Abort prometheus worker on farmer exit.

[shamil-gadelshin]

This PR adds abortion for an optional Prometheus task serving farmer's metrics on the application exit.

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[nazar-pc]

This will not have the desired effect. It will work on Ctrl+C, but the idea was that it should be stopped on drop. Future returned by fn farm doesn't have to complete, it could hypothetically be simply dropped any time.

[shamil-gadelshin]

This will not have the desired effect. It will work on Ctrl+C, but the idea was that it should be stopped on drop. Future returned by fn farm doesn't have to complete, it could hypothetically be simply dropped any time.

Do you mean something like AsyncAbortOnDrop similar to https://github.com/subspace/subspace/blob/51f39b9ccd45616ed9b6c1cb51911fb08c7cfaf2/crates/subspace-farmer/src/utils.rs#L24

[nazar-pc]

Yes, AsyncJoinOnDrop should work

[nazar-pc]

Well, not really. AsyncJoinOnDrop will wait for future to exit, but this one never will. You need to do something extra for that to happen, we have custom Drop implementations in various places for this to work properly. For example SingleDiskPlot ensures shutdown of various things is triggered first, such that on join they do actually exit.

[shamil-gadelshin]

Well, not really. AsyncJoinOnDrop will wait for future to exit, but this one never will. You need to do something extra for that to happen, we have custom Drop implementations in various places for this to work properly. For example SingleDiskPlot ensures shutdown of various things is triggered first, such that on join they do actually exit.

Did you comment on AsyncJoinOnDrop or AsyncAbortOnDrop?

[nazar-pc]

I see, we don't have AsyncAbortOnDrop yet

[nazar-pc]

So there is a wrapper now that is sending abort to the task on drop, which is correct.

The part with Future would have also worked under different circumstances, but in this case it will not because Drop means no one will ever be able to poll the future again, so effectively the wrapper can be simplified to just self.task.abort() in Drop and it will behave exactly the same.

Since you trigger internal abort already is, all you need to do is to additionaly wrap the task in AsyncJoinOnDrop to ensure that it is both aborted on drop and Drop::drop only exits once background task has actually finished.

And I'd call it in more generic way like AsyncAbortOnDrop you suggested before.

[nazar-pc]

Since AsyncJoinOnDrop wraps JoinHandle and not arbitrary future, we don't actually need Fuse, we can call JoinHandle::is_finished instead of is_terminated, in which case we can update AsyncJoinOnDrop::new() with additional argument abort_on_drop: bool and just call abort beore task::block_in_place. It'll be a simpler abstraction here.

[nazar-pc]

This is fairly clean, I'll squash-merge once CI passes