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+/* 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 macro |SCOPED_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/Attributes.h"
+#include "mozilla/GuardObjects.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& value
+                    MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : value(value)
+    {
+      MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    }
+    ~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<Traits>& operator=(const Resource& other) {
+      return reset(other);
+    }
+    Scoped<Traits>& reset(const Resource& other) {
+      Traits::release(value);
+      value = other;
+      return *this;
+    }
+
+  private:
+    explicit Scoped(const Scoped<Traits>& value) MOZ_DELETE;
+    Scoped<Traits>& operator=(const Scoped<Traits>& 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 ptr) {                            \
+      Super::operator=(ptr);                                   \
+      return *this;                                            \
+    }                                                          \
+    explicit name(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)        \
+      : Super(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT)  \
+    {}                                                         \
+    explicit name(Resource ptr                                 \
+                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM)             \
+      : Super(ptr MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)   \
+    {}                                                         \
+  private:                                                     \
+    explicit name(name& source) MOZ_DELETE;                    \
+    name& operator=(name& source) 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 NULL; }
+    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)
+
+} /* namespace mozilla */
+
+#endif // mozilla_Scoped_h_