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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/Attributes.h"
#include "mozilla/fallible.h"
#include "mozilla/UniquePtr.h"
#ifdef XP_WIN
# include <cstdint>
#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) {}
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 {
typedef FileHandleHelper pointer;
MFBT_API void operator()(FileHandleHelper aHelper);
};
} // 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>;
// 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) {
class MOZ_TEMPORARY_CLASS UniquePtrGetterTransfers {
public:
using Ptr = UniquePtr<T, D>;
explicit UniquePtrGetterTransfers(Ptr& p) : mPtr(p) {}
~UniquePtrGetterTransfers() { mPtr.reset(mRawPtr); }
operator typename Ptr::ElementType **() { return &mRawPtr; }
operator void**() { return reinterpret_cast<void**>(&mRawPtr); }
typename Ptr::ElementType*& operator*() { return mRawPtr; }
private:
Ptr& mPtr;
typename Ptr::Pointer mRawPtr = nullptr;
};
return UniquePtrGetterTransfers(up);
}
} // namespace mozilla
#endif // mozilla_UniquePtrExtensions_h
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