. /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   12913 intrusive_list() = default; 47   12913 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   42804 void push_back(T* w) noexcept 72   37115 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   42804 auto* n = static_cast<node*>(w); 74   37115 auto* n = static_cast<node*>(w);
HITCBC 75   42804 n->next_ = nullptr; 75   37115 n->next_ = nullptr;
HITCBC 76   42804 n->prev_ = tail_; 76   37115 n->prev_ = tail_;
HITCBC 77   42804 if (tail_) 77   37115 if (tail_)
HITCBC 78   24465 static_cast<node*>(tail_)->next_ = w; 78   21053 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18339 head_ = w; 80   16062 head_ = w;
HITCBC 81   42804 tail_ = w; 81   37115 tail_ = w;
HITCBC 82   42804 } 82   37115 }
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   286497 T* pop_front() noexcept 103   275674 T* pop_front() noexcept
104   { 104   {
HITCBC 105   286497 if (!head_) 105   275674 if (!head_)
HITCBC 106   269463 return nullptr; 106   260918 return nullptr;
HITCBC 107   17034 T* w = head_; 107   14756 T* w = head_;
HITCBC 108   17034 head_ = static_cast<node*>(head_)->next_; 108   14756 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17034 if (head_) 109   14756 if (head_)
HITCBC 110   42 static_cast<node*>(head_)->prev_ = nullptr; 110   41 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   16992 tail_ = nullptr; 112   14715 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   17034 auto* n = static_cast<node*>(w); 115   14756 auto* n = static_cast<node*>(w);
HITCBC 116   17034 n->next_ = nullptr; 116   14756 n->next_ = nullptr;
HITCBC 117   17034 n->prev_ = nullptr; 117   14756 n->prev_ = nullptr;
HITCBC 118   17034 return w; 118   14756 return w;
119   } 119   }
120   120  
HITCBC 121   25770 void remove(T* w) noexcept 121   22359 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25770 auto* n = static_cast<node*>(w); 123   22359 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25770 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   22359 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   25770 if (n->prev_) 127   22359 if (n->prev_)
HITCBC 128   8135 static_cast<node*>(n->prev_)->next_ = n->next_; 128   6998 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17635 head_ = n->next_; 130   15361 head_ = n->next_;
HITCBC 131   25770 if (n->next_) 131   22359 if (n->next_)
HITCBC 132   16354 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   14080 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9416 tail_ = n->prev_; 134   8279 tail_ = n->prev_;
HITCBC 135   25770 n->next_ = nullptr; 135   22359 n->next_ = nullptr;
HITCBC 136   25770 n->prev_ = nullptr; 136   22359 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   216 void for_each(F f) 141   216 void for_each(F f)
142   { 142   {
HITCBC 143   216 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   216 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   216 } 145   216 }
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   3354 intrusive_queue() = default; 183   3351 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   2154607 bool empty() const noexcept 197   2135480 bool empty() const noexcept
198   { 198   {
HITCBC 199   2154607 return head_ == nullptr; 199   2135480 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   660255 void push(T* w) noexcept 202   655151 void push(T* w) noexcept
203   { 203   {
HITCBC 204   660255 w->next_ = nullptr; 204   655151 w->next_ = nullptr;
HITCBC 205   660255 if (tail_) 205   655151 if (tail_)
HITCBC 206   295419 tail_->next_ = w; 206   290258 tail_->next_ = w;
207   else 207   else
HITCBC 208   364836 head_ = w; 208   364893 head_ = w;
HITCBC 209   660255 tail_ = w; 209   655151 tail_ = w;
HITCBC 210   660255 } 210   655151 }
211   211  
HITCBC 212   339684 void splice(intrusive_queue& other) noexcept 212   343485 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   339684 if (other.empty()) 214   343485 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   339684 if (tail_) 216   343485 if (tail_)
HITCBC 217   113939 tail_->next_ = other.head_; 217   125736 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   225745 head_ = other.head_; 219   217749 head_ = other.head_;
HITCBC 220   339684 tail_ = other.tail_; 220   343485 tail_ = other.tail_;
HITCBC 221   339684 other.head_ = nullptr; 221   343485 other.head_ = nullptr;
HITCBC 222   339684 other.tail_ = nullptr; 222   343485 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   908440 T* pop() noexcept 225   902581 T* pop() noexcept
226   { 226   {
HITCBC 227   908440 if (!head_) 227   902581 if (!head_)
HITCBC 228   248185 return nullptr; 228   247430 return nullptr;
HITCBC 229   660255 T* w = head_; 229   655151 T* w = head_;
HITCBC 230   660255 head_ = head_->next_; 230   655151 head_ = head_->next_;
HITCBC 231   660255 if (!head_) 231   655151 if (!head_)
HITCBC 232   250897 tail_ = nullptr; 232   239157 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   660255 w->next_ = nullptr; 234   655151 w->next_ = nullptr;
HITCBC 235   660255 return w; 235   655151 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif