. /include/boost/corosio /detail /intrusive.hpp
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1   // 1   //
2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com) 2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3   // 3   //
4   // Distributed under the Boost Software License, Version 1.0. (See accompanying 4   // Distributed under the Boost Software License, Version 1.0. (See accompanying
5   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 5   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   // 6   //
7   // Official repository: https://github.com/cppalliance/corosio 7   // Official repository: https://github.com/cppalliance/corosio
8   // 8   //
9   9  
10   #ifndef BOOST_COROSIO_DETAIL_INTRUSIVE_HPP 10   #ifndef BOOST_COROSIO_DETAIL_INTRUSIVE_HPP
11   #define BOOST_COROSIO_DETAIL_INTRUSIVE_HPP 11   #define BOOST_COROSIO_DETAIL_INTRUSIVE_HPP
12   12  
13   namespace boost::corosio::detail { 13   namespace boost::corosio::detail {
14   14  
15   /** An intrusive doubly linked list. 15   /** An intrusive doubly linked list.
16   16  
17   This container provides O(1) push and pop operations for 17   This container provides O(1) push and pop operations for
18   elements that derive from @ref node. Elements are not 18   elements that derive from @ref node. Elements are not
19   copied or moved; they are linked directly into the list. 19   copied or moved; they are linked directly into the list.
20   20  
21   @tparam T The element type. Must derive from `intrusive_list<T>::node`. 21   @tparam T The element type. Must derive from `intrusive_list<T>::node`.
22   */ 22   */
23   template<class T> 23   template<class T>
24   class intrusive_list 24   class intrusive_list
25   { 25   {
26   public: 26   public:
27   /** Base class for list elements. 27   /** Base class for list elements.
28   28  
29   Derive from this class to make a type usable with 29   Derive from this class to make a type usable with
30   @ref intrusive_list. The `next_` and `prev_` pointers 30   @ref intrusive_list. The `next_` and `prev_` pointers
31   are private and accessible only to the list. 31   are private and accessible only to the list.
32   */ 32   */
33   class node 33   class node
34   { 34   {
35   friend class intrusive_list; 35   friend class intrusive_list;
36   36  
37   private: 37   private:
38   T* next_; 38   T* next_;
39   T* prev_; 39   T* prev_;
40   }; 40   };
41   41  
42   private: 42   private:
43   T* head_ = nullptr; 43   T* head_ = nullptr;
44   T* tail_ = nullptr; 44   T* tail_ = nullptr;
45   45  
46   public: 46   public:
HITCBC 47   6327 intrusive_list() = default; 47   6327 intrusive_list() = default;
48   48  
49   intrusive_list(intrusive_list&& other) noexcept 49   intrusive_list(intrusive_list&& other) noexcept
50   : head_(other.head_) 50   : head_(other.head_)
51   , tail_(other.tail_) 51   , tail_(other.tail_)
52   { 52   {
53   other.head_ = nullptr; 53   other.head_ = nullptr;
54   other.tail_ = nullptr; 54   other.tail_ = nullptr;
55   } 55   }
56   56  
57   intrusive_list(intrusive_list const&) = delete; 57   intrusive_list(intrusive_list const&) = delete;
58   intrusive_list& operator=(intrusive_list const&) = delete; 58   intrusive_list& operator=(intrusive_list const&) = delete;
59   intrusive_list& operator=(intrusive_list&&) = delete; 59   intrusive_list& operator=(intrusive_list&&) = delete;
60   60  
HITCBC 61   32 bool empty() const noexcept 61   32 bool empty() const noexcept
62   { 62   {
HITCBC 63   32 return head_ == nullptr; 63   32 return head_ == nullptr;
64   } 64   }
65   65  
HITCBC 66   26608 void push_back(T* w) noexcept 66   19929 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   26608 auto* n = static_cast<node*>(w); 68   19929 auto* n = static_cast<node*>(w);
HITCBC 69   26608 n->next_ = nullptr; 69   19929 n->next_ = nullptr;
HITCBC 70   26608 n->prev_ = tail_; 70   19929 n->prev_ = tail_;
HITCBC 71   26608 if (tail_) 71   19929 if (tail_)
HITCBC 72   15120 static_cast<node*>(tail_)->next_ = w; 72   11114 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   11488 head_ = w; 74   8815 head_ = w;
HITCBC 75   26608 tail_ = w; 75   19929 tail_ = w;
HITCBC 76   26608 } 76   19929 }
77   77  
78   void splice_back(intrusive_list& other) noexcept 78   void splice_back(intrusive_list& other) noexcept
79   { 79   {
80   if (other.empty()) 80   if (other.empty())
81   return; 81   return;
82   if (tail_) 82   if (tail_)
83   { 83   {
84   static_cast<node*>(tail_)->next_ = other.head_; 84   static_cast<node*>(tail_)->next_ = other.head_;
85   static_cast<node*>(other.head_)->prev_ = tail_; 85   static_cast<node*>(other.head_)->prev_ = tail_;
86   tail_ = other.tail_; 86   tail_ = other.tail_;
87   } 87   }
88   else 88   else
89   { 89   {
90   head_ = other.head_; 90   head_ = other.head_;
91   tail_ = other.tail_; 91   tail_ = other.tail_;
92   } 92   }
93   other.head_ = nullptr; 93   other.head_ = nullptr;
94   other.tail_ = nullptr; 94   other.tail_ = nullptr;
95   } 95   }
96   96  
HITCBC 97   168336 T* pop_front() noexcept 97   184470 T* pop_front() noexcept
98   { 98   {
HITCBC 99   168336 if (!head_) 99   184470 if (!head_)
HITCBC 100   157464 return nullptr; 100   176270 return nullptr;
HITCBC 101   10872 T* w = head_; 101   8200 T* w = head_;
HITCBC 102   10872 head_ = static_cast<node*>(head_)->next_; 102   8200 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   10872 if (head_) 103   8200 if (head_)
HITCBC 104   40 static_cast<node*>(head_)->prev_ = nullptr; 104   41 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   10832 tail_ = nullptr; 106   8159 tail_ = nullptr;
107   // Defensive: clear stale linkage so remove() on a 107   // Defensive: clear stale linkage so remove() on a
108   // popped node cannot corrupt the list. 108   // popped node cannot corrupt the list.
HITCBC 109   10872 auto* n = static_cast<node*>(w); 109   8200 auto* n = static_cast<node*>(w);
HITCBC 110   10872 n->next_ = nullptr; 110   8200 n->next_ = nullptr;
HITCBC 111   10872 n->prev_ = nullptr; 111   8200 n->prev_ = nullptr;
HITCBC 112   10872 return w; 112   8200 return w;
113   } 113   }
114   114  
HITCBC 115   15736 void remove(T* w) noexcept 115   11729 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   15736 auto* n = static_cast<node*>(w); 117   11729 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   15736 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   11729 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   15736 if (n->prev_) 121   11729 if (n->prev_)
HITCBC 122   5012 static_cast<node*>(n->prev_)->next_ = n->next_; 122   3675 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   10724 head_ = n->next_; 124   8054 head_ = n->next_;
HITCBC 125   15736 if (n->next_) 125   11729 if (n->next_)
HITCBC 126   10102 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   7432 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   5634 tail_ = n->prev_; 128   4297 tail_ = n->prev_;
HITCBC 129   15736 n->next_ = nullptr; 129   11729 n->next_ = nullptr;
HITCBC 130   15736 n->prev_ = nullptr; 130   11729 n->prev_ = nullptr;
131   } 131   }
132   132  
133   /// Invoke @p f for each element in the list. 133   /// Invoke @p f for each element in the list.
134   template<class F> 134   template<class F>
HITCBC 135   67 void for_each(F f) 135   67 void for_each(F f)
136   { 136   {
HITCBC 137   67 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 137   67 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 138   ✗ f(p); 138   ✗ f(p);
HITCBC 139   67 } 139   67 }
140   }; 140   };
141   141  
142   /** An intrusive singly linked FIFO queue. 142   /** An intrusive singly linked FIFO queue.
143   143  
144   This container provides O(1) push and pop operations for 144   This container provides O(1) push and pop operations for
145   elements that derive from @ref node. Elements are not 145   elements that derive from @ref node. Elements are not
146   copied or moved; they are linked directly into the queue. 146   copied or moved; they are linked directly into the queue.
147   147  
148   Unlike @ref intrusive_list, this uses only a single `next_` 148   Unlike @ref intrusive_list, this uses only a single `next_`
149   pointer per node, saving memory at the cost of not supporting 149   pointer per node, saving memory at the cost of not supporting
150   O(1) removal of arbitrary elements. 150   O(1) removal of arbitrary elements.
151   151  
152   @tparam T The element type. Must derive from `intrusive_queue<T>::node`. 152   @tparam T The element type. Must derive from `intrusive_queue<T>::node`.
153   */ 153   */
154   template<class T> 154   template<class T>
155   class intrusive_queue 155   class intrusive_queue
156   { 156   {
157   public: 157   public:
158   /** Base class for queue elements. 158   /** Base class for queue elements.
159   159  
160   Derive from this class to make a type usable with 160   Derive from this class to make a type usable with
161   @ref intrusive_queue. The `next_` pointer is private 161   @ref intrusive_queue. The `next_` pointer is private
162   and accessible only to the queue. 162   and accessible only to the queue.
163   */ 163   */
164   class node 164   class node
165   { 165   {
166   friend class intrusive_queue; 166   friend class intrusive_queue;
167   167  
168   private: 168   private:
169   T* next_; 169   T* next_;
170   }; 170   };
171   171  
172   private: 172   private:
173   T* head_ = nullptr; 173   T* head_ = nullptr;
174   T* tail_ = nullptr; 174   T* tail_ = nullptr;
175   175  
176   public: 176   public:
HITCBC 177   1713 intrusive_queue() = default; 177   1733 intrusive_queue() = default;
178   178  
179   intrusive_queue(intrusive_queue&& other) noexcept 179   intrusive_queue(intrusive_queue&& other) noexcept
180   : head_(other.head_) 180   : head_(other.head_)
181   , tail_(other.tail_) 181   , tail_(other.tail_)
182   { 182   {
183   other.head_ = nullptr; 183   other.head_ = nullptr;
184   other.tail_ = nullptr; 184   other.tail_ = nullptr;
185   } 185   }
186   186  
187   intrusive_queue(intrusive_queue const&) = delete; 187   intrusive_queue(intrusive_queue const&) = delete;
188   intrusive_queue& operator=(intrusive_queue const&) = delete; 188   intrusive_queue& operator=(intrusive_queue const&) = delete;
189   intrusive_queue& operator=(intrusive_queue&&) = delete; 189   intrusive_queue& operator=(intrusive_queue&&) = delete;
190   190  
HITCBC 191   1420383 bool empty() const noexcept 191   1632009 bool empty() const noexcept
192   { 192   {
HITCBC 193   1420383 return head_ == nullptr; 193   1632009 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   444465 void push(T* w) noexcept 196   507118 void push(T* w) noexcept
197   { 197   {
HITCBC 198   444465 w->next_ = nullptr; 198   507118 w->next_ = nullptr;
HITCBC 199   444465 if (tail_) 199   507118 if (tail_)
HITCBC 200   186645 tail_->next_ = w; 200   212624 tail_->next_ = w;
201   else 201   else
HITCBC 202   257820 head_ = w; 202   294494 head_ = w;
HITCBC 203   444465 tail_ = w; 203   507118 tail_ = w;
HITCBC 204   444465 } 204   507118 }
205   205  
HITCBC 206   242901 void splice(intrusive_queue& other) noexcept 206   283836 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   242901 if (other.empty()) 208   283836 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   242901 if (tail_) 210   283836 if (tail_)
HITCBC 211   120769 tail_->next_ = other.head_; 211   142943 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   122132 head_ = other.head_; 213   140893 head_ = other.head_;
HITCBC 214   242901 tail_ = other.tail_; 214   283836 tail_ = other.tail_;
HITCBC 215   242901 other.head_ = nullptr; 215   283836 other.head_ = nullptr;
HITCBC 216   242901 other.tail_ = nullptr; 216   283836 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   597073 T* pop() noexcept 219   689032 T* pop() noexcept
220   { 220   {
HITCBC 221   597073 if (!head_) 221   689032 if (!head_)
HITCBC 222   152608 return nullptr; 222   181914 return nullptr;
HITCBC 223   444465 T* w = head_; 223   507118 T* w = head_;
HITCBC 224   444465 head_ = head_->next_; 224   507118 head_ = head_->next_;
HITCBC 225   444465 if (!head_) 225   507118 if (!head_)
HITCBC 226   137051 tail_ = nullptr; 226   151551 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   444465 w->next_ = nullptr; 228   507118 w->next_ = nullptr;
HITCBC 229   444465 return w; 229   507118 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif