. /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_ = nullptr; 38   T* next_ = nullptr;
39   T* prev_ = nullptr; 39   T* prev_ = nullptr;
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   14239 intrusive_list() = default; 47   13036 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   1501 bool empty() const noexcept 61   1434 bool empty() const noexcept
62   { 62   {
HITCBC 63   1501 return head_ == nullptr; 63   1434 return head_ == nullptr;
64   } 64   }
65   65  
66   /// Peek at the head element without removing it. 66   /// Peek at the head element without removing it.
67   T* front() const noexcept 67   T* front() const noexcept
68   { 68   {
69   return head_; 69   return head_;
70   } 70   }
71   71  
HITCBC 72   25731 void push_back(T* w) noexcept 72   35619 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   25731 auto* n = static_cast<node*>(w); 74   35619 auto* n = static_cast<node*>(w);
HITCBC 75   25731 n->next_ = nullptr; 75   35619 n->next_ = nullptr;
HITCBC 76   25731 n->prev_ = tail_; 76   35619 n->prev_ = tail_;
HITCBC 77   25731 if (tail_) 77   35619 if (tail_)
HITCBC 78   13263 static_cast<node*>(tail_)->next_ = w; 78   19291 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   12468 head_ = w; 80   16328 head_ = w;
HITCBC 81   25731 tail_ = w; 81   35619 tail_ = w;
HITCBC 82   25731 } 82   35619 }
83   83  
84   void splice_back(intrusive_list& other) noexcept 84   void splice_back(intrusive_list& other) noexcept
85   { 85   {
86   if (other.empty()) 86   if (other.empty())
87   return; 87   return;
88   if (tail_) 88   if (tail_)
89   { 89   {
90   static_cast<node*>(tail_)->next_ = other.head_; 90   static_cast<node*>(tail_)->next_ = other.head_;
91   static_cast<node*>(other.head_)->prev_ = tail_; 91   static_cast<node*>(other.head_)->prev_ = tail_;
92   tail_ = other.tail_; 92   tail_ = other.tail_;
93   } 93   }
94   else 94   else
95   { 95   {
96   head_ = other.head_; 96   head_ = other.head_;
97   tail_ = other.tail_; 97   tail_ = other.tail_;
98   } 98   }
99   other.head_ = nullptr; 99   other.head_ = nullptr;
100   other.tail_ = nullptr; 100   other.tail_ = nullptr;
101   } 101   }
102   102  
HITCBC 103   250248 T* pop_front() noexcept 103   273182 T* pop_front() noexcept
104   { 104   {
HITCBC 105   250248 if (!head_) 105   273182 if (!head_)
HITCBC 106   240760 return nullptr; 106   259534 return nullptr;
HITCBC 107   9488 T* w = head_; 107   13648 T* w = head_;
HITCBC 108   9488 head_ = static_cast<node*>(head_)->next_; 108   13648 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   9488 if (head_) 109   13648 if (head_)
HITCBC 110   50 static_cast<node*>(head_)->prev_ = nullptr; 110   96 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9438 tail_ = nullptr; 112   13552 tail_ = nullptr;
113   // Defensive: clear stale linkage so remove() on a 113   // Defensive: clear stale linkage so remove() on a
114   // popped node cannot corrupt the list. 114   // popped node cannot corrupt the list.
HITCBC 115   9488 auto* n = static_cast<node*>(w); 115   13648 auto* n = static_cast<node*>(w);
HITCBC 116   9488 n->next_ = nullptr; 116   13648 n->next_ = nullptr;
HITCBC 117   9488 n->prev_ = nullptr; 117   13648 n->prev_ = nullptr;
HITCBC 118   9488 return w; 118   13648 return w;
119   } 119   }
120   120  
HITCBC 121   16243 void remove(T* w) noexcept 121   21971 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16243 auto* n = static_cast<node*>(w); 123   21971 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16243 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   21971 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   16243 if (n->prev_) 127   21971 if (n->prev_)
HITCBC 128   4377 static_cast<node*>(n->prev_)->next_ = n->next_; 128   6385 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11866 head_ = n->next_; 130   15586 head_ = n->next_;
HITCBC 131   16243 if (n->next_) 131   21971 if (n->next_)
HITCBC 132   8919 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   12876 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7324 tail_ = n->prev_; 134   9095 tail_ = n->prev_;
HITCBC 135   16243 n->next_ = nullptr; 135   21971 n->next_ = nullptr;
HITCBC 136   16243 n->prev_ = nullptr; 136   21971 n->prev_ = nullptr;
137   } 137   }
138   138  
139   /// Invoke @p f for each element in the list. 139   /// Invoke @p f for each element in the list.
140   template<class F> 140   template<class F>
HITCBC 141   227 void for_each(F f) 141   216 void for_each(F f)
142   { 142   {
HITCBC 143   227 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   216 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   227 } 145   216 }
146   }; 146   };
147   147  
148   /** An intrusive singly linked FIFO queue. 148   /** An intrusive singly linked FIFO queue.
149   149  
150   This container provides O(1) push and pop operations for 150   This container provides O(1) push and pop operations for
151   elements that derive from @ref node. Elements are not 151   elements that derive from @ref node. Elements are not
152   copied or moved; they are linked directly into the queue. 152   copied or moved; they are linked directly into the queue.
153   153  
154   Unlike @ref intrusive_list, this uses only a single `next_` 154   Unlike @ref intrusive_list, this uses only a single `next_`
155   pointer per node, saving memory at the cost of not supporting 155   pointer per node, saving memory at the cost of not supporting
156   O(1) removal of arbitrary elements. 156   O(1) removal of arbitrary elements.
157   157  
158   @tparam T The element type. Must derive from `intrusive_queue<T>::node`. 158   @tparam T The element type. Must derive from `intrusive_queue<T>::node`.
159   */ 159   */
160   template<class T> 160   template<class T>
161   class intrusive_queue 161   class intrusive_queue
162   { 162   {
163   public: 163   public:
164   /** Base class for queue elements. 164   /** Base class for queue elements.
165   165  
166   Derive from this class to make a type usable with 166   Derive from this class to make a type usable with
167   @ref intrusive_queue. The `next_` pointer is private 167   @ref intrusive_queue. The `next_` pointer is private
168   and accessible only to the queue. 168   and accessible only to the queue.
169   */ 169   */
170   class node 170   class node
171   { 171   {
172   friend class intrusive_queue; 172   friend class intrusive_queue;
173   173  
174   private: 174   private:
175   T* next_ = nullptr; 175   T* next_ = nullptr;
176   }; 176   };
177   177  
178   private: 178   private:
179   T* head_ = nullptr; 179   T* head_ = nullptr;
180   T* tail_ = nullptr; 180   T* tail_ = nullptr;
181   181  
182   public: 182   public:
HITCBC 183   1372 intrusive_queue() = default; 183   1241 intrusive_queue() = default;
184   184  
185   intrusive_queue(intrusive_queue&& other) noexcept 185   intrusive_queue(intrusive_queue&& other) noexcept
186   : head_(other.head_) 186   : head_(other.head_)
187   , tail_(other.tail_) 187   , tail_(other.tail_)
188   { 188   {
189   other.head_ = nullptr; 189   other.head_ = nullptr;
190   other.tail_ = nullptr; 190   other.tail_ = nullptr;
191   } 191   }
192   192  
193   intrusive_queue(intrusive_queue const&) = delete; 193   intrusive_queue(intrusive_queue const&) = delete;
194   intrusive_queue& operator=(intrusive_queue const&) = delete; 194   intrusive_queue& operator=(intrusive_queue const&) = delete;
195   intrusive_queue& operator=(intrusive_queue&&) = delete; 195   intrusive_queue& operator=(intrusive_queue&&) = delete;
196   196  
HITCBC 197   904 bool empty() const noexcept 197   1060 bool empty() const noexcept
198   { 198   {
HITCBC 199   904 return head_ == nullptr; 199   1060 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   382 void push(T* w) noexcept 202   375 void push(T* w) noexcept
203   { 203   {
HITCBC 204   382 w->next_ = nullptr; 204   375 w->next_ = nullptr;
HITCBC 205   382 if (tail_) 205   375 if (tail_)
HITCBC 206   254 tail_->next_ = w; 206   247 tail_->next_ = w;
207   else 207   else
HITCBC 208   128 head_ = w; 208   128 head_ = w;
HITCBC 209   382 tail_ = w; 209   375 tail_ = w;
HITCBC 210   382 } 210   375 }
211   211  
212   void splice(intrusive_queue& other) noexcept 212   void splice(intrusive_queue& other) noexcept
213   { 213   {
214   if (other.empty()) 214   if (other.empty())
215   return; 215   return;
216   if (tail_) 216   if (tail_)
217   tail_->next_ = other.head_; 217   tail_->next_ = other.head_;
218   else 218   else
219   head_ = other.head_; 219   head_ = other.head_;
220   tail_ = other.tail_; 220   tail_ = other.tail_;
221   other.head_ = nullptr; 221   other.head_ = nullptr;
222   other.tail_ = nullptr; 222   other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   3137 T* pop() noexcept 225   2868 T* pop() noexcept
226   { 226   {
HITCBC 227   3137 if (!head_) 227   2868 if (!head_)
HITCBC 228   2755 return nullptr; 228   2493 return nullptr;
HITCBC 229   382 T* w = head_; 229   375 T* w = head_;
HITCBC 230   382 head_ = head_->next_; 230   375 head_ = head_->next_;
HITCBC 231   382 if (!head_) 231   375 if (!head_)
HITCBC 232   128 tail_ = nullptr; 232   128 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   382 w->next_ = nullptr; 234   375 w->next_ = nullptr;
HITCBC 235   382 return w; 235   375 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif