none", "static",
"external".
Thanks,
Michael
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