Add support for worker_threads

[xvello]

This is port of Blizzard/node-rdkafka#857 by @Twixes, that registers the module with NAN_MODULE_WORKER_ENABLED, for compatibility with worker_threads.

Testing

• Existing test coverage confirms the main thread usage is unaffected
• Additional test test/index.spec.js confirms that the module is now available in a worker thread

Compatibility

nan transparently falls back to the old API for versions older than 10. I tested it with node-v8.0.0-darwin-x64 (build and test run fine).

Do we need cleanup?

Looking at PRs on other libraries, I found that this one adds a call to node::AddEnvironmentCleanupHook to avoid leaking resources on worker exit. I'll need to check the codebase to see whether it's needed here.

[xvello]

Hello @robinfehr, and thanks for moving this fork forward!

We already moved one workload at @PostHog from kafkajs to this lib and measured order-of-magnitude performance improvements. The other workload we want to migrate uses worker threads, which are not currently supported. We'd appreciate a review on this if you can spare the time.

[robinfehr]

@xvello thanks for the PR!
much appreciated that you checked if it falls back correctly to NAN_MODULE if an older node version is present.

currently im not sure if we'd need AddEnvironmentCleanupHook - according to this:
nodejs/node@5c6cf30
we'd have to check for node version >= 11 instead of 10 though.
could you verify already whether that's needed?

[robinfehr]

a e2e test would be much appreciated.
we're in the process of moving the e2e tests to a new testing frame work which enables us to run tests much easier.

you can find them here
testsNew/e2e

[xvello]

Hello @robinfehr, thanks for your reply! I'll look into these two topics, and also update the README document the multi-threaded behaviours.
I do have a time-sensitive topic on my hands right now, but I'll hopefully circle back to this PR at the end of the month.

[robinfehr]

no worries :) im the meantime i'll cleanup the README - long overdue :)

[xvello]

Hello @robinfehr, sorry for the noise. We decided to move away from worker threads so I'll be closing that PR for now. If we were to reverse that decision I'll add testing and reopen it. If anyone else needs it and want to push that PR to the finish line, feel free to reuse this code!