Thread less autoupdate

[kazu-yamamoto]

@khibino I'm trying to merge your version of AutoUpdate.

• Which module should export mkClosableAutoUpdate? (AutoUpdate or Internal?)
• Could you implement mkAutoUpdateWithModify, too?
• Any other concerns?

[khibino]

Could you implement mkAutoUpdateWithModify, too?

If my understanding is correct,
the action passed additionally to mkAutoUpdateWithModify will always be used
in place of the updateAction in UpdateSettings for update action calls starting from the second call.

Based on that premise, I implemented it as follows.

https://github.com/khibino/wai/compare/extend-thread-less~3..extend-thread-less

https://github.com/khibino/wai/tree/extend-thread-less

[khibino]

Which module should export mkClosableAutoUpdate? (AutoUpdate or Internal?)

Considering exporting the combination of mkAutoUpdateWithModify and mkClosableAutoUpdate,
it seems good to keep the exports from AutoUpdate simple,
and handle complex cases through exports from Internal.

On the other hand, while "thread-less" eliminates the thread leak problem when stopping auto-update midway,
there is a minor issue where timeout registration in GHC's TimeManager remains if mkClosableAutoUpdate is not used.

[kazu-yamamoto]

@khibino I cherry-picked your commits.
Do you agree with merging this branch as is?

[khibino]

Yes. I think that's good.

[kazu-yamamoto]

@khibino The current implementation cannot be built on Windows because GHC.Event cannot be imported.

[kazu-yamamoto]

@khibino I will use the old implementation for Windows.

[kazu-yamamoto]

@khibino CI passes. Would you give one more look?

[kazu-yamamoto]

Merged and released.
Thanks!

[khibino]

informative link:
original code of thread-less auto-udpate
https://github.com/khibino/dnsext/blob/44cc84ae472d75c8fcdd5ecda083c99e8aeb1cca/dnsext-utils/DNS/Utils/AutoUpdate.hs