WPF & Winforms with Blazor app leak 2 file system handles every time app.css is saved

Steps to reproduce:

1. Create a WPF or Winforms app and enable Blazor as described here Build a Windows Presentation Foundation (WPF) Blazor app | Microsoft Learn
2. Run the application
3. In VS, save wwwroot\css\app.css
4. Run the sys internals tool handle.exe on that file path and you will see the number of open handles increase by 2.
5. Save it again and run handle.exe and 2 more open handles are charged to the app.

These open handles seem to cause some issues with the way VS saves the file. It saves correctly but it seems to generate 2 save events, so we process the file change twice.

Here’s a proc mon trace showing this. Note the 3 calls o CreateFile but only one CloseFile.

11:47:22.4461876 AM              WpfApp1.exe            23308       CreateFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  Desired Access: Read Attributes, Disposition: Open, Options: Open Reparse Point, Attributes: n/a, ShareMode: Read, Write, Delete, AllocationSize: n/a, OpenResult: Opened

11:47:22.4462182 AM              WpfApp1.exe            23308                  QueryNetworkOpenInformationFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  CreationTime: 5/9/2022 9:56:21 AM, LastAccessTime: 10/27/2022 11:47:22 AM, LastWriteTime: 10/27/2022 11:47:22 AM, ChangeTime: 10/27/2022 11:47:22 AM, AllocationSize: 4096, EndOfFile: 693, FileAttributes: A

11:47:22.4462266 AM              WpfApp1.exe            23308       CloseFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS 

11:47:22.4462380 AM              WpfApp1.exe            23308       FileSystemControl          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  Control: FSCTL_QUERY_FILE_REGIONS

11:47:22.4463240 AM              WpfApp1.exe            23308       CreateFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  Desired Access: Generic Read, Disposition: Open, Options: Sequential Access, Non-Directory File, Open No Recall, Attributes: n/a, ShareMode: Read, Write, AllocationSize: n/a, OpenResult: Opened

11:47:22.4463757 AM              WpfApp1.exe            23308       QueryEAFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS 

11:47:22.4520798 AM              WpfApp1.exe            23308       CreateFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  Desired Access: Read Attributes, Disposition: Open, Options: Open Reparse Point, Attributes: n/a, ShareMode: Read, Write, Delete, AllocationSize: n/a, OpenResult: Opened

11:47:22.4521047 AM              WpfApp1.exe            23308                  QueryNetworkOpenInformationFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  CreationTime: 5/9/2022 9:56:21 AM, LastAccessTime: 10/27/2022 11:47:22 AM, LastWriteTime: 10/27/2022 11:47:22 AM, ChangeTime: 10/27/2022 11:47:22 AM, AllocationSize: 4096, EndOfFile: 693, FileAttributes: A

11:47:22.4521134 AM              WpfApp1.exe            23308       CloseFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS 

11:47:22.4521969 AM              WpfApp1.exe            23308       CreateFile          C:\Users\user\source\repos\WinFormAppForTesting\WpfApp1\wwwroot\css\app.css                  SUCCESS  Desired Access: Generic Read, Disposition: Open, Options: Sequential Access, Non-Directory File, Open No Recall, Attributes: n/a, ShareMode: Read, Write, AllocationSize: n/a, OpenResult: Opened

https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1659321

[Eilon]

You mean who owns it in the VS world? Possibly someone on @vijayrkn 's team?

[TanayParikh]

Closing this out here, @BillHiebert will confirm on VSTS if he’s still running into the issue.