ts/Task: split iterate into try_next and handle_item

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Previous Task iteration model suffered from the following
shortcomings:

- When an iteration was engaged it could be cancelled at
  await points by Stop or Flush state transitions,
  which could lead to inconsistent states.
- When an iteration was engaged it could not be cancelled
  by a Pause state transition so as to prevent data loss.
  This meant we couldn't block on the Pause request because
  the mechanism couldn't guarantee Paused would be reached
  in a timely manner.

This commit split the Task iteration into:

- `try_next`: this function returns a future that awaits
  for a new iteration to begin. The regular use case is
  to return an item to process. The item can be left to
  `()` if `try_next` acts as a tick generator. It can
  also return an error. This function can be cancelled at
  await points when a state transition request occurs.
- `handle_item`: this function is called with the item
  returned by `try_next` and is guaranteed to run to
  completion even if a transition request is received.

Note that this model plays well with the common Future
cancellation pitfalls in Rust.

...

This commit is contained in:

François Laignel 2022-08-06 18:10:43 +02:00

parent 07cbc2f025

commit 8b54c3fed6

1 changed files with 372 additions and 416 deletions

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generic/threadshare/src/runtime/task.rs

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