. /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   22623 intrusive_list() = default; 47   22623 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   32265 void push_back(T* w) noexcept 72   26743 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   32265 auto* n = static_cast<node*>(w); 74   26743 auto* n = static_cast<node*>(w);
HITCBC 75   32265 n->next_ = nullptr; 75   26743 n->next_ = nullptr;
HITCBC 76   32265 n->prev_ = tail_; 76   26743 n->prev_ = tail_;
HITCBC 77   32265 if (tail_) 77   26743 if (tail_)
HITCBC 78   20342 static_cast<node*>(tail_)->next_ = w; 78   16119 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   11923 head_ = w; 80   10624 head_ = w;
HITCBC 81   32265 tail_ = w; 81   26743 tail_ = w;
HITCBC 82   32265 } 82   26743 }
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   295719 T* pop_front() noexcept 103   292479 T* pop_front() noexcept
104   { 104   {
HITCBC 105   295719 if (!head_) 105   292479 if (!head_)
HITCBC 106   279349 return nullptr; 106   277212 return nullptr;
HITCBC 107   16370 T* w = head_; 107   15267 T* w = head_;
HITCBC 108   16370 head_ = static_cast<node*>(head_)->next_; 108   15267 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16370 if (head_) 109   15267 if (head_)
HITCBC 110   7189 static_cast<node*>(head_)->prev_ = nullptr; 110   7385 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9181 tail_ = nullptr; 112   7882 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   16370 auto* n = static_cast<node*>(w); 115   15267 auto* n = static_cast<node*>(w);
HITCBC 116   16370 n->next_ = nullptr; 116   15267 n->next_ = nullptr;
HITCBC 117   16370 n->prev_ = nullptr; 117   15267 n->prev_ = nullptr;
HITCBC 118   16370 return w; 118   15267 return w;
119   } 119   }
120   120  
HITCBC 121   15893 void remove(T* w) noexcept 121   11474 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   15893 auto* n = static_cast<node*>(w); 123   11474 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   15893 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   11474 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   15892 if (n->prev_) 127   11473 if (n->prev_)
HITCBC 128   4507 static_cast<node*>(n->prev_)->next_ = n->next_; 128   3034 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11385 head_ = n->next_; 130   8439 head_ = n->next_;
HITCBC 131   15892 if (n->next_) 131   11473 if (n->next_)
HITCBC 132   8767 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   5821 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7125 tail_ = n->prev_; 134   5652 tail_ = n->prev_;
HITCBC 135   15892 n->next_ = nullptr; 135   11473 n->next_ = nullptr;
HITCBC 136   15892 n->prev_ = nullptr; 136   11473 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   621 void for_each(F f) 141   621 void for_each(F f)
142   { 142   {
HITCBC 143   630 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   630 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   9 f(p); 144   9 f(p);
HITCBC 145   621 } 145   621 }
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   2244 intrusive_queue() = default; 183   2244 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   1193 bool empty() const noexcept 197   1184 bool empty() const noexcept
198   { 198   {
HITCBC 199   1193 return head_ == nullptr; 199   1184 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   752 void push(T* w) noexcept 202   753 void push(T* w) noexcept
203   { 203   {
HITCBC 204   752 w->next_ = nullptr; 204   753 w->next_ = nullptr;
HITCBC 205   752 if (tail_) 205   753 if (tail_)
HITCBC 206   263 tail_->next_ = w; 206   263 tail_->next_ = w;
207   else 207   else
HITCBC 208   489 head_ = w; 208   490 head_ = w;
HITCBC 209   752 tail_ = w; 209   753 tail_ = w;
HITCBC 210   752 } 210   753 }
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   3282 T* pop() noexcept 225   3283 T* pop() noexcept
226   { 226   {
HITCBC 227   3282 if (!head_) 227   3283 if (!head_)
HITCBC 228   2530 return nullptr; 228   2530 return nullptr;
HITCBC 229   752 T* w = head_; 229   753 T* w = head_;
HITCBC 230   752 head_ = head_->next_; 230   753 head_ = head_->next_;
HITCBC 231   752 if (!head_) 231   753 if (!head_)
HITCBC 232   488 tail_ = nullptr; 232   489 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   752 w->next_ = nullptr; 234   753 w->next_ = nullptr;
HITCBC 235   752 return w; 235   753 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif