Source code
Revision control
Copy as Markdown
Other Tools
/* 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,
const lazy = {};
ChromeUtils.defineESModuleGetters(lazy, {
});
const COLLECT_RESULTS_AFTER_MS = 10000;
const OBSERVED_TOPICS = [
"sessionstore-restoring-on-startup",
"sessionstore-initiating-manual-restore",
];
export var 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() {
for (let topic of OBSERVED_TOPICS) {
Services.obs.addObserver(this, topic);
}
},
/**
* 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(isAutoRestore) {
ChromeUtils.addProfilerMarker("_onRestorationStarts");
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");
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() {
if (this._hasFired) {
return;
}
if (this._deadlineTimer) {
lazy.clearTimeout(this._deadlineTimer);
}
this._deadlineTimer = lazy.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(subject, topic) {
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) {
ChromeUtils.addProfilerMarker("SSTabRestored");
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;
}
},
};