File changed event being called twice

Question

I use a combination of IVsFileChangeEvents and IVsFileChangeEx to monitor, whether file edited in my custom editor extension was modified outside the IDE. However, for some unknown reason, I get the notification twice - thus resulting in asking user for reload twice.

The implementation of FilesChanged looks like the following:

    public int FilesChanged(uint cChanges, string[] rgpszFile, uint[] rggrfChange) {

        foreach (var file in rgpszFile)
        {
            if (file.ToLowerInvariant() == documentPath.ToLowerInvariant()) {

                System.Diagnostics.Debug.WriteLine("File changed - asking for reload");

                if (MessageBox.Show("The file {0} was changed outside the editor. Do you want to reload it?".FillWith(file), 
                    "MyEditor", 
                    MessageBoxButton.YesNo, 
                    MessageBoxImage.Question) == MessageBoxResult.Yes) {

                    fileChangeEx.IgnoreFile(fileCookie, null, 1);

                    // Unloading document
                    DoCloseDocument();

                    // Loading document
                    DoLoadDocument(file);

                    fileChangeEx.SyncFile(documentPath);
                    fileChangeEx.IgnoreFile(fileCookie, null, 0);
                }
            }
        }
        return VSConstants.S_OK;
    }

I test this code by saving the same file in Notepad++.

This is a log from SysInternals' ProcMon:

09:05:21,2272369    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:21,2273658    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:21,2275512    notepad++.exe   256 QueryDirectory  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Filter: settings.definition, 1: settings.definition
09:05:28,7692878    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:28,7694244    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:28,7696066    notepad++.exe   256 QueryDirectory  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Filter: settings.definition, 1: settings.definition
09:05:44,0463636    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:46,4087520    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:46,4088700    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:46,4089646    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 08:50:27, ChangeTime: 2014-05-23 08:50:27, AllocationSize: 4 096, EndOfFile: 1 740, FileAttributes: A
09:05:46,4090631    notepad++.exe   256 CreateFile  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Desired Access: Generic Write, Read Attributes, Dis, Options: Synchronous IO Non-Alert, Non-Directory File, Attributes: N, ShareMode: Read, Write, AllocationSize: 0, OpenResult: Overwritten
09:05:46,4100654    notepad++.exe   256 WriteFile   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Offset: 0, Length: 1 742, Priority: Normal
09:05:46,4101850    notepad++.exe   256 CloseFile   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS 
09:05:46,4102751    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4103088    MsMpEng.exe 956 CreateFileMapping   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   FILE LOCKED WITH WRITERS    SyncType: SyncTypeCreateSection, PageProtection: 
09:05:46,4103322    MsMpEng.exe 956 QueryStandardInformationFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS AllocationSize: 4 096, EndOfFile: 1 742, NumberOfLinks: 1, DeletePending: False, Directory: False
09:05:46,4144664    notepad++.exe   256 QueryDirectory  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Filter: settings.definition, 1: settings.definition
09:05:46,4160238    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4172362    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4173472    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4175063    notepad++.exe   256 QueryDirectory  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Filter: settings.definition, 1: settings.definition
09:05:46,4178437    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4185672    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:05:46,4186404    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:06:06,8788282    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:06:06,8789555    notepad++.exe   256 QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:06:06,8791373    notepad++.exe   256 QueryDirectory  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Filter: settings.definition, 1: settings.definition
09:06:50,6465883    devenv.exe  6884    CreateFile  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Desired Access: Generic Read, Dis, Options: Synchronous IO Non-Alert, Non-Directory File, Open No Recall, Attributes: n/a, ShareMode: Read, AllocationSize: n/a, OpenResult: Opened
09:06:50,6466482    devenv.exe  6884    QueryStandardInformationFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS AllocationSize: 4 096, EndOfFile: 1 742, NumberOfLinks: 1, DeletePending: False, Directory: False
09:06:50,6466665    devenv.exe  6884    ReadFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Offset: 0, Length: 1 742, Priority: Normal
09:06:50,6467374    devenv.exe  6884    ReadFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   END OF FILE Offset: 1 742, Length: 4 096
09:06:50,6469314    devenv.exe  6884    CloseFile   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS 
09:06:50,6477175    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:06:50,6963339    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:07:02,3340501    devenv.exe  6884    CreateFile  D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Desired Access: Generic Read, Dis, Options: Synchronous IO Non-Alert, Non-Directory File, Open No Recall, Attributes: n/a, ShareMode: Read, AllocationSize: n/a, OpenResult: Opened
09:07:02,3341050    devenv.exe  6884    QueryStandardInformationFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS AllocationSize: 4 096, EndOfFile: 1 742, NumberOfLinks: 1, DeletePending: False, Directory: False
09:07:02,3341200    devenv.exe  6884    ReadFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS Offset: 0, Length: 1 742, Priority: Normal
09:07:02,3341887    devenv.exe  6884    ReadFile    D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   END OF FILE Offset: 1 742, Length: 4 096
09:07:02,3343792    devenv.exe  6884    CloseFile   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS 
09:07:02,3351733    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A
09:07:02,3626280    devenv.exe  6884    QueryOpen   D:\VS Projects\Temporary\WindowsFormsApplication1\WindowsFormsApplication1\NewFolder1\settings.definition   SUCCESS CreationTime: 2014-05-21 13:08:34, LastAccessTime: 2014-05-21 13:08:34, LastWriteTime: 2014-05-23 09:05:46, ChangeTime: 2014-05-23 09:05:46, AllocationSize: 4 096, EndOfFile: 1 742, FileAttributes: A

It seems like the MessageBox.Show call is the main reason for the second notification.

