Speed up fieldtypes_cached

[timholy]

xref #988

[timholy]

@lassepe, any chance you can try this branch? On my machine it speeds up 1.12 quite substantially even without JuliaLang/julia#61156

[lassepe]

Nice, with julia 1.12.5 and this PR, revision time in my example from #988 (comment) is down to 20s (from >5min). I would still not consider #988 fixed with this but it is a huge improvement

[lassepe]

JuliaLang/julia#61156 has all sorts of weird precompilation errors for me so I cannot test with that combination (which may be due to the fact that my MWE uses GPU-related packages that don't currently work on julia master)

[timholy]

Great! I just tried your example and saw similar speedup (>800s to 11s).

Do you think type-revision should still be off by default? It's not clear that JuliaLang/julia#61156 will make it any faster on top of this (it's still a useful change, though). So if it needs to be faster to be viable, we will need additional optimizations. JuliaLang/julia#60736 may provide a path forward (one could potentially restrict to names created after the revised type), but it may take a while to get backported to 1.12.

[lassepe]

I would want to do more tests in a real-world use case to make that call. My guess is that it can be enabled by default but that we shouldn't spawn a background thread to build the cache. I think many people implicitly rely on Revise being close to zero-overhead when they don't edit any code (so that it is not devastating to have Revise loaded during "production") but that stops being true if we have a background thread.

[timholy]

Well, a background thread that completes its work fairly quickly would be less intrusive, no?