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  37  *     i.e., when the window is no longer active or cached.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