browser/components/sessionstore/SessionSaver.jsm
author Cosmin Sabou <csabou@mozilla.com>
Sat, 02 Mar 2019 20:40:01 +0200
changeset 520014 bf3cbcc825276823afba2778333cf62cfa75039c
parent 519904 f976c2d4cebb29588222e0c5122c475aae3be509
child 520355 1960442645ea613e13d326252b33448b4d49587f
permissions -rw-r--r--
Backed out 16 changesets (bug 827976) for causing bug 1532054. a=backout Backed out changeset 54c0b12443ed (bug 827976) Backed out changeset 92b45080d080 (bug 827976) Backed out changeset 443087a359f9 (bug 827976) Backed out changeset f976c2d4cebb (bug 827976) Backed out changeset 66cffb171024 (bug 827976) Backed out changeset 845e1d0b2402 (bug 827976) Backed out changeset fd94066a1d76 (bug 827976) Backed out changeset e253b264e7bd (bug 827976) Backed out changeset 07ef335770a8 (bug 827976) Backed out changeset 9d3805d77b99 (bug 827976) Backed out changeset eed600ceb606 (bug 827976) Backed out changeset 3b64368cff52 (bug 827976) Backed out changeset 69d0378e0c09 (bug 827976) Backed out changeset 9203871a5c6f (bug 827976) Backed out changeset 96a507c818e2 (bug 827976) Backed out changeset e254496ff95b (bug 827976)

/* 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";

var EXPORTED_SYMBOLS = ["SessionSaver"];

ChromeUtils.import("resource://gre/modules/Timer.jsm", this);
ChromeUtils.import("resource://gre/modules/Services.jsm", this);
ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm", this);

XPCOMUtils.defineLazyModuleGetters(this, {
  AppConstants: "resource://gre/modules/AppConstants.jsm",
  PrivacyFilter: "resource://gre/modules/sessionstore/PrivacyFilter.jsm",
  RunState: "resource:///modules/sessionstore/RunState.jsm",
  SessionStore: "resource:///modules/sessionstore/SessionStore.jsm",
  SessionFile: "resource:///modules/sessionstore/SessionFile.jsm",
  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
});

/*
 * Minimal interval between two save operations (in milliseconds).
 *
 * To save system resources, we generally do not save changes immediately when
 * a change is detected. Rather, we wait a little to see if this change is
 * followed by other changes, in which case only the last write is necessary.
 * This delay is defined by "browser.sessionstore.interval".
 *
 * Furthermore, when the user is not actively using the computer, webpages
 * may still perform changes that require (re)writing to sessionstore, e.g.
 * updating Session Cookies or DOM Session Storage, or refreshing, etc. We
 * expect that these changes are much less critical to the user and do not
 * need to be saved as often. In such cases, we increase the delay to
 *  "browser.sessionstore.interval.idle".
 *
 * When the user returns to the computer, if a save is pending, we reschedule
 * it to happen soon, with "browser.sessionstore.interval".
 */
const PREF_INTERVAL_ACTIVE = "browser.sessionstore.interval";
const PREF_INTERVAL_IDLE = "browser.sessionstore.interval.idle";
const PREF_IDLE_DELAY = "browser.sessionstore.idleDelay";

// Notify observers about a given topic with a given subject.
function notify(subject, topic) {
  Services.obs.notifyObservers(subject, topic);
}

// TelemetryStopwatch helper functions.
function stopWatch(method) {
  return function(...histograms) {
    for (let hist of histograms) {
      TelemetryStopwatch[method]("FX_SESSION_RESTORE_" + hist);
    }
  };
}

var stopWatchStart = stopWatch("start");
var stopWatchFinish = stopWatch("finish");

/**
 * The external API implemented by the SessionSaver module.
 */
var SessionSaver = Object.freeze({
  /**
   * Immediately saves the current session to disk.
   */
  run() {
    return SessionSaverInternal.run();
  },

  /**
   * Saves the current session to disk delayed by a given amount of time. Should
   * another delayed run be scheduled already, we will ignore the given delay
   * and state saving may occur a little earlier.
   */
  runDelayed() {
    SessionSaverInternal.runDelayed();
  },

  /**
   * Sets the last save time to the current time. This will cause us to wait for
   * at least the configured interval when runDelayed() is called next.
   */
  updateLastSaveTime() {
    SessionSaverInternal.updateLastSaveTime();
  },

  /**
   * Cancels all pending session saves.
   */
  cancel() {
    SessionSaverInternal.cancel();
  },
});

/**
 * The internal API.
 */
var SessionSaverInternal = {
  /**
   * The timeout ID referencing an active timer for a delayed save. When no
   * save is pending, this is null.
   */
  _timeoutID: null,

  /**
   * The idle callback ID referencing an active idle callback. When no idle
   * callback is pending, this is null.
   * */
  _idleCallbackID: null,

  /**
   * A timestamp that keeps track of when we saved the session last. We will
   * this to determine the correct interval between delayed saves to not deceed
   * the configured session write interval.
   */
  _lastSaveTime: 0,

  /**
   * `true` if the user has been idle for at least
   * `SessionSaverInternal._intervalWhileIdle` ms. Idleness is computed
   * with `nsIIdleService`.
   */
  _isIdle: false,

  /**
   * `true` if the user was idle when we last scheduled a delayed save.
   * See `_isIdle` for details on idleness.
   */
  _wasIdle: false,

  /**
   * Minimal interval between two save operations (in ms), while the user
   * is active.
   */
  _intervalWhileActive: null,

  /**
   * Minimal interval between two save operations (in ms), while the user
   * is idle.
   */
  _intervalWhileIdle: null,

  /**
   * How long before we assume that the user is idle (ms).
   */
  _idleDelay: null,

  /**
   * Immediately saves the current session to disk.
   */
  run() {
    return this._saveState(true /* force-update all windows */);
  },

  /**
   * Saves the current session to disk delayed by a given amount of time. Should
   * another delayed run be scheduled already, we will ignore the given delay
   * and state saving may occur a little earlier.
   *
   * @param delay (optional)
   *        The minimum delay in milliseconds to wait for until we collect and
   *        save the current session.
   */
  runDelayed(delay = 2000) {
    // Bail out if there's a pending run.
    if (this._timeoutID) {
      return;
    }

    // Interval until the next disk operation is allowed.
    let interval = this._isIdle ? this._intervalWhileIdle : this._intervalWhileActive;
    delay = Math.max(this._lastSaveTime + interval - Date.now(), delay, 0);

    // Schedule a state save.
    this._wasIdle = this._isIdle;
    this._timeoutID = setTimeout(() => {
      let hiddenDOMWindow = Services.appShell.hiddenDOMWindow;

      // Execute _saveStateAsync when we have enough idle time. Otherwise,
      // another idle request is made to schedule _saveStateAsync again.
      let saveStateAsyncWhenIdle = (deadline) => {
        // When looking at the telemetry data, the time it takes to execute
        // _saveStateAsync is around 5.9ms (median). Therefore,
        // we'll not execute the function when the idle time is less than 5ms.
        if (deadline.timeRemaining() < 5) {
          this._idleCallbackID = hiddenDOMWindow.requestIdleCallback(saveStateAsyncWhenIdle);
          return;
        }
        this._saveStateAsync();
      };

      this._idleCallbackID = hiddenDOMWindow.requestIdleCallback(saveStateAsyncWhenIdle);
    }, delay);
  },

  /**
   * Sets the last save time to the current time. This will cause us to wait for
   * at least the configured interval when runDelayed() is called next.
   */
  updateLastSaveTime() {
    this._lastSaveTime = Date.now();
  },

  /**
   * Cancels all pending session saves.
   */
  cancel() {
    clearTimeout(this._timeoutID);
    this._timeoutID = null;
    Services.appShell.hiddenDOMWindow.cancelIdleCallback(this._idleCallbackID);
    this._idleCallbackID = null;
  },

  /**
   * Observe idle/ active notifications.
   */
  observe(subject, topic, data) {
    switch (topic) {
      case "idle":
        this._isIdle = true;
        break;
      case "active":
        this._isIdle = false;
        if (this._timeoutID && this._wasIdle) {
          // A state save has been scheduled while we were idle.
          // Replace it by an active save.
          clearTimeout(this._timeoutID);
          this._timeoutID = null;
          this.runDelayed();
        }
        break;
      default:
        throw new Error(`Unexpected change value ${topic}`);
    }
  },

  /**
   * Saves the current session state. Collects data and writes to disk.
   *
   * @param forceUpdateAllWindows (optional)
   *        Forces us to recollect data for all windows and will bypass and
   *        update the corresponding caches.
   */
  _saveState(forceUpdateAllWindows = false) {
    // Cancel any pending timeouts.
    this.cancel();

    if (PrivateBrowsingUtils.permanentPrivateBrowsing) {
      // Don't save (or even collect) anything in permanent private
      // browsing mode

      this.updateLastSaveTime();
      return Promise.resolve();
    }

    stopWatchStart("COLLECT_DATA_MS");
    let state = SessionStore.getCurrentState(forceUpdateAllWindows);
    PrivacyFilter.filterPrivateWindowsAndTabs(state);

    // Make sure we only write worth saving tabs to disk.
    SessionStore.keepOnlyWorthSavingTabs(state);

    // Make sure that we keep the previous session if we started with a single
    // private window and no non-private windows have been opened, yet.
    if (state.deferredInitialState) {
      state.windows = state.deferredInitialState.windows || [];
      delete state.deferredInitialState;
    }

    if (AppConstants.platform != "macosx") {
      // We want to restore closed windows that are marked with _shouldRestore.
      // We're doing this here because we want to control this only when saving
      // the file.
      while (state._closedWindows.length) {
        let i = state._closedWindows.length - 1;

        if (!state._closedWindows[i]._shouldRestore) {
          // We only need to go until _shouldRestore
          // is falsy since we're going in reverse.
          break;
        }

        delete state._closedWindows[i]._shouldRestore;
        state.windows.unshift(state._closedWindows.pop());
      }
    }

    // Clear cookies and storage on clean shutdown.
    this._maybeClearCookiesAndStorage(state);

    stopWatchFinish("COLLECT_DATA_MS");
    return this._writeState(state);
  },

  /**
   * Purges cookies and DOMSessionStorage data from the session on clean
   * shutdown, only if requested by the user's preferences.
   */
  _maybeClearCookiesAndStorage(state) {
    // Only do this on shutdown.
    if (!RunState.isClosing) {
      return;
    }

    // Don't clear when restarting.
    if (Services.prefs.getBoolPref("browser.sessionstore.resume_session_once")) {
      return;
    }

    let expireCookies = Services.prefs.getIntPref("network.cookie.lifetimePolicy") ==
                        Services.cookies.QueryInterface(Ci.nsICookieService).ACCEPT_SESSION;
    let sanitizeCookies = Services.prefs.getBoolPref("privacy.sanitize.sanitizeOnShutdown") &&
                          Services.prefs.getBoolPref("privacy.clearOnShutdown.cookies");

    if (expireCookies || sanitizeCookies) {
      // Remove cookies.
      delete state.cookies;

      // Remove DOMSessionStorage data.
      for (let window of state.windows) {
        for (let tab of window.tabs) {
          delete tab.storage;
        }
      }
    }
  },

  /**
   * Saves the current session state. Collects data asynchronously and calls
   * _saveState() to collect data again (with a cache hit rate of hopefully
   * 100%) and write to disk afterwards.
   */
  _saveStateAsync() {
    // Allow scheduling delayed saves again.
    this._timeoutID = null;

    // Write to disk.
    this._saveState();
  },

  /**
   * Write the given state object to disk.
   */
  _writeState(state) {
    // We update the time stamp before writing so that we don't write again
    // too soon, if saving is requested before the write completes. Without
    // this update we may save repeatedly if actions cause a runDelayed
    // before writing has completed. See Bug 902280
    this.updateLastSaveTime();

    // Write (atomically) to a session file, using a tmp file. Once the session
    // file is successfully updated, save the time stamp of the last save and
    // notify the observers.
    return SessionFile.write(state).then(() => {
      this.updateLastSaveTime();
      notify(null, "sessionstore-state-write-complete");
    }, console.error);
  },
};

XPCOMUtils.defineLazyPreferenceGetter(SessionSaverInternal, "_intervalWhileActive", PREF_INTERVAL_ACTIVE,
  15000 /* 15 seconds */, () => {
  // Cancel any pending runs and call runDelayed() with
  // zero to apply the newly configured interval.
  SessionSaverInternal.cancel();
  SessionSaverInternal.runDelayed(0);
});

XPCOMUtils.defineLazyPreferenceGetter(SessionSaverInternal, "_intervalWhileIdle", PREF_INTERVAL_IDLE,
  3600000 /* 1 h */);

XPCOMUtils.defineLazyPreferenceGetter(SessionSaverInternal, "_idleDelay", PREF_IDLE_DELAY,
  180000 /* 3 minutes */, (key, previous, latest) => {
  // Update the idle observer for the new `PREF_IDLE_DELAY` value. Here we need
  // to re-fetch the service instead of the original one in use; This is for a
  // case that the Mock service in the unit test needs to be fetched to
  // replace the original one.
  var idleService = Cc["@mozilla.org/widget/idleservice;1"].getService(Ci.nsIIdleService);
  if (previous != undefined) {
    idleService.removeIdleObserver(SessionSaverInternal, previous);
  }
  if (latest != undefined) {
    idleService.addIdleObserver(SessionSaverInternal, latest);
  }
});

var idleService = Cc["@mozilla.org/widget/idleservice;1"].getService(Ci.nsIIdleService);
idleService.addIdleObserver(SessionSaverInternal, SessionSaverInternal._idleDelay);