Fix ownership in async_scope::detached_spawn #376
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PR #372 has a subtle ownership bug that's mostly attributable to a lack of tests for `detached_spawn` and friends. If `async_scope::cleanup()` triggers `set_done()` on a detached promise because of the stop callback registered on the scope's stope source, we'll delete the operation state while using its `inplace_stop_source`, leading to a use-after-free. This diff fixes the problem by making the guilty stop callback a part-owner in the operation state. There are now three owners: the `future<>` (if there is one), the operation itself, and the stop callback that propagates stop requests from the scope's stop source to each operation's stop source. I'll figure out how to write a unit test that captures the now-fixed failure mode in a future PR.
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PR #372 has a subtle ownership bug that's mostly attributable to a lack
of tests for
detached_spawnand friends. Ifasync_scope::cleanup()triggers
set_done()on a detached promise because of the stop callbackregistered on the scope's stop source, we'll delete the operation state
while using its
inplace_stop_source, leading to a use-after-free.This diff fixes the problem by making the guilty stop callback a
part-owner in the operation state. There are now three owners: the
future<>(if there is one), the operation itself, and the stopcallback that propagates stop requests from the scope's stop source to
each operation's stop source.
I'll figure out how to write a unit test that captures the now-fixed
failure mode in a future PR.