brettw@chromium.org | 064f0d8 | 2014-03-13 04:19:24 +0900 | [diff] [blame] | 1 | // Copyright 2014 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef BASE_SCOPED_GENERIC_H_ |
| 6 | #define BASE_SCOPED_GENERIC_H_ |
| 7 | |
| 8 | #include <stdlib.h> |
| 9 | |
rsesek@chromium.org | ab283e0 | 2014-05-29 08:40:08 +0900 | [diff] [blame] | 10 | #include <algorithm> |
| 11 | |
brettw@chromium.org | 064f0d8 | 2014-03-13 04:19:24 +0900 | [diff] [blame] | 12 | #include "base/compiler_specific.h" |
| 13 | #include "base/move.h" |
| 14 | |
| 15 | namespace base { |
| 16 | |
| 17 | // This class acts like ScopedPtr with a custom deleter (although is slightly |
| 18 | // less fancy in some of the more escoteric respects) except that it keeps a |
| 19 | // copy of the object rather than a pointer, and we require that the contained |
| 20 | // object has some kind of "invalid" value. |
| 21 | // |
| 22 | // Defining a scoper based on this class allows you to get a scoper for |
| 23 | // non-pointer types without having to write custom code for set, reset, and |
| 24 | // move, etc. and get almost identical semantics that people are used to from |
| 25 | // scoped_ptr. |
| 26 | // |
| 27 | // It is intended that you will typedef this class with an appropriate deleter |
| 28 | // to implement clean up tasks for objects that act like pointers from a |
| 29 | // resource management standpoint but aren't, such as file descriptors and |
| 30 | // various types of operating system handles. Using scoped_ptr for these |
| 31 | // things requires that you keep a pointer to the handle valid for the lifetime |
| 32 | // of the scoper (which is easy to mess up). |
| 33 | // |
| 34 | // For an object to be able to be put into a ScopedGeneric, it must support |
| 35 | // standard copyable semantics and have a specific "invalid" value. The traits |
| 36 | // must define a free function and also the invalid value to assign for |
| 37 | // default-constructed and released objects. |
| 38 | // |
| 39 | // struct FooScopedTraits { |
| 40 | // // It's assumed that this is a fast inline function with little-to-no |
| 41 | // // penalty for duplicate calls. This must be a static function even |
| 42 | // // for stateful traits. |
| 43 | // static int InvalidValue() { |
| 44 | // return 0; |
| 45 | // } |
| 46 | // |
| 47 | // // This free function will not be called if f == InvalidValue()! |
| 48 | // static void Free(int f) { |
| 49 | // ::FreeFoo(f); |
| 50 | // } |
| 51 | // }; |
| 52 | // |
| 53 | // typedef ScopedGeneric<int, FooScopedTraits> ScopedFoo; |
| 54 | template<typename T, typename Traits> |
| 55 | class ScopedGeneric { |
| 56 | MOVE_ONLY_TYPE_FOR_CPP_03(ScopedGeneric, RValue) |
| 57 | |
| 58 | private: |
| 59 | // This must be first since it's used inline below. |
| 60 | // |
| 61 | // Use the empty base class optimization to allow us to have a D |
| 62 | // member, while avoiding any space overhead for it when D is an |
| 63 | // empty class. See e.g. http://www.cantrip.org/emptyopt.html for a good |
| 64 | // discussion of this technique. |
| 65 | struct Data : public Traits { |
| 66 | explicit Data(const T& in) : generic(in) {} |
| 67 | Data(const T& in, const Traits& other) : Traits(other), generic(in) {} |
| 68 | T generic; |
| 69 | }; |
| 70 | |
| 71 | public: |
| 72 | typedef T element_type; |
| 73 | typedef Traits traits_type; |
| 74 | |
| 75 | ScopedGeneric() : data_(traits_type::InvalidValue()) {} |
| 76 | |
| 77 | // Constructor. Takes responsibility for freeing the resource associated with |
| 78 | // the object T. |
| 79 | explicit ScopedGeneric(const element_type& value) : data_(value) {} |
| 80 | |
| 81 | // Constructor. Allows initialization of a stateful traits object. |
| 82 | ScopedGeneric(const element_type& value, const traits_type& traits) |
| 83 | : data_(value, traits) { |
| 84 | } |
| 85 | |
| 86 | // Move constructor for C++03 move emulation. |
| 87 | ScopedGeneric(RValue rvalue) |
| 88 | : data_(rvalue.object->release(), rvalue.object->get_traits()) { |
| 89 | } |
| 90 | |
| 91 | ~ScopedGeneric() { |
| 92 | FreeIfNecessary(); |
| 93 | } |
| 94 | |
| 95 | // Frees the currently owned object, if any. Then takes ownership of a new |
| 96 | // object, if given. Self-resets are not allowd as on scoped_ptr. See |
| 97 | // http://crbug.com/162971 |
| 98 | void reset(const element_type& value = traits_type::InvalidValue()) { |
| 99 | if (data_.generic != traits_type::InvalidValue() && data_.generic == value) |
| 100 | abort(); |
| 101 | FreeIfNecessary(); |
| 102 | data_.generic = value; |
| 103 | } |
| 104 | |
| 105 | void swap(ScopedGeneric& other) { |
| 106 | // Standard swap idiom: 'using std::swap' ensures that std::swap is |
| 107 | // present in the overload set, but we call swap unqualified so that |
| 108 | // any more-specific overloads can be used, if available. |
| 109 | using std::swap; |
| 110 | swap(static_cast<Traits&>(data_), static_cast<Traits&>(other.data_)); |
| 111 | swap(data_.generic, other.data_.generic); |
| 112 | } |
| 113 | |
| 114 | // Release the object. The return value is the current object held by this |
| 115 | // object. After this operation, this object will hold a null value, and |
| 116 | // will not own the object any more. |
| 117 | element_type release() WARN_UNUSED_RESULT { |
| 118 | element_type old_generic = data_.generic; |
| 119 | data_.generic = traits_type::InvalidValue(); |
| 120 | return old_generic; |
| 121 | } |
| 122 | |
| 123 | const element_type& get() const { return data_.generic; } |
| 124 | |
| 125 | // Returns true if this object doesn't hold the special null value for the |
| 126 | // associated data type. |
| 127 | bool is_valid() const { return data_.generic != traits_type::InvalidValue(); } |
| 128 | |
| 129 | bool operator==(const element_type& value) const { |
| 130 | return data_.generic == value; |
| 131 | } |
| 132 | bool operator!=(const element_type& value) const { |
| 133 | return data_.generic != value; |
| 134 | } |
| 135 | |
| 136 | Traits& get_traits() { return data_; } |
| 137 | const Traits& get_traits() const { return data_; } |
| 138 | |
| 139 | private: |
| 140 | void FreeIfNecessary() { |
| 141 | if (data_.generic != traits_type::InvalidValue()) { |
| 142 | data_.Free(data_.generic); |
| 143 | data_.generic = traits_type::InvalidValue(); |
| 144 | } |
| 145 | } |
| 146 | |
| 147 | // Forbid comparison. If U != T, it totally doesn't make sense, and if U == |
| 148 | // T, it still doesn't make sense because you should never have the same |
| 149 | // object owned by two different ScopedGenerics. |
| 150 | template <typename T2, typename Traits2> bool operator==( |
| 151 | const ScopedGeneric<T2, Traits2>& p2) const; |
| 152 | template <typename T2, typename Traits2> bool operator!=( |
| 153 | const ScopedGeneric<T2, Traits2>& p2) const; |
| 154 | |
| 155 | Data data_; |
| 156 | }; |
| 157 | |
| 158 | template<class T, class Traits> |
| 159 | void swap(const ScopedGeneric<T, Traits>& a, |
| 160 | const ScopedGeneric<T, Traits>& b) { |
| 161 | a.swap(b); |
| 162 | } |
| 163 | |
| 164 | template<class T, class Traits> |
| 165 | bool operator==(const T& value, const ScopedGeneric<T, Traits>& scoped) { |
| 166 | return value == scoped.get(); |
| 167 | } |
| 168 | |
| 169 | template<class T, class Traits> |
| 170 | bool operator!=(const T& value, const ScopedGeneric<T, Traits>& scoped) { |
| 171 | return value != scoped.get(); |
| 172 | } |
| 173 | |
| 174 | } // namespace base |
| 175 | |
| 176 | #endif // BASE_SCOPED_GENERIC_H_ |