[erlang-questions] enif_send rules questions

Jason Orendorff <>
Fri Jan 13 23:53:07 CET 2017


On Fri, Jan 13, 2017 at 10:09 AM, Sverker Eriksson <
> wrote:

> On 01/12/2017 08:21 PM, Jason Orendorff wrote:
>
>> 4.  We suspect it's actually totally safe to pass a process-independent
>>      environment as the first parameter, regardless of whether there's a
>>      "calling process" or we're "calling from a created thread". Is it?
>>      If so, would you accept a patch to document that that's OK?
>>
> I'm not super excited about such a guarantee, at least not right now.
>

Thank you for the quick, thoughtful response. I appreciate your time.

Is there a way to enforce this rule for our users that we've missed? When
our `send` method is called, I think we have to figure out if there's a
current
calling process, and if so, its environment. I don't see a way to do it
without
storing that information in TLS ahead of time -- at a cost to every NIF
call.

We could make code that runs on created threads statically different from
code that runs in the Erlang scheduler's threads, e.g. by making
`NifCallEnv`, `AllocatedEnvInNifThread`, and `AllocatedEnvInCreatedThread`
three different types, of which only 2 have `.send()` methods. But this
seems horrible.

We have considered several possible approaches, all about as bad as that.

Thanks,
-j
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