. /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   26099 void push_back(T* w) noexcept 72   17997 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   26099 auto* n = static_cast<node*>(w); 74   17997 auto* n = static_cast<node*>(w);
HITCBC 75   26099 n->next_ = nullptr; 75   17997 n->next_ = nullptr;
HITCBC 76   26099 n->prev_ = tail_; 76   17997 n->prev_ = tail_;
HITCBC 77   26099 if (tail_) 77   17997 if (tail_)
HITCBC 78   14482 static_cast<node*>(tail_)->next_ = w; 78   9665 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   11617 head_ = w; 80   8332 head_ = w;
HITCBC 81   26099 tail_ = w; 81   17997 tail_ = w;
HITCBC 82   26099 } 82   17997 }
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   183675 T* pop_front() noexcept 103   167862 T* pop_front() noexcept
104   { 104   {
HITCBC 105   183675 if (!head_) 105   167862 if (!head_)
HITCBC 106   173363 return nullptr; 106   160836 return nullptr;
HITCBC 107   10312 T* w = head_; 107   7026 T* w = head_;
HITCBC 108   10312 head_ = static_cast<node*>(head_)->next_; 108   7026 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   10312 if (head_) 109   7026 if (head_)
HITCBC 110   42 static_cast<node*>(head_)->prev_ = nullptr; 110   41 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   10270 tail_ = nullptr; 112   6985 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   10312 auto* n = static_cast<node*>(w); 115   7026 auto* n = static_cast<node*>(w);
HITCBC 116   10312 n->next_ = nullptr; 116   7026 n->next_ = nullptr;
HITCBC 117   10312 n->prev_ = nullptr; 117   7026 n->prev_ = nullptr;
HITCBC 118   10312 return w; 118   7026 return w;
119   } 119   }
120   120  
HITCBC 121   15787 void remove(T* w) noexcept 121   10971 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   15787 auto* n = static_cast<node*>(w); 123   10971 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   15787 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   10971 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   15787 if (n->prev_) 127   10971 if (n->prev_)
HITCBC 128   4806 static_cast<node*>(n->prev_)->next_ = n->next_; 128   3202 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   10981 head_ = n->next_; 130   7769 head_ = n->next_;
HITCBC 131   15787 if (n->next_) 131   10971 if (n->next_)
HITCBC 132   9700 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   6488 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   6087 tail_ = n->prev_; 134   4483 tail_ = n->prev_;
HITCBC 135   15787 n->next_ = nullptr; 135   10971 n->next_ = nullptr;
HITCBC 136   15787 n->prev_ = nullptr; 136   10971 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   3346 intrusive_queue() = default; 183   3358 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   1504449 bool empty() const noexcept 197   1287814 bool empty() const noexcept
198   { 198   {
HITCBC 199   1504449 return head_ == nullptr; 199   1287814 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   469082 void push(T* w) noexcept 202   396012 void push(T* w) noexcept
203   { 203   {
HITCBC 204   469082 w->next_ = nullptr; 204   396012 w->next_ = nullptr;
HITCBC 205   469082 if (tail_) 205   396012 if (tail_)
HITCBC 206   202927 tail_->next_ = w; 206   175859 tail_->next_ = w;
207   else 207   else
HITCBC 208   266155 head_ = w; 208   220153 head_ = w;
HITCBC 209   469082 tail_ = w; 209   396012 tail_ = w;
HITCBC 210   469082 } 210   396012 }
211   211  
HITCBC 212   251087 void splice(intrusive_queue& other) noexcept 212   209602 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   251087 if (other.empty()) 214   209602 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   251087 if (tail_) 216   209602 if (tail_)
HITCBC 217   112923 tail_->next_ = other.head_; 217   79790 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   138164 head_ = other.head_; 219   129812 head_ = other.head_;
HITCBC 220   251087 tail_ = other.tail_; 220   209602 tail_ = other.tail_;
HITCBC 221   251087 other.head_ = nullptr; 221   209602 other.head_ = nullptr;
HITCBC 222   251087 other.tail_ = nullptr; 222   209602 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   639727 T* pop() noexcept 225   548137 T* pop() noexcept
226   { 226   {
HITCBC 227   639727 if (!head_) 227   548137 if (!head_)
HITCBC 228   170645 return nullptr; 228   152125 return nullptr;
HITCBC 229   469082 T* w = head_; 229   396012 T* w = head_;
HITCBC 230   469082 head_ = head_->next_; 230   396012 head_ = head_->next_;
HITCBC 231   469082 if (!head_) 231   396012 if (!head_)
HITCBC 232   153232 tail_ = nullptr; 232   140363 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   469082 w->next_ = nullptr; 234   396012 w->next_ = nullptr;
HITCBC 235   469082 return w; 235   396012 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif