browser_startupcache_telemetry.js

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/* Any copyright is dedicated to the Public Domain.

   http://creativecommons.org/publicdomain/zero/1.0/ */

"use strict";

const LABELS_STARTUP_CACHE_REQUESTS = {

  HitMemory: 0,

  HitDisk: 1,

  Miss: 2,

};

add_task(async function () {

  // Turn off tab preloading to avoid issues with RemoteController.js

  await SpecialPowers.pushPrefEnv({

    set: [["browser.newtab.preload", false]],

});

  Services.obs.notifyObservers(null, "startupcache-invalidate");

  Services.telemetry.getSnapshotForHistograms("main", true);

  let newWin = await BrowserTestUtils.openNewBrowserWindow();

  let snapshot = Services.telemetry.getSnapshotForHistograms("main", true);

  function histValue(label) {

    return snapshot.parent.STARTUP_CACHE_REQUESTS.values[label] || 0;

  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 0);

  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);

  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 0);

  await BrowserTestUtils.closeWindow(newWin);

  newWin = await BrowserTestUtils.openNewBrowserWindow();

  snapshot = Services.telemetry.getSnapshotForHistograms("main", true);

  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 0);

  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);

  // Here and below, 50 is just a nice round number that should be well over

  // what we should observe under normal circumstances, and well under what

  // we should see if something is seriously wrong. It won't catch everything,

  // but it's better than nothing, and better than a test that cries wolf.

  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 50);

  await BrowserTestUtils.closeWindow(newWin);

  Services.obs.notifyObservers(null, "startupcache-invalidate", "memoryOnly");

  newWin = await BrowserTestUtils.openNewBrowserWindow();

  snapshot = Services.telemetry.getSnapshotForHistograms("main", true);

  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 50);

  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);

  // Some misses can come through - just ensure it's a small number

  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 50);

  await BrowserTestUtils.closeWindow(newWin);

});