Since the `Atomic*` types can not be marked as `Sendable` (because they aren’t C structs), we can change the variables to constants and can remove `nonisolated(unsafe)`.
We used C atomics but these were allocated as Swift variables. Even thought they were atomic, concurrent accesses to them could violate Swift’s exclusivity laws, raising thread sanitizer errors.
Allocate the C atomics using malloc to fix this problem.
rdar://129170128
The comment on `LocalConnection` assumed that all mutable state was guarded by `queue` but `state` and `handler` actually weren’t. This was found by the thread sanitizer.
This allows us to run `sourcekit-lsp index --project /path/to/project` to index a project. Intended to debugging purposes, eg.
- Profile the time it takes to index a project
- See if the project can be indexed successfully
- Look at signposts generated during indexing in Instruments to see whether indexing or preparation is the bottleneck and how well we can parallelize tasks.
