dom/indexedDB/SafeRefPtr.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_saferefptr_h__
   8 #define mozilla_saferefptr_h__
   9
  10 #include "mozilla/ArrayAlgorithm.h"
  11 #include "mozilla/Maybe.h"
  12 #include "mozilla/NotNull.h"
  13 #include "mozilla/RefCounted.h"
  14 #include "mozilla/RefPtr.h"
  15 #include "nsCOMPtr.h"
  16 #include "nsTObserverArray.h"
  17
  18 namespace mozilla {
  19 template <typename T>
  20 class SafeRefPtr;
  21
  22 template <typename T, typename... Args>
  23 SafeRefPtr<T> MakeSafeRefPtr(Args&&... aArgs);
  24
  25 namespace detail {
  26 struct InitialConstructionTag {};
  27
  28 class SafeRefCountedBase {
  29   template <typename U, typename... Args>
  30   friend SafeRefPtr<U> mozilla::MakeSafeRefPtr(Args&&... aArgs);
  31
  32   template <typename T>
  33   friend class SafeRefPtr;
  34
  35   void* operator new(size_t aSize) { return ::operator new(aSize); }
  36
  37  protected:
  38   void operator delete(void* aPtr) { ::operator delete(aPtr); }
  39
  40  public:
  41   void* operator new[](size_t) = delete;
  42 };
  43
  44 // SafeRefCounted is similar to RefCounted, but they differ in their initial
  45 // refcount (here 1), and the visibility of operator new (here private). The
  46 // rest is mostly a copy of RefCounted.
  47 template <typename T, RefCountAtomicity Atomicity>
  48 class SafeRefCounted : public SafeRefCountedBase {
  49  protected:
  50   SafeRefCounted() = default;
  51 #ifdef DEBUG
  52   ~SafeRefCounted() { MOZ_ASSERT(mRefCnt == detail::DEAD); }
  53 #endif
  54
  55  public:
  56   // Compatibility with nsRefPtr.
  57   MozRefCountType AddRef() const {
  58     // Note: this method must be thread safe for AtomicRefCounted.
  59     MOZ_ASSERT(int32_t(mRefCnt) >= 0);
  60     const MozRefCountType cnt = ++mRefCnt;
  61     detail::RefCountLogger::logAddRef(static_cast<const T*>(this), cnt);
  62     return cnt;
  63   }
  64
  65   MozRefCountType Release() const {
  66     // Note: this method must be thread safe for AtomicRefCounted.
  67     MOZ_ASSERT(int32_t(mRefCnt) > 0);
  68     detail::RefCountLogger::ReleaseLogger logger(static_cast<const T*>(this));
  69     const MozRefCountType cnt = --mRefCnt;
  70     // Note: it's not safe to touch |this| after decrementing the refcount,
  71     // except for below.
  72     logger.logRelease(cnt);
  73     if (0 == cnt) {
  74       // Because we have atomically decremented the refcount above, only
  75       // one thread can get a 0 count here, so as long as we can assume that
  76       // everything else in the system is accessing this object through
  77       // RefPtrs, it's safe to access |this| here.
  78 #ifdef DEBUG
  79       mRefCnt = detail::DEAD;
  80 #endif
  81       delete static_cast<const T*>(this);
  82     }
  83     return cnt;
  84   }
  85
  86   // Compatibility with wtf::RefPtr.
  87   void ref() { AddRef(); }
  88   void deref() { Release(); }
  89   MozRefCountType refCount() const { return mRefCnt; }
  90   bool hasOneRef() const {
  91     MOZ_ASSERT(mRefCnt > 0);
  92     return mRefCnt == 1;
  93   }
  94
  95  protected:
  96   SafeRefPtr<T> SafeRefPtrFromThis();
  97
  98  private:
  99   mutable RC<MozRefCountType, Atomicity> mRefCnt =
 100       RC<MozRefCountType, Atomicity>{1};
 101 };
 102 }  // namespace detail
 103
 104 template <typename T>
 105 class SafeRefCounted
 106     : public detail::SafeRefCounted<T, detail::NonAtomicRefCount> {
 107  public:
 108   ~SafeRefCounted() {
 109     static_assert(std::is_base_of<SafeRefCounted, T>::value,
 110                   "T must derive from SafeRefCounted<T>");
 111   }
 112 };
 113
 114 template <typename T>
 115 class AtomicSafeRefCounted
 116     : public detail::SafeRefCounted<T, detail::AtomicRefCount> {
 117  public:
 118   ~AtomicSafeRefCounted() {
 119     static_assert(std::is_base_of<AtomicSafeRefCounted, T>::value,
 120                   "T must derive from AtomicSafeRefCounted<T>");
 121   }
 122 };
 123
 124 struct AcquireStrongRefFromRawPtr {};
 125
 126 // XXX for Apple, clang::trivial_abi is probably also supported, but we need to
 127 // find out the correct version number
 128 #if defined(__clang__) && !defined(__apple_build_version__) && \
 129     __clang_major__ >= 7
 130 #  define MOZ_TRIVIAL_ABI [[clang::trivial_abi]]
 131 #else
 132 #  define MOZ_TRIVIAL_ABI
 133 #endif
 134
 135 // A restricted variant of mozilla::RefPtr<T>, which prohibits some unsafe or
 136 // unperformant misuses, in particular:
 137 // * It is not implicitly convertible from a raw pointer. Unsafe acquisitions
 138 //   from a raw pointer must be made using the verbose
 139 //   AcquireStrongRefFromRawPtr. To create a new object on the heap, use
 140 //   MakeSafeRefPtr.
 141 // * It does not implicitly decay to a raw pointer. unsafeGetRawPtr() must be
 142 // called
 143 //   explicitly.
 144 // * It is not copyable, but must be explicitly copied using clonePtr().
 145 // * Temporaries cannot be dereferenced using operator* or operator->.
 146 template <typename T>
 147 class MOZ_IS_REFPTR MOZ_TRIVIAL_ABI SafeRefPtr {
 148   template <typename U>
 149   friend class SafeRefPtr;
 150
 151   template <typename U, typename... Args>
 152   friend SafeRefPtr<U> mozilla::MakeSafeRefPtr(Args&&... aArgs);
 153
 154   T* MOZ_OWNING_REF mRawPtr = nullptr;
 155
 156   // BEGIN Some things copied from RefPtr.
 157   // We cannot simply use a RefPtr member because we want to be trivial_abi,
 158   // which RefPtr is not.
 159   void assign_with_AddRef(T* aRawPtr) {
 160     if (aRawPtr) {
 161       ConstRemovingRefPtrTraits<T>::AddRef(aRawPtr);
 162     }
 163     assign_assuming_AddRef(aRawPtr);
 164   }
 165
 166   void assign_assuming_AddRef(T* aNewPtr) {
 167     T* oldPtr = mRawPtr;
 168     mRawPtr = aNewPtr;
 169     if (oldPtr) {
 170       ConstRemovingRefPtrTraits<T>::Release(oldPtr);
 171     }
 172   }
 173
 174   template <class U>
 175   struct ConstRemovingRefPtrTraits {
 176     static void AddRef(U* aPtr) { mozilla::RefPtrTraits<U>::AddRef(aPtr); }
 177     static void Release(U* aPtr) { mozilla::RefPtrTraits<U>::Release(aPtr); }
 178   };
 179   template <class U>
 180   struct ConstRemovingRefPtrTraits<const U> {
 181     static void AddRef(const U* aPtr) {
 182       mozilla::RefPtrTraits<U>::AddRef(const_cast<U*>(aPtr));
 183     }
 184     static void Release(const U* aPtr) {
 185       mozilla::RefPtrTraits<U>::Release(const_cast<U*>(aPtr));
 186     }
 187   };
 188   // END Some things copied from RefPtr.
