Follow-up to #161768.
Context: ProcessPool pickles the outputs before sending them back to the main process. Triton kernels have some un-pickleable fields, so `prepare_for_pickle()` is used to strip out those fields. Previously, in the standard case (without triton_bundler.py), `prepare_for_pickle()` would strip out the un-pickleable fields and they would never be added back after unpickling, because the un-pickleable fields were not actually needed after compilation finished.
In #161768 updated `prepare_for_pickle` to also strip out the `fn._hash_lock` field, a newly added field in JITCallable instances which is a `threading.RLock()`, which is not pickleable.
It turns out that we do need to restore the `fn._hash_lock` field, even in the non-triton_bundler case - the MultiKernel case uses the hash lock.
To do this, we add `restore_after_unpickle()` which will restore fields (or if the old fields are not provided, initialize just the hash_lock)
Compile time benchmarks look good, maybe a very minor regression (see the comment below on the PR)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/162244
Approved by: https://github.com/atalman
fb0afa853e