docs: add countdown latch example to Semaphore
#6105
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## Motivation Some users have requested that `tokio::sync` add a countdown latch synchronization primitive. This can be implemented using the existing `Semaphore` API, so rather than adding a countdown latch type, we should add documentation examples showing how the `Semaphore` can be used as a countdown latch. ## Solution This branch adds an example to the `tokio::sync::Semaphore` docs demonstrating its usage as a countdown latch. This example was extracted from #6087 (comment). Closes #6087
Darksonn
added
T-docs
| @@ -322,7 +322,7 @@ use std::sync::Arc; | |||
| /// # #[tokio::main(flavor = "current_thread", start_paused = true)] | |||
| /// async fn main() { | |||
| /// let capacity = 5; | |||
| /// let update_interval = Duration::from_secs_f32(1.0 / capacity as f32); | |||
| /// let update_interval = Duration::from_secs_f32(1.0 / capacity as f32); | |||
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This seems like an accidental change?
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whoops, yeah, i'll undo that
| /// /// A token that holds a countdown latch open until it is dropped. | ||
| /// #[derive(Clone)] | ||
| /// pub struct Countdown(Arc<Semaphore>); |
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This derive(Clone) seems a bit weird to me. It makes it difficult to make sure you have the right number of tokens. In your example, you also create one token more than you need, but the extra one in main is not dropped until after the wait completes.
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yeah, that's a good point. this could maybe have some kind of fn try_clone -> Option<Self> that only allows creating as many guards as there are permits, or something? i'm not sure if the additional complexity is worth including in the example or not...
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Maybe just return a vector of them?
Co-authored-by: Alice Ryhl <aliceryhl@google.com>
Co-authored-by: Alice Ryhl <aliceryhl@google.com>
Co-authored-by: Alice Ryhl <aliceryhl@google.com>
Co-authored-by: Alice Ryhl <aliceryhl@google.com>
Motivation
Some users have requested that
tokio::syncadd a countdown latchsynchronization primitive. This can be implemented using the existing
SemaphoreAPI, so rather than adding a countdown latch type, we shouldadd documentation examples showing how the
Semaphorecan be used as acountdown latch.
Solution
This branch adds an example to the
tokio::sync::Semaphoredocsdemonstrating its usage as a countdown latch. This example was extracted
from #6087 (comment).
Closes #6087
Motivation
Solution