. /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   14897 intrusive_list() = default; 47   14753 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   1883 bool empty() const noexcept 61   1667 bool empty() const noexcept
62   { 62   {
HITCBC 63   1883 return head_ == nullptr; 63   1667 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   26700 void push_back(T* w) noexcept 72   25885 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   26700 auto* n = static_cast<node*>(w); 74   25885 auto* n = static_cast<node*>(w);
HITCBC 75   26700 n->next_ = nullptr; 75   25885 n->next_ = nullptr;
HITCBC 76   26700 n->prev_ = tail_; 76   25885 n->prev_ = tail_;
HITCBC 77   26700 if (tail_) 77   25885 if (tail_)
HITCBC 78   13611 static_cast<node*>(tail_)->next_ = w; 78   13265 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   13089 head_ = w; 80   12620 head_ = w;
HITCBC 81   26700 tail_ = w; 81   25885 tail_ = w;
HITCBC 82   26700 } 82   25885 }
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   247910 T* pop_front() noexcept 103   246514 T* pop_front() noexcept
104   { 104   {
HITCBC 105   247910 if (!head_) 105   246514 if (!head_)
HITCBC 106   238170 return nullptr; 106   237092 return nullptr;
HITCBC 107   9740 T* w = head_; 107   9422 T* w = head_;
HITCBC 108   9740 head_ = static_cast<node*>(head_)->next_; 108   9422 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   9740 if (head_) 109   9422 if (head_)
HITCBC 110   67 static_cast<node*>(head_)->prev_ = nullptr; 110   2 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9673 tail_ = nullptr; 112   9420 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   9740 auto* n = static_cast<node*>(w); 115   9422 auto* n = static_cast<node*>(w);
HITCBC 116   9740 n->next_ = nullptr; 116   9422 n->next_ = nullptr;
HITCBC 117   9740 n->prev_ = nullptr; 117   9422 n->prev_ = nullptr;
HITCBC 118   9740 return w; 118   9422 return w;
119   } 119   }
120   120  
HITCBC 121   16960 void remove(T* w) noexcept 121   16463 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16960 auto* n = static_cast<node*>(w); 123   16463 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16960 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   16463 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   16960 if (n->prev_) 127   16463 if (n->prev_)
HITCBC 128   4486 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4393 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   12474 head_ = n->next_; 130   12070 head_ = n->next_;
HITCBC 131   16960 if (n->next_) 131   16463 if (n->next_)
HITCBC 132   9141 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   8953 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   7819 tail_ = n->prev_; 134   7510 tail_ = n->prev_;
HITCBC 135   16960 n->next_ = nullptr; 135   16463 n->next_ = nullptr;
HITCBC 136   16960 n->prev_ = nullptr; 136   16463 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   227 void for_each(F f) 141   227 void for_each(F f)
142   { 142   {
HITCBC 143   227 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   227 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   227 } 145   227 }
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_ = nullptr; 175   T* next_ = nullptr;
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   1384 intrusive_queue() = default; 183   1384 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   894 bool empty() const noexcept 197   866 bool empty() const noexcept
198   { 198   {
HITCBC 199   894 return head_ == nullptr; 199   866 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   382 void push(T* w) noexcept 202   382 void push(T* w) noexcept
203   { 203   {
HITCBC 204   382 w->next_ = nullptr; 204   382 w->next_ = nullptr;
HITCBC 205   382 if (tail_) 205   382 if (tail_)
HITCBC 206   253 tail_->next_ = w; 206   254 tail_->next_ = w;
207   else 207   else
HITCBC 208   129 head_ = w; 208   128 head_ = w;
HITCBC 209   382 tail_ = w; 209   382 tail_ = w;
HITCBC 210   382 } 210   382 }
211   211  
212   void splice(intrusive_queue& other) noexcept 212   void splice(intrusive_queue& other) noexcept
213   { 213   {
214   if (other.empty()) 214   if (other.empty())
215   return; 215   return;
216   if (tail_) 216   if (tail_)
217   tail_->next_ = other.head_; 217   tail_->next_ = other.head_;
218   else 218   else
219   head_ = other.head_; 219   head_ = other.head_;
220   tail_ = other.tail_; 220   tail_ = other.tail_;
221   other.head_ = nullptr; 221   other.head_ = nullptr;
222   other.tail_ = nullptr; 222   other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   3161 T* pop() noexcept 225   3161 T* pop() noexcept
226   { 226   {
HITCBC 227   3161 if (!head_) 227   3161 if (!head_)
HITCBC 228   2779 return nullptr; 228   2779 return nullptr;
HITCBC 229   382 T* w = head_; 229   382 T* w = head_;
HITCBC 230   382 head_ = head_->next_; 230   382 head_ = head_->next_;
HITCBC 231   382 if (!head_) 231   382 if (!head_)
HITCBC 232   129 tail_ = nullptr; 232   128 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   382 w->next_ = nullptr; 234   382 w->next_ = nullptr;
HITCBC 235   382 return w; 235   382 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif