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PiperOrigin-RevId: 237361882
Change-Id: I109a68f44db867b20f8c6a7732b0ce657133e52a

quic/core/quic_arena_scoped_ptr.h

diff --git a/quic/core/quic_arena_scoped_ptr.h b/quic/core/quic_arena_scoped_ptr.h
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+++ b/quic/core/quic_arena_scoped_ptr.h
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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 "base/macros.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_aligned.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_logging.h"
+
+namespace quic {
+
+template <typename T>
+class QuicArenaScopedPtr {
+  static_assert(QUIC_ALIGN_OF(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();
+    }
+  }
+  DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(value) & kFromArenaMask);
+  value_ = value;
+}
+
+template <typename T>
+QuicArenaScopedPtr<T>::QuicArenaScopedPtr(void* value, ConstructFrom from_arena)
+    : value_(value) {
+  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_