. /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   12913 intrusive_list() = default; 47   12913 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   42769 void push_back(T* w) noexcept 72   42608 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   42769 auto* n = static_cast<node*>(w); 74   42608 auto* n = static_cast<node*>(w);
HITCBC 75   42769 n->next_ = nullptr; 75   42608 n->next_ = nullptr;
HITCBC 76   42769 n->prev_ = tail_; 76   42608 n->prev_ = tail_;
HITCBC 77   42769 if (tail_) 77   42608 if (tail_)
HITCBC 78   24438 static_cast<node*>(tail_)->next_ = w; 78   24337 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18331 head_ = w; 80   18271 head_ = w;
HITCBC 81   42769 tail_ = w; 81   42608 tail_ = w;
HITCBC 82   42769 } 82   42608 }
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   302243 T* pop_front() noexcept 103   279694 T* pop_front() noexcept
104   { 104   {
HITCBC 105   302243 if (!head_) 105   279694 if (!head_)
HITCBC 106   285219 return nullptr; 106   262728 return nullptr;
HITCBC 107   17024 T* w = head_; 107   16966 T* w = head_;
HITCBC 108   17024 head_ = static_cast<node*>(head_)->next_; 108   16966 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17024 if (head_) 109   16966 if (head_)
HITCBC 110   40 static_cast<node*>(head_)->prev_ = nullptr; 110   42 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   16984 tail_ = nullptr; 112   16924 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   17024 auto* n = static_cast<node*>(w); 115   16966 auto* n = static_cast<node*>(w);
HITCBC 116   17024 n->next_ = nullptr; 116   16966 n->next_ = nullptr;
HITCBC 117   17024 n->prev_ = nullptr; 117   16966 n->prev_ = nullptr;
HITCBC 118   17024 return w; 118   16966 return w;
119   } 119   }
120   120  
HITCBC 121   25745 void remove(T* w) noexcept 121   25642 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25745 auto* n = static_cast<node*>(w); 123   25642 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25745 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   25642 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   25745 if (n->prev_) 127   25642 if (n->prev_)
HITCBC 128   8128 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8091 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17617 head_ = n->next_; 130   17551 head_ = n->next_;
HITCBC 131   25745 if (n->next_) 131   25642 if (n->next_)
HITCBC 132   16336 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   16270 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9409 tail_ = n->prev_; 134   9372 tail_ = n->prev_;
HITCBC 135   25745 n->next_ = nullptr; 135   25642 n->next_ = nullptr;
HITCBC 136   25745 n->prev_ = nullptr; 136   25642 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   216 void for_each(F f) 141   216 void for_each(F f)
142   { 142   {
HITCBC 143   216 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   216 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   216 } 145   216 }
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   3348 intrusive_queue() = default; 183   3349 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   2322849 bool empty() const noexcept 197   2142837 bool empty() const noexcept
198   { 198   {
HITCBC 199   2322849 return head_ == nullptr; 199   2142837 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   712105 void push(T* w) noexcept 202   659211 void push(T* w) noexcept
203   { 203   {
HITCBC 204   712105 w->next_ = nullptr; 204   659211 w->next_ = nullptr;
HITCBC 205   712105 if (tail_) 205   659211 if (tail_)
HITCBC 206   315345 tail_->next_ = w; 206   292186 tail_->next_ = w;
207   else 207   else
HITCBC 208   396760 head_ = w; 208   367025 head_ = w;
HITCBC 209   712105 tail_ = w; 209   659211 tail_ = w;
HITCBC 210   712105 } 210   659211 }
211   211  
HITCBC 212   371739 void splice(intrusive_queue& other) noexcept 212   342737 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   371739 if (other.empty()) 214   342737 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   371739 if (tail_) 216   342737 if (tail_)
HITCBC 217   132848 tail_->next_ = other.head_; 217   124333 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   238891 head_ = other.head_; 219   218404 head_ = other.head_;
HITCBC 220   371739 tail_ = other.tail_; 220   342737 tail_ = other.tail_;
HITCBC 221   371739 other.head_ = nullptr; 221   342737 other.head_ = nullptr;
HITCBC 222   371739 other.tail_ = nullptr; 222   342737 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   978637 T* pop() noexcept 225   903910 T* pop() noexcept
226   { 226   {
HITCBC 227   978637 if (!head_) 227   903910 if (!head_)
HITCBC 228   266532 return nullptr; 228   244699 return nullptr;
HITCBC 229   712105 T* w = head_; 229   659211 T* w = head_;
HITCBC 230   712105 head_ = head_->next_; 230   659211 head_ = head_->next_;
HITCBC 231   712105 if (!head_) 231   659211 if (!head_)
HITCBC 232   263912 tail_ = nullptr; 232   242692 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   712105 w->next_ = nullptr; 234   659211 w->next_ = nullptr;
HITCBC 235   712105 return w; 235   659211 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif