1 files changed, 315 insertions, 0 deletions
diff --git a/mfbt/UniquePtrExtensions.h b/mfbt/UniquePtrExtensions.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+/* Useful extensions to UniquePtr. */
+
+#ifndef mozilla_UniquePtrExtensions_h
+#define mozilla_UniquePtrExtensions_h
+
+#include <type_traits>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/fallible.h"
+#include "mozilla/UniquePtr.h"
+
+#ifdef XP_WIN
+#  include <cstdint>
+#endif
+#if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
+#  include <mach/mach.h>
+#endif
+
+namespace mozilla {
+
+/**
+ * MakeUniqueFallible works exactly like MakeUnique, except that the memory
+ * allocation performed is done fallibly, i.e. it can return nullptr.
+ */
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::SingleObject MakeUniqueFallible(
+    Args&&... aArgs) {
+  return UniquePtr<T>(new (fallible) T(std::forward<Args>(aArgs)...));
+}
+
+template <typename T>
+typename detail::UniqueSelector<T>::UnknownBound MakeUniqueFallible(
+    decltype(sizeof(int)) aN) {
+  using ArrayType = std::remove_extent_t<T>;
+  return UniquePtr<T>(new (fallible) ArrayType[aN]());
+}
+
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::KnownBound MakeUniqueFallible(
+    Args&&... aArgs) = delete;
+
+/**
+ * MakeUniqueForOverwrite and MakeUniqueFallibleForOverwrite are like MakeUnique
+ * and MakeUniqueFallible except they use default-initialization. This is
+ * useful, for example, when you have a POD type array that will be overwritten
+ * directly after construction and so zero-initialization is a waste.
+ */
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::SingleObject MakeUniqueForOverwrite() {
+  return UniquePtr<T>(new T);
+}
+
+template <typename T>
+typename detail::UniqueSelector<T>::UnknownBound MakeUniqueForOverwrite(
+    decltype(sizeof(int)) aN) {
+  using ArrayType = std::remove_extent_t<T>;
+  return UniquePtr<T>(new ArrayType[aN]);
+}
+
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::KnownBound MakeUniqueForOverwrite(
+    Args&&... aArgs) = delete;
+
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::SingleObject
+MakeUniqueForOverwriteFallible() {
+  return UniquePtr<T>(new (fallible) T);
+}
+
+template <typename T>
+typename detail::UniqueSelector<T>::UnknownBound MakeUniqueForOverwriteFallible(
+    decltype(sizeof(int)) aN) {
+  using ArrayType = std::remove_extent_t<T>;
+  return UniquePtr<T>(new (fallible) ArrayType[aN]);
+}
+
+template <typename T, typename... Args>
+typename detail::UniqueSelector<T>::KnownBound MakeUniqueForOverwriteFallible(
+    Args&&... aArgs) = delete;
+
+namespace detail {
+
+template <typename T>
+struct FreePolicy {
+  void operator()(const void* ptr) { free(const_cast<void*>(ptr)); }
+};
+
+#if defined(XP_WIN)
+// Can't include <windows.h> to get the actual definition of HANDLE
+// because of namespace pollution.
+typedef void* FileHandleType;
+#elif defined(XP_UNIX)
+typedef int FileHandleType;
+#else
+#  error "Unsupported OS?"
+#endif
+
+struct FileHandleHelper {
+  MOZ_IMPLICIT FileHandleHelper(FileHandleType aHandle) : mHandle(aHandle) {
+#if defined(XP_UNIX) && (defined(DEBUG) || defined(FUZZING))
+    MOZ_RELEASE_ASSERT(aHandle == kInvalidHandle || aHandle > 2);
+#endif
+  }
+
+  MOZ_IMPLICIT constexpr FileHandleHelper(std::nullptr_t)
+      : mHandle(kInvalidHandle) {}
+
+  bool operator!=(std::nullptr_t) const {
+#ifdef XP_WIN
+    // Windows uses both nullptr and INVALID_HANDLE_VALUE (-1 cast to
+    // HANDLE) in different situations, but nullptr is more reliably
+    // null while -1 is also valid input to some calls that take
+    // handles.  So class considers both to be null (since neither
+    // should be closed) but default-constructs as nullptr.
+    if (mHandle == (void*)-1) {
+      return false;
+    }
+#endif
+    return mHandle != kInvalidHandle;
+  }
+
+  operator FileHandleType() const { return mHandle; }
+
+#ifdef XP_WIN
+  // NSPR uses an integer type for PROsfd, so this conversion is
+  // provided for working with it without needing reinterpret casts
+  // everywhere.
+  operator std::intptr_t() const {
+    return reinterpret_cast<std::intptr_t>(mHandle);
+  }
+#endif
+
+  // When there's only one user-defined conversion operator, the
+  // compiler will use that to derive equality, but that doesn't work
+  // when the conversion is ambiguoug (the XP_WIN case above).
+  bool operator==(const FileHandleHelper& aOther) const {
+    return mHandle == aOther.mHandle;
+  }
+
+ private:
+  FileHandleType mHandle;
+
+#ifdef XP_WIN
+  // See above for why this is nullptr.  (Also, INVALID_HANDLE_VALUE
+  // can't be expressed as a constexpr.)
+  static constexpr FileHandleType kInvalidHandle = nullptr;
+#else
+  static constexpr FileHandleType kInvalidHandle = -1;
+#endif
+};
+
+struct FileHandleDeleter {
+  using pointer = FileHandleHelper;
+  using receiver = FileHandleType;
+  MFBT_API void operator()(FileHandleHelper aHelper);
+};
+
+#if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
+struct MachPortHelper {
+  MOZ_IMPLICIT MachPortHelper(mach_port_t aPort) : mPort(aPort) {}
+
+  MOZ_IMPLICIT constexpr MachPortHelper(std::nullptr_t)
+      : mPort(MACH_PORT_NULL) {}
+
+  bool operator!=(std::nullptr_t) const { return mPort != MACH_PORT_NULL; }
+
+  operator const mach_port_t&() const { return mPort; }
+  operator mach_port_t&() { return mPort; }
+
+ private:
+  mach_port_t mPort;
+};
+
+struct MachSendRightDeleter {
+  using pointer = MachPortHelper;
+  using receiver = mach_port_t;
+  MFBT_API void operator()(MachPortHelper aHelper) {
+    DebugOnly<kern_return_t> kr =
+        mach_port_deallocate(mach_task_self(), aHelper);
+    MOZ_ASSERT(kr == KERN_SUCCESS, "failed to deallocate mach send right");
+  }
+};
+
+struct MachReceiveRightDeleter {
+  using pointer = MachPortHelper;
+  using receiver = mach_port_t;
+  MFBT_API void operator()(MachPortHelper aHelper) {
+    DebugOnly<kern_return_t> kr = mach_port_mod_refs(
+        mach_task_self(), aHelper, MACH_PORT_RIGHT_RECEIVE, -1);
+    MOZ_ASSERT(kr == KERN_SUCCESS, "failed to release mach receive right");
+  }
+};
+
+struct MachPortSetDeleter {
+  using pointer = MachPortHelper;
+  using receiver = mach_port_t;
+  MFBT_API void operator()(MachPortHelper aHelper) {
+    DebugOnly<kern_return_t> kr = mach_port_mod_refs(
+        mach_task_self(), aHelper, MACH_PORT_RIGHT_PORT_SET, -1);
+    MOZ_ASSERT(kr == KERN_SUCCESS, "failed to release mach port set");
+  }
+};
+#endif
+
+}  // namespace detail
+
+template <typename T>
+using UniqueFreePtr = UniquePtr<T, detail::FreePolicy<T>>;
+
+// A RAII class for the OS construct used for open files and similar
+// objects: a file descriptor on Unix or a handle on Windows.
+using UniqueFileHandle =
+    UniquePtr<detail::FileHandleType, detail::FileHandleDeleter>;
+
+#if defined(XP_DARWIN) && !defined(RUST_BINDGEN)
+// A RAII class for a Mach port that names a send right.
+using UniqueMachSendRight =
+    UniquePtr<mach_port_t, detail::MachSendRightDeleter>;
+// A RAII class for a Mach port that names a receive right.
+using UniqueMachReceiveRight =
+    UniquePtr<mach_port_t, detail::MachReceiveRightDeleter>;
+// A RAII class for a Mach port set.
+using UniqueMachPortSet = UniquePtr<mach_port_t, detail::MachPortSetDeleter>;
+
+// Increases the user reference count for MACH_PORT_RIGHT_SEND by 1 and returns
+// a new UniqueMachSendRight to manage the additional right.
+inline UniqueMachSendRight RetainMachSendRight(mach_port_t aPort) {
+  kern_return_t kr =
+      mach_port_mod_refs(mach_task_self(), aPort, MACH_PORT_RIGHT_SEND, 1);
+  if (kr == KERN_SUCCESS) {
+    return UniqueMachSendRight(aPort);
+  }
+  return nullptr;
+}
+#endif
+
+namespace detail {
+
+struct HasReceiverTypeHelper {
+  template <class U>
+  static double Test(...);
+  template <class U>
+  static char Test(typename U::receiver* = 0);
+};
+
+template <class T>
+class HasReceiverType
+    : public std::integral_constant<bool, sizeof(HasReceiverTypeHelper::Test<T>(
+                                              0)) == 1> {};
+
+template <class T, class D, bool = HasReceiverType<D>::value>
+struct ReceiverTypeImpl {
+  using Type = typename D::receiver;
+};
+
+template <class T, class D>
+struct ReceiverTypeImpl<T, D, false> {
+  using Type = typename PointerType<T, D>::Type;
+};
+
+template <class T, class D>
+struct ReceiverType {
+  using Type = typename ReceiverTypeImpl<T, std::remove_reference_t<D>>::Type;
+};
+
+template <typename T, typename D>
+class MOZ_TEMPORARY_CLASS UniquePtrGetterTransfers {
+ public:
+  using Ptr = UniquePtr<T, D>;
+  using Receiver = typename detail::ReceiverType<T, D>::Type;
+
+  explicit UniquePtrGetterTransfers(Ptr& p)
+      : mPtr(p), mReceiver(typename Ptr::Pointer(nullptr)) {}
+  ~UniquePtrGetterTransfers() { mPtr.reset(mReceiver); }
+
+  operator Receiver*() { return &mReceiver; }
+  Receiver& operator*() { return mReceiver; }
+
+  // operator void** is conditionally enabled if `Receiver` is a pointer.
+  template <typename U = Receiver,
+            std::enable_if_t<
+                std::is_pointer_v<U> && std::is_same_v<U, Receiver>, int> = 0>
+  operator void**() {
+    return reinterpret_cast<void**>(&mReceiver);
+  }
+
+ private:
+  Ptr& mPtr;
+  Receiver mReceiver;
+};
+
+}  // namespace detail
+
+// Helper for passing a UniquePtr to an old-style function that uses raw
+// pointers for out params. Example usage:
+//
+//   void AllocateFoo(Foo** out) { *out = new Foo(); }
+//   UniquePtr<Foo> foo;
+//   AllocateFoo(getter_Transfers(foo));
+template <typename T, typename D>
+auto getter_Transfers(UniquePtr<T, D>& up) {
+  return detail::UniquePtrGetterTransfers<T, D>(up);
+}
+
+}  // namespace mozilla
+
+#endif  // mozilla_UniquePtrExtensions_h