. /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   43827 void push_back(T* w) noexcept 66   44609 void push_back(T* w) noexcept
67   { 67   {
HITCBC 68   43827 auto* n = static_cast<node*>(w); 68   44609 auto* n = static_cast<node*>(w);
HITCBC 69   43827 n->next_ = nullptr; 69   44609 n->next_ = nullptr;
HITCBC 70   43827 n->prev_ = tail_; 70   44609 n->prev_ = tail_;
HITCBC 71   43827 if (tail_) 71   44609 if (tail_)
HITCBC 72   25431 static_cast<node*>(tail_)->next_ = w; 72   25901 static_cast<node*>(tail_)->next_ = w;
73   else 73   else
HITCBC 74   18396 head_ = w; 74   18708 head_ = w;
HITCBC 75   43827 tail_ = w; 75   44609 tail_ = w;
HITCBC 76   43827 } 76   44609 }
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   191098 T* pop_front() noexcept 97   194845 T* pop_front() noexcept
98   { 98   {
HITCBC 99   191098 if (!head_) 99   194845 if (!head_)
HITCBC 100   173318 return nullptr; 100   176751 return nullptr;
HITCBC 101   17780 T* w = head_; 101   18094 T* w = head_;
HITCBC 102   17780 head_ = static_cast<node*>(head_)->next_; 102   18094 head_ = static_cast<node*>(head_)->next_;
HITCBC 103   17780 if (head_) 103   18094 if (head_)
HITCBC 104   40 static_cast<node*>(head_)->prev_ = nullptr; 104   42 static_cast<node*>(head_)->prev_ = nullptr;
105   else 105   else
HITCBC 106   17740 tail_ = nullptr; 106   18052 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   17780 auto* n = static_cast<node*>(w); 109   18094 auto* n = static_cast<node*>(w);
HITCBC 110   17780 n->next_ = nullptr; 110   18094 n->next_ = nullptr;
HITCBC 111   17780 n->prev_ = nullptr; 111   18094 n->prev_ = nullptr;
HITCBC 112   17780 return w; 112   18094 return w;
113   } 113   }
114   114  
HITCBC 115   26047 void remove(T* w) noexcept 115   26515 void remove(T* w) noexcept
116   { 116   {
HITCBC 117   26047 auto* n = static_cast<node*>(w); 117   26515 auto* n = static_cast<node*>(w);
118   // Already detached — nothing to do. 118   // Already detached — nothing to do.
HITCBC 119   26047 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 119   26515 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 120   ✗ return; 120   ✗ return;
HITCBC 121   26047 if (n->prev_) 121   26515 if (n->prev_)
HITCBC 122   8449 static_cast<node*>(n->prev_)->next_ = n->next_; 122   8605 static_cast<node*>(n->prev_)->next_ = n->next_;
123   else 123   else
HITCBC 124   17598 head_ = n->next_; 124   17910 head_ = n->next_;
HITCBC 125   26047 if (n->next_) 125   26515 if (n->next_)
HITCBC 126   16976 static_cast<node*>(n->next_)->prev_ = n->prev_; 126   17288 static_cast<node*>(n->next_)->prev_ = n->prev_;
127   else 127   else
HITCBC 128   9071 tail_ = n->prev_; 128   9227 tail_ = n->prev_;
HITCBC 129   26047 n->next_ = nullptr; 129   26515 n->next_ = nullptr;
HITCBC 130   26047 n->prev_ = nullptr; 130   26515 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   1712 intrusive_queue() = default; 177   1716 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   1560837 bool empty() const noexcept 191   1573930 bool empty() const noexcept
192   { 192   {
HITCBC 193   1560837 return head_ == nullptr; 193   1573930 return head_ == nullptr;
194   } 194   }
195   195  
HITCBC 196   491093 void push(T* w) noexcept 196   494290 void push(T* w) noexcept
197   { 197   {
HITCBC 198   491093 w->next_ = nullptr; 198   494290 w->next_ = nullptr;
HITCBC 199   491093 if (tail_) 199   494290 if (tail_)
HITCBC 200   206013 tail_->next_ = w; 200   208597 tail_->next_ = w;
201   else 201   else
HITCBC 202   285080 head_ = w; 202   285693 head_ = w;
HITCBC 203   491093 tail_ = w; 203   494290 tail_ = w;
HITCBC 204   491093 } 204   494290 }
205   205  
HITCBC 206   259629 void splice(intrusive_queue& other) noexcept 206   259778 void splice(intrusive_queue& other) noexcept
207   { 207   {
HITCBC 208   259629 if (other.empty()) 208   259778 if (other.empty())
MISUBC 209   ✗ return; 209   ✗ return;
HITCBC 210   259629 if (tail_) 210   259778 if (tail_)
HITCBC 211   124605 tail_->next_ = other.head_; 211   120680 tail_->next_ = other.head_;
212   else 212   else
HITCBC 213   135024 head_ = other.head_; 213   139098 head_ = other.head_;
HITCBC 214   259629 tail_ = other.tail_; 214   259778 tail_ = other.tail_;
HITCBC 215   259629 other.head_ = nullptr; 215   259778 other.head_ = nullptr;
HITCBC 216   259629 other.tail_ = nullptr; 216   259778 other.tail_ = nullptr;
217   } 217   }
218   218  
HITCBC 219   649141 T* pop() noexcept 219   654725 T* pop() noexcept
220   { 220   {
HITCBC 221   649141 if (!head_) 221   654725 if (!head_)
HITCBC 222   158048 return nullptr; 222   160435 return nullptr;
HITCBC 223   491093 T* w = head_; 223   494290 T* w = head_;
HITCBC 224   491093 head_ = head_->next_; 224   494290 head_ = head_->next_;
HITCBC 225   491093 if (!head_) 225   494290 if (!head_)
HITCBC 226   160475 tail_ = nullptr; 226   165013 tail_ = nullptr;
227   // Defensive: clear stale linkage on popped node. 227   // Defensive: clear stale linkage on popped node.
HITCBC 228   491093 w->next_ = nullptr; 228   494290 w->next_ = nullptr;
HITCBC 229   491093 return w; 229   494290 return w;
230   } 230   }
231   }; 231   };
232   232  
233   } // namespace boost::corosio::detail 233   } // namespace boost::corosio::detail
234   234  
235   #endif 235   #endif