Fix cache leaks for pe._cached_abstract_eval; add util.multi_weakref_lru_cache #30009
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The function `pe._cached_abstract_eval` uses `util.cache`, while most other cached functions in JAX use `weakref_lru_cache`. The main difference is that `util.cache` keeps strong references to the function arguments. The modified test `lax_control_flow_test::test_cond_memory_leak` (added a jit for one of the branches) is failing without this fix. This is because the Jaxpr including the closed-over constant leaks due to the strong references kept by the `util.cache` used in `pe._cached_abstract_eval`. We cannot use directly `weakref_lru_cache` because it keeps weak references only to the first positional argument. We add here a variant `multi_weakref_lru_cache` that uses weak references for all the positional and keyword arguments for which `util.is_weakref_cache_key_type` is true. This is set for `Jaxpr`, `ClosedJaxpr` and `Callable`. Eventually, we can decide to generalize the existing `weakref_lru_cache` to have this behavior.
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The function
pe._cached_abstract_evalusesutil.cache, while most other cached functions in JAX useweakref_lru_cache. The main difference is thatutil.cachekeeps strong references to the function arguments.The modified test
lax_control_flow_test::test_cond_memory_leak(added a jit for one of the branches) is failing without this fix. This is because the Jaxpr including the closed-over constant leaks due to the strong references to**paramskept by theutil.cacheused inpe._cached_abstract_eval.We cannot use directly
weakref_lru_cachebecause it keeps weak references only to the first positional argument. We add here a variantmulti_weakref_lru_cachethat uses weak references for all the positional and keyword arguments for whichutil.is_weakref_cache_key_typeis true. This is currently set forJaxpr,ClosedJaxprandCallable.The
multi_weakref_lru_cacheis a wrapper aroundweakref_lru_cache, and in fact if there is exactly oneweakref, it behaves exactly like
weakref_lru_cache. Eventually, we can decide to generalize the existingweakref_lru_cacheto have this behavior.