 189
 190   SafeRefPtr(T* aRawPtr, mozilla::detail::InitialConstructionTag);
 191
 192  public:
 193   SafeRefPtr() = default;
 194
 195   template <typename U,
 196             typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
 197   MOZ_IMPLICIT SafeRefPtr(SafeRefPtr<U>&& aSrc) : mRawPtr(aSrc.mRawPtr) {
 198     aSrc.mRawPtr = nullptr;
 199   }
 200
 201   explicit SafeRefPtr(RefPtr<T>&& aRefPtr) : mRawPtr(aRefPtr.forget().take()) {}
 202
 203   // To prevent implicit conversion of raw pointer to RefPtr and then
 204   // calling the previous overload.
 205   SafeRefPtr(T* const aRawPtr) = delete;
 206
 207   SafeRefPtr(T* const aRawPtr, const AcquireStrongRefFromRawPtr&) {
 208     assign_with_AddRef(aRawPtr);
 209   }
 210
 211   MOZ_IMPLICIT SafeRefPtr(std::nullptr_t) {}
 212
 213   // Prevent implicit copying, use clonePtr() instead.
 214   SafeRefPtr(const SafeRefPtr&) = delete;
 215   SafeRefPtr& operator=(const SafeRefPtr&) = delete;
 216
 217   // Allow moving.
 218   SafeRefPtr(SafeRefPtr&& aOther) noexcept : mRawPtr(aOther.mRawPtr) {
 219     aOther.mRawPtr = nullptr;
 220   }
 221   SafeRefPtr& operator=(SafeRefPtr&& aOther) noexcept {
 222     assign_assuming_AddRef(aOther.forget().take());
 223     return *this;
 224   }
 225
 226   ~SafeRefPtr() {
 227     static_assert(!std::is_copy_constructible_v<T>);
 228     static_assert(!std::is_copy_assignable_v<T>);
 229     static_assert(!std::is_move_constructible_v<T>);
 230     static_assert(!std::is_move_assignable_v<T>);
 231
 232     if (mRawPtr) {
 233       ConstRemovingRefPtrTraits<T>::Release(mRawPtr);
 234     }
 235   }
 236
 237   typedef T element_type;
 238
 239   explicit operator bool() const { return mRawPtr; }
 240   bool operator!() const { return !mRawPtr; }
 241
 242   T& operator*() const&& = delete;
 243
 244   T& operator*() const& {
 245     MOZ_ASSERT(mRawPtr);
 246     return *mRawPtr;
 247   }
 248
 249   T* operator->() const&& = delete;
 250
 251   T* operator->() const& MOZ_NO_ADDREF_RELEASE_ON_RETURN {
 252     MOZ_ASSERT(mRawPtr);
 253     return mRawPtr;
 254   }
 255
 256   Maybe<T&> maybeDeref() const { return ToMaybeRef(mRawPtr); }
 257
 258   T* unsafeGetRawPtr() const { return mRawPtr; }
 259
 260   SafeRefPtr<T> clonePtr() const {
 261     return SafeRefPtr{mRawPtr, AcquireStrongRefFromRawPtr{}};
 262   }
 263
 264   already_AddRefed<T> forget() {
 265     auto* const res = mRawPtr;
 266     mRawPtr = nullptr;
 267     return dont_AddRef(res);
 268   }
 269
 270   bool operator==(const SafeRefPtr<T>& aOther) const {
 271     return mRawPtr == aOther.mRawPtr;
 272   }
 273
 274   bool operator!=(const SafeRefPtr<T>& aOther) const {
 275     return mRawPtr != aOther.mRawPtr;
 276   }
 277
 278   template <typename U, typename = std::enable_if_t<std::is_base_of_v<T, U>>>
 279   SafeRefPtr<U> downcast() && {
 280     SafeRefPtr<U> res;
 281     res.mRawPtr = static_cast<U*>(mRawPtr);
 282     mRawPtr = nullptr;
 283     return res;
 284   }
 285
 286   template <typename U>
 287   friend RefPtr<U> AsRefPtr(SafeRefPtr<U>&& aSafeRefPtr);
 288 };
 289
 290 template <typename T>
 291 SafeRefPtr(RefPtr<T>&&) -> SafeRefPtr<T>;
 292
 293 template <typename T>
 294 SafeRefPtr(already_AddRefed<T>&&) -> SafeRefPtr<T>;
 295
 296 template <typename T>
 297 class CheckedUnsafePtr;
 298
 299 template <typename T>
 300 SafeRefPtr(const CheckedUnsafePtr<T>&,
 301            const AcquireStrongRefFromRawPtr&) -> SafeRefPtr<T>;
 302
 303 template <typename T>
 304 SafeRefPtr<T>::SafeRefPtr(T* aRawPtr, detail::InitialConstructionTag)
 305     : mRawPtr(aRawPtr) {
 306   if (!std::is_base_of_v<detail::SafeRefCountedBase, T> && mRawPtr) {
 307     ConstRemovingRefPtrTraits<T>::AddRef(mRawPtr);
 308   }
 309 }
 310
 311 template <typename T>
 312 bool operator==(std::nullptr_t aLhs, const SafeRefPtr<T>& aRhs) {
 313   return !aRhs;
 314 }
 315
 316 template <typename T>
 317 bool operator!=(std::nullptr_t aLhs, const SafeRefPtr<T>& aRhs) {
 318   return static_cast<bool>(aRhs);
 319 }
 320
 321 template <typename T>
 322 bool operator==(const SafeRefPtr<T>& aLhs, std::nullptr_t aRhs) {
 323   return !aLhs;
 324 }
 325
 326 template <typename T>
 327 bool operator!=(const SafeRefPtr<T>& aLhs, std::nullptr_t aRhs) {
 328   return static_cast<bool>(aLhs);
 329 }
 330
 331 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 332 bool operator==(T* const aLhs, const SafeRefPtr<U>& aRhs) {
 333   return aLhs == aRhs.unsafeGetRawPtr();
 334 }
 335
 336 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 337 bool operator!=(T* const aLhs, const SafeRefPtr<U>& aRhs) {
 338   return !(aLhs == aRhs);
 339 }
 340
 341 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 342 bool operator==(const SafeRefPtr<T>& aLhs, U* const aRhs) {
 343   return aRhs == aLhs;
 344 }
 345
 346 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 347 bool operator!=(const SafeRefPtr<T>& aLhs, U* const aRhs) {
 348   return aRhs != aLhs;
 349 }
 350
 351 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 352 bool operator==(const Maybe<T&> aLhs, const SafeRefPtr<U>& aRhs) {
 353   return &aLhs.ref() == aRhs.unsafeGetRawPtr();
 354 }
 355
 356 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 357 bool operator!=(const Maybe<T&> aLhs, const SafeRefPtr<U>& aRhs) {
 358   return !(aLhs == aRhs);
 359 }
 360
 361 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 362 bool operator==(const SafeRefPtr<T>& aLhs, const Maybe<U&> aRhs) {
 363   return aRhs == aLhs;
 364 }
 365
 366 template <typename T, typename U, typename = std::common_type_t<T*, U*>>
 367 bool operator!=(const SafeRefPtr<T>& aLhs, const Maybe<U&> aRhs) {
 368   return aRhs != aLhs;
 369 }
 370
 371 template <typename T>
 372 RefPtr<T> AsRefPtr(SafeRefPtr<T>&& aSafeRefPtr) {
 373   return aSafeRefPtr.forget();
 374 }
 375
 376 template <typename T, typename... Args>
 377 SafeRefPtr<T> MakeSafeRefPtr(Args&&... aArgs) {
 378   return SafeRefPtr{new T(std::forward<Args>(aArgs)...),
 379                     detail::InitialConstructionTag{}};
 380 }
 381
 382 template <typename T>
 383 void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
 384                                  const SafeRefPtr<T>& aField, const char* aName,
 385                                  uint32_t aFlags = 0) {
 386   CycleCollectionNoteChild(aCallback, aField.unsafeGetRawPtr(), aName, aFlags);
 387 }
 388
 389 template <typename T>
 390 void ImplCycleCollectionUnlink(SafeRefPtr<T>& aField) {
 391   aField = nullptr;
 392 }
 393
 394 namespace detail {
 395
 396 template <typename T, RefCountAtomicity Atomicity>
 397 SafeRefPtr<T> SafeRefCounted<T, Atomicity>::SafeRefPtrFromThis() {
 398   // this actually is safe
 399   return {static_cast<T*>(this), AcquireStrongRefFromRawPtr{}};
 400 }
 401
 402 template <typename T>
 403 struct CopyablePtr<SafeRefPtr<T>> {
 404   SafeRefPtr<T> mPtr;
 405
 406   explicit CopyablePtr(SafeRefPtr<T> aPtr) : mPtr{std::move(aPtr)} {}
 407
 408   CopyablePtr(const CopyablePtr& aOther) : mPtr{aOther.mPtr.clonePtr()} {}
 409   CopyablePtr& operator=(const CopyablePtr& aOther) {
 410     if (this != &aOther) {
 411       mPtr = aOther.mPtr.clonePtr();
 412     }
 413     return *this;
 414   }
 415   CopyablePtr(CopyablePtr&&) = default;
 416   CopyablePtr& operator=(CopyablePtr&&) = default;
 417 };
 418
 419 }  // namespace detail
 420
 421 namespace dom {
 422 /// XXX Move this to BindingUtils.h later on
 423 template <class T, class S>
 424 inline RefPtr<T> StrongOrRawPtr(SafeRefPtr<S>&& aPtr) {
 425   return AsRefPtr(std::move(aPtr));
 426 }
 427
 428 }  // namespace dom
 429
 430 }  // namespace mozilla
 431
 432 template <class T>
 433 class nsTObserverArray<mozilla::SafeRefPtr<T>>
 434     : public nsAutoTObserverArray<mozilla::SafeRefPtr<T>, 0> {
 435  public:
 436   using base_type = nsAutoTObserverArray<mozilla::SafeRefPtr<T>, 0>;
 437   using size_type = nsTObserverArray_base::size_type;
 438
 439   // Initialization methods
 440   nsTObserverArray() = default;
 441
 442   // Initialize this array and pre-allocate some number of elements.
 443   explicit nsTObserverArray(size_type aCapacity) {
 444     base_type::mArray.SetCapacity(aCapacity);
 445   }
 446
 447   nsTObserverArray Clone() const {
 448     auto result = nsTObserverArray{};
 449     result.mArray = mozilla::TransformIntoNewArray(
 450         this->mArray, [](const auto& ptr) { return ptr.clonePtr(); });
 451     return result;
 452   }
 453 };
 454
 455 // Use MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED in a 'Class' derived from a
 456 // 'Super' class which derives from (Atomic)SafeRefCounted, and from some other
 457 // class using NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING.
 458 #if defined(NS_BUILD_REFCNT_LOGGING)
 459 #  define MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED(Class, Super)         \
 460     template <typename T, ::mozilla::detail::RefCountAtomicity Atomicity> \
 461     friend class ::mozilla::detail::SafeRefCounted;                       \
 462     NS_IMETHOD_(MozExternalRefCountType) AddRef() override {              \
 463       NS_IMPL_ADDREF_INHERITED_GUTS(Class, Super);                        \
 464     }                                                                     \
 465     NS_IMETHOD_(MozExternalRefCountType) Release() override {             \
 466       NS_IMPL_RELEASE_INHERITED_GUTS(Class, Super);                       \
 467     }
 468 #else  // NS_BUILD_REFCNT_LOGGING
 469 #  define MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED(Class, Super)         \
 470     template <typename T, ::mozilla::detail::RefCountAtomicity Atomicity> \
 471     friend class ::mozilla::detail::SafeRefCounted;                       \
 472     NS_IMETHOD_(MozExternalRefCountType) AddRef() override {              \
 473       return Super::AddRef();                                             \
 474     }                                                                     \
 475     NS_IMETHOD_(MozExternalRefCountType) Release() override {             \
 476       return Super::Release();                                            \
 477     }
 478 #endif
 479
 480 #endif