tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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perf-service.mjs (3426B)

      1 /* This Source Code Form is subject to the terms of the Mozilla Public
      2 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
      3 * You can obtain one at http://mozilla.org/MPL/2.0/. */
      4 
      5 let usablePerfObj = window.performance;
      6 
      7 export function _PerfService(options) {
      8  // For testing, so that we can use a fake Window.performance object with
      9  // known state.
     10  if (options && options.performanceObj) {
     11    this._perf = options.performanceObj;
     12  } else {
     13    this._perf = usablePerfObj;
     14  }
     15 }
     16 
     17 _PerfService.prototype = {
     18  /**
     19   * Calls the underlying mark() method on the appropriate Window.performance
     20   * object to add a mark with the given name to the appropriate performance
     21   * timeline.
     22   *
     23   * @param  {string} name  the name to give the current mark
     24   * @return {void}
     25   */
     26  mark: function mark(str) {
     27    this._perf.mark(str);
     28  },
     29 
     30  /**
     31   * Calls the underlying getEntriesByName on the appropriate Window.performance
     32   * object.
     33   *
     34   * @param  {string} name
     35   * @param  {string} type eg "mark"
     36   * @return {Array}       Performance* objects
     37   */
     38  getEntriesByName: function getEntriesByName(entryName, type) {
     39    return this._perf.getEntriesByName(entryName, type);
     40  },
     41 
     42  /**
     43   * The timeOrigin property from the appropriate performance object.
     44   * Used to ensure that timestamps from the add-on code and the content code
     45   * are comparable.
     46   *
     47   * Note: If this is called from a context without a window
     48   * (eg a JSM in chrome), it will return the timeOrigin of the XUL hidden
     49   * window, which appears to be the first created window (and thus
     50   * timeOrigin) in the browser.  Note also, however, there is also a private
     51   * hidden window, presumably for private browsing, which appears to be
     52   * created dynamically later.  Exactly how/when that shows up needs to be
     53   * investigated.
     54   *
     55   * @return {number} A double of milliseconds with a precision of 0.5us.
     56   */
     57  get timeOrigin() {
     58    return this._perf.timeOrigin;
     59  },
     60 
     61  /**
     62   * Returns the "absolute" version of performance.now(), i.e. one that
     63   * should ([bug 1401406](https://bugzilla.mozilla.org/show_bug.cgi?id=1401406)
     64   * be comparable across both chrome and content.
     65   *
     66   * @return {number}
     67   */
     68  absNow: function absNow() {
     69    return this.timeOrigin + this._perf.now();
     70  },
     71 
     72  /**
     73   * This returns the absolute startTime from the most recent performance.mark()
     74   * with the given name.
     75   *
     76   * @param  {string} name  the name to lookup the start time for
     77   *
     78   * @return {number}       the returned start time, as a DOMHighResTimeStamp
     79   *
     80   * @throws {Error}        "No Marks with the name ..." if none are available
     81   *
     82   * Note: Always surround calls to this by try/catch.  Otherwise your code
     83   * may fail when the `privacy.resistFingerprinting` pref is true.  When
     84   * this pref is set, all attempts to get marks will likely fail, which will
     85   * cause this method to throw.
     86   *
     87   * See [bug 1369303](https://bugzilla.mozilla.org/show_bug.cgi?id=1369303)
     88   * for more info.
     89   */
     90  getMostRecentAbsMarkStartByName(entryName) {
     91    let entries = this.getEntriesByName(entryName, "mark");
     92 
     93    if (!entries.length) {
     94      throw new Error(`No marks with the name ${entryName}`);
     95    }
     96 
     97    let mostRecentEntry = entries[entries.length - 1];
     98    return this._perf.timeOrigin + mostRecentEntry.startTime;
     99  },
    100 };
    101 
    102 export const perfService = new _PerfService();