Ben Gamari authored Dec 06, 2022 and Marge Bot committed Mar 08, 2023

The current segments are conceptually owned by the mutator, not the
collector. Consequently, it was quite tricky to prove that the mutator
would not race with the collect due to this shared state. It turns out
that such races are possible: when resizing the current segment array
we may concurrently try to take a heap census. This will attempt to walk
the current segment array, causing a data race.

Fix this by moving the current segment array into `Capability`, where it
belongs.

Fixes #22926.