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  1. Apr 12, 2022
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  5. Apr 09, 2022
    • dependabot[bot]'s avatar
      Bump proc-macro2 from 1.0.36 to 1.0.37 (#5265) · 3fef84a6
      dependabot[bot] authored 
      

Bumps [proc-macro2](https://github.com/dtolnay/proc-macro2) from 1.0.36 to 1.0.37.
- [Release notes](https://github.com/dtolnay/proc-macro2/releases)
- [Commits](https://github.com/dtolnay/proc-macro2/compare/1.0.36...1.0.37)

---
updated-dependencies:
- dependency-name: proc-macro2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: default avatardependabot[bot] <[email protected]>

Co-authored-by: default avatardependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
      3fef84a6
    • Sergei Shulepov's avatar
      Fixes the dead lock when any of the channels get at capacity. (#5297) · b89dc00e
      Sergei Shulepov authored 
      The PVF host is designed to avoid spawning tasks to minimize knowledge
of outer code. Using `async_std::task::spawn` (or Tokio's counterpart)
deemed unacceptable, `SpawnNamed` undesirable. Instead there is only one
task returned that is spawned by the candidate-validation subsystem.
The tasks from the sub-components are polled by that root task.

However, the way the tasks are bundled was incorrect. There was a giant
select that was polling those tasks. Particularly, that implies that as soon as
one of the arms of that select goes into await those sub-tasks stop
getting polled. This is a recipe for a deadlock which indeed happened
here.

Specifically, the deadlock happened during sending messages to the
execute queue by calling
[`send_execute`](https://github.com/paritytech/polkadot/blob/a68d9be3/node/core/pvf/src/host.rs#L601).
When the channel to the queue reaches the capacity, the control flow is
suspended until the queue handles those messages. Since this code is
essentially reached from [one of the select
arms](https://github.com/paritytech/polkadot/blob/a68d9be3/node/core/pvf/src/host.rs#L371),
the queue won't be given the control and thus no further progress can be
made.

This problem is solved by bundling the tasks one level higher instead,
by `selecting` over those long-running tasks.

We also stop treating returning from those long-running tasks as error
conditions, since that can happen during legit shutdown.
      b89dc00e
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