mfbt/UniquePtrExtensions.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 /* Useful extensions to UniquePtr. */
   8
   9 #ifndef mozilla_UniquePtrExtensions_h
  10 #define mozilla_UniquePtrExtensions_h
  11
  12 #include <type_traits>
  13
  14 #include "mozilla/Attributes.h"
  15 #include "mozilla/DebugOnly.h"
  16 #include "mozilla/fallible.h"
  17 #include "mozilla/UniquePtr.h"
  18
  19 #ifdef XP_WIN
  20 #  include <cstdint>
  21 #endif
  22 #if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
  23 #  include <mach/mach.h>
  24 #endif
  25
  26 namespace mozilla {
  27
  28 /**
  29  * MakeUniqueFallible works exactly like MakeUnique, except that the memory
  30  * allocation performed is done fallibly, i.e. it can return nullptr.
  31  */
  32 template <typename T, typename... Args>
  33 typename detail::UniqueSelector<T>::SingleObject MakeUniqueFallible(
  34     Args&&... aArgs) {
  35   return UniquePtr<T>(new (fallible) T(std::forward<Args>(aArgs)...));
  36 }
  37
  38 template <typename T>
  39 typename detail::UniqueSelector<T>::UnknownBound MakeUniqueFallible(
  40     decltype(sizeof(int)) aN) {
  41   using ArrayType = std::remove_extent_t<T>;
  42   return UniquePtr<T>(new (fallible) ArrayType[aN]());
  43 }
  44
  45 template <typename T, typename... Args>
  46 typename detail::UniqueSelector<T>::KnownBound MakeUniqueFallible(
  47     Args&&... aArgs) = delete;
  48
  49 /**
  50  * MakeUniqueForOverwrite and MakeUniqueFallibleForOverwrite are like MakeUnique
  51  * and MakeUniqueFallible except they use default-initialization. This is
  52  * useful, for example, when you have a POD type array that will be overwritten
  53  * directly after construction and so zero-initialization is a waste.
  54  */
  55 template <typename T, typename... Args>
  56 typename detail::UniqueSelector<T>::SingleObject MakeUniqueForOverwrite() {
  57   return UniquePtr<T>(new T);
  58 }
  59
  60 template <typename T>
  61 typename detail::UniqueSelector<T>::UnknownBound MakeUniqueForOverwrite(
  62     decltype(sizeof(int)) aN) {
  63   using ArrayType = std::remove_extent_t<T>;
  64   return UniquePtr<T>(new ArrayType[aN]);
  65 }
  66
  67 template <typename T, typename... Args>
  68 typename detail::UniqueSelector<T>::KnownBound MakeUniqueForOverwrite(
  69     Args&&... aArgs) = delete;
  70
  71 template <typename T, typename... Args>
  72 typename detail::UniqueSelector<T>::SingleObject
  73 MakeUniqueForOverwriteFallible() {
  74   return UniquePtr<T>(new (fallible) T);
  75 }
  76
  77 template <typename T>
  78 typename detail::UniqueSelector<T>::UnknownBound MakeUniqueForOverwriteFallible(
  79     decltype(sizeof(int)) aN) {
  80   using ArrayType = std::remove_extent_t<T>;
  81   return UniquePtr<T>(new (fallible) ArrayType[aN]);
  82 }
  83
  84 template <typename T, typename... Args>
  85 typename detail::UniqueSelector<T>::KnownBound MakeUniqueForOverwriteFallible(
  86     Args&&... aArgs) = delete;
  87
  88 namespace detail {
  89
  90 template <typename T>
  91 struct FreePolicy {
  92   void operator()(const void* ptr) { free(const_cast<void*>(ptr)); }
  93 };
  94
  95 #if defined(XP_WIN)
  96 // Can't include <windows.h> to get the actual definition of HANDLE
  97 // because of namespace pollution.
  98 typedef void* FileHandleType;
  99 #elif defined(XP_UNIX)
 100 typedef int FileHandleType;
 101 #else
 102 #  error "Unsupported OS?"
 103 #endif
 104
 105 struct FileHandleHelper {
 106   MOZ_IMPLICIT FileHandleHelper(FileHandleType aHandle) : mHandle(aHandle) {}
 107
 108   MOZ_IMPLICIT constexpr FileHandleHelper(std::nullptr_t)
 109       : mHandle(kInvalidHandle) {}
 110
 111   bool operator!=(std::nullptr_t) const {
 112 #ifdef XP_WIN
 113     // Windows uses both nullptr and INVALID_HANDLE_VALUE (-1 cast to
 114     // HANDLE) in different situations, but nullptr is more reliably
 115     // null while -1 is also valid input to some calls that take
 116     // handles.  So class considers both to be null (since neither
 117     // should be closed) but default-constructs as nullptr.
 118     if (mHandle == (void*)-1) {
 119       return false;
 120     }
 121 #endif
 122     return mHandle != kInvalidHandle;
 123   }
 124
 125   operator FileHandleType() const { return mHandle; }
 126
 127 #ifdef XP_WIN
 128   // NSPR uses an integer type for PROsfd, so this conversion is
 129   // provided for working with it without needing reinterpret casts
 130   // everywhere.
 131   operator std::intptr_t() const {
 132     return reinterpret_cast<std::intptr_t>(mHandle);
 133   }
 134 #endif
 135
 136   // When there's only one user-defined conversion operator, the
 137   // compiler will use that to derive equality, but that doesn't work
 138   // when the conversion is ambiguoug (the XP_WIN case above).
 139   bool operator==(const FileHandleHelper& aOther) const {
 140     return mHandle == aOther.mHandle;
 141   }
 142
 143  private:
 144   FileHandleType mHandle;
 145
 146 #ifdef XP_WIN
 147   // See above for why this is nullptr.  (Also, INVALID_HANDLE_VALUE
 148   // can't be expressed as a constexpr.)
 149   static constexpr FileHandleType kInvalidHandle = nullptr;
 150 #else
 151   static constexpr FileHandleType kInvalidHandle = -1;
 152 #endif
 153 };
 154
 155 struct FileHandleDeleter {
 156   using pointer = FileHandleHelper;
 157   using receiver = FileHandleType;
 158   MFBT_API void operator()(FileHandleHelper aHelper);
 159 };
 160
 161 #if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
 162 struct MachPortHelper {
 163   MOZ_IMPLICIT MachPortHelper(mach_port_t aPort) : mPort(aPort) {}
 164
 165   MOZ_IMPLICIT constexpr MachPortHelper(std::nullptr_t)
 166       : mPort(MACH_PORT_NULL) {}
 167
 168   bool operator!=(std::nullptr_t) const { return mPort != MACH_PORT_NULL; }
 169
 170   operator const mach_port_t&() const { return mPort; }
 171   operator mach_port_t&() { return mPort; }
 172
 173  private:
 174   mach_port_t mPort;
 175 };
 176
 177 struct MachSendRightDeleter {
 178   using pointer = MachPortHelper;
 179   using receiver = mach_port_t;
 180   MFBT_API void operator()(MachPortHelper aHelper) {
 181     DebugOnly<kern_return_t> kr =
 182         mach_port_deallocate(mach_task_self(), aHelper);
 183     MOZ_ASSERT(kr == KERN_SUCCESS, "failed to deallocate mach send right");
 184   }
 185 };
 186
 187 struct MachReceiveRightDeleter {
 188   using pointer = MachPortHelper;
 189   using receiver = mach_port_t;
 190   MFBT_API void operator()(MachPortHelper aHelper) {
 191     DebugOnly<kern_return_t> kr = mach_port_mod_refs(
 192         mach_task_self(), aHelper, MACH_PORT_RIGHT_RECEIVE, -1);
 193     MOZ_ASSERT(kr == KERN_SUCCESS, "failed to release mach receive right");
 194   }
 195 };
 196
 197 struct MachPortSetDeleter {
 198   using pointer = MachPortHelper;
 199   using receiver = mach_port_t;
 200   MFBT_API void operator()(MachPortHelper aHelper) {
 201     DebugOnly<kern_return_t> kr = mach_port_mod_refs(
 202         mach_task_self(), aHelper, MACH_PORT_RIGHT_PORT_SET, -1);
 203     MOZ_ASSERT(kr == KERN_SUCCESS, "failed to release mach port set");
 204   }
 205 };
 206 #endif
 207
 208 }  // namespace detail
 209
 210 template <typename T>
 211 using UniqueFreePtr = UniquePtr<T, detail::FreePolicy<T>>;
 212
 213 // A RAII class for the OS construct used for open files and similar
 214 // objects: a file descriptor on Unix or a handle on Windows.
 215 using UniqueFileHandle =
 216     UniquePtr<detail::FileHandleType, detail::FileHandleDeleter>;
 217
 218 #if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
 219 // A RAII class for a Mach port that names a send right.
 220 using UniqueMachSendRight =
 221     UniquePtr<mach_port_t, detail::MachSendRightDeleter>;
 222 // A RAII class for a Mach port that names a receive right.
 223 using UniqueMachReceiveRight =
 224     UniquePtr<mach_port_t, detail::MachReceiveRightDeleter>;
 225 // A RAII class for a Mach port set.
 226 using UniqueMachPortSet = UniquePtr<mach_port_t, detail::MachPortSetDeleter>;
 227
 228 // Increases the user reference count for MACH_PORT_RIGHT_SEND by 1 and returns
 229 // a new UniqueMachSendRight to manage the additional right.
 230 inline UniqueMachSendRight RetainMachSendRight(mach_port_t aPort) {
 231   kern_return_t kr =
 232       mach_port_mod_refs(mach_task_self(), aPort, MACH_PORT_RIGHT_SEND, 1);
 233   if (kr == KERN_SUCCESS) {
 234     return UniqueMachSendRight(aPort);
 235   }
 236   return nullptr;
 237 }
 238 #endif
 239
 240 namespace detail {
 241
 242 struct HasReceiverTypeHelper {
 243   template <class U>
 244   static double Test(...);
 245   template <class U>
 246   static char Test(typename U::receiver* = 0);
 247 };
 248
 249 template <class T>
 250 class HasReceiverType
 251     : public std::integral_constant<bool, sizeof(HasReceiverTypeHelper::Test<T>(
 252                                               0)) == 1> {};
 253
 254 template <class T, class D, bool = HasReceiverType<D>::value>
 255 struct ReceiverTypeImpl {
 256   using Type = typename D::receiver;
 257 };
 258
 259 template <class T, class D>
 260 struct ReceiverTypeImpl<T, D, false> {
 261   using Type = typename PointerType<T, D>::Type;
 262 };
 263
 264 template <class T, class D>
 265 struct ReceiverType {
 266   using Type = typename ReceiverTypeImpl<T, std::remove_reference_t<D>>::Type;
 267 };
 268
 269 template <typename T, typename D>
 270 class MOZ_TEMPORARY_CLASS UniquePtrGetterTransfers {
 271  public:
 272   using Ptr = UniquePtr<T, D>;
 273   using Receiver = typename detail::ReceiverType<T, D>::Type;
 274
 275   explicit UniquePtrGetterTransfers(Ptr& p)
 276       : mPtr(p), mReceiver(typename Ptr::Pointer(nullptr)) {}
 277   ~UniquePtrGetterTransfers() { mPtr.reset(mReceiver); }
 278
 279   operator Receiver*() { return &mReceiver; }
 280   Receiver& operator*() { return mReceiver; }
 281
 282   // operator void** is conditionally enabled if `Receiver` is a pointer.
 283   template <typename U = Receiver,
 284             std::enable_if_t<
 285                 std::is_pointer_v<U> && std::is_same_v<U, Receiver>, int> = 0>
 286   operator void**() {
 287     return reinterpret_cast<void**>(&mReceiver);
 288   }
 289
 290  private:
 291   Ptr& mPtr;
 292   Receiver mReceiver;
 293 };
 294
 295 }  // namespace detail
 296
 297 // Helper for passing a UniquePtr to an old-style function that uses raw
 298 // pointers for out params. Example usage:
 299 //
 300 //   void AllocateFoo(Foo** out) { *out = new Foo(); }
 301 //   UniquePtr<Foo> foo;
 302 //   AllocateFoo(getter_Transfers(foo));
 303 template <typename T, typename D>
 304 auto getter_Transfers(UniquePtr<T, D>& up) {
 305   return detail::UniquePtrGetterTransfers<T, D>(up);
 306 }
 307
 308 }  // namespace mozilla
 309
 310 #endif  // mozilla_UniquePtrExtensions_h