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/* -*- 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/. */
#ifndef nsWindowMemoryReporter_h__
#define nsWindowMemoryReporter_h__
#include "nsGlobalWindow.h"
#include "nsIMemoryReporter.h"
#include "nsIObserver.h"
#include "nsITimer.h"
#include "nsTHashMap.h"
#include "nsTHashSet.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* i.e., when the window is no longer active or cached.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
* "wiki.mozilla.co.uk" is "mozilla.co.uk".) 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.xhtml or hiddenWindow.html) it's what the address bar shows for
* the tab.
*
*/
class nsWindowMemoryReporter final : public nsIMemoryReporter,
public nsIObserver,
public nsSupportsWeakReference {
public:
NS_DECL_ISUPPORTS
NS_DECL_NSIMEMORYREPORTER
NS_DECL_NSIOBSERVER
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();
#endif
static nsWindowMemoryReporter* Get();
void ObserveDOMWindowDetached(nsGlobalWindowInner* aWindow);
static int64_t GhostWindowsDistinguishedAmount();
private:
~nsWindowMemoryReporter();
// Protect ctor, use Init() instead.
nsWindowMemoryReporter();
/**
* 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(nsTHashSet<uint64_t>* 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.)
*/
nsTHashMap<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;
int64_t mGhostWindowCount;
};
#endif // nsWindowMemoryReporter_h__
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