Introduce Context.suppress_instrumentation

[reyang]

Added Context.suppress_instrumentation flag, which can be used for the following scenarios:

1. avoid instrumentation while running inside exporter.
2. suppress certain call path to avoid excessive/unwanted data.

[reyang]

Maybe we can generalize this concept into a "terminal span" as @a-feld mentioned. Save this for the post alpha v0.1 work.

[reyang]

Changed to suppress_instrumentation as suggested by @Oberon00.

[reyang]

@mauriciovasquezbernal FYI related to #153.

[Oberon00]

Context.is_exporter sounds strange, as if it checks whether the context is an exporter, which wouldn't make sense. Thus I suggest Context.is_exporter_active or maybe Context.is_exporting. Regarding your comment, why not name it Context.suppress_instrumentation?

[mauriciovasquezbernal]

It'd be really nice to have a commit/PR description so one can understand what it is about without having to go to the code.

[Oberon00]

Please update to also cover batch exporter (#153)

[reyang]

Minor: I was a bit struggling whether to put this in finally statement or not.

suppress_instrumentation = Context.suppress_instrumentation
try:
    Context.suppress_instrumentation = True
    self.span_exporter.export((span,))
# pylint: disable=broad-except
except Exception as exc:
    logger.warning("Exception while exporting data: %s", exc)
Context.suppress_instrumentation = suppress_instrumentation

This looks nicer (symmetric), however if there is uncaught exception, or later someone added a return in the try statement, the context could get wrong.

[reyang]

And introducing a context manager seems to be an overkill here.

[c24t]

I agree with the finally here, but also think a context manager in context would make sense.

with Context.set('suppress_instrumentation', True):
    # do stuff that shouldn't be instrumented

This would also let you use the set/reset token, which you can't access here since Context doesn't expose the ContextVars it uses under the hood.

[c24t]

LGTM. You might consider making suppress_instrumentation a first-class citizen since we're likely to use it elsewhere. I don't think context should know about instrumentation, but maybe in opentelemetry-api.

[reyang]

Created #183 and #184 to follow up post Alpha v0.1.