Avoid loading babel in forked processes.

[jamestalmage]

We are paying a hefty penalty to load Babel once per forked process.

I have played around with a way to share one Babel instances across every forked process (though it does not necessarily need to be limited to a single instance).

https://github.com/jamestalmage/__share_transpile_across_process

With some very naive benchmarks I am seeing < 3 seconds using this method compared to > 16 loading up a Babel instance per fork.

[floatdrop]

@jamestalmage thought of this too. We can transpile files with babel in master process and load transpiled code from cache (as soon as I deal with #118).

[sindresorhus]

That's a cool idea. I like it.

[jamestalmage]

@floatdrop
What is your plan for the cache? Write it all to disk before launching forks?

I'm actually firing up an http server and then using child_process.execSync('curl', ...) to fetch the transpiled code.

[jamestalmage]

The major problem with my solution is that it requires actually forking an entirely new process for every fetch, which is not free. Forking an execution of curl vs forking another node process is way better, but still not great.

For the initial test file, we could use IPC (maybe even do static analysis of the Babel AST to find additional require calls).

Dynamic requires will be a problem. That is where I think my strategy will help. If somebody does a lot of dynamic calls there is even a chance my strategy may hurt, so we probably need a way for people to turn it off.

[floatdrop]

@jamestalmage yes, but do it step by step (transpile one test and launch it), not all at once.

[jamestalmage]

Gotcha.
Seems reasonable.

[jamestalmage]

@sindresorhus We need a good real-world library to performance test this against. I know pageres is mentioned in the readme, but given the nature of that project (I am just guessing), that a lot of time is spent on I/O. Is there one with a high test-file count where I/O is minimal (where improvements to the load time of AVA forks would be most noticeable).

[sindresorhus]

@jamestalmage https://github.com/sindresorhus/got has a lot of tests and uses a local server for most, so the tests are pretty fast.

[vadimdemedes]

Really good idea! Well done @jamestalmage

[jamestalmage]

This was fixed in ~0.10.0