winmm: Allow a FORCE_SHUTDOWN on driver close?

[Peter Beutner]

Maarten Lankhorst schrieb:
> Peter Beutner schreef:
>> AFAIK you get the DRVM_EXIT message only when winmm is unloading.
>> Alternatively you could do it in response to the DRV_CLOSE message which winmm
>> sends just before it tries to unload the driver.
>>
>> That said I don't see how your code in ALSA_MixerExit() could deadlock.
>> It effectively tries to exit the thread the same way as MIX_Close, doesn't it?
>> So the thread should exit safely.
>> Imo the question is rather why the thread isn't exiting and you are waiting
>> forever. Forcibly calling TerminateThread just covers the problem
> The deadlock isn't in the alsa code, it's in the kernel code:
> Kernel holds thread lock and calls closing winmm code, closing code
> closes mixer driver, mixer closing waits on thread, thread waits till it
> can hold thread lock -> deadlock.
> 
> Under normal circumstances, MIX_Open will be called as often as
> MIX_Close is. If the programmer is lazy and never closes its handle,
> MIX_Close will be called when winmm is shutting down, in that case I

Are you sure about this? I don't think winmm calls MIX_Close on its own when
it shuts down and the device is still open. It only sends the DRVM_EXIT
message(and throws out a FIXME).
So there shouldn't be a deadlock in MIX_Close() and in ALSA_MixerExit() you
can always call TerminateThread when the thread still exists.