. /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   21173 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   32880 void push_back(T* w) noexcept 72   32923 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   32880 auto* n = static_cast<node*>(w); 74   32923 auto* n = static_cast<node*>(w);
HITCBC 75   32880 n->next_ = nullptr; 75   32923 n->next_ = nullptr;
HITCBC 76   32880 n->prev_ = tail_; 76   32923 n->prev_ = tail_;
HITCBC 77   32880 if (tail_) 77   32923 if (tail_)
HITCBC 78   21014 static_cast<node*>(tail_)->next_ = w; 78   20947 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   11866 head_ = w; 80   11976 head_ = w;
HITCBC 81   32880 tail_ = w; 81   32923 tail_ = w;
HITCBC 82   32880 } 82   32923 }
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   351469 T* pop_front() noexcept 103   360545 T* pop_front() noexcept
104   { 104   {
HITCBC 105   351469 if (!head_) 105   360545 if (!head_)
HITCBC 106   334656 return nullptr; 106   343764 return nullptr;
HITCBC 107   16813 T* w = head_; 107   16781 T* w = head_;
HITCBC 108   16813 head_ = static_cast<node*>(head_)->next_; 108   16781 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16813 if (head_) 109   16781 if (head_)
HITCBC 110   7448 static_cast<node*>(head_)->prev_ = nullptr; 110   7306 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9365 tail_ = nullptr; 112   9475 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   16813 auto* n = static_cast<node*>(w); 115   16781 auto* n = static_cast<node*>(w);
HITCBC 116   16813 n->next_ = nullptr; 116   16781 n->next_ = nullptr;
HITCBC 117   16813 n->prev_ = nullptr; 117   16781 n->prev_ = nullptr;
HITCBC 118   16813 return w; 118   16781 return w;
119   } 119   }
120   120  
HITCBC 121   16065 void remove(T* w) noexcept 121   16140 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16065 auto* n = static_cast<node*>(w); 123   16140 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16065 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   16140 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   16064 if (n->prev_) 127   16139 if (n->prev_)
HITCBC 128   4580 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4605 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11484 head_ = n->next_; 130   11534 head_ = n->next_;
HITCBC 131   16064 if (n->next_) 131   16139 if (n->next_)
HITCBC 132   9105 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   9155 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   6959 tail_ = n->prev_; 134   6984 tail_ = n->prev_;
HITCBC 135   16064 n->next_ = nullptr; 135   16139 n->next_ = nullptr;
HITCBC 136   16064 n->prev_ = nullptr; 136   16139 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   321 void for_each(F f) 141   321 void for_each(F f)
142   { 142   {
HITCBC 143   330 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   321 } 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   2109 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   736 bool empty() const noexcept 197   726 bool empty() const noexcept
198   { 198   {
HITCBC 199   736 return head_ == nullptr; 199   726 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   521 void push(T* w) noexcept 202   521 void push(T* w) noexcept
203   { 203   {
HITCBC 204   521 w->next_ = nullptr; 204   521 w->next_ = nullptr;
HITCBC 205   521 if (tail_) 205   521 if (tail_)
HITCBC 206   261 tail_->next_ = w; 206   259 tail_->next_ = w;
207   else 207   else
HITCBC 208   260 head_ = w; 208   262 head_ = w;
HITCBC 209   521 tail_ = w; 209   521 tail_ = w;
HITCBC 210   521 } 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   2825 T* pop() noexcept 225   2825 T* pop() noexcept
226   { 226   {
HITCBC 227   2825 if (!head_) 227   2825 if (!head_)
HITCBC 228   2304 return nullptr; 228   2304 return nullptr;
HITCBC 229   521 T* w = head_; 229   521 T* w = head_;
HITCBC 230   521 head_ = head_->next_; 230   521 head_ = head_->next_;
HITCBC 231   521 if (!head_) 231   521 if (!head_)
HITCBC 232   259 tail_ = nullptr; 232   261 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   521 w->next_ = nullptr; 234   521 w->next_ = nullptr;
HITCBC 235   521 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