### What does this PR do?
After 10s of inactivity in the thread pool, this releases memory more
aggressively back to the operating system
### How did you verify your code works?
### What does this PR do?
The DevSever's `IncrementalGraph` uses a data-oriented design memory
management style, storing data in lists and using indices instead of
pointers.
In conventional memory management, when we free a pointer and
accidentally use it will trip up asan. Obviously this doesn't apply when
using lists and indices, so this PR adds a check in debug & asan builds.
Everytime we free an `Edge` we better make sure that there are no more
dangling references to that spot.
This caught a case where we weren't setting `g.first_import[file_index]
= .none` when deleting a file's imports, causing a dangling reference
and out of bounds access.
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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
`add` no longer locks a mutex, and `finish` no longer locks a mutex
except for the last task. This could meaningfully improve performance in
cases where we spawn a large number of tasks on a thread pool. This
change doesn't alter the semantics of the type, unlike the standard
library's `WaitGroup`, which also uses atomics but has to be explicitly
reset.
(For internal tracking: fixes ENG-19722)
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Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
