. /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   18286 intrusive_list() = default; 47   18302 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   31073 void push_front(T* w) noexcept 72   30656 void push_front(T* w) noexcept
73   { 73   {
HITCBC 74   31073 auto* n = static_cast<node*>(w); 74   30656 auto* n = static_cast<node*>(w);
HITCBC 75   31073 n->prev_ = nullptr; 75   30656 n->prev_ = nullptr;
HITCBC 76   31073 n->next_ = head_; 76   30656 n->next_ = head_;
HITCBC 77   31073 if (head_) 77   30656 if (head_)
HITCBC 78   17294 static_cast<node*>(head_)->prev_ = w; 78   17329 static_cast<node*>(head_)->prev_ = w;
79   else 79   else
HITCBC 80   13779 tail_ = w; 80   13327 tail_ = w;
HITCBC 81   31073 head_ = w; 81   30656 head_ = w;
HITCBC 82   31073 } 82   30656 }
83   83  
HITCBC 84   75088 void push_back(T* w) noexcept 84   73793 void push_back(T* w) noexcept
85   { 85   {
HITCBC 86   75088 auto* n = static_cast<node*>(w); 86   73793 auto* n = static_cast<node*>(w);
HITCBC 87   75088 n->next_ = nullptr; 87   73793 n->next_ = nullptr;
HITCBC 88   75088 n->prev_ = tail_; 88   73793 n->prev_ = tail_;
HITCBC 89   75088 if (tail_) 89   73793 if (tail_)
HITCBC 90   54005 static_cast<node*>(tail_)->next_ = w; 90   53046 static_cast<node*>(tail_)->next_ = w;
91   else 91   else
HITCBC 92   21083 head_ = w; 92   20747 head_ = w;
HITCBC 93   75088 tail_ = w; 93   73793 tail_ = w;
HITCBC 94   75088 } 94   73793 }
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   235773 T* pop_front() noexcept 115   304258 T* pop_front() noexcept
116   { 116   {
HITCBC 117   235773 if (!head_) 117   304258 if (!head_)
HITCBC 118   185248 return nullptr; 118   254909 return nullptr;
HITCBC 119   50525 T* w = head_; 119   49349 T* w = head_;
HITCBC 120   50525 head_ = static_cast<node*>(head_)->next_; 120   49349 head_ = static_cast<node*>(head_)->next_;
HITCBC 121   50525 if (head_) 121   49349 if (head_)
HITCBC 122   26220 static_cast<node*>(head_)->prev_ = nullptr; 122   25417 static_cast<node*>(head_)->prev_ = nullptr;
123   else 123   else
HITCBC 124   24305 tail_ = nullptr; 124   23932 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   50525 auto* n = static_cast<node*>(w); 127   49349 auto* n = static_cast<node*>(w);
HITCBC 128   50525 n->next_ = nullptr; 128   49349 n->next_ = nullptr;
HITCBC 129   50525 n->prev_ = nullptr; 129   49349 n->prev_ = nullptr;
HITCBC 130   50525 return w; 130   49349 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   55635 bool remove(T* w) noexcept 154   55099 bool remove(T* w) noexcept
155   { 155   {
HITCBC 156   55635 auto* n = static_cast<node*>(w); 156   55099 auto* n = static_cast<node*>(w);
157   // Already detached — nothing to do. 157   // Already detached — nothing to do.
HITCBC 158   55635 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 158   55099 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 159   2 return false; 159   2 return false;
HITCBC 160   55633 if (n->prev_) 160   55097 if (n->prev_)
HITCBC 161   21865 static_cast<node*>(n->prev_)->next_ = n->next_; 161   21688 static_cast<node*>(n->prev_)->next_ = n->next_;
162   else 162   else
HITCBC 163   33768 head_ = n->next_; 163   33409 head_ = n->next_;
HITCBC 164   55633 if (n->next_) 164   55097 if (n->next_)
HITCBC 165   33877 static_cast<node*>(n->next_)->prev_ = n->prev_; 165   33804 static_cast<node*>(n->next_)->prev_ = n->prev_;
166   else 166   else
HITCBC 167   21756 tail_ = n->prev_; 167   21293 tail_ = n->prev_;
HITCBC 168   55633 n->next_ = nullptr; 168   55097 n->next_ = nullptr;
HITCBC 169   55633 n->prev_ = nullptr; 169   55097 n->prev_ = nullptr;
HITCBC 170   55633 return true; 170   55097 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   27349 void for_each(F f) 175   27365 void for_each(F f)
176   { 176   {
HITCBC 177   45783 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 177   45791 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 178   18434 f(p); 178   18426 f(p);
HITCBC 179   27349 } 179   27365 }
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   4417 intrusive_queue() = default; 217   4417 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   6695 bool empty() const noexcept 231   6664 bool empty() const noexcept
232   { 232   {
HITCBC 233   6695 return head_ == nullptr; 233   6664 return head_ == nullptr;
234   } 234   }
235   235  
HITCBC 236   1314 void push(T* w) noexcept 236   4733 void push(T* w) noexcept
237   { 237   {
HITCBC 238   1314 w->next_ = nullptr; 238   4733 w->next_ = nullptr;
HITCBC 239   1314 if (tail_) 239   4733 if (tail_)
HITCBC 240   290 tail_->next_ = w; 240   3723 tail_->next_ = w;
241   else 241   else
HITCBC 242   1024 head_ = w; 242   1010 head_ = w;
HITCBC 243   1314 tail_ = w; 243   4733 tail_ = w;
HITCBC 244   1314 } 244   4733 }
245   245  
HITCBC 246   4437 void splice(intrusive_queue& other) noexcept 246   4437 void splice(intrusive_queue& other) noexcept
247   { 247   {
HITCBC 248   4437 if (other.empty()) 248   4437 if (other.empty())
HITCBC 249   4416 return; 249   4416 return;
HITCBC 250   21 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   20 head_ = other.head_; 253   20 head_ = other.head_;
HITCBC 254   21 tail_ = other.tail_; 254   21 tail_ = other.tail_;
HITCBC 255   21 other.head_ = nullptr; 255   21 other.head_ = nullptr;
HITCBC 256   21 other.tail_ = nullptr; 256   21 other.tail_ = nullptr;
257   } 257   }
258   258  
HITCBC 259   5749 T* pop() noexcept 259   9168 T* pop() noexcept
260   { 260   {
HITCBC 261   5749 if (!head_) 261   9168 if (!head_)
HITCBC 262   4435 return nullptr; 262   4435 return nullptr;
HITCBC 263   1314 T* w = head_; 263   4733 T* w = head_;
HITCBC 264   1314 head_ = head_->next_; 264   4733 head_ = head_->next_;
HITCBC 265   1314 if (!head_) 265   4733 if (!head_)
HITCBC 266   1023 tail_ = nullptr; 266   1009 tail_ = nullptr;
267   // Defensive: clear stale linkage on popped node. 267   // Defensive: clear stale linkage on popped node.
HITCBC 268   1314 w->next_ = nullptr; 268   4733 w->next_ = nullptr;
HITCBC 269   1314 return w; 269   4733 return w;
270   } 270   }
271   }; 271   };
272   272  
273   } // namespace boost::corosio::detail 273   } // namespace boost::corosio::detail
274   274  
275   #endif 275   #endif