. /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   21061 intrusive_list() = default; 47   21173 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   44732 void push_back(T* w) noexcept 72   40836 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   44732 auto* n = static_cast<node*>(w); 74   40836 auto* n = static_cast<node*>(w);
HITCBC 75   44732 n->next_ = nullptr; 75   40836 n->next_ = nullptr;
HITCBC 76   44732 n->prev_ = tail_; 76   40836 n->prev_ = tail_;
HITCBC 77   44732 if (tail_) 77   40836 if (tail_)
HITCBC 78   29504 static_cast<node*>(tail_)->next_ = w; 78   27038 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   15228 head_ = w; 80   13798 head_ = w;
HITCBC 81   44732 tail_ = w; 81   40836 tail_ = w;
HITCBC 82   44732 } 82   40836 }
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   410996 T* pop_front() noexcept 103   409231 T* pop_front() noexcept
104   { 104   {
HITCBC 105   410996 if (!head_) 105   409231 if (!head_)
HITCBC 106   391331 return nullptr; 106   390563 return nullptr;
HITCBC 107   19665 T* w = head_; 107   18668 T* w = head_;
HITCBC 108   19665 head_ = static_cast<node*>(head_)->next_; 108   18668 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   19665 if (head_) 109   18668 if (head_)
HITCBC 110   6926 static_cast<node*>(head_)->prev_ = nullptr; 110   7371 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   12739 tail_ = nullptr; 112   11297 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   19665 auto* n = static_cast<node*>(w); 115   18668 auto* n = static_cast<node*>(w);
HITCBC 116   19665 n->next_ = nullptr; 116   18668 n->next_ = nullptr;
HITCBC 117   19665 n->prev_ = nullptr; 117   18668 n->prev_ = nullptr;
HITCBC 118   19665 return w; 118   18668 return w;
119   } 119   }
120   120  
HITCBC 121   25065 void remove(T* w) noexcept 121   22166 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25065 auto* n = static_cast<node*>(w); 123   22166 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25065 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   22166 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   25064 if (n->prev_) 127   22165 if (n->prev_)
HITCBC 128   7582 static_cast<node*>(n->prev_)->next_ = n->next_; 128   6614 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17482 head_ = n->next_; 130   15551 head_ = n->next_;
HITCBC 131   25064 if (n->next_) 131   22165 if (n->next_)
HITCBC 132   15115 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   13172 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9949 tail_ = n->prev_; 134   8993 tail_ = n->prev_;
HITCBC 135   25064 n->next_ = nullptr; 135   22165 n->next_ = nullptr;
HITCBC 136   25064 n->prev_ = nullptr; 136   22165 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   315 void for_each(F f) 141   321 void for_each(F f)
142   { 142   {
HITCBC 143   324 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   330 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   9 f(p); 144   9 f(p);
HITCBC 145   315 } 145   321 }
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   2097 intrusive_queue() = default; 183   2109 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   727 bool empty() const noexcept 197   737 bool empty() const noexcept
198   { 198   {
HITCBC 199   727 return head_ == nullptr; 199   737 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   514 void push(T* w) noexcept 202   521 void push(T* w) noexcept
203   { 203   {
HITCBC 204   514 w->next_ = nullptr; 204   521 w->next_ = nullptr;
HITCBC 205   514 if (tail_) 205   521 if (tail_)
HITCBC 206   256 tail_->next_ = w; 206   261 tail_->next_ = w;
207   else 207   else
HITCBC 208   258 head_ = w; 208   260 head_ = w;
HITCBC 209   514 tail_ = w; 209   521 tail_ = w;
HITCBC 210   514 } 210   521 }
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   2801 T* pop() noexcept 225   2825 T* pop() noexcept
226   { 226   {
HITCBC 227   2801 if (!head_) 227   2825 if (!head_)
HITCBC 228   2287 return nullptr; 228   2304 return nullptr;
HITCBC 229   514 T* w = head_; 229   521 T* w = head_;
HITCBC 230   514 head_ = head_->next_; 230   521 head_ = head_->next_;
HITCBC 231   514 if (!head_) 231   521 if (!head_)
HITCBC 232   257 tail_ = nullptr; 232   259 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   514 w->next_ = nullptr; 234   521 w->next_ = nullptr;
HITCBC 235   514 return w; 235   521 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif