[PATCH 3/3] mmsystem: Always use CALLBACK_FUNCTION to update MIDI/WAVEHDR.dwFlags.

[Joerg-Cyril.Hoehle at t-systems.com]

Hi,

Some apps may open winmm without any callback as they intend to
poll the whdr flags to know when a packet is ready.
The problem is, 16bit whdr are only updated by the thunk callbacks
(andupon return from (Un)Prepare and Write/AddBuffer).

Hmm, don't we have a race condition? the 16bit whdr may be updated
concurrently by an unsuccessful call to waveOutWrite as well as a DONE callback.
This does not happen to 32bit code, since waveOutWrite would be rejected by
STILLPLAYING without touching the flags! But in 16bit code ... boom!

The code could be simplified further in the WAVE_OPEN_QUERY case, as
I recently showed that there's no notification in that case (nor writing to the handle),
so thunk creation is superfluous. Any volunteer?

Regards,
 Jörg Höhle
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