Frame-onStep-generators-gc-01.js

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// onStep hooks on suspended Frames can keep Debuggers alive, even chaining them.

// The path through the heap we're building and testing here is:

//     gen0 (generator object) -> frame1 (suspended Frame with .onStep) -> dbg1 (Debugger object)

//       -> gen1 -> frame2 -> dbg2

// where everything after `gen1` is otherwise unreachable, and the edges

// `frame1 -> dbg1` and `frames2 -> dbg2` are due to the .onStep handlers, not

// strong refrences.

//

// There is no easy way to thread an event through this whole path; when we

// call gen0.next(), it will fire frame1.onStep(), but from there, making sure

// gen1.next() is called requires some minor heroics (see the WeakMap below).

var gen0;

var hits2 = 0;

var resuming2 = false;

function onStep2() {

    if (resuming2) {

        hits2++;

        resuming2 = false;

function setup() {

    let g1 = newGlobal({newCompartment: true});

    g1.eval(`

        function* gf1() {

             debugger;

             yield 1;

             return 'done';

`);

    gen0 = g1.gf1();

    let g2 = newGlobal({newCompartment: true});

    g2.eval(`

        function* gf2() { debugger; yield 1; return 'done'; }

        var resuming1 = false;

        function makeOnStepHook1(dbg1) {

            // We use this WeakMap as a weak reference from frame1.onStep to dbg1.

            var weak = new WeakMap();

            weak.set(dbg1, {});

            return () => {

                if (resuming1) {

                    var dbg1Arr = nondeterministicGetWeakMapKeys(weak);

                    assertEq(dbg1Arr.length, 1);

                    dbg1Arr[0].gen1.next();

                    resuming1 = false;

};

        function test(g1, gen0) {

            let dbg1 = Debugger(g1);

            dbg1.onDebuggerStatement = frame1 => {

                frame1.onStep = makeOnStepHook1(dbg1);

                dbg1.onDebuggerStatement = undefined;

};

            gen0.next();  // run to yield point, creating frame1 and setting its onStep hook

            resuming1 = true;

            dbg1.gen1 = gf2();

            return dbg1.gen1;

`);

    let dbg2 = Debugger(g2);

    dbg2.onDebuggerStatement = frame2 => {

        frame2.onStep = onStep2;

        dbg2.onDebuggerStatement = undefined;

};

    var gen1 = g2.test(g1, gen0);

    gen1.next();  // run to yield point, creating frame2 and setting its onStep hook

    resuming2 = true;

setup();

gc();

assertEq(hits2, 0);

gen0.next();  // fires frame1.onStep, which calls gen1.next(), which fires frame2.onStep

assertEq(hits2, 1);