Question

Can we execute two different statements together? Suppose these are the two statements

x += 2*y;
y = 2*x+3*y;

Here we can see the statements are dependent. So can we execute them concurrently?

Answer 1

In general, you could calculate the overall change to the two variables and go to that directly (provided you take a snapshot of the values so that there’s no actual data dependencies between them; did you know that a number of microprocessors will do this automatically, though only where the code is free of data dependencies?). Using your example and inventing a little fake syntax:

somehowInParallelWithSnapshotOf(x,y) {
    x <== 1*x + 2*y;
    y <== 2*x + 7*y;
}

But you can’t do this in Javascript as the language doesn’t support direct parallelism. (That has its advantages, of course. For one thing, it massively simplifies the semantics of the code, so allowing implementations to pull of tricks like this behind the scenes if they can prove its correct.) It would also be pointless for something as trivial as this example; there’s quite a lot of overhead involved (in general) in spinning up extra threads, and when it gets up to the point of being worthwhile, it’s usually very difficult to simplify the expressions to the point where you can make them hazard-free.