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Add mark_unchanged method to watch::Receiver #6252

Merged
merged 4 commits into from
Dec 30, 2023
Merged

Add mark_unchanged method to watch::Receiver #6252

merged 4 commits into from
Dec 30, 2023

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PaulOlteanu
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@PaulOlteanu PaulOlteanu commented Dec 27, 2023

Motivation

Closes #6086

Solution

watch::Receiver now has a method mark_unchanged that just sets that receiver's version to the current version

@github-actions github-actions bot added the R-loom-sync Run loom sync tests on this PR label Dec 27, 2023
@PaulOlteanu
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I'm interested in feedback on how to make the doc clearer, I think it might be explained sort of awkwardly

@Darksonn Darksonn added A-tokio Area: The main tokio crate M-sync Module: tokio/sync labels Dec 28, 2023
Comment on lines 676 to 679
/// After invoking this method [`has_changed()`](Self::has_changed)
/// *MAY* return `false` and [`changed()`](Self::changed) *MAY* not return
/// immediately. This is because a new value could be sent before
/// this method returns.
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This is only the case if a value could be sent concurrently with this call. If there are no concurrent sends, then this does not apply.

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Yeah I'll explain that better. Should I also provide a warning that the value being marked as "seen" could change if used concurrently as well? e.g.

  1. receiver version is 2, shared version is 4. mark_unchanged is called
  2. another task sends a message so shared version becomes 6, mark_unchanged sets receiver version to 6
  3. the caller intended to ignore the value associated with version 4 but instead skips 2 values

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I don't know how important the warning really is. It applies to anything that works with concurrency. You could say something along the lines of if another message is sent concurrently with the call to mark_unchanged, then you cannot predict whether the message or the mark_unchanged call comes first.

tokio/src/sync/watch.rs Outdated Show resolved Hide resolved
Comment on lines 676 to 683
/// After calling this method in a single-threaded context, a subsequent call to
/// [`has_changed()`](Self::has_changed) will return `false`, and a subsequent call
/// to [`changed()`](Self::changed) will yield.
///
/// After calling this method in a multi-threaded context, subsequent
/// behaviour will vary depending on if a value is sent concurrently.
/// For example, a new value could be sent before this method returns
/// which would cause a call to [`changed`](Self::changed) to return immediately
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Honestly, I think this is more confusing than it is useful. It's not clear what "single-threaded context" and "multi-threaded context" means. Does code running on a multi-threaded runtime necessarily imply that you are in a "multi-threaded context" according to this paragraph? No, but I anticipate being asked that question in the future. I would rather just take it out entirely.

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Yeah I'm cool with removing it

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Thank you.

@Darksonn Darksonn enabled auto-merge (squash) December 30, 2023 19:53
@Darksonn Darksonn merged commit 02b779e into tokio-rs:master Dec 30, 2023
71 checks passed
kodiakhq bot pushed a commit to pdylanross/fatigue that referenced this pull request Feb 5, 2024
Bumps tokio from 1.35.1 to 1.36.0.

Release notes
Sourced from tokio's releases.

Tokio v1.36.0
1.36.0 (February 2nd, 2024)
Added

io: add tokio::io::Join (#6220)
io: implement AsyncWrite for Empty (#6235)
net: add support for anonymous unix pipes (#6127)
net: add UnixSocket (#6290)
net: expose keepalive option on TcpSocket (#6311)
sync: add {Receiver,UnboundedReceiver}::poll_recv_many (#6236)
sync: add Sender::{try_,}reserve_many (#6205)
sync: add watch::Receiver::mark_unchanged (#6252)
task: add JoinSet::try_join_next (#6280)

Changed

io: make copy cooperative (#6265)
io: make repeat and sink cooperative (#6254)
io: simplify check for empty slice (#6293)
process: use pidfd on Linux when available (#6152)
sync: use AtomicBool in broadcast channel future (#6298)

Documented

io: clarify clear_ready docs (#6304)
net: document that *Fd traits on TcpSocket are unix-only (#6294)
sync: document FIFO behavior of tokio::sync::Mutex (#6279)
chore: typographic improvements (#6262)
runtime: remove obsolete comment (#6303)
task: fix typo (#6261)

#6220: tokio-rs/tokio#6220
#6235: tokio-rs/tokio#6235
#6127: tokio-rs/tokio#6127
#6290: tokio-rs/tokio#6290
#6311: tokio-rs/tokio#6311
#6236: tokio-rs/tokio#6236
#6205: tokio-rs/tokio#6205
#6252: tokio-rs/tokio#6252
#6280: tokio-rs/tokio#6280
#6265: tokio-rs/tokio#6265
#6254: tokio-rs/tokio#6254
#6293: tokio-rs/tokio#6293
#6238: tokio-rs/tokio#6238
#6152: tokio-rs/tokio#6152
#6298: tokio-rs/tokio#6298
#6262: tokio-rs/tokio#6262
#6303: tokio-rs/tokio#6303
#6261: tokio-rs/tokio#6261


... (truncated)


Commits

eaf81ed chore: prepare Tokio v1.36.0 (#6312)
53f9e5a ci: make sure dictionary words are sorted and unique (#6316)
9077762 net: expose keepalive option on TcpSocket (#6311)
131e7b4 ci: add spellchecking (#6297)
e53b92a io: clarify clear_ready docs (#6304)
7536132 sync: use AtomicBool in broadcast channel future (#6298)
b6d0c90 macros: fix trait_method breaking change detection (#6308)
4846959 runtime: remove obsolete comment (#6303)
ec30383 net: add UnixSocket (#6290)
f80bbec io: simplify check for empty slice (#6293)
Additional commits viewable in compare view




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Add mark_unchanged or mark_seen for tokio::sync::watch::Receiver.
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