If I've understood correctly, you could use spmd to do something like this. spmd allows communication between the workers, so that you can exchange values on the workers. It's a bit like your idea of nesting parfor inside while, but everything stays on the workers. Here's a very rough sketch of how things might proceed:
spmd
done = false;
while ~done
% each worker has an independent copy of 'myValue', but
% we'll combine these later. For the sake of this simple
% example, I'm going to assume we're getting a numeric
% increment from each ray-trace, and we want to add them
% all up
myValue = 0;
% for-drange causes each worker to execute a different portion of
% the loop. Worker 1 gets 1:(numRays/numlabs), and so on.
for rIdx = drange(1:numRays)
myValue = myValue + traceRay(rIdx);
end
% Use GPLUS to find the total by communicating across
% all workers
totalValue = gplus(myValue);
% termination condition.
done = totalValue > thresh;
end
end
I hope this makes some sort of sense. Instead of gplus, you might need the more general gop or perhaps you might need to roll your own communication using labSend and labReceive.
