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Rework reusability control in cancellable contination #2581

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merged 6 commits into from Mar 24, 2021
Merged

Rework reusability control in cancellable contination #2581

merged 6 commits into from Mar 24, 2021

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* Update initCancellability documentation and implementation to be aligned with current invariants
* Make parentHandle non-volatile and ensure there are no races around it
* Establish new reusability invariants
  - Reusable continuation can be used _only_ if it's state is not REUSABLE_CLAIMED
  - If it is, spin-loop and wait for release
  - Now the parent is attached to reusable continuation only if it was suspended at least once. Otherwise, the state machine can return via fast-path and noone will be able to release intercepted continuation (-> detach from parent)
  - It implies that the parent is attached after trySuspend call and can be concurrently reused, this is where new invariant comes into play

Fixes #2564

@qwwdfsad
Rework reusability control in cancellable contination
9306f8c 
    * Update initCancellability documentation and implementation to be aligned with current invariants
    * Make parentHandle non-volatile and ensure there are no races around it
    * Establish new reusability invariants
      - Reusable continuation can be used _only_ if it's state is not REUSABLE_CLAIMED
      - If it is, spin-loop and wait for release
      - Now the parent is attached to reusable continuation only if it was suspended at least once. Otherwise, the state machine can return via fast-path and noone will be able to release intercepted continuation (-> detach from parent)
      - It implies that the parent is attached after trySuspend call and can be concurrently reused, this is where new invariant comes into play

Fixes #2564
@qwwdfsad qwwdfsad requested a review from elizarov March 13, 2021 15:38
@qwwdfsad
Simplify reusable continuations ever further
8bc7bb6 
    * Leverage the fact that it's non-atomic and do not check it for cancellation prematurely. It increases the performance of fast-path, but potentially affects rare cancellation cases
    * Fix AwaitContinuation that has parentHandle == null but is not reusable
elizarov
elizarov approved these changes Mar 18, 2021
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Looks great. While studying the code I've made some minor refactoring (mostly to remove duplicated code) and added some more comments.

@qwwdfsad qwwdfsad requested a review from elizarov March 23, 2021 14:58
@qwwdfsad qwwdfsad merged commit e608dfb into develop Mar 24, 2021
@qwwdfsad qwwdfsad deleted the reusable-memory-leak branch March 24, 2021 08:51
@shmuelr shmuelr mentioned this pull request Apr 9, 2021
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pablobaxter pushed a commit to pablobaxter/kotlinx.coroutines that referenced this pull request Sep 14, 2022
@qwwdfsad @pablobaxter
Rework reusability control in cancellable continuation (Kotlin#2581)
245b260 
* Rework reusability control in cancellable continuation

    * Update initCancellability documentation and implementation to be aligned with current invariants
    * Make parentHandle non-volatile and ensure there are no races around it
    * Establish new reusability invariants
      - Reusable continuation can be used _only_ if it states is not REUSABLE_CLAIMED
      - If it is, spin-loop and wait for release
      - Now the parent is attached to reusable continuation only if it was suspended at least once. Otherwise, the state machine can return via fast-path and no one will be able to release intercepted continuation (-> detach from parent)
      - It implies that the parent is attached after trySuspend call and can be concurrently reused, this is where new invariant comes into play
    * Leverage the fact that it's non-atomic and do not check it for cancellation prematurely. It increases the performance of fast-path, but potentially affects rare cancellation cases

Fixes Kotlin#2564
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@elizarov elizarov elizarov approved these changes

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