gecko-dev/dom/base/nsWindowMemoryReporter.cpp

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#include "nsWindowMemoryReporter.h"
#include "nsWindowSizes.h"
#include "nsGlobalWindow.h"
#include "nsIDocument.h"
#include "nsDOMWindowList.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/Preferences.h"
#include "mozilla/Services.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/Telemetry.h"
#include "nsNetCID.h"
#include "nsPrintfCString.h"
#include "XPCJSMemoryReporter.h"
#include "js/MemoryMetrics.h"
#include "nsQueryObject.h"
#include "nsServiceManagerUtils.h"
#ifdef MOZ_XUL
#include "nsXULPrototypeCache.h"
#endif

using namespace mozilla;
using namespace mozilla::dom;

StaticRefPtr<nsWindowMemoryReporter> sWindowReporter;

/**
 * Don't trigger a ghost window check when a DOM window is detached if we've
 * run it this recently.
 */
const int32_t kTimeBetweenChecks = 45; /* seconds */

nsWindowMemoryReporter::nsWindowMemoryReporter()
  : mLastCheckForGhostWindows(TimeStamp::NowLoRes()),
    mCycleCollectorIsRunning(false),
    mCheckTimerWaitingForCCEnd(false),
    mGhostWindowCount(0)
{
}

nsWindowMemoryReporter::~nsWindowMemoryReporter()
{
  KillCheckTimer();
}

NS_IMPL_ISUPPORTS(nsWindowMemoryReporter, nsIMemoryReporter, nsIObserver,
                  nsISupportsWeakReference)

static nsresult
AddNonJSSizeOfWindowAndItsDescendents(nsGlobalWindowOuter* aWindow,
                                      nsTabSizes* aSizes)
{
  // Measure the window.
  SizeOfState state(moz_malloc_size_of);
  nsWindowSizes windowSizes(state);
  aWindow->AddSizeOfIncludingThis(windowSizes);

  // Measure the inner window, if there is one.
  nsGlobalWindowInner* inner = aWindow->GetCurrentInnerWindowInternal();
  if (inner) {
    inner->AddSizeOfIncludingThis(windowSizes);
  }

  windowSizes.addToTabSizes(aSizes);

  nsDOMWindowList* frames = aWindow->GetFrames();

  uint32_t length = frames->GetLength();

  // Measure this window's descendents.
  for (uint32_t i = 0; i < length; i++) {
      nsCOMPtr<nsPIDOMWindowOuter> child = frames->IndexedGetter(i);
      NS_ENSURE_STATE(child);

      nsGlobalWindowOuter* childWin = nsGlobalWindowOuter::Cast(child);

      nsresult rv = AddNonJSSizeOfWindowAndItsDescendents(childWin, aSizes);
      NS_ENSURE_SUCCESS(rv, rv);
  }
  return NS_OK;
}

static nsresult
NonJSSizeOfTab(nsPIDOMWindowOuter* aWindow, size_t* aDomSize, size_t* aStyleSize, size_t* aOtherSize)
{
  nsGlobalWindowOuter* window = nsGlobalWindowOuter::Cast(aWindow);

  nsTabSizes sizes;
  nsresult rv = AddNonJSSizeOfWindowAndItsDescendents(window, &sizes);
  NS_ENSURE_SUCCESS(rv, rv);

  *aDomSize   = sizes.mDom;
  *aStyleSize = sizes.mStyle;
  *aOtherSize = sizes.mOther;
  return NS_OK;
}

/* static */ void
nsWindowMemoryReporter::Init()
{
  MOZ_ASSERT(!sWindowReporter);
  sWindowReporter = new nsWindowMemoryReporter();
  ClearOnShutdown(&sWindowReporter);
  RegisterStrongMemoryReporter(sWindowReporter);
  RegisterNonJSSizeOfTab(NonJSSizeOfTab);

  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
  if (os) {
    os->AddObserver(sWindowReporter, "after-minimize-memory-usage",
                    /* weakRef = */ true);
    os->AddObserver(sWindowReporter, "cycle-collector-begin",
                    /* weakRef = */ true);
    os->AddObserver(sWindowReporter, "cycle-collector-end",
                    /* weakRef = */ true);
  }

  RegisterGhostWindowsDistinguishedAmount(GhostWindowsDistinguishedAmount);
}

/* static */ nsWindowMemoryReporter*
nsWindowMemoryReporter::Get()
{
  return sWindowReporter;
}

static already_AddRefed<nsIURI>
GetWindowURI(nsGlobalWindowInner* aWindow)
{
  NS_ENSURE_TRUE(aWindow, nullptr);

  nsCOMPtr<nsIDocument> doc = aWindow->GetExtantDoc();
  nsCOMPtr<nsIURI> uri;

  if (doc) {
    uri = doc->GetDocumentURI();
  }

  if (!uri) {
    nsCOMPtr<nsIScriptObjectPrincipal> scriptObjPrincipal =
      do_QueryObject(aWindow);
    NS_ENSURE_TRUE(scriptObjPrincipal, nullptr);

    // GetPrincipal() will print a warning if the window does not have an outer
    // window, so check here for an outer window first.  This code is
    // functionally correct if we leave out the GetOuterWindow() check, but we
    // end up printing a lot of warnings during debug mochitests.
    if (aWindow->GetOuterWindow()) {
      nsIPrincipal* principal = scriptObjPrincipal->GetPrincipal();
      if (principal) {
        principal->GetURI(getter_AddRefs(uri));
      }
    }
  }

  return uri.forget();
}

// Forward to the inner window if we need to when getting the window's URI.
static already_AddRefed<nsIURI>
GetWindowURI(nsGlobalWindowOuter* aWindow)
{
  NS_ENSURE_TRUE(aWindow, nullptr);
  return GetWindowURI(aWindow->GetCurrentInnerWindowInternal());
}

static void
AppendWindowURI(nsGlobalWindowInner *aWindow, nsACString& aStr, bool aAnonymize)
{
  nsCOMPtr<nsIURI> uri = GetWindowURI(aWindow);

  if (uri) {
    if (aAnonymize && !aWindow->IsChromeWindow()) {
      aStr.AppendPrintf("<anonymized-%" PRIu64 ">", aWindow->WindowID());
    } else {
      nsCString spec = uri->GetSpecOrDefault();

      // A hack: replace forward slashes with '\\' so they aren't
      // treated as path separators.  Users of the reporters
      // (such as about:memory) have to undo this change.
      spec.ReplaceChar('/', '\\');

      aStr += spec;
    }
  } else {
    // If we're unable to find a URI, we're dealing with a chrome window with
    // no document in it (or somesuch), so we call this a "system window".
    aStr += NS_LITERAL_CSTRING("[system]");
  }
}

MOZ_DEFINE_MALLOC_SIZE_OF(WindowsMallocSizeOf)

// The key is the window ID.
typedef nsDataHashtable<nsUint64HashKey, nsCString> WindowPaths;

static void
ReportAmount(const nsCString& aBasePath, const char* aPathTail,
             size_t aAmount, const nsCString& aDescription,
             uint32_t aKind, uint32_t aUnits,
             nsIHandleReportCallback* aHandleReport,
             nsISupports* aData)
{
  if (aAmount == 0) {
    return;
  }

  nsAutoCString path(aBasePath);
  path += aPathTail;

  aHandleReport->Callback(
    EmptyCString(), path, aKind, aUnits, aAmount, aDescription, aData);
}

static void
ReportSize(const nsCString& aBasePath, const char* aPathTail,
           size_t aAmount, const nsCString& aDescription,
           nsIHandleReportCallback* aHandleReport,
           nsISupports* aData)
{
  ReportAmount(aBasePath, aPathTail, aAmount, aDescription,
               nsIMemoryReporter::KIND_HEAP, nsIMemoryReporter::UNITS_BYTES,
               aHandleReport, aData);
}

static void
ReportCount(const nsCString& aBasePath, const char* aPathTail,
            size_t aAmount, const nsCString& aDescription,
            nsIHandleReportCallback* aHandleReport,
            nsISupports* aData)
{
  ReportAmount(aBasePath, aPathTail, aAmount, aDescription,
               nsIMemoryReporter::KIND_OTHER, nsIMemoryReporter::UNITS_COUNT,
               aHandleReport, aData);
}

static void
CollectWindowReports(nsGlobalWindowInner *aWindow,
                     nsWindowSizes *aWindowTotalSizes,
                     nsTHashtable<nsUint64HashKey> *aGhostWindowIDs,
                     WindowPaths *aWindowPaths,
                     WindowPaths *aTopWindowPaths,
                     nsIHandleReportCallback *aHandleReport,
                     nsISupports *aData,
                     bool aAnonymize)
{
  nsAutoCString windowPath("explicit/");

  // Avoid calling aWindow->GetTop() if there's no outer window.  It will work
  // just fine, but will spew a lot of warnings.
  nsGlobalWindowOuter *top = nullptr;
  nsCOMPtr<nsIURI> location;
  if (aWindow->GetOuterWindow()) {
    // Our window should have a null top iff it has a null docshell.
    MOZ_ASSERT(!!aWindow->GetTopInternal() == !!aWindow->GetDocShell());
    top = aWindow->GetTopInternal();
    if (top) {
      location = GetWindowURI(top);
    }
  }
  if (!location) {
    location = GetWindowURI(aWindow);
  }

  windowPath += NS_LITERAL_CSTRING("window-objects/");

  if (top) {
    windowPath += NS_LITERAL_CSTRING("top(");
    AppendWindowURI(top->GetCurrentInnerWindowInternal(), windowPath, aAnonymize);
    windowPath.AppendPrintf(", id=%" PRIu64 ")", top->WindowID());

    aTopWindowPaths->Put(aWindow->WindowID(), windowPath);

    windowPath += aWindow->IsFrozen() ? NS_LITERAL_CSTRING("/cached/")
                                      : NS_LITERAL_CSTRING("/active/");
  } else {
    if (aGhostWindowIDs->Contains(aWindow->WindowID())) {
      windowPath += NS_LITERAL_CSTRING("top(none)/ghost/");
    } else {
      windowPath += NS_LITERAL_CSTRING("top(none)/detached/");
    }
  }

  windowPath += NS_LITERAL_CSTRING("window(");
  AppendWindowURI(aWindow, windowPath, aAnonymize);
  windowPath += NS_LITERAL_CSTRING(")");

  // Use |windowPath|, but replace "explicit/" with "event-counts/".
  nsCString censusWindowPath(windowPath);
  censusWindowPath.ReplaceLiteral(0, strlen("explicit"), "event-counts");

  // Remember the path for later.
  aWindowPaths->Put(aWindow->WindowID(), windowPath);

// Report the size from windowSizes and add to the appropriate total in
// aWindowTotalSizes.
#define REPORT_SIZE(_pathTail, _field, _desc) \
  ReportSize(windowPath, _pathTail, windowSizes._field, \
             NS_LITERAL_CSTRING(_desc), aHandleReport, aData); \
  aWindowTotalSizes->_field += windowSizes._field;

// Report the size, which is a sum of other sizes, and so doesn't require
// updating aWindowTotalSizes.
#define REPORT_SUM_SIZE(_pathTail, _amount, _desc) \
  ReportSize(windowPath, _pathTail, _amount, NS_LITERAL_CSTRING(_desc), \
             aHandleReport, aData);

// Like REPORT_SIZE, but for a count.
#define REPORT_COUNT(_pathTail, _field, _desc) \
  ReportCount(censusWindowPath, _pathTail, windowSizes._field, \
              NS_LITERAL_CSTRING(_desc), aHandleReport, aData); \
  aWindowTotalSizes->_field += windowSizes._field;

  // This SizeOfState contains the SeenPtrs used for all memory reporting of
  // this window.
  SizeOfState state(WindowsMallocSizeOf);
  nsWindowSizes windowSizes(state);
  aWindow->AddSizeOfIncludingThis(windowSizes);

  REPORT_SIZE("/dom/element-nodes", mDOMElementNodesSize,
              "Memory used by the element nodes in a window's DOM.");

  REPORT_SIZE("/dom/text-nodes", mDOMTextNodesSize,
              "Memory used by the text nodes in a window's DOM.");

  REPORT_SIZE("/dom/cdata-nodes", mDOMCDATANodesSize,
              "Memory used by the CDATA nodes in a window's DOM.");

  REPORT_SIZE("/dom/comment-nodes", mDOMCommentNodesSize,
              "Memory used by the comment nodes in a window's DOM.");

  REPORT_SIZE("/dom/event-targets", mDOMEventTargetsSize,
              "Memory used by the event targets table in a window's DOM, and "
              "the objects it points to, which include XHRs.");

  REPORT_SIZE("/dom/performance/user-entries", mDOMPerformanceUserEntries,
              "Memory used for performance user entries.");

  REPORT_SIZE("/dom/performance/resource-entries",
              mDOMPerformanceResourceEntries,
              "Memory used for performance resource entries.");

  REPORT_SIZE("/dom/media-query-lists", mDOMMediaQueryLists,
              "Memory used by MediaQueryList objects for the window's "
              "document.");

  REPORT_SIZE("/dom/other", mDOMOtherSize,
              "Memory used by a window's DOM that isn't measured by the "
              "other 'dom/' numbers.");

  REPORT_SIZE("/layout/style-sheets", mLayoutStyleSheetsSize,
              "Memory used by document style sheets within a window.");

  REPORT_SIZE("/layout/shadow-dom/style-sheets", mLayoutShadowDomStyleSheetsSize,
              "Memory used by Shadow DOM style sheets within a window.");

  // TODO(emilio): We might want to split this up between invalidation map /
  // element-and-pseudos / revalidation too just like the style set.
  REPORT_SIZE("/layout/shadow-dom/author-styles", mLayoutShadowDomAuthorStyles,
              "Memory used by Shadow DOM computed rule data within a window.");

  REPORT_SIZE("/layout/pres-shell", mLayoutPresShellSize,
              "Memory used by layout's PresShell, along with any structures "
              "allocated in its arena and not measured elsewhere, "
              "within a window.");

  REPORT_SIZE("/layout/style-sets/stylist/rule-tree",
              mLayoutStyleSetsStylistRuleTree,
              "Memory used by rule trees within style sets within a window.");

  REPORT_SIZE("/layout/style-sets/stylist/element-and-pseudos-maps",
              mLayoutStyleSetsStylistElementAndPseudosMaps,
              "Memory used by element and pseudos maps within style "
              "sets within a window.");

  REPORT_SIZE("/layout/style-sets/stylist/invalidation-map",
              mLayoutStyleSetsStylistInvalidationMap,
              "Memory used by invalidation maps within style sets "
              "within a window.");

  REPORT_SIZE("/layout/style-sets/stylist/revalidation-selectors",
              mLayoutStyleSetsStylistRevalidationSelectors,
              "Memory used by selectors for cache revalidation within "
              "style sets within a window.");

  REPORT_SIZE("/layout/style-sets/stylist/other",
              mLayoutStyleSetsStylistOther,
              "Memory used by other Stylist data within style sets "
              "within a window.");

  REPORT_SIZE("/layout/style-sets/other", mLayoutStyleSetsOther,
              "Memory used by other parts of style sets within a window.");

  REPORT_SIZE("/layout/element-data-objects",
              mLayoutElementDataObjects,
              "Memory used for ElementData objects, but not the things"
              "hanging off them.");

  REPORT_SIZE("/layout/text-runs", mLayoutTextRunsSize,
              "Memory used for text-runs (glyph layout) in the PresShell's "
              "frame tree, within a window.");

  REPORT_SIZE("/layout/pres-contexts", mLayoutPresContextSize,
              "Memory used for the PresContext in the PresShell's frame "
              "within a window.");

  REPORT_SIZE("/layout/frame-properties", mLayoutFramePropertiesSize,
              "Memory used for frame properties attached to frames "
              "within a window.");

  REPORT_SIZE("/layout/computed-values/dom", mLayoutComputedValuesDom,
              "Memory used by ComputedValues objects accessible from DOM "
              "elements.");

  REPORT_SIZE("/layout/computed-values/non-dom", mLayoutComputedValuesNonDom,
              "Memory used by ComputedValues objects not accessible from DOM "
              "elements.");

  REPORT_SIZE("/layout/computed-values/visited", mLayoutComputedValuesVisited,
              "Memory used by ComputedValues objects used for visited styles.");

  REPORT_SIZE("/property-tables", mPropertyTablesSize,
              "Memory used for the property tables within a window.");

  REPORT_SIZE("/bindings", mBindingsSize,
              "Memory used by bindings within a window.");

  REPORT_COUNT("/dom/event-targets", mDOMEventTargetsCount,
               "Number of non-node event targets in the event targets table "
               "in a window's DOM, such as XHRs.");

  REPORT_COUNT("/dom/event-listeners", mDOMEventListenersCount,
               "Number of event listeners in a window, including event "
               "listeners on nodes and other event targets.");

  REPORT_SIZE("/layout/line-boxes", mArenaSizes.mLineBoxes,
              "Memory used by line boxes within a window.");

  REPORT_SIZE("/layout/rule-nodes", mArenaSizes.mRuleNodes,
              "Memory used by CSS rule nodes within a window.");

  REPORT_SIZE("/layout/style-contexts", mArenaSizes.mComputedStyles,
              "Memory used by ComputedStyles within a window.");

  // There are many different kinds of style structs, but it is likely that
  // only a few matter. Implement a cutoff so we don't bloat about:memory with
  // many uninteresting entries.
  const size_t STYLE_SUNDRIES_THRESHOLD =
    js::MemoryReportingSundriesThreshold();

  // There are many different kinds of frames, but it is very likely
  // that only a few matter.  Implement a cutoff so we don't bloat
  // about:memory with many uninteresting entries.
  const size_t FRAME_SUNDRIES_THRESHOLD =
    js::MemoryReportingSundriesThreshold();

  size_t frameSundriesSize = 0;
#define FRAME_ID(classname, ...) \
  { \
    size_t size = windowSizes.mArenaSizes.NS_ARENA_SIZES_FIELD(classname); \
    if (size < FRAME_SUNDRIES_THRESHOLD) { \
      frameSundriesSize += size; \
    } else { \
      REPORT_SUM_SIZE( \
        "/layout/frames/" # classname, size, \
        "Memory used by frames of type " #classname " within a window."); \
    } \
    aWindowTotalSizes->mArenaSizes.NS_ARENA_SIZES_FIELD(classname) += size; \
  }
#define ABSTRACT_FRAME_ID(...)
#include "nsFrameIdList.h"
#undef FRAME_ID
#undef ABSTRACT_FRAME_ID

  if (frameSundriesSize > 0) {
    REPORT_SUM_SIZE(
      "/layout/frames/sundries", frameSundriesSize,
      "The sum of all memory used by frames which were too small to be shown "
      "individually.");
  }

  // This is the style structs.
  size_t styleSundriesSize = 0;
#define STYLE_STRUCT(name_) \
  { \
    size_t size = windowSizes.mStyleSizes.NS_STYLE_SIZES_FIELD(name_); \
    if (size < STYLE_SUNDRIES_THRESHOLD) { \
      styleSundriesSize += size; \
    } else { \
      REPORT_SUM_SIZE( \
        "/layout/style-structs/" # name_, size, \
        "Memory used by the " #name_ " style structs within a window."); \
    } \
    aWindowTotalSizes->mStyleSizes.NS_STYLE_SIZES_FIELD(name_) += size; \
  }
#include "nsStyleStructList.h"
#undef STYLE_STRUCT

  if (styleSundriesSize > 0) {
    REPORT_SUM_SIZE(
      "/layout/style-structs/sundries", styleSundriesSize,
      "The sum of all memory used by style structs which were too "
      "small to be shown individually.");
  }

#undef REPORT_SIZE
#undef REPORT_SUM_SIZE
#undef REPORT_COUNT
}

typedef nsTArray< RefPtr<nsGlobalWindowInner> > WindowArray;

NS_IMETHODIMP
nsWindowMemoryReporter::CollectReports(nsIHandleReportCallback* aHandleReport,
                                       nsISupports* aData, bool aAnonymize)
{
  nsGlobalWindowInner::InnerWindowByIdTable* windowsById =
    nsGlobalWindowInner::GetWindowsTable();
  NS_ENSURE_TRUE(windowsById, NS_OK);

  // Hold on to every window in memory so that window objects can't be
  // destroyed while we're calling the memory reporter callback.
  WindowArray windows;
  for (auto iter = windowsById->Iter(); !iter.Done(); iter.Next()) {
    windows.AppendElement(iter.Data());
  }

  // Get the IDs of all the "ghost" windows, and call aHandleReport->Callback()
  // for each one.
  nsTHashtable<nsUint64HashKey> ghostWindows;
  CheckForGhostWindows(&ghostWindows);
  for (auto iter = ghostWindows.ConstIter(); !iter.Done(); iter.Next()) {
    nsGlobalWindowInner::InnerWindowByIdTable* windowsById =
      nsGlobalWindowInner::GetWindowsTable();
    if (!windowsById) {
      NS_WARNING("Couldn't get window-by-id hashtable?");
      continue;
    }

    nsGlobalWindowInner* window = windowsById->Get(iter.Get()->GetKey());
    if (!window) {
      NS_WARNING("Could not look up window?");
      continue;
    }

    nsAutoCString path;
    path.AppendLiteral("ghost-windows/");
    AppendWindowURI(window, path, aAnonymize);

    aHandleReport->Callback(
      /* process = */ EmptyCString(),
      path,
      nsIMemoryReporter::KIND_OTHER,
      nsIMemoryReporter::UNITS_COUNT,
      /* amount = */ 1,
      /* description = */ NS_LITERAL_CSTRING("A ghost window."),
      aData);
  }

  MOZ_COLLECT_REPORT(
    "ghost-windows", KIND_OTHER, UNITS_COUNT, ghostWindows.Count(),
"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, is not in a tab group 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.");

  WindowPaths windowPaths;
  WindowPaths topWindowPaths;

  // Collect window memory usage.
  SizeOfState fakeState(nullptr);   // this won't be used
  nsWindowSizes windowTotalSizes(fakeState);
  for (uint32_t i = 0; i < windows.Length(); i++) {
    CollectWindowReports(windows[i],
                         &windowTotalSizes, &ghostWindows,
                         &windowPaths, &topWindowPaths, aHandleReport,
                         aData, aAnonymize);
  }

  // Report JS memory usage.  We do this from here because the JS memory
  // reporter needs to be passed |windowPaths|.
  xpc::JSReporter::CollectReports(&windowPaths, &topWindowPaths,
                                  aHandleReport, aData, aAnonymize);

#ifdef MOZ_XUL
  nsXULPrototypeCache::CollectMemoryReports(aHandleReport, aData);
#endif

#define REPORT(_path, _amount, _desc) \
  aHandleReport->Callback(EmptyCString(), NS_LITERAL_CSTRING(_path), \
                          KIND_OTHER, UNITS_BYTES, _amount, \
                          NS_LITERAL_CSTRING(_desc), aData);

  REPORT("window-objects/dom/element-nodes",
         windowTotalSizes.mDOMElementNodesSize,
         "This is the sum of all windows' 'dom/element-nodes' numbers.");

  REPORT("window-objects/dom/text-nodes", windowTotalSizes.mDOMTextNodesSize,
         "This is the sum of all windows' 'dom/text-nodes' numbers.");

  REPORT("window-objects/dom/cdata-nodes", windowTotalSizes.mDOMCDATANodesSize,
         "This is the sum of all windows' 'dom/cdata-nodes' numbers.");

  REPORT("window-objects/dom/comment-nodes", windowTotalSizes.mDOMCommentNodesSize,
         "This is the sum of all windows' 'dom/comment-nodes' numbers.");

  REPORT("window-objects/dom/event-targets", windowTotalSizes.mDOMEventTargetsSize,
         "This is the sum of all windows' 'dom/event-targets' numbers.");

  REPORT("window-objects/dom/performance",
         windowTotalSizes.mDOMPerformanceUserEntries +
         windowTotalSizes.mDOMPerformanceResourceEntries,
         "This is the sum of all windows' 'dom/performance/' numbers.");

  REPORT("window-objects/dom/other", windowTotalSizes.mDOMOtherSize,
         "This is the sum of all windows' 'dom/other' numbers.");

  REPORT("window-objects/layout/style-sheets",
         windowTotalSizes.mLayoutStyleSheetsSize,
         "This is the sum of all windows' 'layout/style-sheets' numbers.");

  REPORT("window-objects/layout/pres-shell",
         windowTotalSizes.mLayoutPresShellSize,
         "This is the sum of all windows' 'layout/arenas' numbers.");

  REPORT("window-objects/layout/style-sets",
         windowTotalSizes.mLayoutStyleSetsStylistRuleTree +
         windowTotalSizes.mLayoutStyleSetsStylistElementAndPseudosMaps +
         windowTotalSizes.mLayoutStyleSetsStylistInvalidationMap +
         windowTotalSizes.mLayoutStyleSetsStylistRevalidationSelectors +
         windowTotalSizes.mLayoutStyleSetsStylistOther +
         windowTotalSizes.mLayoutStyleSetsOther,
         "This is the sum of all windows' 'layout/style-sets/' numbers.");

  REPORT("window-objects/layout/element-data-objects",
         windowTotalSizes.mLayoutElementDataObjects,
         "This is the sum of all windows' 'layout/element-data-objects' "
         "numbers.");

  REPORT("window-objects/layout/text-runs", windowTotalSizes.mLayoutTextRunsSize,
         "This is the sum of all windows' 'layout/text-runs' numbers.");

  REPORT("window-objects/layout/pres-contexts",
         windowTotalSizes.mLayoutPresContextSize,
         "This is the sum of all windows' 'layout/pres-contexts' numbers.");

  REPORT("window-objects/layout/frame-properties",
         windowTotalSizes.mLayoutFramePropertiesSize,
         "This is the sum of all windows' 'layout/frame-properties' numbers.");

  REPORT("window-objects/layout/computed-values",
         windowTotalSizes.mLayoutComputedValuesDom +
         windowTotalSizes.mLayoutComputedValuesNonDom +
         windowTotalSizes.mLayoutComputedValuesVisited,
         "This is the sum of all windows' 'layout/computed-values/' numbers.");

  REPORT("window-objects/property-tables",
         windowTotalSizes.mPropertyTablesSize,
         "This is the sum of all windows' 'property-tables' numbers.");

  REPORT("window-objects/layout/line-boxes",
         windowTotalSizes.mArenaSizes.mLineBoxes,
         "This is the sum of all windows' 'layout/line-boxes' numbers.");

  REPORT("window-objects/layout/rule-nodes",
         windowTotalSizes.mArenaSizes.mRuleNodes,
         "This is the sum of all windows' 'layout/rule-nodes' numbers.");

  REPORT("window-objects/layout/style-contexts",
         windowTotalSizes.mArenaSizes.mComputedStyles,
         "This is the sum of all windows' 'layout/style-contexts' numbers.");

  size_t frameTotal = 0;
#define FRAME_ID(classname, ...) \
  frameTotal += windowTotalSizes.mArenaSizes.NS_ARENA_SIZES_FIELD(classname);
#define ABSTRACT_FRAME_ID(...)
#include "nsFrameIdList.h"
#undef FRAME_ID
#undef ABSTRACT_FRAME_ID

  REPORT("window-objects/layout/frames", frameTotal,
         "Memory used for layout frames within windows. "
         "This is the sum of all windows' 'layout/frames/' numbers.");

  size_t styleTotal = 0;
#define STYLE_STRUCT(name_) \
  styleTotal += \
    windowTotalSizes.mStyleSizes.NS_STYLE_SIZES_FIELD(name_);
#include "nsStyleStructList.h"
#undef STYLE_STRUCT

  REPORT("window-objects/layout/style-structs", styleTotal,
         "Memory used for style structs within windows. This is the sum of "
         "all windows' 'layout/style-structs/' numbers.");

#undef REPORT

  return NS_OK;
}

uint32_t
nsWindowMemoryReporter::GetGhostTimeout()
{
  return Preferences::GetUint("memory.ghost_window_timeout_seconds", 60);
}

NS_IMETHODIMP
nsWindowMemoryReporter::Observe(nsISupports *aSubject, const char *aTopic,
                                const char16_t *aData)
{
  if (!strcmp(aTopic, "after-minimize-memory-usage")) {
    ObserveAfterMinimizeMemoryUsage();
  } else if (!strcmp(aTopic, "cycle-collector-begin")) {
    if (mCheckTimer) {
      mCheckTimerWaitingForCCEnd = true;
      KillCheckTimer();
    }
    mCycleCollectorIsRunning = true;
  } else if (!strcmp(aTopic, "cycle-collector-end")) {
    mCycleCollectorIsRunning = false;
    if (mCheckTimerWaitingForCCEnd) {
      mCheckTimerWaitingForCCEnd = false;
      AsyncCheckForGhostWindows();
    }
  } else {
    MOZ_ASSERT(false);
  }

  return NS_OK;
}

void
nsWindowMemoryReporter::ObserveDOMWindowDetached(nsGlobalWindowInner* aWindow)
{
  nsWeakPtr weakWindow = do_GetWeakReference(aWindow);
  if (!weakWindow) {
    NS_WARNING("Couldn't take weak reference to a window?");
    return;
  }

  mDetachedWindows.Put(weakWindow, TimeStamp());

  AsyncCheckForGhostWindows();
}

// static
void
nsWindowMemoryReporter::CheckTimerFired(nsITimer* aTimer, void* aData)
{
  if (sWindowReporter) {
    MOZ_ASSERT(!sWindowReporter->mCycleCollectorIsRunning);
    sWindowReporter->CheckForGhostWindows();
  }
}

void
nsWindowMemoryReporter::AsyncCheckForGhostWindows()
{
  if (mCheckTimer) {
    return;
  }

  if (mCycleCollectorIsRunning) {
    mCheckTimerWaitingForCCEnd = true;
    return;
  }

  // If more than kTimeBetweenChecks seconds have elapsed since the last check,
  // timerDelay is 0.  Otherwise, it is kTimeBetweenChecks, reduced by the time
  // since the last check.  Reducing the delay by the time since the last check
  // prevents the timer from being completely starved if it is repeatedly killed
  // and restarted.
  int32_t timeSinceLastCheck = (TimeStamp::NowLoRes() - mLastCheckForGhostWindows).ToSeconds();
  int32_t timerDelay = (kTimeBetweenChecks - std::min(timeSinceLastCheck, kTimeBetweenChecks)) * PR_MSEC_PER_SEC;

  NS_NewTimerWithFuncCallback(getter_AddRefs(mCheckTimer),
                              CheckTimerFired, nullptr,
                              timerDelay, nsITimer::TYPE_ONE_SHOT,
                              "nsWindowMemoryReporter::AsyncCheckForGhostWindows_timer");
}

void
nsWindowMemoryReporter::ObserveAfterMinimizeMemoryUsage()
{
  // Someone claims they've done enough GC/CCs so that all eligible windows
  // have been free'd.  So we deem that any windows which satisfy ghost
  // criteria (1) and (2) now satisfy criterion (3) as well.
  //
  // To effect this change, we'll backdate some of our timestamps.

  TimeStamp minTimeStamp = TimeStamp::Now() -
                           TimeDuration::FromSeconds(GetGhostTimeout());

  for (auto iter = mDetachedWindows.Iter(); !iter.Done(); iter.Next()) {
    TimeStamp& timeStamp = iter.Data();
    if (!timeStamp.IsNull() && timeStamp > minTimeStamp) {
      timeStamp = minTimeStamp;
    }
  }
}

/**
 * Iterate over mDetachedWindows and update it to reflect the current state of
 * the world.  In particular:
 *
 *   - Remove weak refs to windows which no longer exist.
 *
 *   - Remove references to windows which are no longer detached.
 *
 *   - Reset the timestamp on detached windows which share a domain with a
 *     non-detached window (they no longer meet ghost criterion (2)).
 *
 *   - If a window now meets ghost criterion (2) but didn't before, set its
 *     timestamp to now.
 *
 * Additionally, if aOutGhostIDs is not null, fill it with the window IDs of
 * all ghost windows we found.
 */
void
nsWindowMemoryReporter::CheckForGhostWindows(
  nsTHashtable<nsUint64HashKey> *aOutGhostIDs /* = nullptr */)
{
  nsGlobalWindowInner::InnerWindowByIdTable *windowsById =
    nsGlobalWindowInner::GetWindowsTable();
  if (!windowsById) {
    NS_WARNING("GetWindowsTable returned null");
    return;
  }

  mLastCheckForGhostWindows = TimeStamp::NowLoRes();
  KillCheckTimer();

  nsTHashtable<nsPtrHashKey<TabGroup>> nonDetachedTabGroups;

  // Populate nonDetachedTabGroups.
  for (auto iter = windowsById->Iter(); !iter.Done(); iter.Next()) {
    // Null outer window implies null top, but calling GetTop() when there's no
    // outer window causes us to spew debug warnings.
    nsGlobalWindowInner* window = iter.UserData();
    if (!window->GetOuterWindow() || !window->GetTopInternal()) {
      // This window is detached, so we don't care about its tab group.
      continue;
    }

    nonDetachedTabGroups.PutEntry(window->TabGroup());
  }

  // Update mDetachedWindows and write the ghost window IDs into aOutGhostIDs,
  // if it's not null.
  uint32_t ghostTimeout = GetGhostTimeout();
  TimeStamp now = mLastCheckForGhostWindows;
  mGhostWindowCount = 0;
  for (auto iter = mDetachedWindows.Iter(); !iter.Done(); iter.Next()) {
    nsWeakPtr weakKey = do_QueryInterface(iter.Key());
    nsCOMPtr<mozIDOMWindow> iwindow = do_QueryReferent(weakKey);
    if (!iwindow) {
      // The window object has been destroyed.  Stop tracking its weak ref in
      // our hashtable.
      iter.Remove();
      continue;
    }

    nsPIDOMWindowInner* window = nsPIDOMWindowInner::From(iwindow);

    // Avoid calling GetTop() if we have no outer window.  Nothing will break if
    // we do, but it will spew debug output, which can cause our test logs to
    // overflow.
    nsCOMPtr<nsPIDOMWindowOuter> top;
    if (window->GetOuterWindow()) {
      top = window->GetOuterWindow()->GetTop();
    }

    if (top) {
      // The window is no longer detached, so we no longer want to track it.
      iter.Remove();
      continue;
    }

    TimeStamp& timeStamp = iter.Data();

    if (nonDetachedTabGroups.GetEntry(window->TabGroup())) {
      // This window is in the same tab group as a non-detached
      // window, so reset its clock.
      timeStamp = TimeStamp();
    } else {
      // This window is not in the same tab group as a non-detached
      // window, so it meets ghost criterion (2).
      if (timeStamp.IsNull()) {
        // This may become a ghost window later; start its clock.
        timeStamp = now;
      } else if ((now - timeStamp).ToSeconds() > ghostTimeout) {
        // This definitely is a ghost window, so add it to aOutGhostIDs, if
        // that is not null.
        mGhostWindowCount++;
        if (aOutGhostIDs && window) {
          aOutGhostIDs->PutEntry(window->WindowID());
        }
      }
    }
  }

  Telemetry::ScalarSetMaximum(Telemetry::ScalarID::MEMORYREPORTER_MAX_GHOST_WINDOWS,
                              mGhostWindowCount);
}

/* static */ int64_t
nsWindowMemoryReporter::GhostWindowsDistinguishedAmount()
{
  return sWindowReporter->mGhostWindowCount;
}

void
nsWindowMemoryReporter::KillCheckTimer()
{
  if (mCheckTimer) {
    mCheckTimer->Cancel();
    mCheckTimer = nullptr;
  }
}

#ifdef DEBUG
/* static */ void
nsWindowMemoryReporter::UnlinkGhostWindows()
{
  if (!sWindowReporter) {
    return;
  }

  nsGlobalWindowInner::InnerWindowByIdTable* windowsById =
    nsGlobalWindowInner::GetWindowsTable();
  if (!windowsById) {
    return;
  }

  // Hold on to every window in memory so that window objects can't be
  // destroyed while we're calling the UnlinkGhostWindows callback.
  WindowArray windows;
  for (auto iter = windowsById->Iter(); !iter.Done(); iter.Next()) {
    windows.AppendElement(iter.Data());
  }

  // Get the IDs of all the "ghost" windows, and unlink them all.
  nsTHashtable<nsUint64HashKey> ghostWindows;
  sWindowReporter->CheckForGhostWindows(&ghostWindows);
  for (auto iter = ghostWindows.ConstIter(); !iter.Done(); iter.Next()) {
    nsGlobalWindowInner::InnerWindowByIdTable* windowsById =
      nsGlobalWindowInner::GetWindowsTable();
    if (!windowsById) {
      continue;
    }

    RefPtr<nsGlobalWindowInner> window = windowsById->Get(iter.Get()->GetKey());
    if (window) {
      window->RiskyUnlink();
    }
  }
}
#endif