. /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   10606 intrusive_list() = default; 47   10606 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   42940 void push_back(T* w) noexcept 72   42071 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   42940 auto* n = static_cast<node*>(w); 74   42071 auto* n = static_cast<node*>(w);
HITCBC 75   42940 n->next_ = nullptr; 75   42071 n->next_ = nullptr;
HITCBC 76   42940 n->prev_ = tail_; 76   42071 n->prev_ = tail_;
HITCBC 77   42940 if (tail_) 77   42071 if (tail_)
HITCBC 78   24613 static_cast<node*>(tail_)->next_ = w; 78   24112 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18327 head_ = w; 80   17959 head_ = w;
HITCBC 81   42940 tail_ = w; 81   42071 tail_ = w;
HITCBC 82   42940 } 82   42071 }
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   326946 T* pop_front() noexcept 103   268213 T* pop_front() noexcept
104   { 104   {
HITCBC 105   326946 if (!head_) 105   268213 if (!head_)
HITCBC 106   309670 return nullptr; 106   251303 return nullptr;
HITCBC 107   17276 T* w = head_; 107   16910 T* w = head_;
HITCBC 108   17276 head_ = static_cast<node*>(head_)->next_; 108   16910 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17276 if (head_) 109   16910 if (head_)
HITCBC 110   41 static_cast<node*>(head_)->prev_ = nullptr; 110   43 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   17235 tail_ = nullptr; 112   16867 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   17276 auto* n = static_cast<node*>(w); 115   16910 auto* n = static_cast<node*>(w);
HITCBC 116   17276 n->next_ = nullptr; 116   16910 n->next_ = nullptr;
HITCBC 117   17276 n->prev_ = nullptr; 117   16910 n->prev_ = nullptr;
HITCBC 118   17276 return w; 118   16910 return w;
119   } 119   }
120   120  
HITCBC 121   25664 void remove(T* w) noexcept 121   25161 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25664 auto* n = static_cast<node*>(w); 123   25161 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25664 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   25161 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   25664 if (n->prev_) 127   25161 if (n->prev_)
HITCBC 128   8194 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8026 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17470 head_ = n->next_; 130   17135 head_ = n->next_;
HITCBC 131   25664 if (n->next_) 131   25161 if (n->next_)
HITCBC 132   16425 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   16090 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9239 tail_ = n->prev_; 134   9071 tail_ = n->prev_;
HITCBC 135   25664 n->next_ = nullptr; 135   25161 n->next_ = nullptr;
HITCBC 136   25664 n->prev_ = nullptr; 136   25161 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   122 void for_each(F f) 141   122 void for_each(F f)
142   { 142   {
HITCBC 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   122 } 145   122 }
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_; 175   T* next_;
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   2733 intrusive_queue() = default; 183   2732 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   2587284 bool empty() const noexcept 197   2069109 bool empty() const noexcept
198   { 198   {
HITCBC 199   2587284 return head_ == nullptr; 199   2069109 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   792225 void push(T* w) noexcept 202   635807 void push(T* w) noexcept
203   { 203   {
HITCBC 204   792225 w->next_ = nullptr; 204   635807 w->next_ = nullptr;
HITCBC 205   792225 if (tail_) 205   635807 if (tail_)
HITCBC 206   348005 tail_->next_ = w; 206   279761 tail_->next_ = w;
207   else 207   else
HITCBC 208   444220 head_ = w; 208   356046 head_ = w;
HITCBC 209   792225 tail_ = w; 209   635807 tail_ = w;
HITCBC 210   792225 } 210   635807 }
211   211  
HITCBC 212   419375 void splice(intrusive_queue& other) noexcept 212   332168 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   419375 if (other.empty()) 214   332168 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   419375 if (tail_) 216   332168 if (tail_)
HITCBC 217   156648 tail_->next_ = other.head_; 217   121586 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   262727 head_ = other.head_; 219   210582 head_ = other.head_;
HITCBC 220   419375 tail_ = other.tail_; 220   332168 tail_ = other.tail_;
HITCBC 221   419375 other.head_ = nullptr; 221   332168 other.head_ = nullptr;
HITCBC 222   419375 other.tail_ = nullptr; 222   332168 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   1091011 T* pop() noexcept 225   870472 T* pop() noexcept
226   { 226   {
HITCBC 227   1091011 if (!head_) 227   870472 if (!head_)
HITCBC 228   298786 return nullptr; 228   234665 return nullptr;
HITCBC 229   792225 T* w = head_; 229   635807 T* w = head_;
HITCBC 230   792225 head_ = head_->next_; 230   635807 head_ = head_->next_;
HITCBC 231   792225 if (!head_) 231   635807 if (!head_)
HITCBC 232   287572 tail_ = nullptr; 232   234460 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   792225 w->next_ = nullptr; 234   635807 w->next_ = nullptr;
HITCBC 235   792225 return w; 235   635807 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif