irmin-io polling continues after client kills cat command

[moby]

irmin-io polling continues after client kills cat command

[talex5]

Ah, yes. There's a TODO about this here:

https://github.com/docker/datakit/blob/a38630ff56af4fcb0dbc3c48ca3e44c574f30bdb/src/ivfs/ivfs.ml#L519

There are several things that need fixing:

• 9p operations such as read should pass a cancel notifier to the handler. ocaml-9p added support for this a while back, but we don't plumb it through yet. Here's where it (~cancel) gets thrown away at the moment: https://github.com/docker/datakit/blob/a38630ff56af4fcb0dbc3c48ca3e44c574f30bdb/src/fs9p/fs9p.ml#L283
• We shouldn't have to keep monitoring/publishing events when the client isn't doing a read.
• We shouldn't be logging at debug level by default (#176).

It would probably be best to change (or add to) Irmin's watch API to support something like Store.watch_head ~switch ~current, which would produce a value later than current once one was available. Otherwise, we'll have to keep registering and removing watches all the time, which is clumsy.

/cc @samoht

[samoht]

An other thing we should fix is not do active polling but use FSEvents and Inotify on platforms which support it (e.g. not windows). I know that @dsheets had some plan to work on it at one point, but I guess if someone else wants to help, it's a relatively easy and self-contained task:

• need to implement the callback of Irmin.Private.Watch.set_listen_dir_hook which takes a notification id (for debug purposes) and the path to watch, and a callback to apply any file which changes.
• on OSX, could use https://github.com/dsheets/ocaml-osx-fsevents
• on Linux, could use https://github.com/whitequark/ocaml-inotify

[samoht]

We are now using inotify and fsevents so this is less of an issue.