Prevent the file watching loop from still being alive after we kill it

[lukeblevins]

Under certain conditions, execution of blocks of code inside the file watching loop continues although the loop's condition is false, causing unwanted actions to be performed (e.g. using the closed directory handle)

This PR aims to:

• Prevent a crash from occurring upon changing the working directory quickly
• Remove unneeded checks before adding/removing files during the watcher operation
• Convert any direct uses of the FilesAndFolders property to use a "snapshot" list instead

Please test this PR by doing the following:

1. Removing/Adding/Renaming a file after refreshing the directory multiple times
2. RELEASE MODE: Changing the WorkingDirectory by rapidly invoking various sidebar locations

[yaira2]

@duke7553 Is this supposed to fix the issue where the app sometimes crashes when opening a folder?

[tsvietOK]

Bug with duplicated items still exists.
Sometimes getting an exception after item rename

2020-06-11 16:34:23.6512|ERROR|Files.App|Sequence contains no matching element|System.InvalidOperationException: Sequence contains no matching element
   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source, Func`2 predicate)
   at Files.Filesystem.ItemViewModel.<>c__DisplayClass72_0.<WatchForDirectoryChanges>b__0(IAsyncAction x)
--- End of stack trace from previous location where exception was thrown ---
   at Files.Filesystem.ItemViewModel.WatchForDirectoryChanges(String path)
   at System.Threading.WinRTSynchronizationContextBase.Invoker.InvokeCore()
   at Windows.ApplicationModel.Core.UnhandledError.Propagate()
   at Microsoft.AppCenter.Utils.ApplicationLifecycleHelper.<.ctor>b__17_1(Object sender, UnhandledErrorDetectedEventArgs eventArgs)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AppCenter.Utils.ApplicationLifecycleHelper.<.ctor>b__17_1(Object sender, UnhandledErrorDetectedEventArgs eventArgs)

throwed at line: RemoveFileOrFolder

case FILE_ACTION_RENAMED_OLD_NAME:
        RemoveFileOrFolder(FilesAndFolders.ToList().First(x => x.ItemPath.Equals(FileName)));
        Debug.WriteLine("File " + FileName + " will be renamed in the working directory.");
        break;

[gave92]

I'm not experiencing the duplicated elements bug anymore, but:

• creating a new file
• deleting it
• hitting refresh

results in the same exception mentioned by @tsvietOK

2020-06-11 20:18:10.6754|ERROR|Files.App|Sequence contains no matching element|System.InvalidOperationException: Sequence contains no matching element
at System.Linq.Enumerable.First[TSource](IEnumerable1 source, Func2 predicate)
at Files.Filesystem.ItemViewModel.<>c__DisplayClass72_0.b__0(IAsyncAction x)
--- End of stack trace from previous location where exception was thrown ---
at Files.Filesystem.ItemViewModel.WatchForDirectoryChanges(String path)
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.b__7_0(Object state)
at System.Threading.WinRTSynchronizationContextBase.Invoker.InvokeCore()

[lukeblevins]

@gave92 Do you think a cancellation token would be appropriate to fix this one?

[gave92]

@duke7553 The bug I mentioned above (creating->deleting->refresh->crash) appears to be solved 👍

Edit: [learning mode on]
- Can the call to WaitForSingleObjectEx never return?
-> Tested: it can, if you hit refresh multiple times you'll have many threads waiting for the next event
-> If you move to another directory the previous watcher will still be waiting for a change in the previous directory
- Why you are not closing the hWatchDir handle anymore?

Edit 2:
- I think you need to use CancelIoEx instead of CancelIo as CancelIo only cancels operations issued by the calling thread.

[yaira2]