weak-marking-revealed.js

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// This is really just a minimal example of how to ensure that the weak marking

// mode is required.

gczeal(0);

function big_graph() {

  const root = {};

  let obj = root;

  for (let i = 0; i < 100000; i++) {

    obj = obj.o = {};

  return root;

// "Hide" a large graph behind a WeakMap so that it gets traversed in weak

// marking mode.

//

// Whichever weakmap is traced first (almost certainly wm1 here) will have an

// unmarked key (mid2) that maps to the big graph. But that key is not reachable

// until the other weakmap is traced, so it will only happen when weak marking

// mode is entered.

var wm1 = new WeakMap();

var wm2 = new WeakMap();

var keys = [{}, {}];

var mid1 = {};

var mid2 = {};

var big1 = big_graph();

var big2 = big_graph();

gc();

wm1.set(keys[0], mid1);

var big = big_graph();

wm2.set(mid1, big1);

wm2.set(keys[1], mid2);

wm1.set(mid2, big2);

addMarkObservers([ big1, big2, mid1, mid2 ]);

big1 = big2 = null;

mid1 = mid2 = null;

gc();

var marks = JSON.stringify(getMarks());

print("Marks: " + marks);

assertEq(marks, '["black","black","black","black"]');