gecko-dev/devtools/server/performance/memory.js

/* 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";

const {
  reportException,
} = require("resource://devtools/shared/DevToolsUtils.js");
const { expectState } = require("resource://devtools/server/actors/common.js");

loader.lazyRequireGetter(
  this,
  "EventEmitter",
  "resource://devtools/shared/event-emitter.js"
);
const lazy = {};
ChromeUtils.defineESModuleGetters(lazy, {
  DeferredTask: "resource://gre/modules/DeferredTask.sys.mjs",
});
loader.lazyRequireGetter(
  this,
  "StackFrameCache",
  "resource://devtools/server/actors/utils/stack.js",
  true
);
loader.lazyRequireGetter(
  this,
  "ParentProcessTargetActor",
  "resource://devtools/server/actors/targets/parent-process.js",
  true
);
loader.lazyRequireGetter(
  this,
  "ContentProcessTargetActor",
  "resource://devtools/server/actors/targets/content-process.js",
  true
);

/**
 * A class that returns memory data for a parent actor's window.
 * Using a target-scoped actor with this instance will measure the memory footprint of its
 * parent tab. Using a global-scoped actor instance however, will measure the memory
 * footprint of the chrome window referenced by its root actor.
 *
 * To be consumed by actor's, like MemoryActor using this module to
 * send information over RDP, and TimelineActor for using more light-weight
 * utilities like GC events and measuring memory consumption.
 */
function Memory(parent, frameCache = new StackFrameCache()) {
  EventEmitter.decorate(this);

  this.parent = parent;
  this._mgr = Cc["@mozilla.org/memory-reporter-manager;1"].getService(
    Ci.nsIMemoryReporterManager
  );
  this.state = "detached";
  this._dbg = null;
  this._frameCache = frameCache;

  this._onGarbageCollection = this._onGarbageCollection.bind(this);
  this._emitAllocations = this._emitAllocations.bind(this);
  this._onWindowReady = this._onWindowReady.bind(this);

  EventEmitter.on(this.parent, "window-ready", this._onWindowReady);
}

Memory.prototype = {
  destroy() {
    EventEmitter.off(this.parent, "window-ready", this._onWindowReady);

    this._mgr = null;
    if (this.state === "attached") {
      this.detach();
    }
  },

  get dbg() {
    if (!this._dbg) {
      this._dbg = this.parent.makeDebugger();
    }
    return this._dbg;
  },

  /**
   * Attach to this MemoryBridge.
   *
   * This attaches the MemoryBridge's Debugger instance so that you can start
   * recording allocations or take a census of the heap. In addition, the
   * MemoryBridge will start emitting GC events.
   */
  attach() {
    // The actor may be attached by the Target via recordAllocation configuration
    // or manually by the frontend.
    if (this.state == "attached") {
      return this.state;
    }
    this.dbg.addDebuggees();
    this.dbg.memory.onGarbageCollection = this._onGarbageCollection.bind(this);
    this.state = "attached";
    return this.state;
  },

  /**
   * Detach from this MemoryBridge.
   */
  detach: expectState(
    "attached",
    function() {
      this._clearDebuggees();
      this.dbg.disable();
      this._dbg = null;
      this.state = "detached";
      return this.state;
    },
    "detaching from the debugger"
  ),

  /**
   * Gets the current MemoryBridge attach/detach state.
   */
  getState() {
    return this.state;
  },

  _clearDebuggees() {
    if (this._dbg) {
      if (this.isRecordingAllocations()) {
        this.dbg.memory.drainAllocationsLog();
      }
      this._clearFrames();
      this.dbg.removeAllDebuggees();
    }
  },

  _clearFrames() {
    if (this.isRecordingAllocations()) {
      this._frameCache.clearFrames();
    }
  },

  /**
   * Handler for the parent actor's "window-ready" event.
   */
  _onWindowReady({ isTopLevel }) {
    if (this.state == "attached") {
      this._clearDebuggees();
      if (isTopLevel && this.isRecordingAllocations()) {
        this._frameCache.initFrames();
      }
      this.dbg.addDebuggees();
    }
  },

  /**
   * Returns a boolean indicating whether or not allocation
   * sites are being tracked.
   */
  isRecordingAllocations() {
    return this.dbg.memory.trackingAllocationSites;
  },

  /**
   * Save a heap snapshot scoped to the current debuggees' portion of the heap
   * graph.
   *
   * @param {Object|null} boundaries
   *
   * @returns {String} The snapshot id.
   */
  saveHeapSnapshot: expectState(
    "attached",
    function(boundaries = null) {
      // If we are observing the whole process, then scope the snapshot
      // accordingly. Otherwise, use the debugger's debuggees.
      if (!boundaries) {
        if (
          this.parent instanceof ParentProcessTargetActor ||
          this.parent instanceof ContentProcessTargetActor
        ) {
          boundaries = { runtime: true };
        } else {
          boundaries = { debugger: this.dbg };
        }
      }
      return ChromeUtils.saveHeapSnapshotGetId(boundaries);
    },
    "saveHeapSnapshot"
  ),

  /**
   * Take a census of the heap. See js/src/doc/Debugger/Debugger.Memory.md for
   * more information.
   */
  takeCensus: expectState(
    "attached",
    function() {
      return this.dbg.memory.takeCensus();
    },
    "taking census"
  ),

  /**
   * Start recording allocation sites.
   *
   * @param {number} options.probability
   *                 The probability we sample any given allocation when recording
   *                 allocations. Must be between 0 and 1 -- defaults to 1.
   * @param {number} options.maxLogLength
   *                 The maximum number of allocation events to keep in the
   *                 log. If new allocs occur while at capacity, oldest
   *                 allocations are lost. Must fit in a 32 bit signed integer.
   * @param {number} options.drainAllocationsTimeout
   *                 A number in milliseconds of how often, at least, an `allocation`
   *                 event gets emitted (and drained), and also emits and drains on every
   *                 GC event, resetting the timer.
   */
  startRecordingAllocations: expectState(
    "attached",
    function(options = {}) {
      if (this.isRecordingAllocations()) {
        return this._getCurrentTime();
      }

      this._frameCache.initFrames();

      this.dbg.memory.allocationSamplingProbability =
        options.probability != null ? options.probability : 1.0;

      this.drainAllocationsTimeoutTimer = options.drainAllocationsTimeout;

      if (this.drainAllocationsTimeoutTimer != null) {
        if (this._poller) {
          this._poller.disarm();
        }
        this._poller = new lazy.DeferredTask(
          this._emitAllocations,
          this.drainAllocationsTimeoutTimer,
          0
        );
        this._poller.arm();
      }

      if (options.maxLogLength != null) {
        this.dbg.memory.maxAllocationsLogLength = options.maxLogLength;
      }
      this.dbg.memory.trackingAllocationSites = true;

      return this._getCurrentTime();
    },
    "starting recording allocations"
  ),

  /**
   * Stop recording allocation sites.
   */
  stopRecordingAllocations: expectState(
    "attached",
    function() {
      if (!this.isRecordingAllocations()) {
        return this._getCurrentTime();
      }
      this.dbg.memory.trackingAllocationSites = false;
      this._clearFrames();

      if (this._poller) {
        this._poller.disarm();
        this._poller = null;
      }

      return this._getCurrentTime();
    },
    "stopping recording allocations"
  ),

  /**
   * Return settings used in `startRecordingAllocations` for `probability`
   * and `maxLogLength`. Currently only uses in tests.
   */
  getAllocationsSettings: expectState(
    "attached",
    function() {
      return {
        maxLogLength: this.dbg.memory.maxAllocationsLogLength,
        probability: this.dbg.memory.allocationSamplingProbability,
      };
    },
    "getting allocations settings"
  ),

  /**
   * Get a list of the most recent allocations since the last time we got
   * allocations, as well as a summary of all allocations since we've been
   * recording.
   *
   * @returns Object
   *          An object of the form:
   *
   *            {
   *              allocations: [<index into "frames" below>, ...],
   *              allocationsTimestamps: [
   *                <timestamp for allocations[0]>,
   *                <timestamp for allocations[1]>,
   *                ...
   *              ],
   *              allocationSizes: [
   *                <bytesize for allocations[0]>,
   *                <bytesize for allocations[1]>,
   *                ...
   *              ],
   *              frames: [
   *                {
   *                  line: <line number for this frame>,
   *                  column: <column number for this frame>,
   *                  source: <filename string for this frame>,
   *                  functionDisplayName:
   *                    <this frame's inferred function name function or null>,
   *                  parent: <index into "frames">
   *                },
   *                ...
   *              ],
   *            }
   *
   *          The timestamps' unit is microseconds since the epoch.
   *
   *          Subsequent `getAllocations` request within the same recording and
   *          tab navigation will always place the same stack frames at the same
   *          indices as previous `getAllocations` requests in the same
   *          recording. In other words, it is safe to use the index as a
   *          unique, persistent id for its frame.
   *
   *          Additionally, the root node (null) is always at index 0.
   *
   *          We use the indices into the "frames" array to avoid repeating the
   *          description of duplicate stack frames both when listing
   *          allocations, and when many stacks share the same tail of older
   *          frames. There shouldn't be any duplicates in the "frames" array,
   *          as that would defeat the purpose of this compression trick.
   *
   *          In the future, we might want to split out a frame's "source" and
   *          "functionDisplayName" properties out the same way we have split
   *          frames out with the "frames" array. While this would further
   *          compress the size of the response packet, it would increase CPU
   *          usage to build the packet, and it should, of course, be guided by
   *          profiling and done only when necessary.
   */
  getAllocations: expectState(
    "attached",
    function() {
      if (this.dbg.memory.allocationsLogOverflowed) {
        // Since the last time we drained the allocations log, there have been
        // more allocations than the log's capacity, and we lost some data. There
        // isn't anything actionable we can do about this, but put a message in
        // the browser console so we at least know that it occurred.
        reportException(
          "MemoryBridge.prototype.getAllocations",
          "Warning: allocations log overflowed and lost some data."
        );
      }

