task: Drop the join waker of a task eagerly when the JoinHandle gets dropped or the task completes #6986
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dropped or the task completes Currently, the waker registered with a JoinHandle is not dropped until the task allocation is dropped. This behaviour may cause the memory allocated by a task to not be freed when in the case of two tasks awaiting each others JoinHandle. This commit changes the behaviour by actively dropping the waker when the JoinHandle gets dropped (or the task completes in some cases).
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* `State::transition_do_join_handle_drop` now returns a struct with to booleans to indicate what the JoinHandle should drop * Use `fetch_and` when unsetting JOIN_WAKER after COMPLETE
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* Added missing ';' after unsafe blocks * Improved documentation in `State::transition_to_join_handle_dropped` on the scenarios in which `JOIN_WAKER` gets unset
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ref cycle test into a non-loom test (leaks will be detected by miri)
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Motivation
Currently, the waker registered with a JoinHandle is not dropped until the task allocation is dropped. This behaviour may cause the memory allocated by a task to not be freed when in the case of two tasks awaiting each others JoinHandle.
See #6505 for more details.
Solution
To prevent this we need to actively drop the waker when the
JoinHandlegets dropped (or the task completes in some cases).Closes #6505.