waitForExplicitFinish(); var pageSource = "" + '

' + ""; 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(); }