mfbt/ReentrancyGuard.h
author Andrew Osmond <aosmond@mozilla.com>
Tue, 24 Apr 2018 13:51:35 -0400
changeset 415325 1173dccd114e1c86047a6f01e341cf1c4ea8fe9c
parent 262188 31a26ed444843f086c468a98236e8c98b7115b44
child 448947 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1444537 - Part 3. Fix how redecode errors could cause animated image state inconsistencies. r=tnikkel We can discard frames from an animated image if the memory footprint exceeds the threshold. This will cause us to redecode frames on demand instead. However decoders can fail to produce the same results on subsequent runs due to differences in memory pressure, etc. If this happens our state can get inconsistent. In particular, if we keep failing on the first frame, we end up in an infinite loop on the decoder thread. Since we don't have the owning image to signal, as we had to release our reference to it after the first pass, we can do little but stop decoding. From the user's perspective, the animation will come to a stop.

/* -*- 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/. */

/* Small helper class for asserting uses of a class are non-reentrant. */

#ifndef mozilla_ReentrancyGuard_h
#define mozilla_ReentrancyGuard_h

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/GuardObjects.h"

namespace mozilla {

/* Useful for implementing containers that assert non-reentrancy */
class MOZ_RAII ReentrancyGuard
{
  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
#ifdef DEBUG
  bool& mEntered;
#endif

public:
  template<class T>
#ifdef DEBUG
  explicit ReentrancyGuard(T& aObj
                           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
    : mEntered(aObj.mEntered)
#else
  explicit ReentrancyGuard(T&
                           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
#endif
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
#ifdef DEBUG
    MOZ_ASSERT(!mEntered);
    mEntered = true;
#endif
  }
  ~ReentrancyGuard()
  {
#ifdef DEBUG
    mEntered = false;
#endif
  }

private:
  ReentrancyGuard(const ReentrancyGuard&) = delete;
  void operator=(const ReentrancyGuard&) = delete;
};

} // namespace mozilla

#endif /* mozilla_ReentrancyGuard_h */