Add m-esr52 at 52.6.0

1 files changed, 1000 insertions, 0 deletions

diff --git a/toolkit/components/perfmonitoring/PerformanceStats.jsm b/toolkit/components/perfmonitoring/PerformanceStats.jsm
new file mode 100644
index 000000000..20f27a51b
--- /dev/null
+++ b/toolkit/components/perfmonitoring/PerformanceStats.jsm
@@ -0,0 +1,1000 @@
+// -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+/* 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 = ["PerformanceStats"];
+
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+/**
+ * API for querying and examining performance data.
+ *
+ * This API exposes data from several probes implemented by the JavaScript VM.
+ * See `PerformanceStats.getMonitor()` for information on how to monitor data
+ * from one or more probes and `PerformanceData` for the information obtained
+ * from the probes.
+ *
+ * Data is collected by "Performance Group". Typically, a Performance Group
+ * is an add-on, or a frame, or the internals of the application.
+ *
+ * Generally, if you have the choice between PerformanceStats and PerformanceWatcher,
+ * you should favor PerformanceWatcher.
+ */
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
+Cu.import("resource://gre/modules/Services.jsm", this);
+Cu.import("resource://gre/modules/Task.jsm", this);
+Cu.import("resource://gre/modules/ObjectUtils.jsm", this);
+XPCOMUtils.defineLazyModuleGetter(this, "PromiseUtils",
+  "resource://gre/modules/PromiseUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "setTimeout",
+  "resource://gre/modules/Timer.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "clearTimeout",
+  "resource://gre/modules/Timer.jsm");
+
+// The nsIPerformanceStatsService provides lower-level
+// access to SpiderMonkey and the probes.
+XPCOMUtils.defineLazyServiceGetter(this, "performanceStatsService",
+  "@mozilla.org/toolkit/performance-stats-service;1",
+  Ci.nsIPerformanceStatsService);
+
+// The finalizer lets us automatically release (and when possible deactivate)
+// probes when a monitor is garbage-collected.
+XPCOMUtils.defineLazyServiceGetter(this, "finalizer",
+  "@mozilla.org/toolkit/finalizationwitness;1",
+  Ci.nsIFinalizationWitnessService
+);
+
+// The topic used to notify that a PerformanceMonitor has been garbage-collected
+// and that we can release/close the probes it holds.
+const FINALIZATION_TOPIC = "performancemonitor-finalize";
+
+const PROPERTIES_META_IMMUTABLE = ["addonId", "isSystem", "isChildProcess", "groupId", "processId"];
+const PROPERTIES_META = [...PROPERTIES_META_IMMUTABLE, "windowId", "title", "name"];
+
+// How long we wait for children processes to respond.
+const MAX_WAIT_FOR_CHILD_PROCESS_MS = 5000;
+
+var isContent = Services.appinfo.processType == Services.appinfo.PROCESS_TYPE_CONTENT;
+/**
+ * Access to a low-level performance probe.
+ *
+ * Each probe is dedicated to some form of performance monitoring.
+ * As each probe may have a performance impact, a probe is activated
+ * only when a client has requested a PerformanceMonitor for this probe,
+ * and deactivated once all clients are disposed of.
+ */
+function Probe(name, impl) {
+  this._name = name;
+  this._counter = 0;
+  this._impl = impl;
+}
+Probe.prototype = {
+  /**
+   * Acquire the probe on behalf of a client.
+   *
+   * If the probe was inactive, activate it. Note that activating a probe
+   * can incur a memory or performance cost.
+   */
+  acquire: function() {
+    if (this._counter == 0) {
+      this._impl.isActive = true;
+      Process.broadcast("acquire", [this._name]);
+    }
+    this._counter++;
+  },
+
+  /**
+   * Release the probe on behalf of a client.
+   *
+   * If this was the last client for this probe, deactivate it.
+   */
+  release: function() {
+    this._counter--;
+    if (this._counter == 0) {
+      try {
+        this._impl.isActive = false;
+      } catch (ex) {
+        if (ex && typeof ex == "object" && ex.result == Components.results.NS_ERROR_NOT_AVAILABLE) {
+          // The service has already been shutdown. Ignore further shutdown requests.
+          return;
+        }
+        throw ex;
+      }
+      Process.broadcast("release", [this._name]);
+    }
+  },
+
+  /**
+   * Obtain data from this probe, once it is available.
+   *
+   * @param {nsIPerformanceStats} xpcom A xpcom object obtained from
+   * SpiderMonkey. Only the fields updated by the low-level probe
+   * are in a specified state.
+   * @return {object} An object containing the data extracted from this
+   * probe. Actual format depends on the probe.
+   */
+  extract: function(xpcom) {
+    if (!this._impl.isActive) {
+      throw new Error(`Probe is inactive: ${this._name}`);
+    }
+    return this._impl.extract(xpcom);
+  },
+
+  /**
+   * @param {object} a An object returned by `this.extract()`.
+   * @param {object} b An object returned by `this.extract()`.
+   *
+   * @return {true} If `a` and `b` hold identical values.
+   */
+  isEqual: function(a, b) {
+    if (a == null && b == null) {
+      return true;
+    }
+    if (a != null && b != null) {
+      return this._impl.isEqual(a, b);
+    }
+    return false;
+  },
+
+  /**
+   * @param {object} a An object returned by `this.extract()`. May
+   * NOT be `null`.
+   * @param {object} b An object returned by `this.extract()`. May
+   * be `null`.
+   *
+   * @return {object} An object representing `a - b`. If `b` is
+   * `null`, this is `a`.
+   */
+  subtract: function(a, b) {
+    if (a == null) {
+      throw new TypeError();
+    }
+    if (b == null) {
+      return a;
+    }
+    return this._impl.subtract(a, b);
+  },
+
+  importChildCompartments: function(parent, children) {
+    if (!Array.isArray(children)) {
+      throw new TypeError();
+    }
+    if (!parent || !(parent instanceof PerformanceDataLeaf)) {
+      throw new TypeError();
+    }
+    return this._impl.importChildCompartments(parent, children);
+  },
+
+  /**
+   * The name of the probe.
+   */
+  get name() {
+    return this._name;
+  },
+
+  compose: function(stats) {
+    if (!Array.isArray(stats)) {
+      throw new TypeError();
+    }
+    return this._impl.compose(stats);
+  }
+};
+
+// Utility function. Return the position of the last non-0 item in an
+// array, or -1 if there isn't any such item.
+function lastNonZero(array) {
+  for (let i = array.length - 1; i >= 0; --i) {
+    if (array[i] != 0) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+/**
+ * The actual Probes implemented by SpiderMonkey.
+ */
+var Probes = {
+  /**
+   * A probe measuring jank.
+   *
+   * Data provided by this probe uses the following format:
+   *
+   * @field {number} totalCPUTime The total amount of time spent using the
+   * CPU for this performance group, in µs.
+   * @field {number} totalSystemTime The total amount of time spent in the
+   * kernel for this performance group, in µs.
+   * @field {Array<number>} durations An array containing at each position `i`
+   * the number of times execution of this component has lasted at least `2^i`
+   * milliseconds.
+   * @field {number} longestDuration The index of the highest non-0 value in
+   * `durations`.
+   */
+  jank: new Probe("jank", {
+    set isActive(x) {
+      performanceStatsService.isMonitoringJank = x;
+    },
+    get isActive() {
+      return performanceStatsService.isMonitoringJank;
+    },
+    extract: function(xpcom) {
+      let durations = xpcom.getDurations();
+      return {
+        totalUserTime: xpcom.totalUserTime,
+        totalSystemTime: xpcom.totalSystemTime,
+        totalCPUTime: xpcom.totalUserTime + xpcom.totalSystemTime,
+        durations: durations,
+        longestDuration: lastNonZero(durations)
+      }
+    },
+    isEqual: function(a, b) {
+      // invariant: `a` and `b` are both non-null
+      if (a.totalUserTime != b.totalUserTime) {
+        return false;
+      }
+      if (a.totalSystemTime != b.totalSystemTime) {
+        return false;
+      }
+      for (let i = 0; i < a.durations.length; ++i) {
+        if (a.durations[i] != b.durations[i]) {
+          return false;
+        }
+      }
+      return true;
+    },
+    subtract: function(a, b) {
+      // invariant: `a` and `b` are both non-null
+      let result = {
+        totalUserTime: a.totalUserTime - b.totalUserTime,
+        totalSystemTime: a.totalSystemTime - b.totalSystemTime,
+        totalCPUTime: a.totalCPUTime - b.totalCPUTime,
+        durations: [],
+        longestDuration: -1,
+      };
+      for (let i = 0; i < a.durations.length; ++i) {
+        result.durations[i] = a.durations[i] - b.durations[i];
+      }
+      result.longestDuration = lastNonZero(result.durations);
+      return result;
+    },
+    importChildCompartments: function() { /* nothing to do */ },
+    compose: function(stats) {
+      let result = {
+        totalUserTime: 0,
+        totalSystemTime: 0,
+        totalCPUTime: 0,
+        durations: [],
+        longestDuration: -1
+      };
+      for (let stat of stats) {
+        result.totalUserTime += stat.totalUserTime;
+        result.totalSystemTime += stat.totalSystemTime;
+        result.totalCPUTime += stat.totalCPUTime;
+        for (let i = 0; i < stat.durations.length; ++i) {
+          result.durations[i] += stat.durations[i];
+        }
+        result.longestDuration = Math.max(result.longestDuration, stat.longestDuration);
+      }
+      return result;
+    }
+  }),
+
+  /**
+   * A probe measuring CPOW activity.
+   *
+   * Data provided by this probe uses the following format:
+   *
+   * @field {number} totalCPOWTime The amount of wallclock time
+   * spent executing blocking cross-process calls, in µs.
+   */
+  cpow: new Probe("cpow", {
+    set isActive(x) {
+      performanceStatsService.isMonitoringCPOW = x;
+    },
+    get isActive() {
+      return performanceStatsService.isMonitoringCPOW;
+    },
+    extract: function(xpcom) {
+      return {
+        totalCPOWTime: xpcom.totalCPOWTime
+      };
+    },
+    isEqual: function(a, b) {
+      return a.totalCPOWTime == b.totalCPOWTime;
+    },
+    subtract: function(a, b) {
+      return {
+        totalCPOWTime: a.totalCPOWTime - b.totalCPOWTime
+      };
+    },
+    importChildCompartments: function() { /* nothing to do */ },
+    compose: function(stats) {
+      let totalCPOWTime = 0;
+      for (let stat of stats) {
+        totalCPOWTime += stat.totalCPOWTime;
+      }
+      return { totalCPOWTime };
+    },
+  }),
+
+  /**
+   * A probe measuring activations, i.e. the number
+   * of times code execution has entered a given
+   * PerformanceGroup.
+   *
+   * Note that this probe is always active.
+   *
+   * Data provided by this probe uses the following format:
+   * @type {number} ticks The number of times execution has entered
+   * this performance group.
+   */
+  ticks: new Probe("ticks", {
+    set isActive(x) { /* this probe cannot be deactivated */ },
+    get isActive() { return true; },
+    extract: function(xpcom) {
+      return {
+        ticks: xpcom.ticks
+      };
+    },
+    isEqual: function(a, b) {
+      return a.ticks == b.ticks;
+    },
+    subtract: function(a, b) {
+      return {
+        ticks: a.ticks - b.ticks
+      };
+    },
+    importChildCompartments: function() { /* nothing to do */ },
+    compose: function(stats) {
+      let ticks = 0;
+      for (let stat of stats) {
+        ticks += stat.ticks;
+      }
+      return { ticks };
+    },
+  }),
+
+  compartments: new Probe("compartments", {
+    set isActive(x) {
+      performanceStatsService.isMonitoringPerCompartment = x;
+    },
+    get isActive() {
+      return performanceStatsService.isMonitoringPerCompartment;
+    },
+    extract: function(xpcom) {
+      return null;
+    },
+    isEqual: function(a, b) {
+      return true;
+    },
+    subtract: function(a, b) {
+      return true;
+    },
+    importChildCompartments: function(parent, children) {
+      parent.children = children;
+    },
+    compose: function(stats) {
+      return null;
+    },
+  }),
+};
+
+/**
+ * A monitor for a set of probes.
+ *
+ * Keeping probes active when they are unused is often a bad
+ * idea for performance reasons. Upon destruction, or whenever
+ * a client calls `dispose`, this monitor releases the probes,
+ * which may let the system deactivate them.
+ */
+function PerformanceMonitor(probes) {
+  this._probes = probes;
+
+  // Activate low-level features as needed
+  for (let probe of probes) {
+    probe.acquire();
+  }
+
+  // A finalization witness. At some point after the garbage-collection of
+  // `this` object, a notification of `FINALIZATION_TOPIC` will be triggered
+  // with `id` as message.
+  this._id = PerformanceMonitor.makeId();
+  this._finalizer = finalizer.make(FINALIZATION_TOPIC, this._id)
+  PerformanceMonitor._monitors.set(this._id, probes);
+}
+PerformanceMonitor.prototype = {
+  /**
+   * The names of probes activated in this monitor.
+   */
+  get probeNames() {
+    return this._probes.map(probe => probe.name);
+  },
+
+  /**
+   * Return asynchronously a snapshot with the data
+   * for each probe monitored by this PerformanceMonitor.
+   *
+   * All numeric values are non-negative and can only increase. Depending on
+   * the probe and the underlying operating system, probes may not be available
+   * immediately and may miss some activity.
+   *
+   * Clients should NOT expect that the first call to `promiseSnapshot()`
+   * will return a `Snapshot` in which all values are 0. For most uses,
+   * the appropriate scenario is to perform a first call to `promiseSnapshot()`
+   * to obtain a baseline, and then watch evolution of the values by calling
+   * `promiseSnapshot()` and `subtract()`.
+   *
+   * On the other hand, numeric values are also monotonic across several instances
+   * of a PerformanceMonitor with the same probes.
+   *  let a = PerformanceStats.getMonitor(someProbes);
+   *  let snapshot1 = yield a.promiseSnapshot();
+   *
+   *  // ...
+   *  let b = PerformanceStats.getMonitor(someProbes); // Same list of probes
+   *  let snapshot2 = yield b.promiseSnapshot();
+   *
+   *  // all values of `snapshot2` are greater or equal to values of `snapshot1`.
+   *
+   * @param {object} options If provided, an object that may contain the following
+   *   fields:
+   *   {Array<string>} probeNames The subset of probes to use for this snapshot.
+   *      These probes must be a subset of the probes active in the monitor.
+   *
+   * @return {Promise}
+   * @resolve {Snapshot}
+   */
+  _checkBeforeSnapshot: function(options) {
+    if (!this._finalizer) {
+      throw new Error("dispose() has already been called, this PerformanceMonitor is not usable anymore");
+    }
+    let probes;
+    if (options && options.probeNames || undefined) {
+      if (!Array.isArray(options.probeNames)) {
+        throw new TypeError();
+      }
+      // Make sure that we only request probes that we have
+      for (let probeName of options.probeNames) {
+        let probe = this._probes.find(probe => probe.name == probeName);
+        if (!probe) {
+          throw new TypeError(`I need probe ${probeName} but I only have ${this.probeNames}`);
+        }
+        if (!probes) {
+          probes = [];
+        }
+        probes.push(probe);
+      }
+    } else {
+      probes = this._probes;
+    }
+    return probes;
+  },
+  promiseContentSnapshot: function(options = null) {
+    this._checkBeforeSnapshot(options);
+    return (new ProcessSnapshot(performanceStatsService.getSnapshot()));
+  },
+  promiseSnapshot: function(options = null) {
+    let probes = this._checkBeforeSnapshot(options);
+    return Task.spawn(function*() {
+      let childProcesses = yield Process.broadcastAndCollect("collect", {probeNames: probes.map(p => p.name)});
+      let xpcom = performanceStatsService.getSnapshot();
+      return new ApplicationSnapshot({
+        xpcom,
+        childProcesses,
+        probes,
+        date: Cu.now()
+      });
+    });
+  },
+
+  /**
+   * Release the probes used by this monitor.
+   *
+   * Releasing probes as soon as they are unused is a good idea, as some probes
+   * cost CPU and/or memory.
+   */
+  dispose: function() {
+    if (!this._finalizer) {
+      return;
+    }
+    this._finalizer.forget();
+    PerformanceMonitor.dispose(this._id);
+
+    // As a safeguard against double-release, reset everything to `null`
+    this._probes = null;
+    this._id = null;
+    this._finalizer = null;
+  }
+};
+/**
+ * @type {Map<string, Array<string>>} A map from id (as produced by `makeId`)
+ * to list of probes. Used to deallocate a list of probes during finalization.
+ */
+PerformanceMonitor._monitors = new Map();
+
+/**
+ * Create a `PerformanceMonitor` for a list of probes, register it for
+ * finalization.
+ */
+PerformanceMonitor.make = function(probeNames) {
+  // Sanity checks
+  if (!Array.isArray(probeNames)) {
+    throw new TypeError("Expected an array, got " + probes);
+  }
+  let probes = [];
+  for (let probeName of probeNames) {
+    if (!(probeName in Probes)) {
+      throw new TypeError("Probe not implemented: " + probeName);
+    }
+    probes.push(Probes[probeName]);
+  }
+
+  return (new PerformanceMonitor(probes));
+};
+
+/**
+ * Implementation of `dispose`.
+ *
+ * The actual implementation of `dispose` is as a method of `PerformanceMonitor`,
+ * rather than `PerformanceMonitor.prototype`, to avoid needing a strong reference
+ * to instances of `PerformanceMonitor`, which would defeat the purpose of
+ * finalization.
+ */
+PerformanceMonitor.dispose = function(id) {
+  let probes = PerformanceMonitor._monitors.get(id);
+  if (!probes) {
+    throw new TypeError("`dispose()` has already been called on this monitor");
+  }
+
+  PerformanceMonitor._monitors.delete(id);
+  for (let probe of probes) {
+    probe.release();
+  }
+}
+
+// Generate a unique id for each PerformanceMonitor. Used during
+// finalization.
+PerformanceMonitor._counter = 0;
+PerformanceMonitor.makeId = function() {
+  return "PerformanceMonitor-" + (this._counter++);
+}
+
+// Once a `PerformanceMonitor` has been garbage-collected,
+// release the probes unless `dispose()` has already been called.
+Services.obs.addObserver(function(subject, topic, value) {
+  PerformanceMonitor.dispose(value);
+}, FINALIZATION_TOPIC, false);
+
+// Public API
+this.PerformanceStats = {
+  /**
+   * Create a monitor for observing a set of performance probes.
+   */
+  getMonitor: function(probes) {
+    return PerformanceMonitor.make(probes);
+  }
+};
+
+
+/**
+ * Information on a single performance group.
+ *
+ * This offers the following fields:
+ *
+ * @field {string} name The name of the performance group:
+ * - for the process itself, "<process>";
+ * - for platform code, "<platform>";
+ * - for an add-on, the identifier of the addon (e.g. "myaddon@foo.bar");
+ * - for a webpage, the url of the page.
+ *
+ * @field {string} addonId The identifier of the addon (e.g. "myaddon@foo.bar").
+ *
+ * @field {string|null} title The title of the webpage to which this code
+ *  belongs. Note that this is the title of the entire webpage (i.e. the tab),
+ *  even if the code is executed in an iframe. Also note that this title may
+ *  change over time.
+ *
+ * @field {number} windowId The outer window ID of the top-level nsIDOMWindow
+ *  to which this code belongs. May be 0 if the code doesn't belong to any
+ *  nsIDOMWindow.
+ *
+ * @field {boolean} isSystem `true` if the component is a system component (i.e.
+ *  an add-on or platform-code), `false` otherwise (i.e. a webpage).
+ *
+ * @field {object|undefined} activations See the documentation of probe "ticks".
+ *   `undefined` if this probe is not active.
+ *
+ * @field {object|undefined} jank See the documentation of probe "jank".
+ *   `undefined` if this probe is not active.
+ *
+ * @field {object|undefined} cpow See the documentation of probe "cpow".
+ *   `undefined` if this probe is not active.
+ */
+function PerformanceDataLeaf({xpcom, json, probes}) {
+  if (xpcom && json) {
+    throw new TypeError("Cannot import both xpcom and json data");
+  }
+  let source = xpcom || json;
+  for (let k of PROPERTIES_META) {
+    this[k] = source[k];
+  }
+  if (xpcom) {
+    for (let probe of probes) {
+      this[probe.name] = probe.extract(xpcom);
+    }
+    this.isChildProcess = false;
+  } else {
+    for (let probe of probes) {
+      this[probe.name] = json[probe.name];
+    }
+    this.isChildProcess = true;
+  }
+  this.owner = null;
+}
+PerformanceDataLeaf.prototype = {
+  /**
+   * Compare two instances of `PerformanceData`
+   *
+   * @return `true` if `this` and `to` have equal values in all fields.
+   */
+  equals: function(to) {
+    if (!(to instanceof PerformanceDataLeaf)) {
+      throw new TypeError();
+    }
+    for (let probeName of Object.keys(Probes)) {
+      let probe = Probes[probeName];
+      if (!probe.isEqual(this[probeName], to[probeName])) {
+        return false;
+      }
+    }
+    return true;
+  },
+
+  /**
+   * Compute the delta between two instances of `PerformanceData`.
+   *
+   * @param {PerformanceData|null} to. If `null`, assumed an instance of
+   * `PerformanceData` in which all numeric values are 0.
+   *
+   * @return {PerformanceDiff} The performance usage between `to` and `this`.
+   */
+  subtract: function(to = null) {
+    return (new PerformanceDiffLeaf(this, to));
+  }
+};
+
+function PerformanceData(timestamp) {
+  this._parent = null;
+  this._content = new Map();
+  this._all = [];
+  this._timestamp = timestamp;
+}
+PerformanceData.prototype = {
+  addChild: function(stat) {
+    if (!(stat instanceof PerformanceDataLeaf)) {
+      throw new TypeError(); // FIXME
+    }
+    if (!stat.isChildProcess) {
+      throw new TypeError(); // FIXME
+    }
+    this._content.set(stat.groupId, stat);
+    this._all.push(stat);
+    stat.owner = this;
+  },
+  setParent: function(stat) {
+    if (!(stat instanceof PerformanceDataLeaf)) {
+      throw new TypeError(); // FIXME
+    }
+    if (stat.isChildProcess) {
+      throw new TypeError(); // FIXME
+    }
+    this._parent = stat;
+    this._all.push(stat);
+    stat.owner = this;
+  },
+  equals: function(to) {
+    if (this._parent && !to._parent) {
+      return false;
+    }
+    if (!this._parent && to._parent) {
+      return false;
+    }
+    if (this._content.size != to._content.size) {
+      return false;
+    }
+    if (this._parent && !this._parent.equals(to._parent)) {
+      return false;
+    }
+    for (let [k, v] of this._content) {
+      let v2 = to._content.get(k);
+      if (!v2) {
+        return false;
+      }
+      if (!v.equals(v2)) {
+        return false;
+      }
+    }
+    return true;
+  },
+  subtract: function(to = null) {
+    return (new PerformanceDiff(this, to));
+  },
+  get addonId() {
+    return this._all[0].addonId;
+  },
+  get title() {
+    return this._all[0].title;
+  }
+};
+
+function PerformanceDiff(current, old = null) {
+  this.addonId = current.addonId;
+  this.title = current.title;
+  this.windowId = current.windowId;
+  this.deltaT = old ? current._timestamp - old._timestamp : Infinity;
+  this._all = [];
+
+  // Handle the parent, if any.
+  if (current._parent) {
+    this._parent = old?current._parent.subtract(old._parent):current._parent;
+    this._all.push(this._parent);
+    this._parent.owner = this;
+  } else {
+    this._parent = null;
+  }
+
+  // Handle the children, if any.
+  this._content = new Map();
+  for (let [k, stat] of current._content) {
+    let diff = stat.subtract(old ? old._content.get(k) : null);
+    this._content.set(k, diff);
+    this._all.push(diff);
+    diff.owner = this;
+  }
+
+  // Now consolidate data
+  for (let k of Object.keys(Probes)) {
+    if (!(k in this._all[0])) {
+      // The stats don't contain data from this probe.
+      continue;
+    }
+    let data = this._all.map(item => item[k]);
+    let probe = Probes[k];
+    this[k] = probe.compose(data);
+  }
+}
+PerformanceDiff.prototype = {
+  toString: function() {
+    return `[PerformanceDiff] ${this.key}`;
+  },
+  get windowIds() {
+    return this._all.map(item => item.windowId).filter(x => !!x);
+  },
+  get groupIds() {
+    return this._all.map(item => item.groupId);
+  },
+  get key() {
+    if (this.addonId) {
+      return this.addonId;
+    }
+    if (this._parent) {
+      return this._parent.windowId;
+    }
+    return this._all[0].groupId;
+  },
+  get names() {
+    return this._all.map(item => item.name);
+  },
+  get processes() {
+    return this._all.map(item => ({ isChildProcess: item.isChildProcess, processId: item.processId}));
+  }
+};
+
+/**
+ * The delta between two instances of `PerformanceDataLeaf`.
+ *
+ * Used to monitor resource usage between two timestamps.
+ */
+function PerformanceDiffLeaf(current, old = null) {
+  for (let k of PROPERTIES_META) {
+    this[k] = current[k];
+  }
+
+  for (let probeName of Object.keys(Probes)) {
+    let other = null;
+    if (old && probeName in old) {
+      other = old[probeName];
+    }
+
+    if (probeName in current) {
+      this[probeName] = Probes[probeName].subtract(current[probeName], other);
+    }
+  }
+}
+
+/**
+ * A snapshot of a single process.
+ */
+function ProcessSnapshot({xpcom, probes}) {
+  this.componentsData = [];
+
+  let subgroups = new Map();
+  let enumeration = xpcom.getComponentsData().enumerate();
+  while (enumeration.hasMoreElements()) {
+    let xpcom = enumeration.getNext().QueryInterface(Ci.nsIPerformanceStats);
+    let stat = (new PerformanceDataLeaf({xpcom, probes}));
+
+    if (!xpcom.parentId) {
+      this.componentsData.push(stat);
+    } else {
+      let siblings = subgroups.get(xpcom.parentId);
+      if (!siblings) {
+        subgroups.set(xpcom.parentId, (siblings = []));
+      }
+      siblings.push(stat);
+    }
+  }
+
+  for (let group of this.componentsData) {
+    for (let probe of probes) {
+      probe.importChildCompartments(group, subgroups.get(group.groupId) || []);
+    }
+  }
+
+  this.processData = (new PerformanceDataLeaf({xpcom: xpcom.getProcessData(), probes}));
+}
+
+/**
+ * A snapshot of the performance usage of the application.
+ *
+ * @param {nsIPerformanceSnapshot} xpcom The data acquired from this process.
+ * @param {Array<Object>} childProcesses The data acquired from children processes.
+ * @param {Array<Probe>} probes The active probes.
+ */
+function ApplicationSnapshot({xpcom, childProcesses, probes, date}) {
+  ProcessSnapshot.call(this, {xpcom, probes});
+
+  this.addons = new Map();
+  this.webpages = new Map();
+  this.date = date;
+
+  // Child processes
+  for (let {componentsData} of (childProcesses || [])) {
+    // We are only interested in `componentsData` for the time being.
+    for (let json of componentsData) {
+      let leaf = (new PerformanceDataLeaf({json, probes}));
+      this.componentsData.push(leaf);
+    }
+  }
+
+  for (let leaf of this.componentsData) {
+    let key, map;
+    if (leaf.addonId) {
+      key = leaf.addonId;
+      map = this.addons;
+    } else if (leaf.windowId) {
+      key = leaf.windowId;
+      map = this.webpages;
+    } else {
+      continue;
+    }
+
+    let combined = map.get(key);
+    if (!combined) {
+      combined = new PerformanceData(date);
+      map.set(key, combined);
+    }
+    if (leaf.isChildProcess) {
+      combined.addChild(leaf);
+    } else {
+      combined.setParent(leaf);
+    }
+  }
+}
+
+/**
+ * Communication with other processes
+ */
+var Process = {
+  // a counter used to match responses to requests
+  _idcounter: 0,
+  _loader: null,
+  /**
+   * If we are in a child process, return `null`.
+   * Otherwise, return the global parent process message manager
+   * and load the script to connect to children processes.
+   */
+  get loader() {
+    if (isContent) {
+      return null;
+    }
+    if (this._loader) {
+      return this._loader;
+    }
+    Services.ppmm.loadProcessScript("resource://gre/modules/PerformanceStats-content.js",
+      true/* including future processes*/);
+    return this._loader = Services.ppmm;
+  },
+
+  /**
+   * Broadcast a message to all children processes.
+   *
+   * NOOP if we are in a child process.
+   */
+  broadcast: function(topic, payload) {
+    if (!this.loader) {
+      return;
+    }
+    this.loader.broadcastAsyncMessage("performance-stats-service-" + topic, {payload});
+  },
+
+  /**
+   * Brodcast a message to all children processes and wait for answer.
+   *
+   * NOOP if we are in a child process, or if we have no children processes,
+   * in which case we return `undefined`.
+   *
+   * @return {undefined} If we have no children processes, in particular
+   * if we are in a child process.
+   * @return {Promise<Array<Object>>} If we have children processes, an
+   * array of objects with a structure similar to PerformanceData. Note
+   * that the array may be empty if no child process responded.
+   */
+  broadcastAndCollect: Task.async(function*(topic, payload) {
+    if (!this.loader || this.loader.childCount == 1) {
+      return undefined;
+    }
+    const TOPIC = "performance-stats-service-" + topic;
+    let id = this._idcounter++;
+
+    // The number of responses we are expecting. Note that we may
+    // not receive all responses if a process is too long to respond.
+    let expecting = this.loader.childCount;
+
+    // The responses we have collected, in arbitrary order.
+    let collected = [];
+    let deferred = PromiseUtils.defer();
+
+    let observer = function({data, target}) {
+      if (data.id != id) {
+        // Collision between two collections,
+        // ignore the other one.
+        return;
+      }
+      if (data.data) {
+        collected.push(data.data)
+      }
+      if (--expecting > 0) {
+        // We are still waiting for at least one response.
+        return;
+      }
+      deferred.resolve();
+    };
+    this.loader.addMessageListener(TOPIC, observer);
+    this.loader.broadcastAsyncMessage(
+      TOPIC,
+      {id, payload}
+    );
+
+    // Processes can die/freeze/be busy loading a page..., so don't expect
+    // that they will always respond.
+    let timeout = setTimeout(() => {
+      if (expecting == 0) {
+        return;
+      }
+      deferred.resolve();
+    }, MAX_WAIT_FOR_CHILD_PROCESS_MS);
+
+    deferred.promise.then(() => {
+      clearTimeout(timeout);
+    });
+
+    yield deferred.promise;
+    this.loader.removeMessageListener(TOPIC, observer);
+
+    return collected;
+  })
+};