      const allocations = this.dbg.memory.drainAllocationsLog();
      const packet = {
        allocations: [],
        allocationsTimestamps: [],
        allocationSizes: [],
      };
      for (const { frame: stack, timestamp, size } of allocations) {
        if (stack && Cu.isDeadWrapper(stack)) {
          continue;
        }

        // Safe because SavedFrames are frozen/immutable.
        const waived = Cu.waiveXrays(stack);

        // Ensure that we have a form, size, and index for new allocations
        // because we potentially haven't seen some or all of them yet. After this
        // loop, we can rely on the fact that every frame we deal with already has
        // its metadata stored.
        const index = this._frameCache.addFrame(waived);

        packet.allocations.push(index);
        packet.allocationsTimestamps.push(timestamp);
        packet.allocationSizes.push(size);
      }

      return this._frameCache.updateFramePacket(packet);
    },
    "getting allocations"
  ),

  /*
   * Force a browser-wide GC.
   */
  forceGarbageCollection() {
    for (let i = 0; i < 3; i++) {
      Cu.forceGC();
    }
  },

  /**
   * Force an XPCOM cycle collection. For more information on XPCOM cycle
   * collection, see
   * https://developer.mozilla.org/en-US/docs/Interfacing_with_the_XPCOM_cycle_collector#What_the_cycle_collector_does
   */
  forceCycleCollection() {
    Cu.forceCC();
  },

  /**
   * A method that returns a detailed breakdown of the memory consumption of the
   * associated window.
   *
   * @returns object
   */
  measure() {
    const result = {};

    const jsObjectsSize = {};
    const jsStringsSize = {};
    const jsOtherSize = {};
    const domSize = {};
    const styleSize = {};
    const otherSize = {};
    const totalSize = {};
    const jsMilliseconds = {};
    const nonJSMilliseconds = {};

    try {
      this._mgr.sizeOfTab(
        this.parent.window,
        jsObjectsSize,
        jsStringsSize,
        jsOtherSize,
        domSize,
        styleSize,
        otherSize,
        totalSize,
        jsMilliseconds,
        nonJSMilliseconds
      );
      result.total = totalSize.value;
      result.domSize = domSize.value;
      result.styleSize = styleSize.value;
      result.jsObjectsSize = jsObjectsSize.value;
      result.jsStringsSize = jsStringsSize.value;
      result.jsOtherSize = jsOtherSize.value;
      result.otherSize = otherSize.value;
      result.jsMilliseconds = jsMilliseconds.value.toFixed(1);
      result.nonJSMilliseconds = nonJSMilliseconds.value.toFixed(1);
    } catch (e) {
      reportException("MemoryBridge.prototype.measure", e);
    }

    return result;
  },

  residentUnique() {
    return this._mgr.residentUnique;
  },

  /**
   * Handler for GC events on the Debugger.Memory instance.
   */
  _onGarbageCollection(data) {
    this.emit("garbage-collection", data);

    // If `drainAllocationsTimeout` set, fire an allocations event with the drained log,
    // which will restart the timer.
    if (this._poller) {
      this._poller.disarm();
      this._emitAllocations();
    }
  },

  /**
   * Called on `drainAllocationsTimeoutTimer` interval if and only if set
   * during `startRecordingAllocations`, or on a garbage collection event if
   * drainAllocationsTimeout was set.
   * Drains allocation log and emits as an event and restarts the timer.
   */
  _emitAllocations() {
    this.emit("allocations", this.getAllocations());
    this._poller.arm();
  },

  /**
   * Accesses the docshell to return the current process time.
   */
  _getCurrentTime() {
    const docShell = this.parent.isRootActor
      ? this.parent.docShell
      : this.parent.originalDocShell;
    if (docShell) {
      return docShell.now();
    }
    // When used from the ContentProcessTargetActor, parent has no docShell,
    // so fallback to Cu.now
    return Cu.now();
  },
};

exports.Memory = Memory;