fix: Ensure pending messages are delivered when OutputPort is dropped.

[stuartcarnie]

Summary

This PR ensures that pending messages are delivered when an OutputPort is dropped.

Overview

This PR removes the Drop implementation from OutputPort<T>, which called the stop function on all subscribers:

ractor/ractor/src/port/output/mod.rs

Lines 107 to 113 in 1949d92

	fn drop(&mut self) {
	let mut subs = self.subscriptions.write().unwrap();
	for sub in subs.iter_mut() {
	sub.stop();
	}
	subs.clear();
	}

Calling the stop function would abort the JoinHandle of the subscriber:

ractor/ractor/src/port/output/mod.rs

Lines 132 to 134 in 1949d92

	pub(crate) fn stop(&mut self) {
	self.handle.abort();
	}

which would immediately terminate the tokio task responsible for delivering messages to the subscriber:

ractor/ractor/src/port/output/mod.rs

Lines 147 to 156 in 1949d92

	let handle = crate::concurrency::spawn(async move {
	while let Ok(Some(msg)) = port.recv().await {
	if let Some(new_msg) = converter(msg) {
	if receiver.cast(new_msg).is_err() {
	// kill the subscription process, as the forwarding agent is stopped
	return;
	}
	}
	}
	});

Removing the Drop implementation still results in the tasks properly shutting down, as per the tokio documentation for closing broadcast channels:

Closing

When all Sender handles have been dropped, no new values may be sent. At this point, the channel is “closed”. Once a receiver has received all values retained by the channel, the next call to recv will return with RecvError::Closed.

The implementation of the receive pump will exit when the channel does not return an Ok result:

ractor/ractor/src/port/output/mod.rs

Line 148 in 1949d92

while let Ok(Some(msg)) = port.recv().await {

[stuartcarnie]

This test consistently fails with the version on the main branch, and passes when Drop is removed

[slawlor]

Looks good! Thanks for the contribution

[codecov]

Codecov Report

Attention: Patch coverage is 93.18182% with 3 lines in your changes missing coverage. Please review.

Project coverage is 81.33%. Comparing base (1949d92) to head (811f629).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ractor/src/port/output/tests.rs	93.18%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #293      +/-   ##
==========================================
+ Coverage   81.30%   81.33%   +0.03%     
==========================================
  Files          60       60              
  Lines       10856    10890      +34     
==========================================
+ Hits         8826     8857      +31     
- Misses       2030     2033       +3     

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[slawlor]

Please run rustfmt then update the pr, then it's good to merge!

[stuartcarnie]

@slawlor sorry I missed that – done!

[slawlor]

I'll try and get a version cut today with this fix included

[philjb]

I'll try and get a version cut today with this fix included

appreciate it @slawlor!

[slawlor]

V0.13.2 has this included.