[BUG] WinMM app stops receiving messages.

[m-komo]

Describe the bug

This issue was observed with the Internal Preview (2025-02-18 Customer Preview 2 Daily).

WinMM app stops receiving messages.
This issue can be reproduced with both MIDI 1.0 device and MIDI 2.0 device regardless of the driver.

To Reproduce
Following steps may not be required steps but they are reproducible steps.

1. Set the Roland UM-ONE mk2 to class-compliant mode (set the switch to "TAB") and short INPUPT and OUTPUT to loop back messages.
2. Attach the UM-ONE to PC.
3. Open the Pocket MIDI and choose the "UM-ONE" as an InputPort and an OutputPort.
4. From the "File" menu, open the attached "test.pocketmidi" file.
5. Open midi.exe and monitor the "UM-ONE".
6. Open midi1monitor.exe and monitor the "UM-ONE".
7. In the two System Exclusive windows, click the "Transmit" buttons to send messages.

8. Close the Pocket MIDI.
9. Open midi.exe and send 0x20904040 to the UM-ONE to make sure both monitors still working.
10. Double click the attached "test.pocketmidi" file and click the "Transmit" button on the System Exclusive windows.

The midi1monitor.exe does not receive any messages.

Expected behavior
The midi1monitor.exe continues receiving messages.

Installer Name or Version

• [Internal Preview] Windows MIDI Services (In-Box Service) 1.0.3-preview-11.250218-1656-x64.exe
• [Internal Preview] Windows MIDI Services (SDK Runtime and Tools) 1.0.3-preview-11.250218-1656-x64.exe

Desktop (please complete the following information):

• OS: Windows 11 24H2 build 27788.1000 (Insider Canary channel)

Device information, if this is with an external MIDI device:

• Roland UM-ONE mk2

Application Information

• MORSON Pocket MIDI (64bit MME MID app)
  https://www.morson.jp/pocketmidi-webpage/

[Psychlist1972]

FYI. I cannot repro this on 1.0.3-preview-11.250228-139 which I plan to release later today.

Both midi1monitor and midi.exe receive all sent messages. I tried clicking on them in different orders, but the messages still got through.

[m-komo]

@Psychlist1972 Thank you for your prompt response.
I will check this with the next release.

[m-komo]

@Psychlist1972
The conditions or steps are unclear, but there is still a case WinMM app stops receiving or sending messages.

Follow steps below as a preparation.

1. Set the Roland UM-ONE mk2 to class-compliant mode (set the switch to "TAB") and short INPUPT and OUTPUT to loop back messages.
2. Attach the UM-ONE to PC.
3. Open the Pocket MIDI and choose the "UM-ONE" as an InputPort and an OutputPort.
4. In the Pocket MIDI, open MIDI In Monitor, MIDI Out Monitor and Keyboard windows.
5. Open midi.exe and monitor the "UM-ONE".
6. Open midi1monitor.exe and monitor the "UM-ONE".
7. Play keys in the Keyboard window of the Pocket MIDI and make sure the Pocket MIDI is sending and receiving MIDI Note On/Off messages.
8. Check active sessions with the 'midi enum sessions' command or the MIDI Settings app. There should be three active sessions for Pocket MIDI, midi.exe and midi1monitor.exe.

Then try followings.

1. Quit the Pocket MIDI and re-open it. Then verify that the Pocket MIDI can send/receive MIDI messages.
2. On the midi.exe, press escape to stop monitoring. This also stops midi1monitor.exe. Make sure that the Pocket MIDI can still send/receive MIDI messages.
3. Reopen the midi.exe monitor and the midi1monitor.exe. Make sure that the Pocket MIDI can still send/receive MIDI messages.
4. On the midi1monitor.exe, press escape to stop monitoring. Make sure that the Pocket MIDI can still send/receive MIDI messages.
5. Reopen the midi1monitor and make sure that the Pocket MIDI can still send/receive MIDI messages.

Repeat above steps dozen of times with the random order.
Suddenly, the Pocket MIDI stops sending and receiving MIDI messages.
You can see the no blink of the IN/OUT indicators on the UM-ONE.
It happens just after closing midi1monitor.exe.

I checked active sessions when the issue happened, there was the no session for the Pocket MIDI even it is still running. Instead, there was the session for the midi1monitor.exe it had already been closed.

Installer Name or Version

• [CP2 + x64-full] Windows MIDI Services (In-Box Service) 1.0.3-preview-11.250228-237-x64.exe
• [CP2 + x64-full] Windows MIDI Services (SDK Runtime and Tools) 1.0.3-preview-11.250228-237-x64.exe

Desktop (please complete the following information):

• OS: Windows 11 24H2 build 27802.1000 (Insider Canary channel)