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// Copyright (c) 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// unique_ptr-style pointer that stores values that may be from an arena. Takes
// up the same storage as the platform's native pointer type. Takes ownership
// of the value it's constructed with; if holding a value in an arena, and the
// type has a non-trivial destructor, the arena must outlive the
// QuicArenaScopedPtr. Does not support array overloads.
#ifndef QUICHE_QUIC_CORE_QUIC_ARENA_SCOPED_PTR_H_
#define QUICHE_QUIC_CORE_QUIC_ARENA_SCOPED_PTR_H_
#include <cstdint> // for uintptr_t
#include "quiche/quic/platform/api/quic_export.h"
#include "quiche/quic/platform/api/quic_logging.h"
namespace quic {
template <typename T>
class QUIC_NO_EXPORT QuicArenaScopedPtr {
static_assert(alignof(T*) > 1,
"QuicArenaScopedPtr can only store objects that are aligned to "
"greater than 1 byte.");
public:
// Constructs an empty QuicArenaScopedPtr.
QuicArenaScopedPtr();
// Constructs a QuicArenaScopedPtr referencing the heap-allocated memory
// provided.
explicit QuicArenaScopedPtr(T* value);
template <typename U>
QuicArenaScopedPtr(QuicArenaScopedPtr<U>&& other); // NOLINT
template <typename U>
QuicArenaScopedPtr& operator=(QuicArenaScopedPtr<U>&& other);
~QuicArenaScopedPtr();
// Returns a pointer to the value.
T* get() const;
// Returns a reference to the value.
T& operator*() const;
// Returns a pointer to the value.
T* operator->() const;
// Swaps the value of this pointer with |other|.
void swap(QuicArenaScopedPtr& other);
// Resets the held value to |value|.
void reset(T* value = nullptr);
// Returns true if |this| came from an arena. Primarily exposed for testing
// and assertions.
bool is_from_arena();
private:
// Friends with other derived types of QuicArenaScopedPtr, to support the
// derived-types case.
template <typename U>
friend class QuicArenaScopedPtr;
// Also befriend all known arenas, only to prevent misuse.
template <uint32_t ArenaSize>
friend class QuicOneBlockArena;
// Tag to denote that a QuicArenaScopedPtr is being explicitly created by an
// arena.
enum class ConstructFrom { kHeap, kArena };
// Constructs a QuicArenaScopedPtr with the given representation.
QuicArenaScopedPtr(void* value, ConstructFrom from);
QuicArenaScopedPtr(const QuicArenaScopedPtr&) = delete;
QuicArenaScopedPtr& operator=(const QuicArenaScopedPtr&) = delete;
// Low-order bits of value_ that determine if the pointer came from an arena.
static const uintptr_t kFromArenaMask = 0x1;
// Every platform we care about has at least 4B aligned integers, so store the
// is_from_arena bit in the least significant bit.
void* value_;
};
template <typename T>
bool operator==(const QuicArenaScopedPtr<T>& left,
const QuicArenaScopedPtr<T>& right) {
return left.get() == right.get();
}
template <typename T>
bool operator!=(const QuicArenaScopedPtr<T>& left,
const QuicArenaScopedPtr<T>& right) {
return left.get() != right.get();
}
template <typename T>
bool operator==(std::nullptr_t, const QuicArenaScopedPtr<T>& right) {
return nullptr == right.get();
}
template <typename T>
bool operator!=(std::nullptr_t, const QuicArenaScopedPtr<T>& right) {
return nullptr != right.get();
}
template <typename T>
bool operator==(const QuicArenaScopedPtr<T>& left, std::nullptr_t) {
return left.get() == nullptr;
}
template <typename T>
bool operator!=(const QuicArenaScopedPtr<T>& left, std::nullptr_t) {
return left.get() != nullptr;
}
template <typename T>
QuicArenaScopedPtr<T>::QuicArenaScopedPtr() : value_(nullptr) {}
template <typename T>
QuicArenaScopedPtr<T>::QuicArenaScopedPtr(T* value)
: QuicArenaScopedPtr(value, ConstructFrom::kHeap) {}
template <typename T>
template <typename U>
QuicArenaScopedPtr<T>::QuicArenaScopedPtr(QuicArenaScopedPtr<U>&& other)
: value_(other.value_) {
static_assert(
std::is_base_of<T, U>::value || std::is_same<T, U>::value,
"Cannot construct QuicArenaScopedPtr; type is not derived or same.");
other.value_ = nullptr;
}
template <typename T>
template <typename U>
QuicArenaScopedPtr<T>& QuicArenaScopedPtr<T>::operator=(
QuicArenaScopedPtr<U>&& other) {
static_assert(
std::is_base_of<T, U>::value || std::is_same<T, U>::value,
"Cannot assign QuicArenaScopedPtr; type is not derived or same.");
swap(other);
return *this;
}
template <typename T>
QuicArenaScopedPtr<T>::~QuicArenaScopedPtr() {
reset();
}
template <typename T>
T* QuicArenaScopedPtr<T>::get() const {
return reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(value_) &
~kFromArenaMask);
}
template <typename T>
T& QuicArenaScopedPtr<T>::operator*() const {
return *get();
}
template <typename T>
T* QuicArenaScopedPtr<T>::operator->() const {
return get();
}
template <typename T>
void QuicArenaScopedPtr<T>::swap(QuicArenaScopedPtr& other) {
using std::swap;
swap(value_, other.value_);
}
template <typename T>
bool QuicArenaScopedPtr<T>::is_from_arena() {
return (reinterpret_cast<uintptr_t>(value_) & kFromArenaMask) != 0;
}
template <typename T>
void QuicArenaScopedPtr<T>::reset(T* value) {
if (value_ != nullptr) {
if (is_from_arena()) {
// Manually invoke the destructor.
get()->~T();
} else {
delete get();
}
}
QUICHE_DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(value) & kFromArenaMask);
value_ = value;
}
template <typename T>
QuicArenaScopedPtr<T>::QuicArenaScopedPtr(void* value, ConstructFrom from_arena)
: value_(value) {
QUICHE_DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(value_) & kFromArenaMask);
switch (from_arena) {
case ConstructFrom::kHeap:
break;
case ConstructFrom::kArena:
value_ = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(value_) |
QuicArenaScopedPtr<T>::kFromArenaMask);
break;
}
}
} // namespace quic
#endif // QUICHE_QUIC_CORE_QUIC_ARENA_SCOPED_PTR_H_
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