. /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   14420 intrusive_list() = default; 47   14580 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   38042 void push_back(T* w) noexcept 72   36504 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   38042 auto* n = static_cast<node*>(w); 74   36504 auto* n = static_cast<node*>(w);
HITCBC 75   38042 n->next_ = nullptr; 75   36504 n->next_ = nullptr;
HITCBC 76   38042 n->prev_ = tail_; 76   36504 n->prev_ = tail_;
HITCBC 77   38042 if (tail_) 77   36504 if (tail_)
HITCBC 78   27120 static_cast<node*>(tail_)->next_ = w; 78   25950 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   10922 head_ = w; 80   10554 head_ = w;
HITCBC 81   38042 tail_ = w; 81   36504 tail_ = w;
HITCBC 82   38042 } 82   36504 }
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   428493 T* pop_front() noexcept 103   421329 T* pop_front() noexcept
104   { 104   {
HITCBC 105   428493 if (!head_) 105   421329 if (!head_)
HITCBC 106   419117 return nullptr; 106   412352 return nullptr;
HITCBC 107   9376 T* w = head_; 107   8977 T* w = head_;
HITCBC 108   9376 head_ = static_cast<node*>(head_)->next_; 108   8977 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   9376 if (head_) 109   8977 if (head_)
HITCBC 110   14 static_cast<node*>(head_)->prev_ = nullptr; 110   13 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9362 tail_ = nullptr; 112   8964 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   9376 auto* n = static_cast<node*>(w); 115   8977 auto* n = static_cast<node*>(w);
HITCBC 116   9376 n->next_ = nullptr; 116   8977 n->next_ = nullptr;
HITCBC 117   9376 n->prev_ = nullptr; 117   8977 n->prev_ = nullptr;
HITCBC 118   9376 return w; 118   8977 return w;
119   } 119   }
120   120  
HITCBC 121   28664 void remove(T* w) noexcept 121   27525 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   28664 auto* n = static_cast<node*>(w); 123   27525 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   28664 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   27525 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   28663 if (n->prev_) 127   27524 if (n->prev_)
HITCBC 128   9019 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8637 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   19644 head_ = n->next_; 130   18887 head_ = n->next_;
HITCBC 131   28663 if (n->next_) 131   27524 if (n->next_)
HITCBC 132   18170 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   17391 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   10493 tail_ = n->prev_; 134   10133 tail_ = n->prev_;
HITCBC 135   28663 n->next_ = nullptr; 135   27524 n->next_ = nullptr;
HITCBC 136   28663 n->prev_ = nullptr; 136   27524 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   228 void for_each(F f) 141   228 void for_each(F f)
142   { 142   {
HITCBC 143   231 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   231 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   3 f(p); 144   3 f(p);
HITCBC 145   228 } 145   228 }
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   1436 intrusive_queue() = default; 183   1452 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   1957 bool empty() const noexcept 197   1935 bool empty() const noexcept
198   { 198   {
HITCBC 199   1957 return head_ == nullptr; 199   1935 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   391 void push(T* w) noexcept 202   391 void push(T* w) noexcept
203   { 203   {
HITCBC 204   391 w->next_ = nullptr; 204   391 w->next_ = nullptr;
HITCBC 205   391 if (tail_) 205   391 if (tail_)
HITCBC 206   113 tail_->next_ = w; 206   119 tail_->next_ = w;
207   else 207   else
HITCBC 208   278 head_ = w; 208   272 head_ = w;
HITCBC 209   391 tail_ = w; 209   391 tail_ = w;
HITCBC 210   391 } 210   391 }
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   3275 T* pop() noexcept 225   3307 T* pop() noexcept
226   { 226   {
HITCBC 227   3275 if (!head_) 227   3307 if (!head_)
HITCBC 228   2884 return nullptr; 228   2916 return nullptr;
HITCBC 229   391 T* w = head_; 229   391 T* w = head_;
HITCBC 230   391 head_ = head_->next_; 230   391 head_ = head_->next_;
HITCBC 231   391 if (!head_) 231   391 if (!head_)
HITCBC 232   277 tail_ = nullptr; 232   271 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   391 w->next_ = nullptr; 234   391 w->next_ = nullptr;
HITCBC 235   391 return w; 235   391 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif