base/memory/ref_counted.h

   1 // Copyright (c) 2012 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_MEMORY_REF_COUNTED_H_
   6 #define BASE_MEMORY_REF_COUNTED_H_
   7
   8 #include <cassert>
   9 #include <iosfwd>
  10
  11 #include "base/atomic_ref_count.h"
  12 #include "base/base_export.h"
  13 #include "base/compiler_specific.h"
  14 #ifndef NDEBUG
  15 #include "base/logging.h"
  16 #endif
  17 #include "base/threading/thread_collision_warner.h"
  18 #include "build/build_config.h"
  19
  20 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)
  21 #define DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR
  22 #endif
  23
  24 namespace base {
  25
  26 namespace subtle {
  27
  28 class BASE_EXPORT RefCountedBase {
  29  public:
  30   bool HasOneRef() const { return ref_count_ == 1; }
  31
  32  protected:
  33   RefCountedBase()
  34       : ref_count_(0)
  35   #ifndef NDEBUG
  36       , in_dtor_(false)
  37   #endif
  38       {
  39   }
  40
  41   ~RefCountedBase() {
  42   #ifndef NDEBUG
  43     DCHECK(in_dtor_) << "RefCounted object deleted without calling Release()";
  44   #endif
  45   }
  46
  47
  48   void AddRef() const {
  49     // TODO(maruel): Add back once it doesn't assert 500 times/sec.
  50     // Current thread books the critical section "AddRelease"
  51     // without release it.
  52     // DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
  53   #ifndef NDEBUG
  54     DCHECK(!in_dtor_);
  55   #endif
  56     ++ref_count_;
  57   }
  58
  59   // Returns true if the object should self-delete.
  60   bool Release() const {
  61     // TODO(maruel): Add back once it doesn't assert 500 times/sec.
  62     // Current thread books the critical section "AddRelease"
  63     // without release it.
  64     // DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
  65   #ifndef NDEBUG
  66     DCHECK(!in_dtor_);
  67   #endif
  68     if (--ref_count_ == 0) {
  69   #ifndef NDEBUG
  70       in_dtor_ = true;
  71   #endif
  72       return true;
  73     }
  74     return false;
  75   }
  76
  77  private:
  78   mutable int ref_count_;
  79 #ifndef NDEBUG
  80   mutable bool in_dtor_;
  81 #endif
  82
  83   DFAKE_MUTEX(add_release_);
  84
  85   DISALLOW_COPY_AND_ASSIGN(RefCountedBase);
  86 };
  87
  88 class BASE_EXPORT RefCountedThreadSafeBase {
  89  public:
  90   bool HasOneRef() const;
  91
  92  protected:
  93   RefCountedThreadSafeBase();
  94   ~RefCountedThreadSafeBase();
  95
  96   void AddRef() const;
  97
  98   // Returns true if the object should self-delete.
  99   bool Release() const;
 100
 101  private:
 102   mutable AtomicRefCount ref_count_;
 103 #ifndef NDEBUG
 104   mutable bool in_dtor_;
 105 #endif
 106
 107   DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
 108 };
 109
 110 }  // namespace subtle
 111
 112 //
 113 // A base class for reference counted classes.  Otherwise, known as a cheap
 114 // knock-off of WebKit's RefCounted<T> class.  To use this guy just extend your
 115 // class from it like so:
 116 //
 117 //   class MyFoo : public base::RefCounted<MyFoo> {
 118 //    ...
 119 //    private:
 120 //     friend class base::RefCounted<MyFoo>;
 121 //     ~MyFoo();
 122 //   };
 123 //
 124 // You should always make your destructor private, to avoid any code deleting
 125 // the object accidently while there are references to it.
 126 template <class T>
 127 class RefCounted : public subtle::RefCountedBase {
 128  public:
 129   RefCounted() {}
 130
 131   void AddRef() const {
 132     subtle::RefCountedBase::AddRef();
 133   }
 134
 135   void Release() const {
 136     if (subtle::RefCountedBase::Release()) {
 137       delete static_cast<const T*>(this);
 138     }
 139   }
 140
 141  protected:
 142   ~RefCounted() {}
 143
 144  private:
 145   DISALLOW_COPY_AND_ASSIGN(RefCounted<T>);
 146 };
 147
 148 // Forward declaration.
 149 template <class T, typename Traits> class RefCountedThreadSafe;
 150
 151 // Default traits for RefCountedThreadSafe<T>.  Deletes the object when its ref
 152 // count reaches 0.  Overload to delete it on a different thread etc.
 153 template<typename T>
 154 struct DefaultRefCountedThreadSafeTraits {
 155   static void Destruct(const T* x) {
 156     // Delete through RefCountedThreadSafe to make child classes only need to be
 157     // friend with RefCountedThreadSafe instead of this struct, which is an
 158     // implementation detail.
 159     RefCountedThreadSafe<T,
 160                          DefaultRefCountedThreadSafeTraits>::DeleteInternal(x);
 161   }
 162 };
 163
 164 //
 165 // A thread-safe variant of RefCounted<T>
 166 //
 167 //   class MyFoo : public base::RefCountedThreadSafe<MyFoo> {
 168 //    ...
 169 //   };
 170 //
 171 // If you're using the default trait, then you should add compile time
 172 // asserts that no one else is deleting your object.  i.e.
 173 //    private:
 174 //     friend class base::RefCountedThreadSafe<MyFoo>;
 175 //     ~MyFoo();
 176 template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T> >
 177 class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
 178  public:
 179   RefCountedThreadSafe() {}
 180
 181   void AddRef() const {
 182     subtle::RefCountedThreadSafeBase::AddRef();
 183   }
 184
 185   void Release() const {
 186     if (subtle::RefCountedThreadSafeBase::Release()) {
 187       Traits::Destruct(static_cast<const T*>(this));
 188     }
 189   }
 190
 191  protected:
 192   ~RefCountedThreadSafe() {}
 193
 194  private:
 195   friend struct DefaultRefCountedThreadSafeTraits<T>;
 196   static void DeleteInternal(const T* x) { delete x; }
 197
 198   DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
 199 };
 200
 201 //
 202 // A thread-safe wrapper for some piece of data so we can place other
 203 // things in scoped_refptrs<>.
 204 //
 205 template<typename T>
 206 class RefCountedData
 207     : public base::RefCountedThreadSafe< base::RefCountedData<T> > {
 208  public:
 209   RefCountedData() : data() {}
 210   RefCountedData(const T& in_value) : data(in_value) {}
 211
 212   T data;
 213
 214  private:
 215   friend class base::RefCountedThreadSafe<base::RefCountedData<T> >;
 216   ~RefCountedData() {}
 217 };
 218
 219 }  // namespace base
 220
 221 //
 222 // A smart pointer class for reference counted objects.  Use this class instead
 223 // of calling AddRef and Release manually on a reference counted object to
 224 // avoid common memory leaks caused by forgetting to Release an object
 225 // reference.  Sample usage:
 226 //
 227 //   class MyFoo : public RefCounted<MyFoo> {
 228 //    ...
 229 //   };
 230 //
 231 //   void some_function() {
 232 //     scoped_refptr<MyFoo> foo = new MyFoo();
 233 //     foo->Method(param);
 234 //     // |foo| is released when this function returns
 235 //   }
 236 //
 237 //   void some_other_function() {
 238 //     scoped_refptr<MyFoo> foo = new MyFoo();
 239 //     ...
 240 //     foo = NULL;  // explicitly releases |foo|
 241 //     ...
 242 //     if (foo)
 243 //       foo->Method(param);
 244 //   }
 245 //
 246 // The above examples show how scoped_refptr<T> acts like a pointer to T.
 247 // Given two scoped_refptr<T> classes, it is also possible to exchange
 248 // references between the two objects, like so:
 249 //
 250 //   {
 251 //     scoped_refptr<MyFoo> a = new MyFoo();
 252 //     scoped_refptr<MyFoo> b;
 253 //
 254 //     b.swap(a);
 255 //     // now, |b| references the MyFoo object, and |a| references NULL.
 256 //   }
 257 //
 258 // To make both |a| and |b| in the above example reference the same MyFoo
 259 // object, simply use the assignment operator:
 260 //
 261 //   {
 262 //     scoped_refptr<MyFoo> a = new MyFoo();
 263 //     scoped_refptr<MyFoo> b;
 264 //
 265 //     b = a;
 266 //     // now, |a| and |b| each own a reference to the same MyFoo object.
 267 //   }
 268 //
 269 template <class T>
 270 class scoped_refptr {
 271  public:
 272   typedef T element_type;
 273
 274   scoped_refptr() : ptr_(NULL) {
 275   }
 276
 277   scoped_refptr(T* p) : ptr_(p) {
 278     if (ptr_)
 279       ptr_->AddRef();
 280   }
 281
 282   scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
 283     if (ptr_)
 284       ptr_->AddRef();
 285   }
 286
 287   template <typename U>
 288   scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
 289     if (ptr_)
 290       ptr_->AddRef();
 291   }
 292
 293   ~scoped_refptr() {
 294     if (ptr_)
 295       ptr_->Release();
 296   }
 297
 298   T* get() const { return ptr_; }
 299
 300 #if !defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
 301   // Allow scoped_refptr<C> to be used in boolean expression
 302   // and comparison operations.
 303   operator T*() const { return ptr_; }
 304 #endif
 305
 306   T& operator*() const {
 307     assert(ptr_ != NULL);
 308     return *ptr_;
 309   }
 310
 311   T* operator->() const {
 312     assert(ptr_ != NULL);
 313     return ptr_;
 314   }
 315
 316   scoped_refptr<T>& operator=(T* p) {
 317     // AddRef first so that self assignment should work
 318     if (p)
 319       p->AddRef();
 320     T* old_ptr = ptr_;
 321     ptr_ = p;
 322     if (old_ptr)
 323       old_ptr->Release();
 324     return *this;
 325   }
 326
 327   scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
 328     return *this = r.ptr_;
 329   }
 330
 331   template <typename U>
 332   scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
 333     return *this = r.get();
 334   }
 335
 336   void swap(T** pp) {
 337     T* p = ptr_;
 338     ptr_ = *pp;
 339     *pp = p;
 340   }
 341
 342   void swap(scoped_refptr<T>& r) {
 343     swap(&r.ptr_);
 344   }
 345
 346 #if defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
 347   template <typename U>
 348   bool operator==(const scoped_refptr<U>& rhs) const {
 349     return ptr_ == rhs.get();
 350   }
 351
 352   template <typename U>
 353   bool operator!=(const scoped_refptr<U>& rhs) const {
 354     return !operator==(rhs);
 355   }
 356
 357   template <typename U>
 358   bool operator<(const scoped_refptr<U>& rhs) const {
 359     return ptr_ < rhs.get();
 360   }
 361 #endif
 362
 363  protected:
 364   T* ptr_;
 365 };
 366
 367 // Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
 368 // having to retype all the template arguments
 369 template <typename T>
 370 scoped_refptr<T> make_scoped_refptr(T* t) {
 371   return scoped_refptr<T>(t);
 372 }
 373
 374 #if defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
 375 // Temporary operator overloads to facilitate the transition...
 376 template <typename T, typename U>
 377 bool operator==(const scoped_refptr<T>& lhs, const U* rhs) {
 378   return lhs.get() == rhs;
 379 }
 380
 381 template <typename T, typename U>
 382 bool operator==(const T* lhs, const scoped_refptr<U>& rhs) {
 383   return lhs == rhs.get();
 384 }
 385
 386 template <typename T, typename U>
 387 bool operator!=(const scoped_refptr<T>& lhs, const U* rhs) {
 388   return !operator==(lhs, rhs);
 389 }
 390
 391 template <typename T, typename U>
 392 bool operator!=(const T* lhs, const scoped_refptr<U>& rhs) {
 393   return !operator==(lhs, rhs);
 394 }
 395
 396 template <typename T>
 397 std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p) {
 398   return out << p.get();
 399 }
 400 #endif  // defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
 401
 402 #endif  // BASE_MEMORY_REF_COUNTED_H_