Detect coverage earlier

[burke]

@grosser @jules2689

This should bail out of the iseq caching early enough. Testing whether the constant is defined is very fast. This should add less than 2ms to shopify boot.

Where this falls down is if coverage is eager-loaded by something, but not actually used.

The only ruby-land API available to us to test whether coverage is actually running is Coverage.peek_result, which appears to be quite expensive if coverage is currently running. I think that's unviable. I wonder if we can add a little function to the C extension to check this more economically.

[grosser]

a ruby issue could be nice to track it, but looks good

[burke]

rb_get_coverages exists, though not in ruby.h. I extern'd it and this seems to work fine. I'll make a ruby issue too, it would be nice to have Coverage.running?

[grosser]

oh, sneaky :)

[burke]

https://bugs.ruby-lang.org/issues/13667

[jules2689]

So this would add 1ms of time to check for coverage? 💩 I guess it's needed though

[burke]

> Benchmark.realtime { $LOADED_FEATURES.size.times { defined?(Coverage) && Bootsnap::CompileCache::Native.coverage_running? } } - Benchmark.realtime { $LOADED_FEATURES.size.times { } }
=> 0.0005639999872073531

So yeah I'm not too worried about that.

[jules2689]

Ah, ok. 👍.
I had just divided the 1.36s by 100 from here.