. /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   6471 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   45285 void push_back(T* w) noexcept 66   43752 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   45285 auto* n = static_cast<node*>(w); 68   43752 auto* n = static_cast<node*>(w);
HITCBC 69   45285 n->next_ = nullptr; 69   43752 n->next_ = nullptr;
HITCBC 70   45285 n->prev_ = tail_; 70   43752 n->prev_ = tail_;
HITCBC 71   45285 if (tail_) 71   43752 if (tail_)
HITCBC 72   26305 static_cast<node*>(tail_)->next_ = w; 72   25378 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   18980 head_ = w; 74   18374 head_ = w;
HITCBC 75   45285 tail_ = w; 75   43752 tail_ = w;
HITCBC 76   45285 } 76   43752 }
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   186785 T* pop_front() noexcept 97   189350 T* pop_front() noexcept
98   { 98   {
HITCBC 99   186785 if (!head_) 99   189350 if (!head_)
HITCBC 100   168421 return nullptr; 100   171616 return nullptr;
HITCBC 101   18364 T* w = head_; 101   17734 T* w = head_;
HITCBC 102   18364 head_ = static_cast<node*>(head_)->next_; 102   17734 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   18364 if (head_) 103   17734 if (head_)
HITCBC 104   40 static_cast<node*>(head_)->prev_ = nullptr; 104   40 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   18324 tail_ = nullptr; 106   17694 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   18364 auto* n = static_cast<node*>(w); 109   17734 auto* n = static_cast<node*>(w);
HITCBC 110   18364 n->next_ = nullptr; 110   17734 n->next_ = nullptr;
HITCBC 111   18364 n->prev_ = nullptr; 111   17734 n->prev_ = nullptr;
HITCBC 112   18364 return w; 112   17734 return w;
113   } 113   }
114   114  
HITCBC 115   26921 void remove(T* w) noexcept 115   26018 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   26921 auto* n = static_cast<node*>(w); 117   26018 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   26921 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   26018 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   26921 if (n->prev_) 121   26018 if (n->prev_)
HITCBC 122   8739 static_cast<node*>(n->prev_)->next_ = n->next_; 122   8426 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   18182 head_ = n->next_; 124   17592 head_ = n->next_;
HITCBC 125   26921 if (n->next_) 125   26018 if (n->next_)
HITCBC 126   17560 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   16946 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   9361 tail_ = n->prev_; 128   9072 tail_ = n->prev_;
HITCBC 129   26921 n->next_ = nullptr; 129   26018 n->next_ = nullptr;
HITCBC 130   26921 n->prev_ = nullptr; 130   26018 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   1770 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   1552432 bool empty() const noexcept 191   1538204 bool empty() const noexcept
192   { 192   {
HITCBC 193   1552432 return head_ == nullptr; 193   1538204 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   490590 void push(T* w) noexcept 196   482996 void push(T* w) noexcept
197   { 197   {
HITCBC 198   490590 w->next_ = nullptr; 198   482996 w->next_ = nullptr;
HITCBC 199   490590 if (tail_) 199   482996 if (tail_)
HITCBC 200   203999 tail_->next_ = w; 200   204222 tail_->next_ = w;
201   else 201   else
HITCBC 202   286591 head_ = w; 202   278774 head_ = w;
HITCBC 203   490590 tail_ = w; 203   482996 tail_ = w;
HITCBC 204   490590 } 204   482996 }
205   205  
HITCBC 206   260162 void splice(intrusive_queue& other) noexcept 206   253678 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   260162 if (other.empty()) 208   253678 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   260162 if (tail_) 210   253678 if (tail_)
HITCBC 211   130469 tail_->next_ = other.head_; 211   118250 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   129693 head_ = other.head_; 213   135428 head_ = other.head_;
HITCBC 214   260162 tail_ = other.tail_; 214   253678 tail_ = other.tail_;
HITCBC 215   260162 other.head_ = nullptr; 215   253678 other.head_ = nullptr;
HITCBC 216   260162 other.tail_ = nullptr; 216   253678 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   645501 T* pop() noexcept 219   640600 T* pop() noexcept
220   { 220   {
HITCBC 221   645501 if (!head_) 221   640600 if (!head_)
HITCBC 222   154911 return nullptr; 222   157604 return nullptr;
HITCBC 223   490590 T* w = head_; 223   482996 T* w = head_;
HITCBC 224   490590 head_ = head_->next_; 224   482996 head_ = head_->next_;
HITCBC 225   490590 if (!head_) 225   482996 if (!head_)
HITCBC 226   156122 tail_ = nullptr; 226   160524 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   490590 w->next_ = nullptr; 228   482996 w->next_ = nullptr;
HITCBC 229   490590 return w; 229   482996 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif