The Tor Browser: mfbt/Scoped.h@97036ab72558 (annotated)

mfbt/Scoped.h@97036ab72558 (annotated)

mfbt/Scoped.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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/. */
 /* A number of structures to simplify scope-based RAII management. */
 #ifndef mozilla_Scoped_h
 #define mozilla_Scoped_h
 /*
  * 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 in this header perform the
  * deallocation of the resource they hold once program execution
  * reaches the end of the scope for which they have been defined.
  *
  * This header provides the following RAII classes:
  *
  * - |ScopedFreePtr| - a container for a pointer, that automatically calls
  *   |free()| at the end of the scope;
  * - |ScopedDeletePtr| - a container for a pointer, that automatically calls
  *   |delete| at the end of the scope;
  * - |ScopedDeleteArray| - a container for a pointer to an array, that
  *   automatically calls |delete[]| at the end of the scope.
  *
  * The general scenario for each of the RAII classes 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.
  *
  * Extension:
  *
  * In addition, this header provides class |Scoped| and macros |SCOPED_TEMPLATE|
  * and |MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLATE|  to simplify the definition
  * of RAII classes for other scenarios. These macros have been used to
  * automatically close file descriptors/file handles when reaching the end of
  * the scope, graphics contexts, etc.
  */
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/GuardObjects.h"
 #include "mozilla/Move.h"
 #include "mozilla/NullPtr.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 Scoped
 {
   public:
     typedef typename Traits::type Resource;
     explicit Scoped(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)
       : value(Traits::empty())
     {
       MOZ_GUARD_OBJECT_NOTIFIER_INIT;
     }
     explicit Scoped(const Resource& v
                     MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
       : value(v)
     {
       MOZ_GUARD_OBJECT_NOTIFIER_INIT;
     }
     /* Move constructor. */
     explicit Scoped(Scoped&& v
                     MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
       : value(Move(v.value))
     {
       MOZ_GUARD_OBJECT_NOTIFIER_INIT;
       v.value = Traits::empty();
     }
     ~Scoped() {
       Traits::release(value);
     }
     // Constant getter
     operator const Resource&() const { return value; }
     const Resource& operator->() const { return value; }
     const Resource& get() const { return value; }
     // Non-constant getter.
     Resource& rwget() { return value; }
     /*
      * 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 = value;
       value = 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(value);
       value = Traits::empty();
     }
     bool operator==(const Resource& other) const {
       return value == other;
     }
     /*
      * 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& other) {
       return reset(other);
     }
     Scoped& reset(const Resource& other) {
       Traits::release(value);
       value = other;
       return *this;
     }
     /* Move assignment operator. */
     Scoped& operator=(Scoped&& rhs) {
       MOZ_ASSERT(&rhs != this, "self-move-assignment not allowed");
       this->~Scoped();
       new(this) Scoped(Move(rhs));
       return *this;
     }
   private:
     explicit Scoped(const Scoped& value) MOZ_DELETE;
     Scoped& operator=(const Scoped& value) MOZ_DELETE;
   private:
     Resource value;
     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 name : public mozilla::Scoped<Traits<Type> >            \
 {                                                              \
     typedef mozilla::Scoped<Traits<Type> > Super;              \
     typedef typename Super::Resource Resource;                 \
     name& operator=(Resource rhs) {                            \
       Super::operator=(rhs);                                   \
       return *this;                                            \
     }                                                          \
     name& operator=(name&& rhs) {                              \
       Super::operator=(Move(rhs));                             \
       return *this;                                            \
     }                                                          \
     explicit name(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)        \
       : Super(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT)  \
     {}                                                         \
     explicit name(Resource rhs                                 \
                   MOZ_GUARD_OBJECT_NOTIFIER_PARAM)             \
       : Super(rhs                                              \
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)       \
     {}                                                         \
     explicit name(name&& rhs                                   \
                   MOZ_GUARD_OBJECT_NOTIFIER_PARAM)             \
       : Super(Move(rhs)                                        \
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)       \
     {}                                                         \
   private:                                                     \
     explicit name(name&) MOZ_DELETE;                           \
     name& operator=(name&) MOZ_DELETE;                         \
 };
 /*
  * ScopedFreePtr is a RAII wrapper for pointers that need to be free()d.
  *
  *   struct S { ... };
  *   ScopedFreePtr<S> foo = malloc(sizeof(S));
  *   ScopedFreePtr<char> bar = strdup(str);
  */
 template<typename T>
 struct ScopedFreePtrTraits
 {
     typedef T* type;
     static T* empty() { return nullptr; }
     static void release(T* ptr) { free(ptr); }
 };
 SCOPED_TEMPLATE(ScopedFreePtr, ScopedFreePtrTraits)
 /*
  * ScopedDeletePtr is a RAII wrapper for pointers that need to be deleted.
  *
  *   struct S { ... };
  *   ScopedDeletePtr<S> foo = new S();
  */
 template<typename T>
 struct ScopedDeletePtrTraits : public ScopedFreePtrTraits<T>
 {
     static void release(T* ptr) { delete ptr; }
 };
 SCOPED_TEMPLATE(ScopedDeletePtr, ScopedDeletePtrTraits)
 /*
  * ScopedDeleteArray is a RAII wrapper for pointers that need to be delete[]ed.
  *
  *   struct S { ... };
  *   ScopedDeleteArray<S> foo = new S[42];
  */
 template<typename T>
 struct ScopedDeleteArrayTraits : public ScopedFreePtrTraits<T>
 {
     static void release(T* ptr) { delete [] ptr; }
 };
 SCOPED_TEMPLATE(ScopedDeleteArray, ScopedDeleteArrayTraits)
 /*
  * 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 * value) { Deleter(value); } \
 typedef ::mozilla::TypeSpecificScopedPointer<Type> name;
 template <typename T> void TypeSpecificDelete(T * value);
 template <typename T>
 struct TypeSpecificScopedPointerTraits
 {
     typedef T* type;
     const static type empty() { return nullptr; }
     const static void release(type value)
     {
       if (value)
         TypeSpecificDelete(value);
     }
 };
 SCOPED_TEMPLATE(TypeSpecificScopedPointer, TypeSpecificScopedPointerTraits)
 } /* namespace mozilla */
 #endif /* mozilla_Scoped_h */

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mfbt/Scoped.h@97036ab72558 (annotated)

mfbt/Scoped.h