RFR: 8293067: (fs) Implement WatchService using system library (macOS)

[Maxim Kartashev]

On Mon, 3 Oct 2022 08:36:22 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> It's on my list to do another pass on this. 

Thank you!

> I think the main thing that I'd like us to explore is using interfaces that would avoid the upcall. It would be good to see if there are any options that are feasible there.

It greatly depends on the definition of "upcall". I understand this as any call from native to Java code. The FSEvents API employs a callback-based approach, there's nothing to be explored there. 

However, as Brian suggested earlier, there are still options like reducing the complexity of the upcall to a mere `Object.notify()` or other simple means of synchronization. The side effect of such a change would be a much more complicated native portion of the callback, which I understood is something to be avoided. So I'm at a crossroads and would like a clearer guidance on the matter.

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PR: https://git.openjdk.org/jdk/pull/10140