. /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   33183 void push_back(T* w) noexcept 66   39237 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   33183 auto* n = static_cast<node*>(w); 68   39237 auto* n = static_cast<node*>(w);
HITCBC 69   33183 n->next_ = nullptr; 69   39237 n->next_ = nullptr;
HITCBC 70   33183 n->prev_ = tail_; 70   39237 n->prev_ = tail_;
HITCBC 71   33183 if (tail_) 71   39237 if (tail_)
HITCBC 72   19059 static_cast<node*>(tail_)->next_ = w; 72   22689 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   14124 head_ = w; 74   16548 head_ = w;
HITCBC 75   33183 tail_ = w; 75   39237 tail_ = w;
HITCBC 76   33183 } 76   39237 }
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   174285 T* pop_front() noexcept 97   184454 T* pop_front() noexcept
98   { 98   {
HITCBC 99   174285 if (!head_) 99   184454 if (!head_)
HITCBC 100   160775 return nullptr; 100   168522 return nullptr;
HITCBC 101   13510 T* w = head_; 101   15932 T* w = head_;
HITCBC 102   13510 head_ = static_cast<node*>(head_)->next_; 102   15932 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   13510 if (head_) 103   15932 if (head_)
HITCBC 104   42 static_cast<node*>(head_)->prev_ = nullptr; 104   40 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   13468 tail_ = nullptr; 106   15892 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   13510 auto* n = static_cast<node*>(w); 109   15932 auto* n = static_cast<node*>(w);
HITCBC 110   13510 n->next_ = nullptr; 110   15932 n->next_ = nullptr;
HITCBC 111   13510 n->prev_ = nullptr; 111   15932 n->prev_ = nullptr;
HITCBC 112   13510 return w; 112   15932 return w;
113   } 113   }
114   114  
HITCBC 115   19673 void remove(T* w) noexcept 115   23305 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   19673 auto* n = static_cast<node*>(w); 117   23305 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   19673 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   23305 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   19673 if (n->prev_) 121   23305 if (n->prev_)
HITCBC 122   6323 static_cast<node*>(n->prev_)->next_ = n->next_; 122   7535 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   13350 head_ = n->next_; 124   15770 head_ = n->next_;
HITCBC 125   19673 if (n->next_) 125   23305 if (n->next_)
HITCBC 126   12728 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   15148 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   6945 tail_ = n->prev_; 128   8157 tail_ = n->prev_;
HITCBC 129   19673 n->next_ = nullptr; 129   23305 n->next_ = nullptr;
HITCBC 130   19673 n->prev_ = nullptr; 130   23305 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   1712 intrusive_queue() = default; 177   1721 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   1456210 bool empty() const noexcept 191   1532622 bool empty() const noexcept
192   { 192   {
HITCBC 193   1456210 return head_ == nullptr; 193   1532622 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   457317 void push(T* w) noexcept 196   482132 void push(T* w) noexcept
197   { 197   {
HITCBC 198   457317 w->next_ = nullptr; 198   482132 w->next_ = nullptr;
HITCBC 199   457317 if (tail_) 199   482132 if (tail_)
HITCBC 200   191341 tail_->next_ = w; 200   200952 tail_->next_ = w;
201   else 201   else
HITCBC 202   265976 head_ = w; 202   281180 head_ = w;
HITCBC 203   457317 tail_ = w; 203   482132 tail_ = w;
HITCBC 204   457317 } 204   482132 }
205   205  
HITCBC 206   246926 void splice(intrusive_queue& other) noexcept 206   258560 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   246926 if (other.empty()) 208   258560 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   246926 if (tail_) 210   258560 if (tail_)
HITCBC 211   123063 tail_->next_ = other.head_; 211   127621 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   123863 head_ = other.head_; 213   130939 head_ = other.head_;
HITCBC 214   246926 tail_ = other.tail_; 214   258560 tail_ = other.tail_;
HITCBC 215   246926 other.head_ = nullptr; 215   258560 other.head_ = nullptr;
HITCBC 216   246926 other.tail_ = nullptr; 216   258560 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   609426 T* pop() noexcept 219   638946 T* pop() noexcept
220   { 220   {
HITCBC 221   609426 if (!head_) 221   638946 if (!head_)
HITCBC 222   152109 return nullptr; 222   156814 return nullptr;
HITCBC 223   457317 T* w = head_; 223   482132 T* w = head_;
HITCBC 224   457317 head_ = head_->next_; 224   482132 head_ = head_->next_;
HITCBC 225   457317 if (!head_) 225   482132 if (!head_)
HITCBC 226   142913 tail_ = nullptr; 226   153559 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   457317 w->next_ = nullptr; 228   482132 w->next_ = nullptr;
HITCBC 229   457317 return w; 229   482132 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif