sync: avoid deadlocks in broadcast with custom wakers
#5578
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Darksonn
reviewed
Mar 24, 2023
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| assert!(waiter.queued); | ||
| waiter.queued = false; | ||
| wakers.wake_all(); |
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What happens here on panic?
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If one of the wakers panics, then the remaining waiters in the queue will not be notified, i.e. their wakers will not be called, they will have to be polled manually. This is the same issue which is currently present in Notify and I think we do not have a clear solution yet (#4069).
Darksonn
approved these changes
Apr 16, 2023
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| #[test] | ||
| fn send_in_waker_drop() { | ||
| use futures::task::ArcWake; | ||
| use std::future::Future; | ||
| use std::task::Context; |
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I verified that this test deadlocks without your changes. ✔️
crapStone
pushed a commit
to Calciumdibromid/CaBr2
that referenced
this pull request
Apr 29, 2023
This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dependencies | minor | `1.27.0` -> `1.28.0` | | [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dev-dependencies | minor | `1.27.0` -> `1.28.0` | --- ### Release Notes <details> <summary>tokio-rs/tokio</summary> ### [`v1.28.0`](https://github.com/tokio-rs/tokio/releases/tag/tokio-1.28.0): Tokio v1.28.0 [Compare Source](tokio-rs/tokio@tokio-1.27.0...tokio-1.28.0) ##### 1.28.0 (April 25th, 2023) ##### Added - io: add `AsyncFd::async_io` ([#​5542]) - io: impl BufMut for ReadBuf ([#​5590]) - net: add `recv_buf` for `UdpSocket` and `UnixDatagram` ([#​5583]) - sync: add `OwnedSemaphorePermit::semaphore` ([#​5618]) - sync: add `same_channel` to broadcast channel ([#​5607]) - sync: add `watch::Receiver::wait_for` ([#​5611]) - task: add `JoinSet::spawn_blocking` and `JoinSet::spawn_blocking_on` ([#​5612]) ##### Changed - deps: update windows-sys to 0.48 ([#​5591]) - io: make `read_to_end` not grow unnecessarily ([#​5610]) - macros: make entrypoints more efficient ([#​5621]) - sync: improve Debug impl for `RwLock` ([#​5647]) - sync: reduce contention in `Notify` ([#​5503]) ##### Fixed - net: support `get_peer_cred` on AIX ([#​5065]) - sync: avoid deadlocks in `broadcast` with custom wakers ([#​5578]) ##### Documented - sync: fix typo in `Semaphore::MAX_PERMITS` ([#​5645]) - sync: fix typo in `tokio::sync::watch::Sender` docs ([#​5587]) [#​5065]: tokio-rs/tokio#5065 [#​5503]: tokio-rs/tokio#5503 [#​5542]: tokio-rs/tokio#5542 [#​5578]: tokio-rs/tokio#5578 [#​5583]: tokio-rs/tokio#5583 [#​5587]: tokio-rs/tokio#5587 [#​5590]: tokio-rs/tokio#5590 [#​5591]: tokio-rs/tokio#5591 [#​5607]: tokio-rs/tokio#5607 [#​5610]: tokio-rs/tokio#5610 [#​5611]: tokio-rs/tokio#5611 [#​5612]: tokio-rs/tokio#5612 [#​5618]: tokio-rs/tokio#5618 [#​5621]: tokio-rs/tokio#5621 [#​5645]: tokio-rs/tokio#5645 [#​5647]: tokio-rs/tokio#5647 </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about these updates again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNS42My4xIiwidXBkYXRlZEluVmVyIjoiMzUuNjQuMCJ9--> Co-authored-by: cabr2-bot <cabr2.help@gmail.com> Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1875 Reviewed-by: crapStone <crapstone@noreply.codeberg.org> Co-authored-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org> Co-committed-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
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Motivation
Currently, the
broadcastchannel drops wakers while holding the lock to the internal state. This can lead to a deadlock if a user provides a custom waker implementation, see #5429.Solution
Notifyand the IO driver.