[BUG]: `midiOutOpen` without `midiOutGetNumDevs` returns 2

[Libamidi]

Windows Version

24H2

Service Installation Method

GitHub

SDK version, if appropriate

1.0.16-rc.3.7 (x64)

Location

Application using WinMM MIDI 1.0 (Classic API)

Type of bug

Application not working as expected

Steps to reproduce

NOTE: my application uses Java FFM API

1. Make sure that the process hasn't called midiOutGetNumDevs() function before
2. Call midiOutOpen() with loopback MIDI device ID
3. midiOutOpen() returns 2 (MMSYSERR_BADDEVICEID)

Expected behavior

midiOutOpen() returns 0

Additional notes

No response

[Psychlist1972]

Thanks. Yes, we recently discussed this on Discord

When we rewrote the WinMM guts, we didn't expect apps to call midiOutOpen without first checking to see how many devices were present. That's the usual and expected pattern. So in the new stack, we actually build the device list when you make the call to get the number of devices.

How are you getting the loopback MIDI device id without calling getNumDevs first? Indexes are not guaranteed -- device add/remove will shift indexes around.

We're looking to change that around both to reduce the time taken in the midiIn/OutGetNumDevs calls, and to handle the scenario where apps try to open devices without getting the number of devices first.

We have a fix in development that does the enumeration asynchronously, but that fix will take a few months to get into Windows.

Pete
Microsoft

[Psychlist1972]

Related #976

[Psychlist1972]

Related internal ADO issue 61756891

[Falcosoft]

How are you getting the loopback MIDI device id without calling getNumDevs first? Indexes are not guaranteed -- device add/remove will shift indexes around.

Using MIDIMAPPER (-1) as a deviceId has always been a legitimate choice in WinMM to select the default Midi mapper device.
So not using midiOutGetNumDevs() before calling midiOutOpen() is not as rare and unusual as you think.

[Psychlist1972]

How are you getting the loopback MIDI device id without calling getNumDevs first? Indexes are not guaranteed -- device add/remove will shift indexes around.

Using MIDIMAPPER (-1) as a deviceId has always been a legitimate choice in WinMM to select the default Midi mapper device. So not using midiOutGetNumDevs() before calling midiOutOpen() is not as rare and unusual as you think.

Yes, but midimapper and the in-box GS synth have a different code path and would work without calling getNumDevs. I'm taking more about all the other devices.

Regardless, we're rewriting how this code works, but the intent was always for apps to get the number of devices before opening them. That just wasn't clearly communicated in the docs (the WinMM docs are not very informative at all, leave out some key structures that are actually in the API, etc.)

Pete
Microsoft