In this case, the parallel.pool.Constant you're creating has a cell array of 20 elements on each worker. In your first parfor loop, each worker gets some of the 20 loop iterates, and modifies those elements of the cell array inside the Constant value. If you modify your parfor loops, hopefully this will help explain what's happening. For the first loop,
parfor i = 1 : 20
t = getCurrentTask();
c.Value{i}.changeMyParameter();
fprintf('Changing element %d on worker %d\n', i, t.ID);
end
This will show you which elements of c.Value are modified on which worker. (Note that each worker has its own independent copy of c.Value).
Then, when you run the second parfor loop, the iterates are not necessarily dispatched to the same workers in the same order, so if you run:
parfor i = 1 : 20
t = getCurrentTask();
fprintf('Checking element %d on worker %d\n', i, t.ID);
disp(c.Value{i}.myParameter);
end
You can see that in some cases, you're checking an element of c.Value on a worker where it wasn't modified.
