. /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   37681 void push_back(T* w) noexcept 66   41052 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   37681 auto* n = static_cast<node*>(w); 68   41052 auto* n = static_cast<node*>(w);
HITCBC 69   37681 n->next_ = nullptr; 69   41052 n->next_ = nullptr;
HITCBC 70   37681 n->prev_ = tail_; 70   41052 n->prev_ = tail_;
HITCBC 71   37681 if (tail_) 71   41052 if (tail_)
HITCBC 72   21752 static_cast<node*>(tail_)->next_ = w; 72   23772 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   15929 head_ = w; 74   17280 head_ = w;
HITCBC 75   37681 tail_ = w; 75   41052 tail_ = w;
HITCBC 76   37681 } 76   41052 }
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   168742 T* pop_front() noexcept 97   177382 T* pop_front() noexcept
98   { 98   {
HITCBC 99   168742 if (!head_) 99   177382 if (!head_)
HITCBC 100   153428 return nullptr; 100   160716 return nullptr;
HITCBC 101   15314 T* w = head_; 101   16666 T* w = head_;
HITCBC 102   15314 head_ = static_cast<node*>(head_)->next_; 102   16666 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   15314 if (head_) 103   16666 if (head_)
HITCBC 104   41 static_cast<node*>(head_)->prev_ = nullptr; 104   42 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   15273 tail_ = nullptr; 106   16624 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   15314 auto* n = static_cast<node*>(w); 109   16666 auto* n = static_cast<node*>(w);
HITCBC 110   15314 n->next_ = nullptr; 110   16666 n->next_ = nullptr;
HITCBC 111   15314 n->prev_ = nullptr; 111   16666 n->prev_ = nullptr;
HITCBC 112   15314 return w; 112   16666 return w;
113   } 113   }
114   114  
HITCBC 115   22367 void remove(T* w) noexcept 115   24386 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   22367 auto* n = static_cast<node*>(w); 117   24386 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   22367 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   24386 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   22367 if (n->prev_) 121   24386 if (n->prev_)
HITCBC 122   7221 static_cast<node*>(n->prev_)->next_ = n->next_; 122   7894 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   15146 head_ = n->next_; 124   16492 head_ = n->next_;
HITCBC 125   22367 if (n->next_) 125   24386 if (n->next_)
HITCBC 126   14524 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   15870 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   7843 tail_ = n->prev_; 128   8516 tail_ = n->prev_;
HITCBC 129   22367 n->next_ = nullptr; 129   24386 n->next_ = nullptr;
HITCBC 130   22367 n->prev_ = nullptr; 130   24386 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   1716 intrusive_queue() = default; 177   1714 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   1378276 bool empty() const noexcept 191   1465514 bool empty() const noexcept
192   { 192   {
HITCBC 193   1378276 return head_ == nullptr; 193   1465514 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   433578 void push(T* w) noexcept 196   462265 void push(T* w) noexcept
197   { 197   {
HITCBC 198   433578 w->next_ = nullptr; 198   462265 w->next_ = nullptr;
HITCBC 199   433578 if (tail_) 199   462265 if (tail_)
HITCBC 200   181167 tail_->next_ = w; 200   192074 tail_->next_ = w;
201   else 201   else
HITCBC 202   252411 head_ = w; 202   270191 head_ = w;
HITCBC 203   433578 tail_ = w; 203   462265 tail_ = w;
HITCBC 204   433578 } 204   462265 }
205   205  
HITCBC 206   230780 void splice(intrusive_queue& other) noexcept 206   246479 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   230780 if (other.empty()) 208   246479 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   230780 if (tail_) 210   246479 if (tail_)
HITCBC 211   111407 tail_->next_ = other.head_; 211   123024 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   119373 head_ = other.head_; 213   123455 head_ = other.head_;
HITCBC 214   230780 tail_ = other.tail_; 214   246479 tail_ = other.tail_;
HITCBC 215   230780 other.head_ = nullptr; 215   246479 other.head_ = nullptr;
HITCBC 216   230780 other.tail_ = nullptr; 216   246479 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   573474 T* pop() noexcept 219   608812 T* pop() noexcept
220   { 220   {
HITCBC 221   573474 if (!head_) 221   608812 if (!head_)
HITCBC 222   139896 return nullptr; 222   146547 return nullptr;
HITCBC 223   433578 T* w = head_; 223   462265 T* w = head_;
HITCBC 224   433578 head_ = head_->next_; 224   462265 head_ = head_->next_;
HITCBC 225   433578 if (!head_) 225   462265 if (!head_)
HITCBC 226   141004 tail_ = nullptr; 226   147167 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   433578 w->next_ = nullptr; 228   462265 w->next_ = nullptr;
HITCBC 229   433578 return w; 229   462265 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif