Added a way to obtain an indication of the current task state

[VictorKoenders]

I ran into the issue a couple of times where I spawned a task with async_std::task::spawn, and I was interested in getting an indication of the state of this task.

In my specific case I'm spawning up a task that takes data from a TcpStream and sends it to a Sender. This task does not have a noticeable output, however I would like to periodically check if this task is still running and didn't panic or something.

let handle = task::spawn(receiver_loop(stream.clone(), self.sender.clone()));
self.stream = Some((
	stream,
	handle
));

// Periodically run this:
if let Some((_, handle)) = self.stream.as_mut() {
	if handle.task().state() == TaskState::Completed {
		// Something went wrong
		log_error("...");
		self.reconnect()
	}
}

[VictorKoenders]

Some options to remove the #[non_exhaustive]:

• Have an exhaustive enum
• Create a struct that contains the enum, with functions on it
• Add #[doc(hidden)] __Nonexhaustive
• Something else?

[taiki-e]

I'm fine with bumping MSRV to 1.40.

[VictorKoenders]

Rebased onto master

[taiki-e]

Considering that TaskState is non_exhaustive, the user can really only rely on state==Completed (since state==Running may change its meaning in the future).

So I am starting to think that it might actually be preferable to have a method that returns a bool like is_completed.

[taiki-e]

std JoinHandle has a similar unstable feature, which appears to be planned to be renamed is_finished.
rust-lang/rust#94549

[VictorKoenders]

Switched to .is_finished()

[taiki-e]

LGTM. Could you revert MSRV bump?

[taiki-e]

Thanks!

[taiki-e]

Published in 4.2.0.