Remake PollWatcher

[passcod]

For those not familiar with the background who want to help:

What was done:

• Support was achieved for both Linux and OS X.
• Windows native support (windows implementation #4) may be worked on.
• The polling backend requires the ability to get the mtime of a file, which cannot currently be done in stable Rust, so it was dropped.

What is needed:

• To get a replacement for stat.modified().
• To implement anew (or adapt from the old code) a polling backend.

[octplane]

Hello,

Two ideas for that:

• Finish integrating fsevent in the package (I've started working on this tonight and this is going more or less ok). Then deprecate poll until we have a working solution with stable rust. Most of our users, I reckon, are using OSX or an enabled inotify linux, so leaving out the poll solution could be acceptable (or not ?)
• Use ffi to connect to fstat api from rsnotify directly and provide a working solution that allows poll to work correctly in stable rust.

Without poll, the lib seems to compile pretty much ok (cf https://github.com/octplane/rsnotify/tree/fsevent_integration ) and there doesn't seem to be any outdated package.

[passcod]

I think most of the flack could come from Windows users who'll be left out, but that's better than nothing working at all.

[passcod]

I'm going to rip out Poll straight up, though. It will make this library not much more than an inotify wrapper until fsevent lands, but that's how it was for a while before, too. Then the work will be to rebuild a polling implementation or two. I'm thinking of applying some actual CS theory to the problem, when I have time.

[passcod]

I've ripped out Poll and released a 2.0.0-pre1 with a NullWatcher that… does nothing. That should at least help things along, something that compiles but does nothing on unsupported platforms is still better than something that just fails.

[andelf]

@octplane I copied your fsevent code and made some changes. Now its works. (unwatch , drop left unimplemented) => https://github.com/andelf/rsnotify
It was cloned before NullWatcher introduced，so “4 commits ahead, 1 commit behind passcod:master”.
Maybe we can start from it?

[octplane]

@andelf indeed! I think the merge is not too difficult to perform. The unwatch/drop might be more complicated. I had to fight against threads to make things work correctly. I will not be available until tomorrow morning CET, so go ahead if you have some cycles.

[maurizi]

I have been using the poll backend on Windows, so I'll be sad to see it go.
That said, I might try and whip up an initial implementation of using winapi.rs to do real file watching and fix #4.

[retep998]

For getting the file modified time on Windows call GetFileAttributesExW if you have a Path or GetFileInformationByHandle if you have a HANDLE or FindNextFile if you're iterating over directory entries, at which point you'll get some file information including the last modified time as a FILETIME which is "the number of 100-nanosecond intervals since January 1, 1601 (UTC)."

[maurizi]

@retep998 I was looking at using ReadDirectoryChangesW to just directly get file modification events, so I won't really need to get file modification time.

That said, I need to get a directory handle to use ReadDirectoryChangesW, which I think means I need to call CreateFileW. Do you know a simple way to go from a &Path to the LPCWSTR CreateFileW wants?

[retep998]

let x: Vec<_> = somepath.as_os_str().encode_wide().chain(Some(0)).collect();
CreateFileW(x.as_ptr(), ...);

[blaenk]

Niiice thanks for helping us out @retep998 :)

Pretty sure that should be a Some(0).into_iter() @maurizi

[blaenk]

Nevermind! You don't need the into_iter() because chain takes an IntoIterator :D