mfbt/Scoped.h
author Bryce Van Dyk <bvandyk@mozilla.com>
Mon, 27 Aug 2018 16:25:54 +0000
changeset 488616 259675bd67f96acf1ae0f2ed6115de4331a94d32
parent 475080 b54db66223586b4e04f5cb926fccdacf8a176b91
child 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1486502 - Add widevine CDM headers to third party paths, clang-format ignore. r=sylvestre We wish to keep the widevine headers in the same formatting as upstream to ease comparison and as we do not modify these files. This patch adds the existing headers, as well as another we anticipate pulling down for our next bump (content_decryption_module_proxy.h) to the ignored paths. These files are ignored individually rather than the whole directory they're in, as we also have Mozilla code in that dir. Differential Revision: https://phabricator.services.mozilla.com/D4347

/* -*- 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 */