hal/WindowIdentifier.h
author Andrew McCreight <continuation@gmail.com>
Mon, 22 Apr 2019 16:34:51 +0000
changeset 470376 3073770e06f157040f4c64951b7e8425e1ad7bbe
parent 448947 6f3709b3878117466168c40affa7bca0b60cf75b
child 482216 9d2191d704555dd3e535ad9b5c451919af3c8bb1
permissions -rw-r--r--
Bug 1535403 - Take indirection into account for the CC optimizations for the outer window wrapper. r=peterv Most wrapper cached C++ objects are held alive by their wrapper. The cycle collector takes advantage of this in many classes and ignores the C++ object if the wrapper is marked black. However, this is not true for the outer window's wrapper. Instead, the outer window's wrapper keeps the inner window alive. The inner window usually keeps its outer window alive, but not after it has been unlinked. For reasons I do not yet understand, the outer window's wrapper can be kept alive after the inner window it is a proxy for is unlinked. This patch fixes the cycle collector optimization for the outer window by only applying it if the outer window still has a weak reference to the inner window, which it will until the inner no longer holds the outer alive. This in turn fixes, or at least helps fix, window leaks seen intermittently when the lifetime of outer windows and docshells are tied together. The code comment is based on a review comment by peterv. Differential Revision: https://phabricator.services.mozilla.com/D27981

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=8 et ft=cpp : */
/* 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 mozilla_hal_WindowIdentifier_h
#define mozilla_hal_WindowIdentifier_h

#include "mozilla/Types.h"
#include "nsCOMPtr.h"
#include "nsTArray.h"

class nsPIDOMWindowInner;

namespace mozilla {
namespace hal {

/**
 * This class serves two purposes.
 *
 * First, this class wraps a pointer to a window.
 *
 * Second, WindowIdentifier lets us uniquely identify a window across
 * processes.  A window exposes an ID which is unique only within its
 * process.  Thus to identify a window, we need to know the ID of the
 * process which contains it.  But the scope of a process's ID is its
 * parent; that is, two processes with different parents might have
 * the same ID.
 *
 * So to identify a window, we need its ID plus the IDs of all the
 * processes in the path from the window's process to the root
 * process.  We throw in the IDs of the intermediate windows (a
 * content window is contained in a window at each level of the
 * process tree) for good measures.
 *
 * You can access this list of IDs by calling AsArray().
 */
class WindowIdentifier {
 public:
  /**
   * Create an empty WindowIdentifier.  Calls to any of this object's
   * public methods will assert -- an empty WindowIdentifier may be
   * used only as a placeholder to code which promises not to touch
   * the object.
   */
  WindowIdentifier();

  /**
   * Copy constructor.
   */
  WindowIdentifier(const WindowIdentifier& other);

  /**
   * Wrap the given window in a WindowIdentifier.  These two
   * constructors automatically grab the window's ID and append it to
   * the array of IDs.
   *
   * Note that these constructors allow an implicit conversion to a
   * WindowIdentifier.
   */
  explicit WindowIdentifier(nsPIDOMWindowInner* window);

  /**
   * Create a new WindowIdentifier with the given id array and window.
   * This automatically grabs the window's ID and appends it to the
   * array.
   */
  WindowIdentifier(const InfallibleTArray<uint64_t>& id,
                   nsPIDOMWindowInner* window);

  /**
   * Get the list of window and process IDs we contain.
   */
  typedef InfallibleTArray<uint64_t> IDArrayType;
  const IDArrayType& AsArray() const;

  /**
   * Append the ID of the ContentChild singleton to our array of
   * window/process IDs.
   */
  void AppendProcessID();

  /**
   * Does this WindowIdentifier identify both a window and the process
   * containing that window?  If so, we say it has traveled through
   * IPC.
   */
  bool HasTraveledThroughIPC() const;

  /**
   * Get the window this object wraps.
   */
  nsPIDOMWindowInner* GetWindow() const;

 private:
  /**
   * Get the ID of the window object we wrap.
   */
  uint64_t GetWindowID() const;

  AutoTArray<uint64_t, 3> mID;
  nsCOMPtr<nsPIDOMWindowInner> mWindow;
  bool mIsEmpty;
};

}  // namespace hal
}  // namespace mozilla

#endif  // mozilla_hal_WindowIdentifier_h