weak-marking-budget.js

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// Make enterWeakMarkingMode expensive so it gets forced into a single slice.

gczeal(0); // We need full control here.

var maps = Array(1000).fill().map(() => new WeakMap);

for (const map of maps) {

    for (let i = 0; i < 100; i++) {

        map.set({}, {}); // These will all die, but will need to be put into the ephemeron table first.

// Slowly work forward until we reach Mark.

startgc(10);

while (["Prepare", "MarkRoots"].includes(gcstate())) {

    gcslice(10);

assertEq(gcstate(), "Mark");

// This will yield before leaving marking, in order to give the first sweep

// slice a full budget.

print("gcslice(10000) #1");

gcslice(10000);

assertEq(gcstate(), "Mark");

// First Sweep slice will hit the long enterWeakMarkingMode and yield as soon as

// the budget runs out, and set up the next Sweep slice to finish.

print("gcslice(10000) #2");

gcslice(10000);

assertEq(gcstate(), "Sweep");

hasFunction["currentgc"] && assertEq(currentgc().finishMarkingDuringSweeping, true);

// This slice will finish the marking, but will go way over budget and so will

// yield as soon as the marking is done. This will still be during Sweep (in the

// middle of sweepWeakCaches).

print("gcslice(1) #3");

// Use more than gcslice(1) because it is possible to get a few things added to

// the mark stack from read barriers.

gcslice(100);

assertEq(gcstate(), "Sweep");

hasFunction["currentgc"] && assertEq(currentgc().finishMarkingDuringSweeping, false);

// There's still a lot of sweeping left to do, because all of the dead stuff

// needs to be finalized.

finishgc();

// Do another GC without a slow enterWMM, to confirm that the extra slice is not

// requested. (The previous GC will have thrown out all of the WeakMaps'

// entries, so this will just be doing one step for each of the 1000 WeakMaps

// instead of 1000 * (1 + 100) for the WeakMaps plus their keys.)

startgc(10);

while (["Prepare", "MarkRoots"].includes(gcstate())) {

    gcslice(10);

assertEq(gcstate(), "Mark");

gcslice(10000);

assertEq(gcstate(), "Mark");

gcslice(1);

assertEq(gcstate(), "Sweep");

hasFunction["currentgc"] && assertEq(currentgc().finishMarkingDuringSweeping, false);

gcslice(1);

assertEq(gcstate(), "Sweep");

hasFunction["currentgc"] && assertEq(currentgc().finishMarkingDuringSweeping, false);