browser_bug666317.js

Enable keyboard shortcuts

waitForExplicitFinish();

var pageSource =

  "<html><body>" +

  '<img id="testImg" src="' +

  TESTROOT +

  'big.png">' +

  "</body></html>";

var oldDiscardingPref, oldTab, newTab;

var prefBranch = Services.prefs.getBranch("image.mem.");

var gWaitingForDiscard = false;

var gScriptedObserver;

var gClonedRequest;

function ImageObserver(decodeCallback, discardCallback) {

  this.decodeComplete = function onDecodeComplete() {

    decodeCallback();

};

  this.discard = function onDiscard() {

    if (!gWaitingForDiscard) {

      return;

    this.synchronous = false;

    discardCallback();

};

  this.synchronous = true;

function currentRequest() {

  let img = gBrowser

    .getBrowserForTab(newTab)

    .contentWindow.document.getElementById("testImg");

  return img.getRequest(Ci.nsIImageLoadingContent.CURRENT_REQUEST);

function isImgDecoded() {

  let request = currentRequest();

  return !!(request.imageStatus & Ci.imgIRequest.STATUS_DECODE_COMPLETE);

// Ensure that the image is decoded by drawing it to a canvas.

function forceDecodeImg() {

  let doc = gBrowser.getBrowserForTab(newTab).contentWindow.document;

  let img = doc.getElementById("testImg");

  let canvas = doc.createElement("canvas");

  let ctx = canvas.getContext("2d");

  ctx.drawImage(img, 0, 0);

function runAfterAsyncEvents(aCallback) {

  function handlePostMessage(aEvent) {

    if (aEvent.data == "next") {

      window.removeEventListener("message", handlePostMessage);

      aCallback();

  window.addEventListener("message", handlePostMessage);

  // We'll receive the 'message' event after everything else that's currently in

  // the event queue (which is a stronger guarantee than setTimeout, because

  // setTimeout events may be coalesced). This lets us ensure that we run

  // aCallback *after* any asynchronous events are delivered.

  window.postMessage("next", "*");

function test() {

  // Enable the discarding pref.

  oldDiscardingPref = prefBranch.getBoolPref("discardable");

  prefBranch.setBoolPref("discardable", true);

  // Create and focus a new tab.

  oldTab = gBrowser.selectedTab;

  newTab = BrowserTestUtils.addTab(gBrowser, "data:text/html," + pageSource);

  gBrowser.selectedTab = newTab;

  // Run step2 after the tab loads.

  gBrowser.getBrowserForTab(newTab).addEventListener("pageshow", step2);

function step2() {

  // Create the image observer.

  var observer = new ImageObserver(

    () => runAfterAsyncEvents(step3), // DECODE_COMPLETE

    () => runAfterAsyncEvents(step5)

  ); // DISCARD

  gScriptedObserver = Cc["@mozilla.org/image/tools;1"]

    .getService(Ci.imgITools)

    .createScriptedObserver(observer);

  // Clone the current imgIRequest with our new observer.

  var request = currentRequest();

  gClonedRequest = request.clone(gScriptedObserver);

  // Check that the image is decoded.

  forceDecodeImg();

  // The DECODE_COMPLETE notification is delivered asynchronously. ImageObserver will

  // eventually call step3.

function step3() {

  ok(isImgDecoded(), "Image should initially be decoded.");

  // Focus the old tab, then fire a memory-pressure notification.  This should

  // cause the decoded image in the new tab to be discarded.

  gBrowser.selectedTab = oldTab;

  // Allow time to process the tab change.

  runAfterAsyncEvents(step4);

function step4() {

  gWaitingForDiscard = true;

  var os = Services.obs;

  os.notifyObservers(null, "memory-pressure", "heap-minimize");

  // The DISCARD notification is delivered asynchronously. ImageObserver will

  // eventually call step5. (Or else, sadly, the test will time out.)

function step5() {

  ok(true, "Image should be discarded.");

  // And we're done.

  gBrowser.removeTab(newTab);

  prefBranch.setBoolPref("discardable", oldDiscardingPref);

  gClonedRequest.cancelAndForgetObserver(0);

  finish();