Cache to disk

[willow-ahrens]

Some notes:
We need to use PIDFiles with the stale_age set to a nonzero value otherwise we might run into issues with deadlocking when we control c.

[vchuravy]

How dependent is Finch cache on the state of Julia functions? Julia 1.11 and upwards have some better support for provenance tracking for things like a code cache.

https://github.com/JuliaGPU/GPUCompiler.jl/blob/09b4708ba12e0b19e40f85c64e9105cf666c4d62/src/execution.jl#L63

[willow-ahrens]

That's awesome! Finch does depend on a few overloaded trait functions (the functions declare whether e.g. f is associative). It would be possible to instead store those traits in a struct that can be hashed (e.g. a list of mutable functions). However, I worry that modifications to Finch traits would not live past precompilation in that case. It would be easier if we could hash the state of the world somehow.

In these lines https://github.com/JuliaGPU/GPUCompiler.jl/blob/09b4708ba12e0b19e40f85c64e9105cf666c4d62/src/execution.jl#L139-L140, is it safe to use the world as a key? If I started a julia session at world age e.g. 42, then define foo, I get world age 43. If I start a different session and define bar, wouldn't I still get world age 43?

I'm curious if there's a simple interface to the provenance tracking (like a call/dependency graph). If not, I would probably design my own "rewriter state object"

[vchuravy]

is it safe to use the world as a key?

Within a session, it is safe to use world as a key, across sessions it is not. (Worlds get truncated during precompilation)
Compilation results are also valid across a range of worlds, so the use there is more an "optimistic" cache lookup
before doing the more complicated one that considers world-ranges.

Note that the hash calculcation in https://github.com/JuliaGPU/GPUCompiler.jl/blob/09b4708ba12e0b19e40f85c64e9105cf666c4d62/src/execution.jl#L160 doesn't use world.

I'm curious if there's a simple interface to the provenance tracking

Yeah, https://github.com/JuliaGPU/GPUCompiler.jl/blob/09b4708ba12e0b19e40f85c64e9105cf666c4d62/src/execution.jl#L162
is meant to capture the provenance of an object, but the object needs to be serialized into a precompilation cache.