. /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   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   44234 void push_back(T* w) noexcept 72   43705 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   44234 auto* n = static_cast<node*>(w); 74   43705 auto* n = static_cast<node*>(w);
HITCBC 75   44234 n->next_ = nullptr; 75   43705 n->next_ = nullptr;
HITCBC 76   44234 n->prev_ = tail_; 76   43705 n->prev_ = tail_;
HITCBC 77   44234 if (tail_) 77   43705 if (tail_)
HITCBC 78   25311 static_cast<node*>(tail_)->next_ = w; 78   24997 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18923 head_ = w; 80   18708 head_ = w;
HITCBC 81   44234 tail_ = w; 81   43705 tail_ = w;
HITCBC 82   44234 } 82   43705 }
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   302867 T* pop_front() noexcept 103   295687 T* pop_front() noexcept
104   { 104   {
HITCBC 105   302867 if (!head_) 105   295687 if (!head_)
HITCBC 106   285251 return nullptr; 106   278285 return nullptr;
HITCBC 107   17616 T* w = head_; 107   17402 T* w = head_;
HITCBC 108   17616 head_ = static_cast<node*>(head_)->next_; 108   17402 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17616 if (head_) 109   17402 if (head_)
HITCBC 110   40 static_cast<node*>(head_)->prev_ = nullptr; 110   41 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   17576 tail_ = nullptr; 112   17361 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   17616 auto* n = static_cast<node*>(w); 115   17402 auto* n = static_cast<node*>(w);
HITCBC 116   17616 n->next_ = nullptr; 116   17402 n->next_ = nullptr;
HITCBC 117   17616 n->prev_ = nullptr; 117   17402 n->prev_ = nullptr;
HITCBC 118   17616 return w; 118   17402 return w;
119   } 119   }
120   120  
HITCBC 121   26618 void remove(T* w) noexcept 121   26303 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   26618 auto* n = static_cast<node*>(w); 123   26303 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   26618 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   26303 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   26618 if (n->prev_) 127   26303 if (n->prev_)
HITCBC 128   8419 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8314 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   18199 head_ = n->next_; 130   17989 head_ = n->next_;
HITCBC 131   26618 if (n->next_) 131   26303 if (n->next_)
HITCBC 132   16918 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   16708 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9700 tail_ = n->prev_; 134   9595 tail_ = n->prev_;
HITCBC 135   26618 n->next_ = nullptr; 135   26303 n->next_ = nullptr;
HITCBC 136   26618 n->prev_ = nullptr; 136   26303 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_ = 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   3345 intrusive_queue() = default; 183   3350 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   2318873 bool empty() const noexcept 197   2289029 bool empty() const noexcept
198   { 198   {
HITCBC 199   2318873 return head_ == nullptr; 199   2289029 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   710355 void push(T* w) noexcept 202   703287 void push(T* w) noexcept
203   { 203   {
HITCBC 204   710355 w->next_ = nullptr; 204   703287 w->next_ = nullptr;
HITCBC 205   710355 if (tail_) 205   703287 if (tail_)
HITCBC 206   316914 tail_->next_ = w; 206   311766 tail_->next_ = w;
207   else 207   else
HITCBC 208   393441 head_ = w; 208   391521 head_ = w;
HITCBC 209   710355 tail_ = w; 209   703287 tail_ = w;
HITCBC 210   710355 } 210   703287 }
211   211  
HITCBC 212   367284 void splice(intrusive_queue& other) noexcept 212   366366 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   367284 if (other.empty()) 214   366366 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   367284 if (tail_) 216   366366 if (tail_)
HITCBC 217   125997 tail_->next_ = other.head_; 217   132203 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   241287 head_ = other.head_; 219   234163 head_ = other.head_;
HITCBC 220   367284 tail_ = other.tail_; 220   366366 tail_ = other.tail_;
HITCBC 221   367284 other.head_ = nullptr; 221   366366 other.head_ = nullptr;
HITCBC 222   367284 other.tail_ = nullptr; 222   366366 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   978720 T* pop() noexcept 225   966584 T* pop() noexcept
226   { 226   {
HITCBC 227   978720 if (!head_) 227   966584 if (!head_)
HITCBC 228   268365 return nullptr; 228   263297 return nullptr;
HITCBC 229   710355 T* w = head_; 229   703287 T* w = head_;
HITCBC 230   710355 head_ = head_->next_; 230   703287 head_ = head_->next_;
HITCBC 231   710355 if (!head_) 231   703287 if (!head_)
HITCBC 232   267444 tail_ = nullptr; 232   259318 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   710355 w->next_ = nullptr; 234   703287 w->next_ = nullptr;
HITCBC 235   710355 return w; 235   703287 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif