. /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   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   34206 void push_back(T* w) noexcept 72   34329 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   34206 auto* n = static_cast<node*>(w); 74   34329 auto* n = static_cast<node*>(w);
HITCBC 75   34206 n->next_ = nullptr; 75   34329 n->next_ = nullptr;
HITCBC 76   34206 n->prev_ = tail_; 76   34329 n->prev_ = tail_;
HITCBC 77   34206 if (tail_) 77   34329 if (tail_)
HITCBC 78   21858 static_cast<node*>(tail_)->next_ = w; 78   21546 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   12348 head_ = w; 80   12783 head_ = w;
HITCBC 81   34206 tail_ = w; 81   34329 tail_ = w;
HITCBC 82   34206 } 82   34329 }
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   316002 T* pop_front() noexcept 103   319245 T* pop_front() noexcept
104   { 104   {
HITCBC 105   316002 if (!head_) 105   319245 if (!head_)
HITCBC 106   299134 return nullptr; 106   302475 return nullptr;
HITCBC 107   16868 T* w = head_; 107   16770 T* w = head_;
HITCBC 108   16868 head_ = static_cast<node*>(head_)->next_; 108   16770 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16868 if (head_) 109   16770 if (head_)
HITCBC 110   7272 static_cast<node*>(head_)->prev_ = nullptr; 110   6739 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9596 tail_ = nullptr; 112   10031 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   16868 auto* n = static_cast<node*>(w); 115   16770 auto* n = static_cast<node*>(w);
HITCBC 116   16868 n->next_ = nullptr; 116   16770 n->next_ = nullptr;
HITCBC 117   16868 n->prev_ = nullptr; 117   16770 n->prev_ = nullptr;
HITCBC 118   16868 return w; 118   16770 return w;
119   } 119   }
120   120  
HITCBC 121   17336 void remove(T* w) noexcept 121   17557 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   17336 auto* n = static_cast<node*>(w); 123   17557 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   17336 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   17557 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   17335 if (n->prev_) 127   17556 if (n->prev_)
HITCBC 128   4985 static_cast<node*>(n->prev_)->next_ = n->next_; 128   5063 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   12350 head_ = n->next_; 130   12493 head_ = n->next_;
HITCBC 131   17335 if (n->next_) 131   17556 if (n->next_)
HITCBC 132   9725 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   9871 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7610 tail_ = n->prev_; 134   7685 tail_ = n->prev_;
HITCBC 135   17335 n->next_ = nullptr; 135   17556 n->next_ = nullptr;
HITCBC 136   17335 n->prev_ = nullptr; 136   17556 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   625 void for_each(F f)
142   { 142   {
HITCBC 143   634 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   625 } 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   2246 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   1146 bool empty() const noexcept 197   1145 bool empty() const noexcept
198   { 198   {
HITCBC 199   1146 return head_ == nullptr; 199   1145 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   736 void push(T* w) noexcept 202   753 void push(T* w) noexcept
203   { 203   {
HITCBC 204   736 w->next_ = nullptr; 204   753 w->next_ = nullptr;
HITCBC 205   736 if (tail_) 205   753 if (tail_)
HITCBC 206   253 tail_->next_ = w; 206   260 tail_->next_ = w;
207   else 207   else
HITCBC 208   483 head_ = w; 208   493 head_ = w;
HITCBC 209   736 tail_ = w; 209   753 tail_ = w;
HITCBC 210   736 } 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   3268 T* pop() noexcept 225   3285 T* pop() noexcept
226   { 226   {
HITCBC 227   3268 if (!head_) 227   3285 if (!head_)
HITCBC 228   2532 return nullptr; 228   2532 return nullptr;
HITCBC 229   736 T* w = head_; 229   753 T* w = head_;
HITCBC 230   736 head_ = head_->next_; 230   753 head_ = head_->next_;
HITCBC 231   736 if (!head_) 231   753 if (!head_)
HITCBC 232   482 tail_ = nullptr; 232   492 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   736 w->next_ = nullptr; 234   753 w->next_ = nullptr;
HITCBC 235   736 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