Add package to provide gevent compatibiliy (#628)

[aberres]

No description provided.

[reyang]

Thanks @aberres!

Having this in the core library README is a bit weird (as one can imagine, eventually we'll end up with workarounds for all kinds of 3rd party stuff in the main README, which could confuse/scare the audiences), probably having an extension opencensus-ext-gevent makes more sense? @aberres @c24t

What's in my mind:

1. Having opencensus-ext-gevent package.
2. Specify the gevent version in setup.py (so that in the future if gevent supports async, people won't install the wrong package and flip the context back to thread-local-storage by mistake).
3. In the __init__.py, flip the context.
4. Mention in the package README how to use it properly (e.g. needs to be imported before any other OpenCensus components).

[aberres]

@reyang fair enough.

I just pushed a commit containing a new package which makes things "just work" when it is installed.
After gevent did its patching matching a setuptools entry point is called. See http://www.gevent.org/api/gevent.monkey.html#plugins for details.

I did not polish this yet, I want to check first of this is more to your liking.

[reyang]

Looks good overall, I've left some minor suggestions.

[reyang]

I just pushed a commit containing a new package which makes things "just work" when it is installed.
After gevent did its patching matching a setuptools entry point is called. See http://www.gevent.org/api/gevent.monkey.html#plugins for details.

This approach is amazing!

I did not polish this yet, I want to check first of this is more to your liking.

This is great, thanks for the contribution @aberres!

[c24t]

As @reyang said, we need a test that the patch works as expected before we can merge this. It would also be useful to check the entry point, i.e. load the patched gevent first.

[reyang]

LGTM, will merge once CI is clean.

[reyang]

nice!

[reyang]

Thanks @aberres for the great work!

[allenjohnashton]

How long until this package hits pypi?

[reyang]

@allenjohnashton sorry for the delay, here you go https://pypi.org/project/opencensus-ext-gevent/.

In general we try to have at least a release per month.

[allenjohnashton]

Thanks!