[wdmaudiodev] Re: GUID's for MMDevices Render and Capture

  • From: Eugene Muzychenko <emuzychenko@xxxxxxxxx>
  • To: Tim Roberts <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Thu, 28 Jan 2010 00:47:22 +0600

Hello Tim,

> On the other hand, the type 1 GUID also includes the current time in
> 100-nanosecond units, so the odds against producing duplicate GUIDs
> are still very, very small.

Yes, collision probability of these GUIDs is very small but only if you
generate a small amount of them. Generating a huge amount of GUIDs
based on a non-unique MAC address may significantly increase collision

Adopting my driver to Vista, I added MediaCategories GUID support. For
future compatibility, I decided to encode some driver/device
parameters into these GUIDs, it required 2^48 sequential GUID space.
Generating these GUIDs by UuidCreateSequential would be slow and
unreliable. So I got an unique MAC address from an old broken ISA
network card and constructed type 1 GUIDs from it. :) An unique MAC
address can be obtained from any non-desktop-Windows device (mobile
phone, PDA, network router/printer etc.). It strongly guarantees that
there will be no collisions at all.



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