The call stack looks like the following:

MyAssembly.dll!MyClass.FilesChanged(uint cChanges = 1, string[] rgpszFile = {string[1]}, uint[] rggrfChange = {uint[1]}) Line 284   C#
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.FileChangeSubscription.Notify.AnonymousMethod__0() Unknown
Microsoft.VisualStudio.Shell.12.0.dll!Microsoft.VisualStudio.ErrorHandler.CallWithCOMConvention(System.Func<int> method, bool reportError = false, bool setShellErrorInfo = true)   Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.FileChangeSubscription.Notify(Microsoft.VisualStudio.Shell.Interop._VSFILECHANGEFLAGS changes) Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.FileChangeSubscription.Notify(System.IO.WatcherChangeTypes changeTypes, Microsoft.VisualStudio.Services.FileProperties props)  Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.FileWatcher.Notify(Microsoft.VisualStudio.Services.ChangeStreamDigest digest)  Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.DirectoryWatcher.ProcessFileChanges(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string,Microsoft.VisualStudio.Services.ChangeStreamDigest>> digests, int depth) Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.DirectoryWatcher.ProcessChanges(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string,Microsoft.VisualStudio.Services.ChangeStreamDigest>> digests = Count = 1, int depth = 3) Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.DirectoryWatcher.ProcessChanges(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string,Microsoft.VisualStudio.Services.ChangeStreamDigest>> digests = Count = 1, int depth = 2) Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.DirectoryWatcher.ProcessChanges(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string,Microsoft.VisualStudio.Services.ChangeStreamDigest>> digests = {Microsoft.Internal.VisualStudio.PlatformUI.HybridDictionary<string,Microsoft.VisualStudio.Services.ChangeStreamDigest>}, int depth = 1)  Unknown
Microsoft.VisualStudio.Shell.UI.Internal.dll!Microsoft.VisualStudio.Services.DirectoryWatcher.OnChangedAsync()  Unknown
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source = {System.Windows.Threading.Dispatcher}, System.Delegate method, object args, int numArgs, System.Delegate catchHandler = null)  Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeImpl()   Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)  Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.Invoke()   Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.ProcessQueue()  Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)  Unknown
WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd = 264738, int msg = 49778, System.IntPtr wParam = 0, System.IntPtr lParam = 0, ref bool handled = false)    Unknown
WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) Unknown
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source = {System.Windows.Threading.Dispatcher}, System.Delegate method, object args, int numArgs, System.Delegate catchHandler = null)  Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)   Unknown
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd = 264738, int msg = 49778, System.IntPtr wParam = 0, System.IntPtr lParam = 0) Unknown
[Native to Managed Transition]  
[Managed to Native Transition]  
PresentationFramework.dll!System.Windows.MessageBox.ShowCore(System.IntPtr owner, string messageBoxText, string caption, System.Windows.MessageBoxButton button, System.Windows.MessageBoxImage icon, System.Windows.MessageBoxResult defaultResult, System.Windows.MessageBoxOptions options)  Unknown
PresentationFramework.dll!System.Windows.MessageBox.Show(string messageBoxText, string caption, System.Windows.MessageBoxButton button, System.Windows.MessageBoxImage icon)    Unknown
MyAssembly.dll!MyClass.FilesChanged(uint cChanges = 1, string[] rgpszFile = {string[1]}, uint[] rggrfChange = {uint[1]}) Line 290   C#

What should I do to receive the event only once?

Answer 1

I got it to work by detaching the notifications in the method and re-attaching them at the end.

Looks something like this (note that I omitted some details regardingserviceProvider, fileChangeCookie, filesChanged-array, ...)

int IVsFileChangeEvents.FilesChanged(uint numberOfFilesChanged, string[] filesChanged, uint[] flags) 
{
    IVsFileChangeEx fileChangeService = yourServiceProvider.GetService(typeof(SVsFileChangeEx));
    // Detach from notifications
    fileChangeService.UnadviseFileChange(GetCookieFromFile(filesChanged[0]));
    // Do your stuff with the file
    ...
    // Re-attach to notifications
    fileChangeService.AdviseFileChange(filesChanged[0], (uint)(_VSFILECHANGEFLAGS.VSFILECHG_Time | _VSFILECHANGEFLAGS.VSFILECHG_Del), this, out fileChangeCookie);
}

Answer 2

I've had similar problems with the Win32-level file changed events. There are a lot of things you can to do reduce the problems (like disconnecting the events). In reality, you have no idea how many times a file might get "changed" during the handling of the event. For message-based events, all it takes is a call to anything that processes messages to get reentered, for multithreaded events, you don't even have to call something--it can happen no matter what you do. As a result, you should be very careful about what you do when you receive the notification. Ideally your event handler should be written in a way that it can handle being called again while it's still processing the previous event. Depending on what the dialog and subsequent processing does, you may be able to just keep track of whether or not it is open and/or processing and ignore any concurrent events, or you may need to notify the dialog or processing code that another change has occurred. Disconnecting and reconnecting the notifications works for message-based events, but not if there is any threading going on.