. /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   2862 intrusive_list() = default; 47   2937 intrusive_list() = default;
48   48  
HITCBC 49   1 intrusive_list(intrusive_list&& other) noexcept 49   1 intrusive_list(intrusive_list&& other) noexcept
HITCBC 50   1 : head_(other.head_) 50   1 : head_(other.head_)
HITCBC 51   1 , tail_(other.tail_) 51   1 , tail_(other.tail_)
52   { 52   {
HITCBC 53   1 other.head_ = nullptr; 53   1 other.head_ = nullptr;
HITCBC 54   1 other.tail_ = nullptr; 54   1 other.tail_ = nullptr;
HITCBC 55   1 } 55   1 }
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   12 bool empty() const noexcept 61   12 bool empty() const noexcept
62   { 62   {
HITCBC 63   12 return head_ == nullptr; 63   12 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.
HITCBC 67   6 T* front() const noexcept 67   6 T* front() const noexcept
68   { 68   {
HITCBC 69   6 return head_; 69   6 return head_;
70   } 70   }
71   71  
HITCBC 72   33024 void push_back(T* w) noexcept 72   33359 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   33024 auto* n = static_cast<node*>(w); 74   33359 auto* n = static_cast<node*>(w);
HITCBC 75   33024 n->next_ = nullptr; 75   33359 n->next_ = nullptr;
HITCBC 76   33024 n->prev_ = tail_; 76   33359 n->prev_ = tail_;
HITCBC 77   33024 if (tail_) 77   33359 if (tail_)
HITCBC 78   20809 static_cast<node*>(tail_)->next_ = w; 78   21055 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   12215 head_ = w; 80   12304 head_ = w;
HITCBC 81   33024 tail_ = w; 81   33359 tail_ = w;
HITCBC 82   33024 } 82   33359 }
83   83  
HITCBC 84   3 void splice_back(intrusive_list& other) noexcept 84   3 void splice_back(intrusive_list& other) noexcept
85   { 85   {
HITCBC 86   3 if (other.empty()) 86   3 if (other.empty())
HITCBC 87   1 return; 87   1 return;
HITCBC 88   2 if (tail_) 88   2 if (tail_)
89   { 89   {
HITCBC 90   1 static_cast<node*>(tail_)->next_ = other.head_; 90   1 static_cast<node*>(tail_)->next_ = other.head_;
HITCBC 91   1 static_cast<node*>(other.head_)->prev_ = tail_; 91   1 static_cast<node*>(other.head_)->prev_ = tail_;
HITCBC 92   1 tail_ = other.tail_; 92   1 tail_ = other.tail_;
93   } 93   }
94   else 94   else
95   { 95   {
HITCBC 96   1 head_ = other.head_; 96   1 head_ = other.head_;
HITCBC 97   1 tail_ = other.tail_; 97   1 tail_ = other.tail_;
98   } 98   }
HITCBC 99   2 other.head_ = nullptr; 99   2 other.head_ = nullptr;
HITCBC 100   2 other.tail_ = nullptr; 100   2 other.tail_ = nullptr;
101   } 101   }
102   102  
HITCBC 103   305025 T* pop_front() noexcept 103   359380 T* pop_front() noexcept
104   { 104   {
HITCBC 105   305025 if (!head_) 105   359380 if (!head_)
HITCBC 106   288609 return nullptr; 106   342743 return nullptr;
HITCBC 107   16416 T* w = head_; 107   16637 T* w = head_;
HITCBC 108   16416 head_ = static_cast<node*>(head_)->next_; 108   16637 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16416 if (head_) 109   16637 if (head_)
HITCBC 110   6953 static_cast<node*>(head_)->prev_ = nullptr; 110   7156 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9463 tail_ = nullptr; 112   9481 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   16416 auto* n = static_cast<node*>(w); 115   16637 auto* n = static_cast<node*>(w);
HITCBC 116   16416 n->next_ = nullptr; 116   16637 n->next_ = nullptr;
HITCBC 117   16416 n->prev_ = nullptr; 117   16637 n->prev_ = nullptr;
HITCBC 118   16416 return w; 118   16637 return w;
119   } 119   }
120   120  
HITCBC 121   16606 void remove(T* w) noexcept 121   16720 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16606 auto* n = static_cast<node*>(w); 123   16720 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16606 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   16720 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   16605 if (n->prev_) 127   16719 if (n->prev_)
HITCBC 128   4743 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4761 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11862 head_ = n->next_; 130   11958 head_ = n->next_;
HITCBC 131   16605 if (n->next_) 131   16719 if (n->next_)
HITCBC 132   9239 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   9262 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7366 tail_ = n->prev_; 134   7457 tail_ = n->prev_;
HITCBC 135   16605 n->next_ = nullptr; 135   16719 n->next_ = nullptr;
HITCBC 136   16605 n->prev_ = nullptr; 136   16719 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   625 void for_each(F f) 141   646 void for_each(F f)
142   { 142   {
HITCBC 143   634 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   657 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   9 f(p); 144   11 f(p);
HITCBC 145   625 } 145   646 }
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   2246 intrusive_queue() = default; 183   2313 intrusive_queue() = default;
184   184  
HITCBC 185   1 intrusive_queue(intrusive_queue&& other) noexcept 185   1 intrusive_queue(intrusive_queue&& other) noexcept
HITCBC 186   1 : head_(other.head_) 186   1 : head_(other.head_)
HITCBC 187   1 , tail_(other.tail_) 187   1 , tail_(other.tail_)
188   { 188   {
HITCBC 189   1 other.head_ = nullptr; 189   1 other.head_ = nullptr;
HITCBC 190   1 other.tail_ = nullptr; 190   1 other.tail_ = nullptr;
HITCBC 191   1 } 191   1 }
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   1190 bool empty() const noexcept 197   1135 bool empty() const noexcept
198   { 198   {
HITCBC 199   1190 return head_ == nullptr; 199   1135 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   755 void push(T* w) noexcept 202   727 void push(T* w) noexcept
203   { 203   {
HITCBC 204   755 w->next_ = nullptr; 204   727 w->next_ = nullptr;
HITCBC 205   755 if (tail_) 205   727 if (tail_)
HITCBC 206   259 tail_->next_ = w; 206   265 tail_->next_ = w;
207   else 207   else
HITCBC 208   496 head_ = w; 208   462 head_ = w;
HITCBC 209   755 tail_ = w; 209   727 tail_ = w;
HITCBC 210   755 } 210   727 }
211   211  
HITCBC 212   3 void splice(intrusive_queue& other) noexcept 212   3 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   3 if (other.empty()) 214   3 if (other.empty())
HITCBC 215   1 return; 215   1 return;
HITCBC 216   2 if (tail_) 216   2 if (tail_)
HITCBC 217   1 tail_->next_ = other.head_; 217   1 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   1 head_ = other.head_; 219   1 head_ = other.head_;
HITCBC 220   2 tail_ = other.tail_; 220   2 tail_ = other.tail_;
HITCBC 221   2 other.head_ = nullptr; 221   2 other.head_ = nullptr;
HITCBC 222   2 other.tail_ = nullptr; 222   2 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   3287 T* pop() noexcept 225   3330 T* pop() noexcept
226   { 226   {
HITCBC 227   3287 if (!head_) 227   3330 if (!head_)
HITCBC 228   2532 return nullptr; 228   2603 return nullptr;
HITCBC 229   755 T* w = head_; 229   727 T* w = head_;
HITCBC 230   755 head_ = head_->next_; 230   727 head_ = head_->next_;
HITCBC 231   755 if (!head_) 231   727 if (!head_)
HITCBC 232   495 tail_ = nullptr; 232   461 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   755 w->next_ = nullptr; 234   727 w->next_ = nullptr;
HITCBC 235   755 return w; 235   727 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif