author Sylvestre Ledru <>
Thu, 17 Aug 2017 11:13:01 +0200
changeset 648192 c236dfe7dc98c387219d7cb45d0693560db708fd
parent 645449 a8aa2a5c2870498d9c21b05fed673d786591f817
permissions -rw-r--r--
indent all (with js specific coding style) MozReview-Commit-ID: LU1md2wyB8

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 */

#ifndef nsWindowMemoryReporter_h__
#define nsWindowMemoryReporter_h__

#include "nsGlobalWindow.h"
#include "nsIMemoryReporter.h"
#include "nsIObserver.h"
#include "nsITimer.h"
#include "nsDataHashtable.h"
#include "nsWeakReference.h"
#include "mozilla/Attributes.h"
#include "mozilla/Assertions.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/PodOperations.h"
#include "mozilla/TimeStamp.h"

 * nsWindowMemoryReporter is responsible for the 'explicit/window-objects'
 * memory reporter.
 * We classify DOM window objects into one of three categories:
 *   - "active" windows, which are displayed in a tab (as the top-level window
 *     or an iframe),
 *   - "cached" windows, which are in the fastback cache (aka the bfcache), and
 *   - "detached" windows, which have a null docshell.  A window becomes
 *     detached when its <iframe> or tab containing the window is destroyed --
 *     i.e., when the window is no longer active or cached.
 * Additionally, we classify a subset of detached windows as "ghost" windows.
 * Although ghost windows can happen legitimately (a page can hold a reference
 * to a cross-domain window and then close its container), the presence of
 * ghost windows is often indicative of a memory leak.
 * A window is a ghost if it meets the following three criteria:
 *   1) The window is detached.
 *   2) There exist no non-detached windows with the same base domain as
 *      the window's principal.  (For example, the base domain of
 *      "" is "".)  This criterion makes us less
 *      likely to flag a legitimately held-alive detached window as a ghost.
 *   3) The window has met criteria (1) and (2) above for at least
 *      memory.ghost_window_timeout_seconds.  This criterion is in place so we
 *      don't immediately declare a window a ghost before the GC/CC has had a
 *      chance to run.
 * nsWindowMemoryReporter observes window detachment and uses mDetachedWindows
 * to remember when a window first met criteria (1) and (2).  When we generate
 * a memory report, we use this accounting to determine which windows are
 * ghosts.
 * We use the following memory reporter path for active and cached windows:
 *   explicit/window-objects/top(<top-outer-uri>, id=<top-outer-id>)/<category>/window(<window-uri>)/...
 * For detached and ghost windows, we use
 *   explicit/window-objects/top(none)/<category>/window(<window-uri>)/...
 * Where
 * - <category> is "active", "cached", "detached", or "ghost", as described
 *   above.
 * - <top-outer-id> is the window id of the top outer window (i.e. the tab, or
 *   the top level chrome window).  Exposing this ensures that each tab gets
 *   its own sub-tree, even if multiple tabs are showing the same URI.
 * - <top-uri> is the URI of the top window.  Excepting special windows (such
 *   as browser.xul or hiddenWindow.html) it's what the address bar shows for
 *   the tab.
class nsWindowMemoryReporter final
  : public nsIMemoryReporter
  , public nsIObserver
  , public nsSupportsWeakReference

  static void Init();

#ifdef DEBUG
   * Unlink all known ghost windows, to enable investigating what caused them
   * to become ghost windows in the first place.
  static void UnlinkGhostWindows();

  static nsWindowMemoryReporter* Get();
  void ObserveDOMWindowDetached(nsGlobalWindow* aWindow);


   * nsGhostWindowReporter generates the "ghost-windows" report, which counts
   * the number of ghost windows present.
  class GhostWindowsReporter final : public nsIMemoryReporter
    ~GhostWindowsReporter() {}


    static int64_t DistinguishedAmount();

    CollectReports(nsIHandleReportCallback* aHandleReport,
                   nsISupports* aData,
                   bool aAnonymize) override
        "The number of ghost windows present (the number of nodes underneath "
        "explicit/window-objects/top(none)/ghost, modulo race conditions).  A "
        "ghost "
        "window is not shown in any tab, does not share a domain with any "
        "non-detached "
        "windows, and has met these criteria for at least "
        "memory.ghost_window_timeout_seconds, or has survived a round of "
        "about:memory's minimize memory usage button.\n\n"
        "Ghost windows can happen legitimately, but they are often indicative "
        "of "
        "leaks in the browser or add-ons.");

      return NS_OK;

  // Protect ctor, use Init() instead.

   * Get the number of seconds for which a window must satisfy ghost criteria
   * (1) and (2) before we deem that it satisfies criterion (3).
  uint32_t GetGhostTimeout();

  void ObserveAfterMinimizeMemoryUsage();

   * Iterate over all weak window pointers in mDetachedWindows and update our
   * accounting of which windows meet ghost criterion (2).
   * This method also cleans up mDetachedWindows, removing entries for windows
   * which have been destroyed or are no longer detached.
   * If aOutGhostIDs is non-null, we populate it with the Window IDs of the
   * ghost windows.
   * This is called asynchronously after we observe a DOM window being detached
   * from its docshell, and also right before we generate a memory report.
  void CheckForGhostWindows(
    nsTHashtable<nsUint64HashKey>* aOutGhostIDs = nullptr);

   * Eventually do a check for ghost windows, if we haven't done one recently
   * and we aren't already planning to do one soon.
  void AsyncCheckForGhostWindows();

   * Kill the check timer, if it exists.
  void KillCheckTimer();

  static void CheckTimerFired(nsITimer* aTimer, void* aClosure);

   * Maps a weak reference to a detached window (nsIWeakReference) to the time
   * when we observed that the window met ghost criterion (2) above.
   * If the window has not yet met criterion (2) it maps to the null timestamp.
   * (Although windows are not added to this table until they're detached, it's
   * possible for a detached window to become non-detached, and we won't
   * remove it from the table until CheckForGhostWindows runs.)
  nsDataHashtable<nsISupportsHashKey, mozilla::TimeStamp> mDetachedWindows;

   * Track the last time we ran CheckForGhostWindows(), to avoid running it
   * too often after a DOM window is detached.
  mozilla::TimeStamp mLastCheckForGhostWindows;

  nsCOMPtr<nsITimer> mCheckTimer;

  bool mCycleCollectorIsRunning;

  bool mCheckTimerWaitingForCCEnd;

#endif // nsWindowMemoryReporter_h__