dom/base/nsWindowMemoryReporter.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsWindowMemoryReporter_h__
   8 #define nsWindowMemoryReporter_h__
   9
  10 #include "nsGlobalWindow.h"
  11 #include "nsIMemoryReporter.h"
  12 #include "nsIObserver.h"
  13 #include "nsITimer.h"
  14 #include "nsTHashMap.h"
  15 #include "nsTHashSet.h"
  16 #include "nsWeakReference.h"
  17 #include "mozilla/Attributes.h"
  18 #include "mozilla/Assertions.h"
  19 #include "mozilla/MemoryReporting.h"
  20 #include "mozilla/PodOperations.h"
  21 #include "mozilla/TimeStamp.h"
  22
  23 /**
  24  * nsWindowMemoryReporter is responsible for the 'explicit/window-objects'
  25  * memory reporter.
  26  *
  27  * We classify DOM window objects into one of three categories:
  28  *
  29  *   - "active" windows, which are displayed in a tab (as the top-level window
  30  *     or an iframe),
  31  *
  32  *   - "cached" windows, which are in the fastback cache (aka the bfcache), and
  33  *
  34  *   - "detached" windows, which have a null docshell.  A window becomes
  35  *     detached when its <iframe> or tab containing the window is destroyed --
  36  *     i.e., when the window is no longer active or cached.
  37  *
  38  * Additionally, we classify a subset of detached windows as "ghost" windows.
  39  * Although ghost windows can happen legitimately (a page can hold a reference
  40  * to a cross-domain window and then close its container), the presence of
  41  * ghost windows is often indicative of a memory leak.
  42  *
  43  * A window is a ghost if it meets the following three criteria:
  44  *
  45  *   1) The window is detached.
  46  *
  47  *   2) There exist no non-detached windows with the same base domain as
  48  *      the window's principal.  (For example, the base domain of
  49  *      "wiki.mozilla.co.uk" is "mozilla.co.uk".)  This criterion makes us less
  50  *      likely to flag a legitimately held-alive detached window as a ghost.
  51  *
  52  *   3) The window has met criteria (1) and (2) above for at least
  53  *      memory.ghost_window_timeout_seconds.  This criterion is in place so we
  54  *      don't immediately declare a window a ghost before the GC/CC has had a
  55  *      chance to run.
  56  *
  57  * nsWindowMemoryReporter observes window detachment and uses mDetachedWindows
  58  * to remember when a window first met criteria (1) and (2).  When we generate
  59  * a memory report, we use this accounting to determine which windows are
  60  * ghosts.
  61  *
  62  *
  63  * We use the following memory reporter path for active and cached windows:
  64  *
  65  *   explicit/window-objects/top(<top-outer-uri>, id=<top-outer-id>)/
  66  *       <category>/window(<window-uri>)/...
  67  *
  68  * For detached and ghost windows, we use
  69  *
  70  *   explicit/window-objects/top(none)/<category>/window(<window-uri>)/...
  71  *
  72  * Where
  73  *
  74  * - <category> is "active", "cached", "detached", or "ghost", as described
  75  *   above.
  76  *
  77  * - <top-outer-id> is the window id of the top outer window (i.e. the tab, or
  78  *   the top level chrome window).  Exposing this ensures that each tab gets
  79  *   its own sub-tree, even if multiple tabs are showing the same URI.
  80  *
  81  * - <top-uri> is the URI of the top window.  Excepting special windows (such
  82  *   as browser.xhtml or hiddenWindow.html) it's what the address bar shows for
  83  *   the tab.
  84  *
  85  */
  86 class nsWindowMemoryReporter final : public nsIMemoryReporter,
  87                                      public nsIObserver,
  88                                      public nsSupportsWeakReference {
  89  public:
  90   NS_DECL_ISUPPORTS
  91   NS_DECL_NSIMEMORYREPORTER
  92   NS_DECL_NSIOBSERVER
  93
  94   static void Init();
  95
  96 #ifdef DEBUG
  97   /**
  98    * Unlink all known ghost windows, to enable investigating what caused them
  99    * to become ghost windows in the first place.
 100    */
 101   static void UnlinkGhostWindows();
 102 #endif
 103
 104   static nsWindowMemoryReporter* Get();
 105   void ObserveDOMWindowDetached(nsGlobalWindowInner* aWindow);
 106
 107   static int64_t GhostWindowsDistinguishedAmount();
 108
 109  private:
 110   ~nsWindowMemoryReporter();
 111
 112   // Protect ctor, use Init() instead.
 113   nsWindowMemoryReporter();
 114
 115   /**
 116    * Get the number of seconds for which a window must satisfy ghost criteria
 117    * (1) and (2) before we deem that it satisfies criterion (3).
 118    */
 119   uint32_t GetGhostTimeout();
 120
 121   void ObserveAfterMinimizeMemoryUsage();
 122
 123   /**
 124    * Iterate over all weak window pointers in mDetachedWindows and update our
 125    * accounting of which windows meet ghost criterion (2).
 126    *
 127    * This method also cleans up mDetachedWindows, removing entries for windows
 128    * which have been destroyed or are no longer detached.
 129    *
 130    * If aOutGhostIDs is non-null, we populate it with the Window IDs of the
 131    * ghost windows.
 132    *
 133    * This is called asynchronously after we observe a DOM window being detached
 134    * from its docshell, and also right before we generate a memory report.
 135    */
 136   void CheckForGhostWindows(nsTHashSet<uint64_t>* aOutGhostIDs = nullptr);
 137
 138   /**
 139    * Eventually do a check for ghost windows, if we haven't done one recently
 140    * and we aren't already planning to do one soon.
 141    */
 142   void AsyncCheckForGhostWindows();
 143
 144   /**
 145    * Kill the check timer, if it exists.
 146    */
 147   void KillCheckTimer();
 148
 149   static void CheckTimerFired(nsITimer* aTimer, void* aClosure);
 150
 151   /**
 152    * Maps a weak reference to a detached window (nsIWeakReference) to the time
 153    * when we observed that the window met ghost criterion (2) above.
 154    *
 155    * If the window has not yet met criterion (2) it maps to the null timestamp.
 156    *
 157    * (Although windows are not added to this table until they're detached, it's
 158    * possible for a detached window to become non-detached, and we won't
 159    * remove it from the table until CheckForGhostWindows runs.)
 160    */
 161   nsTHashMap<nsISupportsHashKey, mozilla::TimeStamp> mDetachedWindows;
 162
 163   /**
 164    * Track the last time we ran CheckForGhostWindows(), to avoid running it
 165    * too often after a DOM window is detached.
 166    */
 167   mozilla::TimeStamp mLastCheckForGhostWindows;
 168
 169   nsCOMPtr<nsITimer> mCheckTimer;
 170
 171   bool mCycleCollectorIsRunning;
 172
 173   bool mCheckTimerWaitingForCCEnd;
 174
 175   int64_t mGhostWindowCount;
 176 };
 177
 178 #endif  // nsWindowMemoryReporter_h__