. /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   11632 intrusive_list() = default; 47   11640 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   22 bool empty() const noexcept 61   21 bool empty() const noexcept
62   { 62   {
HITCBC 63   22 return head_ == nullptr; 63   21 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   30225 void push_front(T* w) noexcept 72   30916 void push_front(T* w) noexcept
73   { 73   {
HITCBC 74   30225 auto* n = static_cast<node*>(w); 74   30916 auto* n = static_cast<node*>(w);
HITCBC 75   30225 n->prev_ = nullptr; 75   30916 n->prev_ = nullptr;
HITCBC 76   30225 n->next_ = head_; 76   30916 n->next_ = head_;
HITCBC 77   30225 if (head_) 77   30916 if (head_)
HITCBC 78   16743 static_cast<node*>(head_)->prev_ = w; 78   17395 static_cast<node*>(head_)->prev_ = w;
79   else 79   else
HITCBC 80   13482 tail_ = w; 80   13521 tail_ = w;
HITCBC 81   30225 head_ = w; 81   30916 head_ = w;
HITCBC 82   30225 } 82   30916 }
83   83  
HITCBC 84   74071 void push_back(T* w) noexcept 84   74192 void push_back(T* w) noexcept
85   { 85   {
HITCBC 86   74071 auto* n = static_cast<node*>(w); 86   74192 auto* n = static_cast<node*>(w);
HITCBC 87   74071 n->next_ = nullptr; 87   74192 n->next_ = nullptr;
HITCBC 88   74071 n->prev_ = tail_; 88   74192 n->prev_ = tail_;
HITCBC 89   74071 if (tail_) 89   74192 if (tail_)
HITCBC 90   52986 static_cast<node*>(tail_)->next_ = w; 90   53518 static_cast<node*>(tail_)->next_ = w;
91   else 91   else
HITCBC 92   21085 head_ = w; 92   20674 head_ = w;
HITCBC 93   74071 tail_ = w; 93   74192 tail_ = w;
HITCBC 94   74071 } 94   74192 }
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   116769 T* pop_front() noexcept 115   115856 T* pop_front() noexcept
116   { 116   {
HITCBC 117   116769 if (!head_) 117   115856 if (!head_)
HITCBC 118   67134 return nullptr; 118   66030 return nullptr;
HITCBC 119   49635 T* w = head_; 119   49826 T* w = head_;
HITCBC 120   49635 head_ = static_cast<node*>(head_)->next_; 120   49826 head_ = static_cast<node*>(head_)->next_;
HITCBC 121   49635 if (head_) 121   49826 if (head_)
HITCBC 122   25872 static_cast<node*>(head_)->prev_ = nullptr; 122   26074 static_cast<node*>(head_)->prev_ = nullptr;
123   else 123   else
HITCBC 124   23763 tail_ = nullptr; 124   23752 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   49635 auto* n = static_cast<node*>(w); 127   49826 auto* n = static_cast<node*>(w);
HITCBC 128   49635 n->next_ = nullptr; 128   49826 n->next_ = nullptr;
HITCBC 129   49635 n->prev_ = nullptr; 129   49826 n->prev_ = nullptr;
HITCBC 130   49635 return w; 130   49826 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   54660 bool remove(T* w) noexcept 154   55281 bool remove(T* w) noexcept
155   { 155   {
HITCBC 156   54660 auto* n = static_cast<node*>(w); 156   55281 auto* n = static_cast<node*>(w);
157   // Already detached — nothing to do. 157   // Already detached — nothing to do.
HITCBC 158   54660 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 158   55281 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 159   2 return false; 159   2 return false;
HITCBC 160   54658 if (n->prev_) 160   55279 if (n->prev_)
HITCBC 161   21081 static_cast<node*>(n->prev_)->next_ = n->next_; 161   21695 static_cast<node*>(n->prev_)->next_ = n->next_;
162   else 162   else
HITCBC 163   33577 head_ = n->next_; 163   33584 head_ = n->next_;
HITCBC 164   54658 if (n->next_) 164   55279 if (n->next_)
HITCBC 165   32746 static_cast<node*>(n->next_)->prev_ = n->prev_; 165   33418 static_cast<node*>(n->next_)->prev_ = n->prev_;
166   else 166   else
HITCBC 167   21912 tail_ = n->prev_; 167   21861 tail_ = n->prev_;
HITCBC 168   54658 n->next_ = nullptr; 168   55279 n->next_ = nullptr;
HITCBC 169   54658 n->prev_ = nullptr; 169   55279 n->prev_ = nullptr;
HITCBC 170   54658 return true; 170   55279 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   11873 void for_each(F f) 175   11883 void for_each(F f)
176   { 176   {
HITCBC 177   30336 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 177   30336 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 178   18463 f(p); 178   18453 f(p);
HITCBC 179   11873 } 179   11883 }
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   4508 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   6752 bool empty() const noexcept 231   6741 bool empty() const noexcept
232   { 232   {
HITCBC 233   6752 return head_ == nullptr; 233   6741 return head_ == nullptr;
234   } 234   }
235   235  
HITCBC 236   4295 void push(T* w) noexcept 236   4628 void push(T* w) noexcept
237   { 237   {
HITCBC 238   4295 w->next_ = nullptr; 238   4628 w->next_ = nullptr;
HITCBC 239   4295 if (tail_) 239   4628 if (tail_)
HITCBC 240   3279 tail_->next_ = w; 240   3597 tail_->next_ = w;
241   else 241   else
HITCBC 242   1016 head_ = w; 242   1031 head_ = w;
HITCBC 243   4295 tail_ = w; 243   4628 tail_ = w;
HITCBC 244   4295 } 244   4628 }
245   245  
HITCBC 246   4528 void splice(intrusive_queue& other) noexcept 246   4528 void splice(intrusive_queue& other) noexcept
247   { 247   {
HITCBC 248   4528 if (other.empty()) 248   4528 if (other.empty())
HITCBC 249   4505 return; 249   4505 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   8821 T* pop() noexcept 259   9154 T* pop() noexcept
260   { 260   {
HITCBC 261   8821 if (!head_) 261   9154 if (!head_)
HITCBC 262   4526 return nullptr; 262   4526 return nullptr;
HITCBC 263   4295 T* w = head_; 263   4628 T* w = head_;
HITCBC 264   4295 head_ = head_->next_; 264   4628 head_ = head_->next_;
HITCBC 265   4295 if (!head_) 265   4628 if (!head_)
HITCBC 266   1015 tail_ = nullptr; 266   1030 tail_ = nullptr;
267   // Defensive: clear stale linkage on popped node. 267   // Defensive: clear stale linkage on popped node.
HITCBC 268   4295 w->next_ = nullptr; 268   4628 w->next_ = nullptr;
HITCBC 269   4295 return w; 269   4628 return w;
270   } 270   }
271   }; 271   };
272   272  
273   } // namespace boost::corosio::detail 273   } // namespace boost::corosio::detail
274   274  
275   #endif 275   #endif