Fix race condition that could lose a transfer completion wakup #92
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If `poll_completion_generic` runs between `notify_completion`'s `waker.take()` and `state.swap(STATE_COMPLETED, ...)`, it could see the transfer as pending and register its waker, but that waker would never be called. This adds an Arc because once the transfer is set to `STATE_COMPLETED`, the other thread might free it, so we need to ensure the AtomicWaker stays alive while we use it. That's what the `take()` was intended to work around, but reading the waker before writing the status introduces the race.
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If
poll_completion_genericruns betweennotify_completion'swaker.take()andstate.swap(STATE_COMPLETED, ...), it could see the transfer as pending and register its waker, but that waker would never be called.This adds an Arc because once the transfer is set to
STATE_COMPLETED, the other thread might free it, so we need to ensure the AtomicWaker stays alive while we use it. That's what thetake()was intended to work around, but reading the waker before writing the status introduces the race.Fixes #89