. /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   10644 intrusive_list() = default; 47   10644 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   42311 void push_back(T* w) noexcept 72   39042 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   42311 auto* n = static_cast<node*>(w); 74   39042 auto* n = static_cast<node*>(w);
HITCBC 75   42311 n->next_ = nullptr; 75   39042 n->next_ = nullptr;
HITCBC 76   42311 n->prev_ = tail_; 76   39042 n->prev_ = tail_;
HITCBC 77   42311 if (tail_) 77   39042 if (tail_)
HITCBC 78   24238 static_cast<node*>(tail_)->next_ = w; 78   22292 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18073 head_ = w; 80   16750 head_ = w;
HITCBC 81   42311 tail_ = w; 81   39042 tail_ = w;
HITCBC 82   42311 } 82   39042 }
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   316817 T* pop_front() noexcept 103   288540 T* pop_front() noexcept
104   { 104   {
HITCBC 105   316817 if (!head_) 105   288540 if (!head_)
HITCBC 106   299803 return nullptr; 106   272850 return nullptr;
HITCBC 107   17014 T* w = head_; 107   15690 T* w = head_;
HITCBC 108   17014 head_ = static_cast<node*>(head_)->next_; 108   15690 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17014 if (head_) 109   15690 if (head_)
HITCBC 110   41 static_cast<node*>(head_)->prev_ = nullptr; 110   40 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   16973 tail_ = nullptr; 112   15650 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   17014 auto* n = static_cast<node*>(w); 115   15690 auto* n = static_cast<node*>(w);
HITCBC 116   17014 n->next_ = nullptr; 116   15690 n->next_ = nullptr;
HITCBC 117   17014 n->prev_ = nullptr; 117   15690 n->prev_ = nullptr;
HITCBC 118   17014 return w; 118   15690 return w;
119   } 119   }
120   120  
HITCBC 121   25297 void remove(T* w) noexcept 121   23352 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25297 auto* n = static_cast<node*>(w); 123   23352 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25297 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   23352 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   25297 if (n->prev_) 127   23352 if (n->prev_)
HITCBC 128   8074 static_cast<node*>(n->prev_)->next_ = n->next_; 128   7427 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17223 head_ = n->next_; 130   15925 head_ = n->next_;
HITCBC 131   25297 if (n->next_) 131   23352 if (n->next_)
HITCBC 132   16174 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   14876 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9123 tail_ = n->prev_; 134   8476 tail_ = n->prev_;
HITCBC 135   25297 n->next_ = nullptr; 135   23352 n->next_ = nullptr;
HITCBC 136   25297 n->prev_ = nullptr; 136   23352 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   2744 intrusive_queue() = default; 183   2746 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   2530435 bool empty() const noexcept 197   2305868 bool empty() const noexcept
198   { 198   {
HITCBC 199   2530435 return head_ == nullptr; 199   2305868 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   777634 void push(T* w) noexcept 202   709916 void push(T* w) noexcept
203   { 203   {
HITCBC 204   777634 w->next_ = nullptr; 204   709916 w->next_ = nullptr;
HITCBC 205   777634 if (tail_) 205   709916 if (tail_)
HITCBC 206   340664 tail_->next_ = w; 206   309283 tail_->next_ = w;
207   else 207   else
HITCBC 208   436970 head_ = w; 208   400633 head_ = w;
HITCBC 209   777634 tail_ = w; 209   709916 tail_ = w;
HITCBC 210   777634 } 210   709916 }
211   211  
HITCBC 212   415618 void splice(intrusive_queue& other) noexcept 212   380032 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   415618 if (other.empty()) 214   380032 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   415618 if (tail_) 216   380032 if (tail_)
HITCBC 217   162868 tail_->next_ = other.head_; 217   154024 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   252750 head_ = other.head_; 219   226008 head_ = other.head_;
HITCBC 220   415618 tail_ = other.tail_; 220   380032 tail_ = other.tail_;
HITCBC 221   415618 other.head_ = nullptr; 221   380032 other.head_ = nullptr;
HITCBC 222   415618 other.tail_ = nullptr; 222   380032 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   1068889 T* pop() noexcept 225   972924 T* pop() noexcept
226   { 226   {
HITCBC 227   1068889 if (!head_) 227   972924 if (!head_)
HITCBC 228   291255 return nullptr; 228   263008 return nullptr;
HITCBC 229   777634 T* w = head_; 229   709916 T* w = head_;
HITCBC 230   777634 head_ = head_->next_; 230   709916 head_ = head_->next_;
HITCBC 231   777634 if (!head_) 231   709916 if (!head_)
HITCBC 232   274102 tail_ = nullptr; 232   246609 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   777634 w->next_ = nullptr; 234   709916 w->next_ = nullptr;
HITCBC 235   777634 return w; 235   709916 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif