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Add a has_changed function to watch::Receiver #4342

merged 2 commits into from
Dec 31, 2021


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@elichai elichai commented Dec 24, 2021


I'm using sync::watch to tell a bunch of workers to do some work, and once in a while they check to see what's the latest job, and if there's no new job they should keep doing what they're already doing, and currently the only way to do that is via rex.changed().now_or_never().is_some() which has some Waker overhead (see asm in


Add a has_changed method to check if the value had changed.


  1. This method doesn't change the version that the receiver currently holds, this is the only function in the API that observes the version without changing it, should it maybe also change it? (that comes at the cost of being a &mut self function).
  2. Implement a try_changed function that doesn't block if the value hasn't changed.

@github-actions github-actions bot added the R-loom Run loom tests on this PR label Dec 24, 2021
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@Darksonn Darksonn added A-tokio Area: The main tokio crate M-sync Module: tokio/sync labels Dec 30, 2021
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@Darksonn Darksonn merged commit 12dd063 into tokio-rs:master Dec 31, 2021
@elichai elichai deleted the watch-hash-changed branch January 2, 2022 08:41
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3 participants