. /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   6327 intrusive_list() = default; 47   6327 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   32 bool empty() const noexcept 61   32 bool empty() const noexcept
62   { 62   {
HITCBC 63   32 return head_ == nullptr; 63   32 return head_ == nullptr;
64   } 64   }
65   65  
HITCBC 66   37469 void push_back(T* w) noexcept 66   39697 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   37469 auto* n = static_cast<node*>(w); 68   39697 auto* n = static_cast<node*>(w);
HITCBC 69   37469 n->next_ = nullptr; 69   39697 n->next_ = nullptr;
HITCBC 70   37469 n->prev_ = tail_; 70   39697 n->prev_ = tail_;
HITCBC 71   37469 if (tail_) 71   39697 if (tail_)
HITCBC 72   21622 static_cast<node*>(tail_)->next_ = w; 72   22946 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   15847 head_ = w; 74   16751 head_ = w;
HITCBC 75   37469 tail_ = w; 75   39697 tail_ = w;
HITCBC 76   37469 } 76   39697 }
77   77  
78   void splice_back(intrusive_list& other) noexcept 78   void splice_back(intrusive_list& other) noexcept
79   { 79   {
80   if (other.empty()) 80   if (other.empty())
81   return; 81   return;
82   if (tail_) 82   if (tail_)
83   { 83   {
84   static_cast<node*>(tail_)->next_ = other.head_; 84   static_cast<node*>(tail_)->next_ = other.head_;
85   static_cast<node*>(other.head_)->prev_ = tail_; 85   static_cast<node*>(other.head_)->prev_ = tail_;
86   tail_ = other.tail_; 86   tail_ = other.tail_;
87   } 87   }
88   else 88   else
89   { 89   {
90   head_ = other.head_; 90   head_ = other.head_;
91   tail_ = other.tail_; 91   tail_ = other.tail_;
92   } 92   }
93   other.head_ = nullptr; 93   other.head_ = nullptr;
94   other.tail_ = nullptr; 94   other.tail_ = nullptr;
95   } 95   }
96   96  
HITCBC 97   188788 T* pop_front() noexcept 97   262394 T* pop_front() noexcept
98   { 98   {
HITCBC 99   188788 if (!head_) 99   262394 if (!head_)
HITCBC 100   173556 return nullptr; 100   246258 return nullptr;
HITCBC 101   15232 T* w = head_; 101   16136 T* w = head_;
HITCBC 102   15232 head_ = static_cast<node*>(head_)->next_; 102   16136 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   15232 if (head_) 103   16136 if (head_)
HITCBC 104   41 static_cast<node*>(head_)->prev_ = nullptr; 104   41 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   15191 tail_ = nullptr; 106   16095 tail_ = nullptr;
107   // Defensive: clear stale linkage so remove() on a 107   // Defensive: clear stale linkage so remove() on a
108   // popped node cannot corrupt the list. 108   // popped node cannot corrupt the list.
HITCBC 109   15232 auto* n = static_cast<node*>(w); 109   16136 auto* n = static_cast<node*>(w);
HITCBC 110   15232 n->next_ = nullptr; 110   16136 n->next_ = nullptr;
HITCBC 111   15232 n->prev_ = nullptr; 111   16136 n->prev_ = nullptr;
HITCBC 112   15232 return w; 112   16136 return w;
113   } 113   }
114   114  
HITCBC 115   22237 void remove(T* w) noexcept 115   23561 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   22237 auto* n = static_cast<node*>(w); 117   23561 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   22237 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   23561 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   22237 if (n->prev_) 121   23561 if (n->prev_)
HITCBC 122   7179 static_cast<node*>(n->prev_)->next_ = n->next_; 122   7619 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   15058 head_ = n->next_; 124   15942 head_ = n->next_;
HITCBC 125   22237 if (n->next_) 125   23561 if (n->next_)
HITCBC 126   14436 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   15320 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   7801 tail_ = n->prev_; 128   8241 tail_ = n->prev_;
HITCBC 129   22237 n->next_ = nullptr; 129   23561 n->next_ = nullptr;
HITCBC 130   22237 n->prev_ = nullptr; 130   23561 n->prev_ = nullptr;
131   } 131   }
132   132  
133   /// Invoke @p f for each element in the list. 133   /// Invoke @p f for each element in the list.
134   template<class F> 134   template<class F>
HITCBC 135   67 void for_each(F f) 135   67 void for_each(F f)
136   { 136   {
HITCBC 137   67 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 137   67 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 138   ✗ f(p); 138   ✗ f(p);
HITCBC 139   67 } 139   67 }
140   }; 140   };
141   141  
142   /** An intrusive singly linked FIFO queue. 142   /** An intrusive singly linked FIFO queue.
143   143  
144   This container provides O(1) push and pop operations for 144   This container provides O(1) push and pop operations for
145   elements that derive from @ref node. Elements are not 145   elements that derive from @ref node. Elements are not
146   copied or moved; they are linked directly into the queue. 146   copied or moved; they are linked directly into the queue.
147   147  
148   Unlike @ref intrusive_list, this uses only a single `next_` 148   Unlike @ref intrusive_list, this uses only a single `next_`
149   pointer per node, saving memory at the cost of not supporting 149   pointer per node, saving memory at the cost of not supporting
150   O(1) removal of arbitrary elements. 150   O(1) removal of arbitrary elements.
151   151  
152   @tparam T The element type. Must derive from `intrusive_queue<T>::node`. 152   @tparam T The element type. Must derive from `intrusive_queue<T>::node`.
153   */ 153   */
154   template<class T> 154   template<class T>
155   class intrusive_queue 155   class intrusive_queue
156   { 156   {
157   public: 157   public:
158   /** Base class for queue elements. 158   /** Base class for queue elements.
159   159  
160   Derive from this class to make a type usable with 160   Derive from this class to make a type usable with
161   @ref intrusive_queue. The `next_` pointer is private 161   @ref intrusive_queue. The `next_` pointer is private
162   and accessible only to the queue. 162   and accessible only to the queue.
163   */ 163   */
164   class node 164   class node
165   { 165   {
166   friend class intrusive_queue; 166   friend class intrusive_queue;
167   167  
168   private: 168   private:
169   T* next_; 169   T* next_;
170   }; 170   };
171   171  
172   private: 172   private:
173   T* head_ = nullptr; 173   T* head_ = nullptr;
174   T* tail_ = nullptr; 174   T* tail_ = nullptr;
175   175  
176   public: 176   public:
HITCBC 177   1714 intrusive_queue() = default; 177   1734 intrusive_queue() = default;
178   178  
179   intrusive_queue(intrusive_queue&& other) noexcept 179   intrusive_queue(intrusive_queue&& other) noexcept
180   : head_(other.head_) 180   : head_(other.head_)
181   , tail_(other.tail_) 181   , tail_(other.tail_)
182   { 182   {
183   other.head_ = nullptr; 183   other.head_ = nullptr;
184   other.tail_ = nullptr; 184   other.tail_ = nullptr;
185   } 185   }
186   186  
187   intrusive_queue(intrusive_queue const&) = delete; 187   intrusive_queue(intrusive_queue const&) = delete;
188   intrusive_queue& operator=(intrusive_queue const&) = delete; 188   intrusive_queue& operator=(intrusive_queue const&) = delete;
189   intrusive_queue& operator=(intrusive_queue&&) = delete; 189   intrusive_queue& operator=(intrusive_queue&&) = delete;
190   190  
HITCBC 191   1558822 bool empty() const noexcept 191   2294081 bool empty() const noexcept
192   { 192   {
HITCBC 193   1558822 return head_ == nullptr; 193   2294081 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   488783 void push(T* w) noexcept 196   715319 void push(T* w) noexcept
197   { 197   {
HITCBC 198   488783 w->next_ = nullptr; 198   715319 w->next_ = nullptr;
HITCBC 199   488783 if (tail_) 199   715319 if (tail_)
HITCBC 200   206037 tail_->next_ = w; 200   299027 tail_->next_ = w;
201   else 201   else
HITCBC 202   282746 head_ = w; 202   416292 head_ = w;
HITCBC 203   488783 tail_ = w; 203   715319 tail_ = w;
HITCBC 204   488783 } 204   715319 }
205   205  
HITCBC 206   261377 void splice(intrusive_queue& other) noexcept 206   393330 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   261377 if (other.empty()) 208   393330 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   261377 if (tail_) 210   393330 if (tail_)
HITCBC 211   125436 tail_->next_ = other.head_; 211   194737 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   135941 head_ = other.head_; 213   198593 head_ = other.head_;
HITCBC 214   261377 tail_ = other.tail_; 214   393330 tail_ = other.tail_;
HITCBC 215   261377 other.head_ = nullptr; 215   393330 other.head_ = nullptr;
HITCBC 216   261377 other.tail_ = nullptr; 216   393330 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   652318 T* pop() noexcept 219   963025 T* pop() noexcept
220   { 220   {
HITCBC 221   652318 if (!head_) 221   963025 if (!head_)
HITCBC 222   163535 return nullptr; 222   247706 return nullptr;
HITCBC 223   488783 T* w = head_; 223   715319 T* w = head_;
HITCBC 224   488783 head_ = head_->next_; 224   715319 head_ = head_->next_;
HITCBC 225   488783 if (!head_) 225   715319 if (!head_)
HITCBC 226   157310 tail_ = nullptr; 226   221555 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   488783 w->next_ = nullptr; 228   715319 w->next_ = nullptr;
HITCBC 229   488783 return w; 229   715319 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif