9 Dec
2002
9 Dec
'02
10:05 a.m.
On Monday 09 December 2002 14.49, Steve Harris wrote:
On Mon, Dec 09, 2002 at 11:39:38AM +0100, David
Olofson wrote:
That's the feedback loop problem. As long as the host runs plugins in
the correct order, you'll never see this unless you *actually* have
loops in your network.
In theory, the problem is very easy to solve:
Have the host throw
in "shadow event ports", and then have it sort/merge the queues
from those into a single, ordered queue that is passed to the
actual target port.
I dont think this totally solves the problem.
There is also the latency problem, if the instrument generates
output events with the same timestamp as some input event
(reasonable) then it wont receive those same event until its next
processing block, what does it do then? They are all arriving
"late". Should the host add latency to the events (by adding
one blocks
worth to the event time)?
In an actual loop, yes, it would have to do that - at least the way
timestamps work in Audiality. (Running time, wrapping, not related to
buffer boundaries.)
The way VST does it however, that wouldn't be needed, since
timestamps are related to buffers. 0 == start of this buffer. Might
look nice to plugins, but I forsee minor nightmares in multithreaded
hosts, hosts that want to split buffers, hosts that support different
buffer sizes in parts of the net, hosts that support multiple sample
rates in the system, communication over wire,... (Yet another reason
why I think the VST event system is a pretty bad design.)
Of course this is only a problem when you have graphs
with
feedback, otherwise there is a linear execution order that ensures
this kind of problem wont happen.
Exactly.
BTW, feedback loops would be the major reason why a host would want
to run parts of the net with smaller buffers. See why I discarded the
idea of buffer related timestamps? :-)
//David Olofson - Programmer, Composer, Open Source Advocate
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