mciavi: Prevent deadlock when closing while playing or when paused.

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

Hi,

Maarten Lankhorst wrote:
>Using a winmm timer there would remove the
>need for that thread altogether
Please explain the idea.

>as part of my sound rewrite I will write a new winmm driver
My understanding is that there will be a new winmm, but all MCI* drivers
operate on top of that and are not changed.  Thus the question still
remains what "Quality of Implementation" to implement there w.r.t. multiple
threads sending MCI commands to the same device:
 - ignore the issue;
 - make each device/unit robust against concurrent use;
 - make only MCI_Close robust;
 - ...?

This can perhaps be considered independently on the same questions w.r.t.
winmm:midi/waveXyz functions.  The winmm MUST deal with concurrency IMHO
because of the callback practice.  There's nothing like this in the MCI.

Regards,
 Jörg Höhle.