. /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   12783 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   40982 void push_back(T* w) noexcept 72   43423 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   40982 auto* n = static_cast<node*>(w); 74   43423 auto* n = static_cast<node*>(w);
HITCBC 75   40982 n->next_ = nullptr; 75   43423 n->next_ = nullptr;
HITCBC 76   40982 n->prev_ = tail_; 76   43423 n->prev_ = tail_;
HITCBC 77   40982 if (tail_) 77   43423 if (tail_)
HITCBC 78   23455 static_cast<node*>(tail_)->next_ = w; 78   24829 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   17527 head_ = w; 80   18594 head_ = w;
HITCBC 81   40982 tail_ = w; 81   43423 tail_ = w;
HITCBC 82   40982 } 82   43423 }
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   270308 T* pop_front() noexcept 103   287126 T* pop_front() noexcept
104   { 104   {
HITCBC 105   270308 if (!head_) 105   287126 if (!head_)
HITCBC 106   253840 return nullptr; 106   269834 return nullptr;
HITCBC 107   16468 T* w = head_; 107   17292 T* w = head_;
HITCBC 108   16468 head_ = static_cast<node*>(head_)->next_; 108   17292 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16468 if (head_) 109   17292 if (head_)
HITCBC 110   41 static_cast<node*>(head_)->prev_ = nullptr; 110   41 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   16427 tail_ = nullptr; 112   17251 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   16468 auto* n = static_cast<node*>(w); 115   17292 auto* n = static_cast<node*>(w);
HITCBC 116   16468 n->next_ = nullptr; 116   17292 n->next_ = nullptr;
HITCBC 117   16468 n->prev_ = nullptr; 117   17292 n->prev_ = nullptr;
HITCBC 118   16468 return w; 118   17292 return w;
119   } 119   }
120   120  
HITCBC 121   24514 void remove(T* w) noexcept 121   26131 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   24514 auto* n = static_cast<node*>(w); 123   26131 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   24514 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   26131 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   24514 if (n->prev_) 127   26131 if (n->prev_)
HITCBC 128   7813 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8258 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   16701 head_ = n->next_; 130   17873 head_ = n->next_;
HITCBC 131   24514 if (n->next_) 131   26131 if (n->next_)
HITCBC 132   15652 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   16596 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   8862 tail_ = n->prev_; 134   9535 tail_ = n->prev_;
HITCBC 135   24514 n->next_ = nullptr; 135   26131 n->next_ = nullptr;
HITCBC 136   24514 n->prev_ = nullptr; 136   26131 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   216 void for_each(F f)
142   { 142   {
HITCBC 143   122 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   122 } 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   2745 intrusive_queue() = default; 183   3330 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   2092268 bool empty() const noexcept 197   2211799 bool empty() const noexcept
198   { 198   {
HITCBC 199   2092268 return head_ == nullptr; 199   2211799 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   642403 void push(T* w) noexcept 202   679409 void push(T* w) noexcept
203   { 203   {
HITCBC 204   642403 w->next_ = nullptr; 204   679409 w->next_ = nullptr;
HITCBC 205   642403 if (tail_) 205   679409 if (tail_)
HITCBC 206   282667 tail_->next_ = w; 206   300169 tail_->next_ = w;
207   else 207   else
HITCBC 208   359736 head_ = w; 208   379240 head_ = w;
HITCBC 209   642403 tail_ = w; 209   679409 tail_ = w;
HITCBC 210   642403 } 210   679409 }
211   211  
HITCBC 212   335947 void splice(intrusive_queue& other) noexcept 212   353489 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   335947 if (other.empty()) 214   353489 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   335947 if (tail_) 216   353489 if (tail_)
HITCBC 217   122616 tail_->next_ = other.head_; 217   126466 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   213331 head_ = other.head_; 219   227023 head_ = other.head_;
HITCBC 220   335947 tail_ = other.tail_; 220   353489 tail_ = other.tail_;
HITCBC 221   335947 other.head_ = nullptr; 221   353489 other.head_ = nullptr;
HITCBC 222   335947 other.tail_ = nullptr; 222   353489 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   880694 T* pop() noexcept 225   931907 T* pop() noexcept
226   { 226   {
HITCBC 227   880694 if (!head_) 227   931907 if (!head_)
HITCBC 228   238291 return nullptr; 228   252498 return nullptr;
HITCBC 229   642403 T* w = head_; 229   679409 T* w = head_;
HITCBC 230   642403 head_ = head_->next_; 230   679409 head_ = head_->next_;
HITCBC 231   642403 if (!head_) 231   679409 if (!head_)
HITCBC 232   237120 tail_ = nullptr; 232   252774 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   642403 w->next_ = nullptr; 234   679409 w->next_ = nullptr;
HITCBC 235   642403 return w; 235   679409 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif