feat: Refine runtime trait

[martintmk]

Contributes to #2643

Changes

This PR cleans-up and simplifies the Runtime trait.

Before:

pub trait Runtime: Clone + Send + Sync + 'static {
    type Interval: Stream + Send;

    type Delay: Future + Send + Unpin;

    fn interval(&self, duration: Duration) -> Self::Interval;

    fn spawn(&self, future: BoxFuture<'static, ()>);

    fn delay(&self, duration: Duration) -> Self::Delay;
}

After:

pub trait Runtime: Clone + Send + Sync + 'static {
    fn spawn<F>(&self, future: F) where F: Future<Output = ()> + Send + 'static;

    fn delay(&self, duration: Duration) -> impl Future<Output = ()> + Send + 'static;
}

The main changes is the drop of the interval, which can be moved to an internal helper method.

Future Improvements:

This trait could even made to be agnostic to single-threaded and multi-threaded runtimes and be simplified to:

pub trait Runtime {
    fn spawn<F>(&self, future: F) where F: Future<Output = ()> + Send + 'static;

    async fn delay(&self, duration: Duration);
}

The trait requirements would have to be specified on the consuming side:

impl<E, RT> PeriodicReaderBuilder<E, RT>
where
    E: PushMetricExporter,
    RT: Runtime + Send + Sync + 'static,
    RT::delay(..): send + 'static
{
   fn new(exporter: E, runtime: RT) -> Self {
      ...
   }
}

However, this requires the return type notation support which is not yet stable.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: martintmk (a7290ac, eac43a8, b26d1e4, 2e2937e, cf4f15c, 9f082a7, 3f8ca2c, 2b9931b, 9987869)

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.3%. Comparing base (367e484) to head (2b9931b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...try-sdk/src/trace/sampler/jaeger_remote/sampler.rs	0.0%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2641     +/-   ##
=======================================
- Coverage   79.3%   79.3%   -0.1%     
=======================================
  Files        123     123             
  Lines      22670   22682     +12     
=======================================
+ Hits       17986   17993      +7     
- Misses      4684    4689      +5     

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[cijothomas]

This would be towards # 1 in #2643

[cijothomas]

Thanks!

[cijothomas]

@martintmk https://github.com/hyperium/hyper/blob/master/src/rt/mod.rs is what Hyper has. Maybe we should also need just that?

[martintmk]

@cijothomas:

https://github.com/hyperium/hyper/blob/master/src/rt/mod.rs is what Hyper has. Maybe we should also need just that?

The also have a different trait definition for timers:
https://github.com/hyperium/hyper/blob/master/src/rt/timer.rs

It works for them because the timers are only necessary if one wants to do keep-alive for connections, so they are not bound to their runtime trait definition.