. /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   18326 intrusive_list() = default; 47   18294 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   17 bool empty() const noexcept 61   17 bool empty() const noexcept
62   { 62   {
HITCBC 63   17 return head_ == nullptr; 63   17 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   29869 void push_front(T* w) noexcept 72   29369 void push_front(T* w) noexcept
73   { 73   {
HITCBC 74   29869 auto* n = static_cast<node*>(w); 74   29369 auto* n = static_cast<node*>(w);
HITCBC 75   29869 n->prev_ = nullptr; 75   29369 n->prev_ = nullptr;
HITCBC 76   29869 n->next_ = head_; 76   29369 n->next_ = head_;
HITCBC 77   29869 if (head_) 77   29369 if (head_)
HITCBC 78   16774 static_cast<node*>(head_)->prev_ = w; 78   16519 static_cast<node*>(head_)->prev_ = w;
79   else 79   else
HITCBC 80   13095 tail_ = w; 80   12850 tail_ = w;
HITCBC 81   29869 head_ = w; 81   29369 head_ = w;
HITCBC 82   29869 } 82   29369 }
83   83  
HITCBC 84   73448 void push_back(T* w) noexcept 84   72742 void push_back(T* w) noexcept
85   { 85   {
HITCBC 86   73448 auto* n = static_cast<node*>(w); 86   72742 auto* n = static_cast<node*>(w);
HITCBC 87   73448 n->next_ = nullptr; 87   72742 n->next_ = nullptr;
HITCBC 88   73448 n->prev_ = tail_; 88   72742 n->prev_ = tail_;
HITCBC 89   73448 if (tail_) 89   72742 if (tail_)
HITCBC 90   53135 static_cast<node*>(tail_)->next_ = w; 90   51798 static_cast<node*>(tail_)->next_ = w;
91   else 91   else
HITCBC 92   20313 head_ = w; 92   20944 head_ = w;
HITCBC 93   73448 tail_ = w; 93   72742 tail_ = w;
HITCBC 94   73448 } 94   72742 }
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   234966 T* pop_front() noexcept 115   236489 T* pop_front() noexcept
116   { 116   {
HITCBC 117   234966 if (!head_) 117   236489 if (!head_)
HITCBC 118   185864 return nullptr; 118   188223 return nullptr;
HITCBC 119   49102 T* w = head_; 119   48266 T* w = head_;
HITCBC 120   49102 head_ = static_cast<node*>(head_)->next_; 120   48266 head_ = static_cast<node*>(head_)->next_;
HITCBC 121   49102 if (head_) 121   48266 if (head_)
HITCBC 122   25623 static_cast<node*>(head_)->prev_ = nullptr; 122   24989 static_cast<node*>(head_)->prev_ = nullptr;
123   else 123   else
HITCBC 124   23479 tail_ = nullptr; 124   23277 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   49102 auto* n = static_cast<node*>(w); 127   48266 auto* n = static_cast<node*>(w);
HITCBC 128   49102 n->next_ = nullptr; 128   48266 n->next_ = nullptr;
HITCBC 129   49102 n->prev_ = nullptr; 129   48266 n->prev_ = nullptr;
HITCBC 130   49102 return w; 130   48266 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   54214 bool remove(T* w) noexcept 154   53844 bool remove(T* w) noexcept
155   { 155   {
HITCBC 156   54214 auto* n = static_cast<node*>(w); 156   53844 auto* n = static_cast<node*>(w);
157   // Already detached — nothing to do. 157   // Already detached — nothing to do.
HITCBC 158   54214 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 158   53844 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 159   2 return false; 159   2 return false;
HITCBC 160   54212 if (n->prev_) 160   53842 if (n->prev_)
HITCBC 161   21509 static_cast<node*>(n->prev_)->next_ = n->next_; 161   20786 static_cast<node*>(n->prev_)->next_ = n->next_;
162   else 162   else
HITCBC 163   32703 head_ = n->next_; 163   33056 head_ = n->next_;
HITCBC 164   54212 if (n->next_) 164   53842 if (n->next_)
HITCBC 165   33466 static_cast<node*>(n->next_)->prev_ = n->prev_; 165   32795 static_cast<node*>(n->next_)->prev_ = n->prev_;
166   else 166   else
HITCBC 167   20746 tail_ = n->prev_; 167   21047 tail_ = n->prev_;
HITCBC 168   54212 n->next_ = nullptr; 168   53842 n->next_ = nullptr;
HITCBC 169   54212 n->prev_ = nullptr; 169   53842 n->prev_ = nullptr;
HITCBC 170   54212 return true; 170   53842 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   27401 void for_each(F f) 175   27361 void for_each(F f)
176   { 176   {
HITCBC 177   45885 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 177   45801 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 178   18484 f(p); 178   18440 f(p);
HITCBC 179   27401 } 179   27361 }
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   4421 intrusive_queue() = default; 217   4419 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   6683 bool empty() const noexcept 231   6702 bool empty() const noexcept
232   { 232   {
HITCBC 233   6683 return head_ == nullptr; 233   6702 return head_ == nullptr;
234   } 234   }
235   235  
HITCBC 236   6628 void push(T* w) noexcept 236   5391 void push(T* w) noexcept
237   { 237   {
HITCBC 238   6628 w->next_ = nullptr; 238   5391 w->next_ = nullptr;
HITCBC 239   6628 if (tail_) 239   5391 if (tail_)
HITCBC 240   5610 tail_->next_ = w; 240   4363 tail_->next_ = w;
241   else 241   else
HITCBC 242   1018 head_ = w; 242   1028 head_ = w;
HITCBC 243   6628 tail_ = w; 243   5391 tail_ = w;
HITCBC 244   6628 } 244   5391 }
245   245  
HITCBC 246   4441 void splice(intrusive_queue& other) noexcept 246   4439 void splice(intrusive_queue& other) noexcept
247   { 247   {
HITCBC 248   4441 if (other.empty()) 248   4439 if (other.empty())
HITCBC 249   4418 return; 249   4418 return;
HITCBC 250   23 if (tail_) 250   21 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   20 head_ = other.head_;
HITCBC 254   23 tail_ = other.tail_; 254   21 tail_ = other.tail_;
HITCBC 255   23 other.head_ = nullptr; 255   21 other.head_ = nullptr;
HITCBC 256   23 other.tail_ = nullptr; 256   21 other.tail_ = nullptr;
257   } 257   }
258   258  
HITCBC 259   11067 T* pop() noexcept 259   9828 T* pop() noexcept
260   { 260   {
HITCBC 261   11067 if (!head_) 261   9828 if (!head_)
HITCBC 262   4439 return nullptr; 262   4437 return nullptr;
HITCBC 263   6628 T* w = head_; 263   5391 T* w = head_;
HITCBC 264   6628 head_ = head_->next_; 264   5391 head_ = head_->next_;
HITCBC 265   6628 if (!head_) 265   5391 if (!head_)
HITCBC 266   1017 tail_ = nullptr; 266   1027 tail_ = nullptr;
267   // Defensive: clear stale linkage on popped node. 267   // Defensive: clear stale linkage on popped node.
HITCBC 268   6628 w->next_ = nullptr; 268   5391 w->next_ = nullptr;
HITCBC 269   6628 return w; 269   5391 return w;
270   } 270   }
271   }; 271   };
272   272  
273   } // namespace boost::corosio::detail 273   } // namespace boost::corosio::detail
274   274  
275   #endif 275   #endif