Add m-esr52 at 52.6.0

1 files changed, 234 insertions, 0 deletions

diff --git a/browser/components/sessionstore/StartupPerformance.jsm b/browser/components/sessionstore/StartupPerformance.jsm
new file mode 100644
index 000000000..d1b77a237
--- /dev/null
+++ b/browser/components/sessionstore/StartupPerformance.jsm
@@ -0,0 +1,234 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["StartupPerformance"];
+
+const { utils: Cu, classes: Cc, interfaces: Ci } = Components;
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
+
+XPCOMUtils.defineLazyModuleGetter(this, "Services",
+  "resource://gre/modules/Services.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "console",
+  "resource://gre/modules/Console.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "setTimeout",
+  "resource://gre/modules/Timer.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "clearTimeout",
+  "resource://gre/modules/Timer.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Promise",
+  "resource://gre/modules/Promise.jsm");
+
+const COLLECT_RESULTS_AFTER_MS = 10000;
+
+const OBSERVED_TOPICS = ["sessionstore-restoring-on-startup", "sessionstore-initiating-manual-restore"];
+
+this.StartupPerformance = {
+  /**
+   * Once we have finished restoring initial tabs, we broadcast on this topic.
+   */
+  RESTORED_TOPIC: "sessionstore-finished-restoring-initial-tabs",
+
+  // Instant at which we have started restoration (notification "sessionstore-restoring-on-startup")
+  _startTimeStamp: null,
+
+  // Latest instant at which we have finished restoring a tab (DOM event "SSTabRestored")
+  _latestRestoredTimeStamp: null,
+
+  // A promise resolved once we have finished restoring all the startup tabs.
+  _promiseFinished: null,
+
+  // Function `resolve()` for `_promiseFinished`.
+  _resolveFinished: null,
+
+  // A timer
+  _deadlineTimer: null,
+
+  // `true` once the timer has fired
+  _hasFired: false,
+
+  // `true` once we are restored
+  _isRestored: false,
+
+  // Statistics on the session we need to restore.
+  _totalNumberOfEagerTabs: 0,
+  _totalNumberOfTabs: 0,
+  _totalNumberOfWindows: 0,
+
+  init: function() {
+    for (let topic of OBSERVED_TOPICS) {
+      Services.obs.addObserver(this, topic, false);
+    }
+  },
+
+  /**
+   * Return the timestamp at which we finished restoring the latest tab.
+   *
+   * This information is not really interesting until we have finished restoring
+   * tabs.
+   */
+  get latestRestoredTimeStamp() {
+    return this._latestRestoredTimeStamp;
+  },
+
+  /**
+   * `true` once we have finished restoring startup tabs.
+   */
+  get isRestored() {
+    return this._isRestored;
+  },
+
+  // Called when restoration starts.
+  // Record the start timestamp, setup the timer and `this._promiseFinished`.
+  // Behavior is unspecified if there was already an ongoing measure.
+  _onRestorationStarts: function(isAutoRestore) {
+    this._latestRestoredTimeStamp = this._startTimeStamp = Date.now();
+    this._totalNumberOfEagerTabs = 0;
+    this._totalNumberOfTabs = 0;
+    this._totalNumberOfWindows = 0;
+
+    // While we may restore several sessions in a single run of the browser,
+    // that's a very unusual case, and not really worth measuring, so let's
+    // stop listening for further restorations.
+
+    for (let topic of OBSERVED_TOPICS) {
+      Services.obs.removeObserver(this, topic);
+    }
+
+    Services.obs.addObserver(this, "sessionstore-single-window-restored", false);
+    this._promiseFinished = new Promise(resolve => {
+      this._resolveFinished = resolve;
+    });
+    this._promiseFinished.then(() => {
+      try {
+        this._isRestored = true;
+        Services.obs.notifyObservers(null, this.RESTORED_TOPIC, "");
+
+        if (this._latestRestoredTimeStamp == this._startTimeStamp) {
+          // Apparently, we haven't restored any tab.
+          return;
+        }
+
+        // Once we are done restoring tabs, update Telemetry.
+        let histogramName = isAutoRestore ?
+          "FX_SESSION_RESTORE_AUTO_RESTORE_DURATION_UNTIL_EAGER_TABS_RESTORED_MS" :
+          "FX_SESSION_RESTORE_MANUAL_RESTORE_DURATION_UNTIL_EAGER_TABS_RESTORED_MS";
+        let histogram = Services.telemetry.getHistogramById(histogramName);
+        let delta = this._latestRestoredTimeStamp - this._startTimeStamp;
+        histogram.add(delta);
+
+        Services.telemetry.getHistogramById("FX_SESSION_RESTORE_NUMBER_OF_EAGER_TABS_RESTORED").add(this._totalNumberOfEagerTabs);
+        Services.telemetry.getHistogramById("FX_SESSION_RESTORE_NUMBER_OF_TABS_RESTORED").add(this._totalNumberOfTabs);
+        Services.telemetry.getHistogramById("FX_SESSION_RESTORE_NUMBER_OF_WINDOWS_RESTORED").add(this._totalNumberOfWindows);
+
+        // Reset
+        this._startTimeStamp = null;
+     } catch (ex) {
+        console.error("StartupPerformance: error after resolving promise", ex);
+      }
+    });
+  },
+
+  _startTimer: function() {
+    if (this._hasFired) {
+      return;
+    }
+    if (this._deadlineTimer) {
+      clearTimeout(this._deadlineTimer);
+    }
+    this._deadlineTimer = setTimeout(() => {
+      try {
+        this._resolveFinished();
+      } catch (ex) {
+        console.error("StartupPerformance: Error in timeout handler", ex);
+      } finally {
+        // Clean up.
+        this._deadlineTimer = null;
+        this._hasFired = true;
+        this._resolveFinished = null;
+        Services.obs.removeObserver(this, "sessionstore-single-window-restored");
+      }
+    }, COLLECT_RESULTS_AFTER_MS);
+  },
+
+  observe: function(subject, topic, details) {
+    try {
+      switch (topic) {
+        case "sessionstore-restoring-on-startup":
+          this._onRestorationStarts(true);
+          break;
+        case "sessionstore-initiating-manual-restore":
+          this._onRestorationStarts(false);
+          break;
+        case "sessionstore-single-window-restored": {
+          // Session Restore has just opened a window with (initially empty) tabs.
+          // Some of these tabs will be restored eagerly, while others will be
+          // restored on demand. The process becomes usable only when all windows
+          // have finished restored their eager tabs.
+          //
+          // While it would be possible to track the restoration of each tab
+          // from within SessionRestore to determine exactly when the process
+          // becomes usable, experience shows that this is too invasive. Rather,
+          // we employ the following heuristic:
+          // - we maintain a timer of `COLLECT_RESULTS_AFTER_MS` that we expect
+          //   will be triggered only once all tabs have been restored;
+          // - whenever we restore a new window (hence a bunch of eager tabs),
+          //   we postpone the timer to ensure that the new eager tabs have
+          //   `COLLECT_RESULTS_AFTER_MS` to be restored;
+          // - whenever a tab is restored, we update
+          //   `this._latestRestoredTimeStamp`;
+          // - after `COLLECT_RESULTS_AFTER_MS`, we collect the final version
+          //   of `this._latestRestoredTimeStamp`, and use it to determine the
+          //   entire duration of the collection.
+          //
+          // Note that this heuristic may be inaccurate if a user clicks
+          // immediately on a restore-on-demand tab before the end of
+          // `COLLECT_RESULTS_AFTER_MS`. We assume that this will not
+          // affect too much the results.
+          //
+          // Reset the delay, to give the tabs a little (more) time to restore.
+          this._startTimer();
+
+          this._totalNumberOfWindows += 1;
+
+          // Observe the restoration of all tabs. We assume that all tabs of this
+          // window will have been restored before `COLLECT_RESULTS_AFTER_MS`.
+          // The last call to `observer` will let us determine how long it took
+          // to reach that point.
+          let win = subject;
+
+          let observer = (event) => {
+            // We don't care about tab restorations that are due to
+            // a browser flipping from out-of-main-process to in-main-process
+            // or vice-versa. We only care about restorations that are due
+            // to the user switching to a lazily restored tab, or for tabs
+            // that are restoring eagerly.
+            if (!event.detail.isRemotenessUpdate) {
+              this._latestRestoredTimeStamp = Date.now();
+              this._totalNumberOfEagerTabs += 1;
+            }
+          };
+          win.gBrowser.tabContainer.addEventListener("SSTabRestored", observer);
+          this._totalNumberOfTabs += win.gBrowser.tabContainer.itemCount;
+
+          // Once we have finished collecting the results, clean up the observers.
+          this._promiseFinished.then(() => {
+            if (!win.gBrowser.tabContainer) {
+              // May be undefined during shutdown and/or some tests.
+              return;
+            }
+            win.gBrowser.tabContainer.removeEventListener("SSTabRestored", observer);
+          });
+        }
+        break;
+        default:
+          throw new Error(`Unexpected topic ${topic}`);
+      }
+    } catch (ex) {
+      console.error("StartupPerformance error", ex, ex.stack);
+      throw ex;
+    }
+  }
+};