foo.js

var x = 1

function a() {
    var i = 0
    do {
        x = 1;
        hm();
    } while (x === 1 && ++i<1e9);
    assert(x === 1)
    assert(i === 1e9)
}

function b() {
    var i = 0
    do {
        x = 100;
        hm();
    } while (x === 100 && ++i<1e9);
    assert(x === 100)
    assert(i === 1e9)
}

// will this blow up?
// ie, is parallel *actually* running the JS in parallel?
// or just parallelizing the yields?
// is hm() yielding?  does that matter?
parallel(a, b)