. /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_; 38   T* next_;
39   T* prev_; 39   T* prev_;
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   10646 intrusive_list() = default; 47   10604 intrusive_list() = default;
48   48  
49   intrusive_list(intrusive_list&& other) noexcept 49   intrusive_list(intrusive_list&& other) noexcept
50   : head_(other.head_) 50   : head_(other.head_)
51   , tail_(other.tail_) 51   , tail_(other.tail_)
52   { 52   {
53   other.head_ = nullptr; 53   other.head_ = nullptr;
54   other.tail_ = nullptr; 54   other.tail_ = nullptr;
55   } 55   }
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   38 bool empty() const noexcept 61   38 bool empty() const noexcept
62   { 62   {
HITCBC 63   38 return head_ == nullptr; 63   38 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.
67   T* front() const noexcept 67   T* front() const noexcept
68   { 68   {
69   return head_; 69   return head_;
70   } 70   }
71   71  
HITCBC 72   34160 void push_back(T* w) noexcept 72   45087 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   34160 auto* n = static_cast<node*>(w); 74   45087 auto* n = static_cast<node*>(w);
HITCBC 75   34160 n->next_ = nullptr; 75   45087 n->next_ = nullptr;
HITCBC 76   34160 n->prev_ = tail_; 76   45087 n->prev_ = tail_;
HITCBC 77   34160 if (tail_) 77   45087 if (tail_)
HITCBC 78   19362 static_cast<node*>(tail_)->next_ = w; 78   25923 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   14798 head_ = w; 80   19164 head_ = w;
HITCBC 81   34160 tail_ = w; 81   45087 tail_ = w;
HITCBC 82   34160 } 82   45087 }
83   83  
84   void splice_back(intrusive_list& other) noexcept 84   void splice_back(intrusive_list& other) noexcept
85   { 85   {
86   if (other.empty()) 86   if (other.empty())
87   return; 87   return;
88   if (tail_) 88   if (tail_)
89   { 89   {
90   static_cast<node*>(tail_)->next_ = other.head_; 90   static_cast<node*>(tail_)->next_ = other.head_;
91   static_cast<node*>(other.head_)->prev_ = tail_; 91   static_cast<node*>(other.head_)->prev_ = tail_;
92   tail_ = other.tail_; 92   tail_ = other.tail_;
93   } 93   }
94   else 94   else
95   { 95   {
96   head_ = other.head_; 96   head_ = other.head_;
97   tail_ = other.tail_; 97   tail_ = other.tail_;
98   } 98   }
99   other.head_ = nullptr; 99   other.head_ = nullptr;
100   other.tail_ = nullptr; 100   other.tail_ = nullptr;
101   } 101   }
102   102  
HITCBC 103   290137 T* pop_front() noexcept 103   278917 T* pop_front() noexcept
104   { 104   {
HITCBC 105   290137 if (!head_) 105   278917 if (!head_)
HITCBC 106   276397 return nullptr; 106   260805 return nullptr;
HITCBC 107   13740 T* w = head_; 107   18112 T* w = head_;
HITCBC 108   13740 head_ = static_cast<node*>(head_)->next_; 108   18112 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   13740 if (head_) 109   18112 if (head_)
HITCBC 110   42 static_cast<node*>(head_)->prev_ = nullptr; 110   40 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   13698 tail_ = nullptr; 112   18072 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   13740 auto* n = static_cast<node*>(w); 115   18112 auto* n = static_cast<node*>(w);
HITCBC 116   13740 n->next_ = nullptr; 116   18112 n->next_ = nullptr;
HITCBC 117   13740 n->prev_ = nullptr; 117   18112 n->prev_ = nullptr;
HITCBC 118   13740 return w; 118   18112 return w;
119   } 119   }
120   120  
HITCBC 121   20420 void remove(T* w) noexcept 121   26975 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   20420 auto* n = static_cast<node*>(w); 123   26975 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   20420 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   26975 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   20420 if (n->prev_) 127   26975 if (n->prev_)
HITCBC 128   6447 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8632 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   13973 head_ = n->next_; 130   18343 head_ = n->next_;
HITCBC 131   20420 if (n->next_) 131   26975 if (n->next_)
HITCBC 132   12924 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   17298 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7496 tail_ = n->prev_; 134   9677 tail_ = n->prev_;
HITCBC 135   20420 n->next_ = nullptr; 135   26975 n->next_ = nullptr;
HITCBC 136   20420 n->prev_ = nullptr; 136   26975 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   122 void for_each(F f) 141   122 void for_each(F f)
142   { 142   {
HITCBC 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   122 } 145   122 }
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_; 175   T* next_;
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   2743 intrusive_queue() = default; 183   2730 intrusive_queue() = default;
184   184  
185   intrusive_queue(intrusive_queue&& other) noexcept 185   intrusive_queue(intrusive_queue&& other) noexcept
186   : head_(other.head_) 186   : head_(other.head_)
187   , tail_(other.tail_) 187   , tail_(other.tail_)
188   { 188   {
189   other.head_ = nullptr; 189   other.head_ = nullptr;
190   other.tail_ = nullptr; 190   other.tail_ = nullptr;
191   } 191   }
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   2329333 bool empty() const noexcept 197   2171701 bool empty() const noexcept
198   { 198   {
HITCBC 199   2329333 return head_ == nullptr; 199   2171701 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   712968 void push(T* w) noexcept 202   668121 void push(T* w) noexcept
203   { 203   {
HITCBC 204   712968 w->next_ = nullptr; 204   668121 w->next_ = nullptr;
HITCBC 205   712968 if (tail_) 205   668121 if (tail_)
HITCBC 206   312174 tail_->next_ = w; 206   295457 tail_->next_ = w;
207   else 207   else
HITCBC 208   400794 head_ = w; 208   372664 head_ = w;
HITCBC 209   712968 tail_ = w; 209   668121 tail_ = w;
HITCBC 210   712968 } 210   668121 }
211   211  
HITCBC 212   381255 void splice(intrusive_queue& other) noexcept 212   348239 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   381255 if (other.empty()) 214   348239 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   381255 if (tail_) 216   348239 if (tail_)
HITCBC 217   145757 tail_->next_ = other.head_; 217   127670 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   235498 head_ = other.head_; 219   220569 head_ = other.head_;
HITCBC 220   381255 tail_ = other.tail_; 220   348239 tail_ = other.tail_;
HITCBC 221   381255 other.head_ = nullptr; 221   348239 other.head_ = nullptr;
HITCBC 222   381255 other.tail_ = nullptr; 222   348239 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   984231 T* pop() noexcept 225   916468 T* pop() noexcept
226   { 226   {
HITCBC 227   984231 if (!head_) 227   916468 if (!head_)
HITCBC 228   271263 return nullptr; 228   248347 return nullptr;
HITCBC 229   712968 T* w = head_; 229   668121 T* w = head_;
HITCBC 230   712968 head_ = head_->next_; 230   668121 head_ = head_->next_;
HITCBC 231   712968 if (!head_) 231   668121 if (!head_)
HITCBC 232   255037 tail_ = nullptr; 232   244994 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   712968 w->next_ = nullptr; 234   668121 w->next_ = nullptr;
HITCBC 235   712968 return w; 235   668121 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif