. /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   2862 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   33288 void push_back(T* w) noexcept 72   32927 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   33288 auto* n = static_cast<node*>(w); 74   32927 auto* n = static_cast<node*>(w);
HITCBC 75   33288 n->next_ = nullptr; 75   32927 n->next_ = nullptr;
HITCBC 76   33288 n->prev_ = tail_; 76   32927 n->prev_ = tail_;
HITCBC 77   33288 if (tail_) 77   32927 if (tail_)
HITCBC 78   21127 static_cast<node*>(tail_)->next_ = w; 78   20893 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   12161 head_ = w; 80   12034 head_ = w;
HITCBC 81   33288 tail_ = w; 81   32927 tail_ = w;
HITCBC 82   33288 } 82   32927 }
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   331112 T* pop_front() noexcept 103   324000 T* pop_front() noexcept
104   { 104   {
HITCBC 105   331112 if (!head_) 105   324000 if (!head_)
HITCBC 106   314278 return nullptr; 106   307490 return nullptr;
HITCBC 107   16834 T* w = head_; 107   16510 T* w = head_;
HITCBC 108   16834 head_ = static_cast<node*>(head_)->next_; 108   16510 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16834 if (head_) 109   16510 if (head_)
HITCBC 110   7415 static_cast<node*>(head_)->prev_ = nullptr; 110   7228 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9419 tail_ = nullptr; 112   9282 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   16834 auto* n = static_cast<node*>(w); 115   16510 auto* n = static_cast<node*>(w);
HITCBC 116   16834 n->next_ = nullptr; 116   16510 n->next_ = nullptr;
HITCBC 117   16834 n->prev_ = nullptr; 117   16510 n->prev_ = nullptr;
HITCBC 118   16834 return w; 118   16510 return w;
119   } 119   }
120   120  
HITCBC 121   16452 void remove(T* w) noexcept 121   16415 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16452 auto* n = static_cast<node*>(w); 123   16415 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16452 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   16415 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   16451 if (n->prev_) 127   16414 if (n->prev_)
HITCBC 128   4692 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4683 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11759 head_ = n->next_; 130   11731 head_ = n->next_;
HITCBC 131   16451 if (n->next_) 131   16414 if (n->next_)
HITCBC 132   9141 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   9109 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7310 tail_ = n->prev_; 134   7305 tail_ = n->prev_;
HITCBC 135   16451 n->next_ = nullptr; 135   16414 n->next_ = nullptr;
HITCBC 136   16451 n->prev_ = nullptr; 136   16414 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   625 void for_each(F f)
142   { 142   {
HITCBC 143   630 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   634 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   9 f(p); 144   9 f(p);
HITCBC 145   621 } 145   625 }
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   2246 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   1116 bool empty() const noexcept 197   1122 bool empty() const noexcept
198   { 198   {
HITCBC 199   1116 return head_ == nullptr; 199   1122 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   713 void push(T* w) noexcept 202   715 void push(T* w) noexcept
203   { 203   {
HITCBC 204   713 w->next_ = nullptr; 204   715 w->next_ = nullptr;
HITCBC 205   713 if (tail_) 205   715 if (tail_)
HITCBC 206   263 tail_->next_ = w; 206   260 tail_->next_ = w;
207   else 207   else
HITCBC 208   450 head_ = w; 208   455 head_ = w;
HITCBC 209   713 tail_ = w; 209   715 tail_ = w;
HITCBC 210   713 } 210   715 }
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   3243 T* pop() noexcept 225   3247 T* pop() noexcept
226   { 226   {
HITCBC 227   3243 if (!head_) 227   3247 if (!head_)
HITCBC 228   2530 return nullptr; 228   2532 return nullptr;
HITCBC 229   713 T* w = head_; 229   715 T* w = head_;
HITCBC 230   713 head_ = head_->next_; 230   715 head_ = head_->next_;
HITCBC 231   713 if (!head_) 231   715 if (!head_)
HITCBC 232   449 tail_ = nullptr; 232   454 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   713 w->next_ = nullptr; 234   715 w->next_ = nullptr;
HITCBC 235   713 return w; 235   715 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif