mfbt/Scoped.h
author Petru Lingurar <petru.lingurar@softvision.ro>
Fri, 21 Dec 2018 08:56:47 +0000
changeset 501492 65621d0fe1262af0643cec37c23b2d9ec42588ad
parent 477586 b54db66223586b4e04f5cb926fccdacf8a176b91
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1513938 - Enforce a Bundle size limit and drop `privateSession` if exceeds it. r=JanH, a=jcristau The `privateSession` key would normally allow persisting the Private Browsing session across OOMs in Activity's Bundle. We need to do that to avoid storing private, sensible data on disk like we do with the normal browsing session. In some cases `privateSession` would contain a lot of data which, along with other possible concurrent transactions could overflow Binder's buffer which has a limited fixed size, currently 1Mb. To avoid this, we will drop `privateSession` from the Bundle if the resulting size is greater than a _speculative_ size of 300KBs which would mean that in the case of an OOM all Private Browsing state would be lost. Bug 1515592 is filed to investigate for a better solution. Differential Revision: https://phabricator.services.mozilla.com/D15067

/* -*- 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/. */

/* DEPRECATED: Use UniquePtr.h instead. */

#ifndef mozilla_Scoped_h
#define mozilla_Scoped_h

/*
 * DEPRECATED: Use UniquePtr.h instead.
 *
 * Resource Acquisition Is Initialization is a programming idiom used
 * to write robust code that is able to deallocate resources properly,
 * even in presence of execution errors or exceptions that need to be
 * propagated.  The Scoped* classes defined via the |SCOPED_TEMPLATE|
 * and |MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLTE| macros perform the
 * deallocation of the resource they hold once program execution
 * reaches the end of the scope for which they have been defined.
 * These macros have been used to automatically close file
 * descriptors/file handles when reaching the end of the scope,
 * graphics contexts, etc.
 *
 * The general scenario for RAII classes created by the above macros
 * is the following:
 *
 * ScopedClass foo(create_value());
 * // ... In this scope, |foo| is defined. Use |foo.get()| or |foo.rwget()|
 *        to access the value.
 * // ... In case of |return| or |throw|, |foo| is deallocated automatically.
 * // ... If |foo| needs to be returned or stored, use |foo.forget()|
 *
 * Note that the RAII classes defined in this header do _not_ perform any form
 * of reference-counting or garbage-collection. These classes have exactly two
 * behaviors:
 *
 * - if |forget()| has not been called, the resource is always deallocated at
 *   the end of the scope;
 * - if |forget()| has been called, any control on the resource is unbound
 *   and the resource is not deallocated by the class.
 */

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

namespace mozilla {

/*
 * Scoped is a helper to create RAII wrappers
 * Type argument |Traits| is expected to have the following structure:
 *
 *   struct Traits
 *   {
 *     // Define the type of the value stored in the wrapper
 *     typedef value_type type;
 *     // Returns the value corresponding to the uninitialized or freed state
 *     const static type empty();
 *     // Release resources corresponding to the wrapped value
 *     // This function is responsible for not releasing an |empty| value
 *     const static void release(type);
 *   }
 */
template<typename Traits>
class MOZ_NON_TEMPORARY_CLASS Scoped
{
public:
  typedef typename Traits::type Resource;

  explicit Scoped(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)
    : mValue(Traits::empty())
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
  }

  explicit Scoped(const Resource& aValue
                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
    : mValue(aValue)
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
  }

  /* Move constructor. */
  Scoped(Scoped&& aOther
         MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
    : mValue(std::move(aOther.mValue))
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    aOther.mValue = Traits::empty();
  }

  ~Scoped() { Traits::release(mValue); }

  // Constant getter
  operator const Resource&() const { return mValue; }
  const Resource& operator->() const { return mValue; }
  const Resource& get() const { return mValue; }
  // Non-constant getter.
  Resource& rwget() { return mValue; }

  /*
   * Forget the resource.
   *
   * Once |forget| has been called, the |Scoped| is neutralized, i.e. it will
   * have no effect at destruction (unless it is reset to another resource by
   * |operator=|).
   *
   * @return The original resource.
   */
  Resource forget()
  {
    Resource tmp = mValue;
    mValue = Traits::empty();
    return tmp;
  }

  /*
   * Perform immediate clean-up of this |Scoped|.
   *
   * If this |Scoped| is currently empty, this method has no effect.
   */
  void dispose()
  {
    Traits::release(mValue);
    mValue = Traits::empty();
  }

  bool operator==(const Resource& aOther) const { return mValue == aOther; }

  /*
   * Replace the resource with another resource.
   *
   * Calling |operator=| has the side-effect of triggering clean-up. If you do
   * not want to trigger clean-up, you should first invoke |forget|.
   *
   * @return this
   */
  Scoped& operator=(const Resource& aOther) { return reset(aOther); }

  Scoped& reset(const Resource& aOther)
  {
    Traits::release(mValue);
    mValue = aOther;
    return *this;
  }

  /* Move assignment operator. */
  Scoped& operator=(Scoped&& aRhs)
  {
    MOZ_ASSERT(&aRhs != this, "self-move-assignment not allowed");
    this->~Scoped();
    new(this) Scoped(std::move(aRhs));
    return *this;
  }

private:
  explicit Scoped(const Scoped& aValue) = delete;
  Scoped& operator=(const Scoped& aValue) = delete;

private:
  Resource mValue;
  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

/*
 * SCOPED_TEMPLATE defines a templated class derived from Scoped
 * This allows to implement templates such as ScopedFreePtr.
 *
 * @param name The name of the class to define.
 * @param Traits A struct implementing clean-up. See the implementations
 * for more details.
 */
#define SCOPED_TEMPLATE(name, Traits)                                         \
template<typename Type>                                                       \
struct MOZ_NON_TEMPORARY_CLASS name : public mozilla::Scoped<Traits<Type> >   \
{                                                                             \
  typedef mozilla::Scoped<Traits<Type> > Super;                               \
  typedef typename Super::Resource Resource;                                  \
  name& operator=(Resource aRhs)                                              \
  {                                                                           \
    Super::operator=(aRhs);                                                   \
    return *this;                                                             \
  }                                                                           \
  name& operator=(name&& aRhs)                                                \
  {                                                                           \
    Super::operator=(std::move(aRhs));                                             \
    return *this;                                                             \
  }                                                                           \
  explicit name(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)                         \
    : Super(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT)                   \
  {}                                                                          \
  explicit name(Resource aRhs                                                 \
                MOZ_GUARD_OBJECT_NOTIFIER_PARAM)                              \
    : Super(aRhs                                                              \
            MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)                        \
  {}                                                                          \
  name(name&& aRhs                                                            \
       MOZ_GUARD_OBJECT_NOTIFIER_PARAM)                                       \
    : Super(std::move(aRhs)                                                        \
            MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)                        \
  {}                                                                          \
private:                                                                      \
  explicit name(name&) = delete;                                              \
  name& operator=(name&) = delete;                                            \
};

/*
 * MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLATE makes it easy to create scoped
 * pointers for types with custom deleters; just overload
 * TypeSpecificDelete(T*) in the same namespace as T to call the deleter for
 * type T.
 *
 * @param name The name of the class to define.
 * @param Type A struct implementing clean-up. See the implementations
 * for more details.
 * *param Deleter The function that is used to delete/destroy/free a
 *        non-null value of Type*.
 *
 * Example:
 *
 *   MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLATE(ScopedPRFileDesc, PRFileDesc, \
 *                                             PR_Close)
 *   ...
 *   {
 *       ScopedPRFileDesc file(PR_OpenFile(...));
 *       ...
 *   } // file is closed with PR_Close here
 */
#define MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLATE(name, Type, Deleter) \
template <> inline void TypeSpecificDelete(Type* aValue) { Deleter(aValue); } \
typedef ::mozilla::TypeSpecificScopedPointer<Type> name;

template <typename T> void TypeSpecificDelete(T* aValue);

template <typename T>
struct TypeSpecificScopedPointerTraits
{
  typedef T* type;
  static type empty() { return nullptr; }
  static void release(type aValue)
  {
    if (aValue) {
      TypeSpecificDelete(aValue);
    }
  }
};

SCOPED_TEMPLATE(TypeSpecificScopedPointer, TypeSpecificScopedPointerTraits)

} /* namespace mozilla */

#endif /* mozilla_Scoped_h */