[PATCH xextproto 1/4] Document changes in XSync version 3.1

[Adam Jackson]

Apologies for the slow review here...

On Thu, 2010-08-12 at 16:40 -0700, James Jones wrote:

>  <para>
> -The extension adds <function>Counter</function> and
> -<function>Alarm</function> to the set of resources managed by the
> +The extension adds <function>Counter</function>, <function>Alarm</function>,
> +and <function>Fence</function> to the set of resources managed by the
>  server. A counter has a 64-bit integer value that may be increased or
>  decreased by client requests or by the server internally. A client can block
>  by sending an Await request that waits until one of a set of synchronization
> -conditions, called TRIGGERs, becomes TRUE.
> +conditions, called TRIGGERs, becomes TRUE.  A fence has two possible states:
> +triggered and not triggered. Client requests can put the fence in either of
> +these states. A client can block until one of a set of fences becomes
> +triggered by sending an AwaitFence request.
>  </para>

I feel like this whole section wants a rewrite, since Alarms aren't
discussed until much later.  Would be worthwhile if doing so to note
that Fences are explicitly bound to a screen (though I wouldn't insist
on it to get this merged).  And on that subject...
  
> +<para>
> +The <function>CreateFence</function> request allows a client to create a
> +<function>Fence</function> that can be triggered and reset using
> +<function>TriggerFence</function> and <function>ResetFence</function>
> +requests, respectively.  The <function>TriggerFence</function> request changes
> +the fence's state only after all previous rendering commands affecting objects
> +owned by the given fence's screen have completed.
> +</para>

I'm a little unclear on _why_ they're bound to screens.  What semantics
does that imply?  The only reason I can imagine wanting to do so in the
protocol is if the server itself would ever trigger a Fence on a
Drawable, because then you'd need to wire the Fence to the right
ScreenRec.  But it seems like that should never happen for
client-created Fences, only for server-created Fences.

- ajax
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