Add OpentelemetryMonitor to contrib

[derekkraan]

Hi all,

We have been using this in prod for a good number of months now. This has helped us catch a number of issues, since if a process dies before its span can be closed, the span is simply lost.

I thought about how best to get this into opentelemetry. Not 100% sure this is the correct place, but I think this might be a good way to start the discussion, and it's a lower barrier to getting something into the contrib library than into the core library itself.

If there is the feeling that this doesn't belong here then I will release it as a standalone library.

Looking forward to any feedback on this PR.

[bryannaegele]

Thanks Derek! I think we actually want this in the sdk which means it also needs to be in erlang. Any interest in taking this up?

open-telemetry/opentelemetry-erlang#84

[tsloughter]

Yes, would like this in SDK. Do you have interest/time in converting to Erlang? If not there may be someone else who is and we should ask in Slack.

[derekkraan]

I think it should be manageable. I'll close this PR and open a new one in the otel-erlang repo once I have converted to Erlang (hopefully next week sometime).

[hkrutzer]

@derekkraan I was integrating this in my codebase and I was wondering if there was a specific reason for doing :ets.insert(__MODULE__, {self(), span_ctx}) inside monitor() instead of handle_call({:monitor, pid})?

[derekkraan]

@hkrutzer the reason is: it's faster. GenServers are by nature single-threaded.

[hkrutzer]

Sure, but aren't you waiting to the handle_call to complete anyway? So the throughput of the single Genserver is still the bottleneck in this situation. I suppose that throughput could increase by having the ETS call be performed outside of the Genserver 🙂

[derekkraan]

Yes, I meant throughput.