[BUG]: WinMM app cannot detect MIDI devices attached after the app has launched.

[m-komo]

Windows Version

Build 27959.br_release.250926-1432

Service Installation Method

GitHub

SDK version, if appropriate

1.0.13-preview.13.192

Location

Application using WinMM MIDI 1.0 (Classic API)

Type of bug

Application not working as expected

Steps to reproduce

1. Ensure no MIDI input devices are connected.
2. Open a command console and launch the attached MMEGetNumDevs.exe.
   The app enumerates available MIDI input devices. It shows "No input devices found." at this time.
3. Attach any MIDI device to the PC running MidiSrv.
4. In the same command console where MMEGetNmDevs.exe is running, press the Enter key to enumerate devices again.
   The app still shows "No input devices found." The device attached in step 3 should be enumerated.
5. Open a second command console and launch MMEGetNumDevs.exe.
   This instance correctly shows the MIDI input device attached in step 3.
6. Detach the MIDI device and press Enter in the second console to re-enemerate devices.
   The app still shows the disconnected device. It should no longer be enumerated.

It seems that WinMM caches available devices at applicaton launch and does not update it dynamically.
On Windows 11 without MidiSrv, the same steps result in correct and updated device enumeration.

MMEGetNumDevs.zip

Expected behavior

The application should reflect changes in MIDI device availability without needing to restart.

Additional notes

No response

[ReinholdH]

I can confirm the issue.

On Windows 11, 26100.6584 the app runs fine but on Canary 27965.br_release.251006-1425 with the driver from 1.0.13-preview.13.192 the app shows the reported issue.

[Psychlist1972]

@judzmura this looks like the midiIn/midiOutGetNumDevs winmm caching problem Rekordbox reported.

[Psychlist1972]

Thanks all. We have a fix in the pipeline for this. Not sure which version of Windows it will hit first, and when. Your assumption that it is related to WinMM caching is correct. :)