. /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   6471 intrusive_list() = default; 47   6467 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   44783 void push_back(T* w) noexcept 66   43846 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   44783 auto* n = static_cast<node*>(w); 68   43846 auto* n = static_cast<node*>(w);
HITCBC 69   44783 n->next_ = nullptr; 69   43846 n->next_ = nullptr;
HITCBC 70   44783 n->prev_ = tail_; 70   43846 n->prev_ = tail_;
HITCBC 71   44783 if (tail_) 71   43846 if (tail_)
HITCBC 72   25981 static_cast<node*>(tail_)->next_ = w; 72   25424 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   18802 head_ = w; 74   18422 head_ = w;
HITCBC 75   44783 tail_ = w; 75   43846 tail_ = w;
HITCBC 76   44783 } 76   43846 }
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   291015 T* pop_front() noexcept 97   283650 T* pop_front() noexcept
98   { 98   {
HITCBC 99   291015 if (!head_) 99   283650 if (!head_)
HITCBC 100   272853 return nullptr; 100   265868 return nullptr;
HITCBC 101   18162 T* w = head_; 101   17782 T* w = head_;
HITCBC 102   18162 head_ = static_cast<node*>(head_)->next_; 102   17782 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   18162 if (head_) 103   17782 if (head_)
HITCBC 104   40 static_cast<node*>(head_)->prev_ = nullptr; 104   40 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   18122 tail_ = nullptr; 106   17742 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   18162 auto* n = static_cast<node*>(w); 109   17782 auto* n = static_cast<node*>(w);
HITCBC 110   18162 n->next_ = nullptr; 110   17782 n->next_ = nullptr;
HITCBC 111   18162 n->prev_ = nullptr; 111   17782 n->prev_ = nullptr;
HITCBC 112   18162 return w; 112   17782 return w;
113   } 113   }
114   114  
HITCBC 115   26621 void remove(T* w) noexcept 115   26064 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   26621 auto* n = static_cast<node*>(w); 117   26064 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   26621 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   26064 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   26621 if (n->prev_) 121   26064 if (n->prev_)
HITCBC 122   8627 static_cast<node*>(n->prev_)->next_ = n->next_; 122   8440 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   17994 head_ = n->next_; 124   17624 head_ = n->next_;
HITCBC 125   26621 if (n->next_) 125   26064 if (n->next_)
HITCBC 126   17348 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   16978 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   9273 tail_ = n->prev_; 128   9086 tail_ = n->prev_;
HITCBC 129   26621 n->next_ = nullptr; 129   26064 n->next_ = nullptr;
HITCBC 130   26621 n->prev_ = nullptr; 130   26064 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   1773 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   2535551 bool empty() const noexcept 191   2483866 bool empty() const noexcept
192   { 192   {
HITCBC 193   2535551 return head_ == nullptr; 193   2483866 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   790993 void push(T* w) noexcept 196   775732 void push(T* w) noexcept
197   { 197   {
HITCBC 198   790993 w->next_ = nullptr; 198   775732 w->next_ = nullptr;
HITCBC 199   790993 if (tail_) 199   775732 if (tail_)
HITCBC 200   330875 tail_->next_ = w; 200   323292 tail_->next_ = w;
201   else 201   else
HITCBC 202   460118 head_ = w; 202   452440 head_ = w;
HITCBC 203   790993 tail_ = w; 203   775732 tail_ = w;
HITCBC 204   790993 } 204   775732 }
205   205  
HITCBC 206   434503 void splice(intrusive_queue& other) noexcept 206   427528 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   434503 if (other.empty()) 208   427528 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   434503 if (tail_) 210   427528 if (tail_)
HITCBC 211   215444 tail_->next_ = other.head_; 211   215175 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   219059 head_ = other.head_; 213   212353 head_ = other.head_;
HITCBC 214   434503 tail_ = other.tail_; 214   427528 tail_ = other.tail_;
HITCBC 215   434503 other.head_ = nullptr; 215   427528 other.head_ = nullptr;
HITCBC 216   434503 other.tail_ = nullptr; 216   427528 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   1064404 T* pop() noexcept 219   1042468 T* pop() noexcept
220   { 220   {
HITCBC 221   1064404 if (!head_) 221   1042468 if (!head_)
HITCBC 222   273411 return nullptr; 222   266736 return nullptr;
HITCBC 223   790993 T* w = head_; 223   775732 T* w = head_;
HITCBC 224   790993 head_ = head_->next_; 224   775732 head_ = head_->next_;
HITCBC 225   790993 if (!head_) 225   775732 if (!head_)
HITCBC 226   244674 tail_ = nullptr; 226   237265 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   790993 w->next_ = nullptr; 228   775732 w->next_ = nullptr;
HITCBC 229   790993 return w; 229   775732 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif