. /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   11618 intrusive_list() = default; 47   11652 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   21 bool empty() const noexcept 61   22 bool empty() const noexcept
62   { 62   {
HITCBC 63   21 return head_ == nullptr; 63   22 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   30082 void push_front(T* w) noexcept 72   31205 void push_front(T* w) noexcept
73   { 73   {
HITCBC 74   30082 auto* n = static_cast<node*>(w); 74   31205 auto* n = static_cast<node*>(w);
HITCBC 75   30082 n->prev_ = nullptr; 75   31205 n->prev_ = nullptr;
HITCBC 76   30082 n->next_ = head_; 76   31205 n->next_ = head_;
HITCBC 77   30082 if (head_) 77   31205 if (head_)
HITCBC 78   16855 static_cast<node*>(head_)->prev_ = w; 78   17546 static_cast<node*>(head_)->prev_ = w;
79   else 79   else
HITCBC 80   13227 tail_ = w; 80   13659 tail_ = w;
HITCBC 81   30082 head_ = w; 81   31205 head_ = w;
HITCBC 82   30082 } 82   31205 }
83   83  
HITCBC 84   72515 void push_back(T* w) noexcept 84   74793 void push_back(T* w) noexcept
85   { 85   {
HITCBC 86   72515 auto* n = static_cast<node*>(w); 86   74793 auto* n = static_cast<node*>(w);
HITCBC 87   72515 n->next_ = nullptr; 87   74793 n->next_ = nullptr;
HITCBC 88   72515 n->prev_ = tail_; 88   74793 n->prev_ = tail_;
HITCBC 89   72515 if (tail_) 89   74793 if (tail_)
HITCBC 90   51961 static_cast<node*>(tail_)->next_ = w; 90   53272 static_cast<node*>(tail_)->next_ = w;
91   else 91   else
HITCBC 92   20554 head_ = w; 92   21521 head_ = w;
HITCBC 93   72515 tail_ = w; 93   74793 tail_ = w;
HITCBC 94   72515 } 94   74793 }
95   95  
HITCBC 96   3 void splice_back(intrusive_list& other) noexcept 96   3 void splice_back(intrusive_list& other) noexcept
97   { 97   {
HITCBC 98   3 if (other.empty()) 98   3 if (other.empty())
HITCBC 99   1 return; 99   1 return;
HITCBC 100   2 if (tail_) 100   2 if (tail_)
101   { 101   {
HITCBC 102   1 static_cast<node*>(tail_)->next_ = other.head_; 102   1 static_cast<node*>(tail_)->next_ = other.head_;
HITCBC 103   1 static_cast<node*>(other.head_)->prev_ = tail_; 103   1 static_cast<node*>(other.head_)->prev_ = tail_;
HITCBC 104   1 tail_ = other.tail_; 104   1 tail_ = other.tail_;
105   } 105   }
106   else 106   else
107   { 107   {
HITCBC 108   1 head_ = other.head_; 108   1 head_ = other.head_;
HITCBC 109   1 tail_ = other.tail_; 109   1 tail_ = other.tail_;
110   } 110   }
HITCBC 111   2 other.head_ = nullptr; 111   2 other.head_ = nullptr;
HITCBC 112   2 other.tail_ = nullptr; 112   2 other.tail_ = nullptr;
113   } 113   }
114   114  
HITCBC 115   113379 T* pop_front() noexcept 115   116641 T* pop_front() noexcept
116   { 116   {
HITCBC 117   113379 if (!head_) 117   116641 if (!head_)
HITCBC 118   65208 return nullptr; 118   66226 return nullptr;
HITCBC 119   48171 T* w = head_; 119   50415 T* w = head_;
HITCBC 120   48171 head_ = static_cast<node*>(head_)->next_; 120   50415 head_ = static_cast<node*>(head_)->next_;
HITCBC 121   48171 if (head_) 121   50415 if (head_)
HITCBC 122   24609 static_cast<node*>(head_)->prev_ = nullptr; 122   25753 static_cast<node*>(head_)->prev_ = nullptr;
123   else 123   else
HITCBC 124   23562 tail_ = nullptr; 124   24662 tail_ = nullptr;
125   // Defensive: clear stale linkage so remove() on a 125   // Defensive: clear stale linkage so remove() on a
126   // popped node cannot corrupt the list. 126   // popped node cannot corrupt the list.
HITCBC 127   48171 auto* n = static_cast<node*>(w); 127   50415 auto* n = static_cast<node*>(w);
HITCBC 128   48171 n->next_ = nullptr; 128   50415 n->next_ = nullptr;
HITCBC 129   48171 n->prev_ = nullptr; 129   50415 n->prev_ = nullptr;
HITCBC 130   48171 return w; 130   50415 return w;
131   } 131   }
132   132  
133   /** Unlink @p w if it is a member of this list. 133   /** Unlink @p w if it is a member of this list.
134   134  
135   @pre @p w is either a genuine member of `*this` list, or is 135   @pre @p w is either a genuine member of `*this` list, or is
136   fully detached (not linked in *any* `intrusive_list<T>`, 136   fully detached (not linked in *any* `intrusive_list<T>`,
137   including a different instance over the same `T`). This is 137   including a different instance over the same `T`). This is
138   not a membership test: `T::node` holds one shared `next_`/ 138   not a membership test: `T::node` holds one shared `next_`/
139   `prev_` pair regardless of which list currently owns it, so a 139   `prev_` pair regardless of which list currently owns it, so a
140   node actually linked in a different list looks "not detached" 140   node actually linked in a different list looks "not detached"
141   here and would be spliced out using *this* list's `head_`/ 141   here and would be spliced out using *this* list's `head_`/
142   `tail_` for the boundary cases — corrupting both lists. A 142   `tail_` for the boundary cases — corrupting both lists. A
143   caller that cannot rule that out needs its own bookkeeping 143   caller that cannot rule that out needs its own bookkeeping
144   (e.g. a flag for which list currently owns the node) before 144   (e.g. a flag for which list currently owns the node) before
145   calling this. 145   calling this.
146   146  
147   @return True if @p w was linked in and has now been removed; 147   @return True if @p w was linked in and has now been removed;
148   false if it was already detached (e.g. a reentrant call from 148   false if it was already detached (e.g. a reentrant call from
149   a self-referential keepalive dropping during the same 149   a self-referential keepalive dropping during the same
150   teardown that already popped it elsewhere). Callers that gate 150   teardown that already popped it elsewhere). Callers that gate
151   a one-time action (recycling, deleting) on actually having 151   a one-time action (recycling, deleting) on actually having
152   removed something rely on this to make that action idempotent. 152   removed something rely on this to make that action idempotent.
153   */ 153   */
HITCBC 154   54425 bool remove(T* w) noexcept 154   55582 bool remove(T* w) noexcept
155   { 155   {
HITCBC 156   54425 auto* n = static_cast<node*>(w); 156   55582 auto* n = static_cast<node*>(w);
157   // Already detached — nothing to do. 157   // Already detached — nothing to do.
HITCBC 158   54425 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 158   55582 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 159   2 return false; 159   2 return false;
HITCBC 160   54423 if (n->prev_) 160   55580 if (n->prev_)
HITCBC 161   21444 static_cast<node*>(n->prev_)->next_ = n->next_; 161   21662 static_cast<node*>(n->prev_)->next_ = n->next_;
162   else 162   else
HITCBC 163   32979 head_ = n->next_; 163   33918 head_ = n->next_;
HITCBC 164   54423 if (n->next_) 164   55580 if (n->next_)
HITCBC 165   32759 static_cast<node*>(n->next_)->prev_ = n->prev_; 165   33539 static_cast<node*>(n->next_)->prev_ = n->prev_;
166   else 166   else
HITCBC 167   21664 tail_ = n->prev_; 167   22041 tail_ = n->prev_;
HITCBC 168   54423 n->next_ = nullptr; 168   55580 n->next_ = nullptr;
HITCBC 169   54423 n->prev_ = nullptr; 169   55580 n->prev_ = nullptr;
HITCBC 170   54423 return true; 170   55580 return true;
171   } 171   }
172   172  
173   /// Invoke @p f for each element in the list. 173   /// Invoke @p f for each element in the list.
174   template<class F> 174   template<class F>
HITCBC 175   11861 void for_each(F f) 175   11893 void for_each(F f)
176   { 176   {
HITCBC 177   30330 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 177   30364 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 178   18469 f(p); 178   18471 f(p);
HITCBC 179   11861 } 179   11893 }
180   }; 180   };
181   181  
182   /** An intrusive singly linked FIFO queue. 182   /** An intrusive singly linked FIFO queue.
183   183  
184   This container provides O(1) push and pop operations for 184   This container provides O(1) push and pop operations for
185   elements that derive from @ref node. Elements are not 185   elements that derive from @ref node. Elements are not
186   copied or moved; they are linked directly into the queue. 186   copied or moved; they are linked directly into the queue.
187   187  
188   Unlike @ref intrusive_list, this uses only a single `next_` 188   Unlike @ref intrusive_list, this uses only a single `next_`
189   pointer per node, saving memory at the cost of not supporting 189   pointer per node, saving memory at the cost of not supporting
190   O(1) removal of arbitrary elements. 190   O(1) removal of arbitrary elements.
191   191  
192   @tparam T The element type. Must derive from `intrusive_queue<T>::node`. 192   @tparam T The element type. Must derive from `intrusive_queue<T>::node`.
193   */ 193   */
194   template<class T> 194   template<class T>
195   class intrusive_queue 195   class intrusive_queue
196   { 196   {
197   public: 197   public:
198   /** Base class for queue elements. 198   /** Base class for queue elements.
199   199  
200   Derive from this class to make a type usable with 200   Derive from this class to make a type usable with
201   @ref intrusive_queue. The `next_` pointer is private 201   @ref intrusive_queue. The `next_` pointer is private
202   and accessible only to the queue. 202   and accessible only to the queue.
203   */ 203   */
204   class node 204   class node
205   { 205   {
206   friend class intrusive_queue; 206   friend class intrusive_queue;
207   207  
208   private: 208   private:
209   T* next_ = nullptr; 209   T* next_ = nullptr;
210   }; 210   };
211   211  
212   private: 212   private:
213   T* head_ = nullptr; 213   T* head_ = nullptr;
214   T* tail_ = nullptr; 214   T* tail_ = nullptr;
215   215  
216   public: 216   public:
HITCBC 217   4508 intrusive_queue() = default; 217   4506 intrusive_queue() = default;
218   218  
HITCBC 219   1 intrusive_queue(intrusive_queue&& other) noexcept 219   1 intrusive_queue(intrusive_queue&& other) noexcept
HITCBC 220   1 : head_(other.head_) 220   1 : head_(other.head_)
HITCBC 221   1 , tail_(other.tail_) 221   1 , tail_(other.tail_)
222   { 222   {
HITCBC 223   1 other.head_ = nullptr; 223   1 other.head_ = nullptr;
HITCBC 224   1 other.tail_ = nullptr; 224   1 other.tail_ = nullptr;
HITCBC 225   1 } 225   1 }
226   226  
227   intrusive_queue(intrusive_queue const&) = delete; 227   intrusive_queue(intrusive_queue const&) = delete;
228   intrusive_queue& operator=(intrusive_queue const&) = delete; 228   intrusive_queue& operator=(intrusive_queue const&) = delete;
229   intrusive_queue& operator=(intrusive_queue&&) = delete; 229   intrusive_queue& operator=(intrusive_queue&&) = delete;
230   230  
HITCBC 231   6737 bool empty() const noexcept 231   6764 bool empty() const noexcept
232   { 232   {
HITCBC 233   6737 return head_ == nullptr; 233   6764 return head_ == nullptr;
234   } 234   }
235   235  
HITCBC 236   3369 void push(T* w) noexcept 236   3798 void push(T* w) noexcept
237   { 237   {
HITCBC 238   3369 w->next_ = nullptr; 238   3798 w->next_ = nullptr;
HITCBC 239   3369 if (tail_) 239   3798 if (tail_)
HITCBC 240   2365 tail_->next_ = w; 240   2777 tail_->next_ = w;
241   else 241   else
HITCBC 242   1004 head_ = w; 242   1021 head_ = w;
HITCBC 243   3369 tail_ = w; 243   3798 tail_ = w;
HITCBC 244   3369 } 244   3798 }
245   245  
HITCBC 246   4528 void splice(intrusive_queue& other) noexcept 246   4526 void splice(intrusive_queue& other) noexcept
247   { 247   {
HITCBC 248   4528 if (other.empty()) 248   4526 if (other.empty())
HITCBC 249   4505 return; 249   4503 return;
HITCBC 250   23 if (tail_) 250   23 if (tail_)
HITCBC 251   1 tail_->next_ = other.head_; 251   1 tail_->next_ = other.head_;
252   else 252   else
HITCBC 253   22 head_ = other.head_; 253   22 head_ = other.head_;
HITCBC 254   23 tail_ = other.tail_; 254   23 tail_ = other.tail_;
HITCBC 255   23 other.head_ = nullptr; 255   23 other.head_ = nullptr;
HITCBC 256   23 other.tail_ = nullptr; 256   23 other.tail_ = nullptr;
257   } 257   }
258   258  
HITCBC 259   7895 T* pop() noexcept 259   8322 T* pop() noexcept
260   { 260   {
HITCBC 261   7895 if (!head_) 261   8322 if (!head_)
HITCBC 262   4526 return nullptr; 262   4524 return nullptr;
HITCBC 263   3369 T* w = head_; 263   3798 T* w = head_;
HITCBC 264   3369 head_ = head_->next_; 264   3798 head_ = head_->next_;
HITCBC 265   3369 if (!head_) 265   3798 if (!head_)
HITCBC 266   1003 tail_ = nullptr; 266   1020 tail_ = nullptr;
267   // Defensive: clear stale linkage on popped node. 267   // Defensive: clear stale linkage on popped node.
HITCBC 268   3369 w->next_ = nullptr; 268   3798 w->next_ = nullptr;
HITCBC 269   3369 return w; 269   3798 return w;
270   } 270   }
271   }; 271   };
272   272  
273   } // namespace boost::corosio::detail 273   } // namespace boost::corosio::detail
274   274  
275   #endif 275   #endif