. /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   10646 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   17864 void push_back(T* w) noexcept 72   22997 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   17864 auto* n = static_cast<node*>(w); 74   22997 auto* n = static_cast<node*>(w);
HITCBC 75   17864 n->next_ = nullptr; 75   22997 n->next_ = nullptr;
HITCBC 76   17864 n->prev_ = tail_; 76   22997 n->prev_ = tail_;
HITCBC 77   17864 if (tail_) 77   22997 if (tail_)
HITCBC 78   9614 static_cast<node*>(tail_)->next_ = w; 78   12688 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   8250 head_ = w; 80   10309 head_ = w;
HITCBC 81   17864 tail_ = w; 81   22997 tail_ = w;
HITCBC 82   17864 } 82   22997 }
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   216480 T* pop_front() noexcept 103   189027 T* pop_front() noexcept
104   { 104   {
HITCBC 105   216480 if (!head_) 105   189027 if (!head_)
HITCBC 106   209288 return nullptr; 106   179767 return nullptr;
HITCBC 107   7192 T* w = head_; 107   9260 T* w = head_;
HITCBC 108   7192 head_ = static_cast<node*>(head_)->next_; 108   9260 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   7192 if (head_) 109   9260 if (head_)
HITCBC 110   42 static_cast<node*>(head_)->prev_ = nullptr; 110   43 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   7150 tail_ = nullptr; 112   9217 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   7192 auto* n = static_cast<node*>(w); 115   9260 auto* n = static_cast<node*>(w);
HITCBC 116   7192 n->next_ = nullptr; 116   9260 n->next_ = nullptr;
HITCBC 117   7192 n->prev_ = nullptr; 117   9260 n->prev_ = nullptr;
HITCBC 118   7192 return w; 118   9260 return w;
119   } 119   }
120   120  
HITCBC 121   10672 void remove(T* w) noexcept 121   13737 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   10672 auto* n = static_cast<node*>(w); 123   13737 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   10672 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   13737 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   10672 if (n->prev_) 127   13737 if (n->prev_)
HITCBC 128   3198 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4217 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   7474 head_ = n->next_; 130   9520 head_ = n->next_;
HITCBC 131   10672 if (n->next_) 131   13737 if (n->next_)
HITCBC 132   6425 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   8475 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   4247 tail_ = n->prev_; 134   5262 tail_ = n->prev_;
HITCBC 135   10672 n->next_ = nullptr; 135   13737 n->next_ = nullptr;
HITCBC 136   10672 n->prev_ = nullptr; 136   13737 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   2750 intrusive_queue() = default; 183   2730 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   1774088 bool empty() const noexcept 197   1523484 bool empty() const noexcept
198   { 198   {
HITCBC 199   1774088 return head_ == nullptr; 199   1523484 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   542775 void push(T* w) noexcept 202   468947 void push(T* w) noexcept
203   { 203   {
HITCBC 204   542775 w->next_ = nullptr; 204   468947 w->next_ = nullptr;
HITCBC 205   542775 if (tail_) 205   468947 if (tail_)
HITCBC 206   235692 tail_->next_ = w; 206   202985 tail_->next_ = w;
207   else 207   else
HITCBC 208   307083 head_ = w; 208   265962 head_ = w;
HITCBC 209   542775 tail_ = w; 209   468947 tail_ = w;
HITCBC 210   542775 } 210   468947 }
211   211  
HITCBC 212   297336 void splice(intrusive_queue& other) noexcept 212   253693 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   297336 if (other.empty()) 214   253693 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   297336 if (tail_) 216   253693 if (tail_)
HITCBC 217   121574 tail_->next_ = other.head_; 217   103233 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   175762 head_ = other.head_; 219   150460 head_ = other.head_;
HITCBC 220   297336 tail_ = other.tail_; 220   253693 tail_ = other.tail_;
HITCBC 221   297336 other.head_ = nullptr; 221   253693 other.head_ = nullptr;
HITCBC 222   297336 other.tail_ = nullptr; 222   253693 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   753162 T* pop() noexcept 225   645432 T* pop() noexcept
226   { 226   {
HITCBC 227   753162 if (!head_) 227   645432 if (!head_)
HITCBC 228   210387 return nullptr; 228   176485 return nullptr;
HITCBC 229   542775 T* w = head_; 229   468947 T* w = head_;
HITCBC 230   542775 head_ = head_->next_; 230   468947 head_ = head_->next_;
HITCBC 231   542775 if (!head_) 231   468947 if (!head_)
HITCBC 232   185509 tail_ = nullptr; 232   162729 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   542775 w->next_ = nullptr; 234   468947 w->next_ = nullptr;
HITCBC 235   542775 return w; 235   468947 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif