compartment-revived-gc.js

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// Test 'compartment revived' GCs, where we do an extra GC if there are

// compartments which we expected to die but were kept alive.

// A global used as the destination for transplants.

let transplantTargetGlobal = newGlobal();

function didCompartmentRevivedGC() {

  return performance.mozMemory.gc.lastStartReason === "COMPARTMENT_REVIVED";

function compartmentCount() {

  let r = performance.mozMemory.gc.compartmentCount;

  return r;

function startIncrementalGC() {

  startgc(1);

  while (gcstate() === "Prepare") {

    gcslice(100, {dontStart: true});

  assertEq(gcstate(), "Mark");

function finishIncrementalGC() {

  while (gcstate() !== "NotActive") {

    gcslice(100, {dontStart: true});

  assertEq(gcstate(), "NotActive");

// Create a new compartment and global and return the global.

function createCompartment() {

  return newGlobal({newCompartment: true});

// Create a transplantable object and create a wrapper to it from a new

// compartment. Return a function to transplant the target object.

function createTransplantableWrapperTarget(wrapperGlobal) {

  let {object: target, transplant} = transplantableObject();

  wrapperGlobal.wrapper = target;

  return transplant;

// Transplant an object to a new global by calling the transplant

// function. This remaps all wrappers pointing to the target object,

// potentially keeping dead compartments alive.

function transplantTargetAndRemapWrappers(transplant) {

  transplant(transplantTargetGlobal);

// Test no compartment revived GC triggered in normal cases.

function testNormal() {

  gc();

  assertEq(didCompartmentRevivedGC(), false);

  startIncrementalGC();

  finishIncrementalGC();

  assertEq(didCompartmentRevivedGC(), false);

  let initialCount = compartmentCount();

  createCompartment();

  startIncrementalGC();

  finishIncrementalGC();

  assertEq(compartmentCount(), initialCount);

// Test compartment revived GC is triggered by wrapper remapping.

function testCompartmentRevived1() {

  let initialCount = compartmentCount();

  let compartment = createCompartment();

  let transplant = createTransplantableWrapperTarget(compartment);

  compartment = null;

  startIncrementalGC();

  transplantTargetAndRemapWrappers(transplant);

  finishIncrementalGC();

  assertEq(didCompartmentRevivedGC(), true);

  assertEq(compartmentCount(), initialCount);

// Test no compartment revived GC is triggered for compartments transitively

// kept alive by black roots.

function testCompartmentRevived2() {

  let initialCount = compartmentCount();

  let compartment = createCompartment();

  let transplant = createTransplantableWrapperTarget(compartment);

  let liveCompartment = createCompartment();

  liveCompartment.wrapper = compartment;

  compartment = null;

  startIncrementalGC();

  transplantTargetAndRemapWrappers(transplant);

  finishIncrementalGC();

  assertEq(didCompartmentRevivedGC(), false);

  assertEq(compartmentCount(), initialCount + 2);

  liveCompartment = null;

  gc();

  assertEq(compartmentCount(), initialCount);

// Test no compartment revived GC is triggered for compartments transitively

// kept alive by gray roots.

function testCompartmentRevived3() {

  let initialCount = compartmentCount();

  let compartment = createCompartment();

  let transplant = createTransplantableWrapperTarget(compartment);

  let liveCompartment = createCompartment();

  liveCompartment.wrapper = compartment;

  liveCompartment.eval('grayRoot()[0] = this');

  liveCompartment = null;

  gc();

  startIncrementalGC();

  transplantTargetAndRemapWrappers(transplant);

  finishIncrementalGC();

  assertEq(didCompartmentRevivedGC(), false);

  assertEq(compartmentCount(), initialCount + 2);

  // There's no easy way to clear gray roots for a compartment we don't have

  // any reference to.

gczeal(0);

testNormal();

testCompartmentRevived1();

testCompartmentRevived2();

testCompartmentRevived3();