[Vm-dev] InputSemaphore on Windows

Igor Stasenko siguctua at gmail.com
Sun Apr 18 01:00:02 UTC 2010

On 16 April 2010 02:07, Andreas Raab <andreas.raab at gmx.de> wrote:
> On 4/15/2010 3:18 PM, Henrik Sperre Johansen wrote:
>> Is there a reason why this isn't signalled when inputSemaphoreIndex > 0?
> None. It just doesn't bite me. If it did I would've fixed it already. Got
> patch?
>> In sqWin32Window.c, the comment for synchronizedSignalSemaphoreWithIndex
>> looks somewhat scary...
>> But looking at the svn logs, it seems it never was used in the
>> record...Event() functions at all, so I wondered if a problem was
>> encountered before svn was in use that lead to its removal, or if it's
>> just not done by default?
> The short answer is that there are so many potential issues with handling
> semaphore signals properly that at some point I just gave up. At this point,
> there is no reliable way to deliver semaphore signals, they can and they
> *do* get dropped (we've proven that).
Wait.. lets us separate the issues.
1) synchronizedSignalSemaphoreWithIndex() & friends, for signaling an
arbitrary semaphore
2) an input semaphore, which should be signaled if there are any
events pending for delivery into language side.

For (2) , i remember you promised to fix that in no time (a fix is
quite trivial) , so then newer images could finally
stop using polling and use an input semaphore instead.
Usually, it is not a big problem with dropping an input semaphore
signals ( if that's ever possible),
because events tend to come at a regular basis, so even if image-side
missed a signal, it can catch up later,
when next event will come by.

> Cheers,
>  - Andreas

Best regards,
Igor Stasenko AKA sig.

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