sync: add len and is_empty methods to mpsc senders
#7103
+156
−2
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Darksonn
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Jan 21, 2025
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| pub fn len(&self) -> usize { | ||
| self.chan.semaphore().bound - self.chan.semaphore().semaphore.available_permits() | ||
| } |
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Unfortunately, this seems incorrect to me. This will include permits in the count, but to match the receiver length method, permits should not be counted.
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Hmm true, I've updated the test locally and it does seem to be affected by reserved permits. I am not well versed in the internals of tokio, but it seems like the length may not be able to be derived from the bounded sender as is due to this reserved permits issue? I'd like to be wrong, but if not then perhaps it would require an atomic counter added to keep track of reserved permits vs messages?
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I believe I commented on this issue previously: #6314 (comment)
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Motivation
Closes #7077
Tldr; adds
lenandis_emptymethods to both bounded and unbounded Senders.Solution
@conradludgate mentioned in the issue in a comment that the unbounded len can be derived from the seamphore's available permits / 2. However it seems like I didn't need to divide the semaphore available permits based on tests.
The implementation of
lenfor boundedSenderdid not use the semaphore's available permits directly, and instead used the semaphore'sbound - available_permits.I've added tests for these new methods which are passing.
Related PR #7092