. /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   21173 intrusive_list() = default; 47   22413 intrusive_list() = default;
48   48  
HITCBC 49   1 intrusive_list(intrusive_list&& other) noexcept 49   1 intrusive_list(intrusive_list&& other) noexcept
HITCBC 50   1 : head_(other.head_) 50   1 : head_(other.head_)
HITCBC 51   1 , tail_(other.tail_) 51   1 , tail_(other.tail_)
52   { 52   {
HITCBC 53   1 other.head_ = nullptr; 53   1 other.head_ = nullptr;
HITCBC 54   1 other.tail_ = nullptr; 54   1 other.tail_ = nullptr;
HITCBC 55   1 } 55   1 }
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   12 bool empty() const noexcept 61   12 bool empty() const noexcept
62   { 62   {
HITCBC 63   12 return head_ == nullptr; 63   12 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.
HITCBC 67   6 T* front() const noexcept 67   6 T* front() const noexcept
68   { 68   {
HITCBC 69   6 return head_; 69   6 return head_;
70   } 70   }
71   71  
HITCBC 72   32667 void push_back(T* w) noexcept 72   32913 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   32667 auto* n = static_cast<node*>(w); 74   32913 auto* n = static_cast<node*>(w);
HITCBC 75   32667 n->next_ = nullptr; 75   32913 n->next_ = nullptr;
HITCBC 76   32667 n->prev_ = tail_; 76   32913 n->prev_ = tail_;
HITCBC 77   32667 if (tail_) 77   32913 if (tail_)
HITCBC 78   20773 static_cast<node*>(tail_)->next_ = w; 78   20842 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   11894 head_ = w; 80   12071 head_ = w;
HITCBC 81   32667 tail_ = w; 81   32913 tail_ = w;
HITCBC 82   32667 } 82   32913 }
83   83  
HITCBC 84   3 void splice_back(intrusive_list& other) noexcept 84   3 void splice_back(intrusive_list& other) noexcept
85   { 85   {
HITCBC 86   3 if (other.empty()) 86   3 if (other.empty())
HITCBC 87   1 return; 87   1 return;
HITCBC 88   2 if (tail_) 88   2 if (tail_)
89   { 89   {
HITCBC 90   1 static_cast<node*>(tail_)->next_ = other.head_; 90   1 static_cast<node*>(tail_)->next_ = other.head_;
HITCBC 91   1 static_cast<node*>(other.head_)->prev_ = tail_; 91   1 static_cast<node*>(other.head_)->prev_ = tail_;
HITCBC 92   1 tail_ = other.tail_; 92   1 tail_ = other.tail_;
93   } 93   }
94   else 94   else
95   { 95   {
HITCBC 96   1 head_ = other.head_; 96   1 head_ = other.head_;
HITCBC 97   1 tail_ = other.tail_; 97   1 tail_ = other.tail_;
98   } 98   }
HITCBC 99   2 other.head_ = nullptr; 99   2 other.head_ = nullptr;
HITCBC 100   2 other.tail_ = nullptr; 100   2 other.tail_ = nullptr;
101   } 101   }
102   102  
HITCBC 103   358098 T* pop_front() noexcept 103   348388 T* pop_front() noexcept
104   { 104   {
HITCBC 105   358098 if (!head_) 105   348388 if (!head_)
HITCBC 106   341452 return nullptr; 106   331790 return nullptr;
HITCBC 107   16646 T* w = head_; 107   16598 T* w = head_;
HITCBC 108   16646 head_ = static_cast<node*>(head_)->next_; 108   16598 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16646 if (head_) 109   16598 if (head_)
HITCBC 110   7253 static_cast<node*>(head_)->prev_ = nullptr; 110   7246 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   9393 tail_ = nullptr; 112   9352 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   16646 auto* n = static_cast<node*>(w); 115   16598 auto* n = static_cast<node*>(w);
HITCBC 116   16646 n->next_ = nullptr; 116   16598 n->next_ = nullptr;
HITCBC 117   16646 n->prev_ = nullptr; 117   16598 n->prev_ = nullptr;
HITCBC 118   16646 return w; 118   16598 return w;
119   } 119   }
120   120  
HITCBC 121   16019 void remove(T* w) noexcept 121   16313 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   16019 auto* n = static_cast<node*>(w); 123   16313 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   16019 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   16313 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
HITCBC 126   1 return; 126   1 return;
HITCBC 127   16018 if (n->prev_) 127   16312 if (n->prev_)
HITCBC 128   4566 static_cast<node*>(n->prev_)->next_ = n->next_; 128   4651 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   11452 head_ = n->next_; 130   11661 head_ = n->next_;
HITCBC 131   16018 if (n->next_) 131   16312 if (n->next_)
HITCBC 132   9073 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   9066 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   6945 tail_ = n->prev_; 134   7246 tail_ = n->prev_;
HITCBC 135   16018 n->next_ = nullptr; 135   16312 n->next_ = nullptr;
HITCBC 136   16018 n->prev_ = nullptr; 136   16312 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   321 void for_each(F f) 141   621 void for_each(F f)
142   { 142   {
HITCBC 143   330 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   630 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
HITCBC 144   9 f(p); 144   9 f(p);
HITCBC 145   321 } 145   621 }
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   2109 intrusive_queue() = default; 183   2223 intrusive_queue() = default;
184   184  
HITCBC 185   1 intrusive_queue(intrusive_queue&& other) noexcept 185   1 intrusive_queue(intrusive_queue&& other) noexcept
HITCBC 186   1 : head_(other.head_) 186   1 : head_(other.head_)
HITCBC 187   1 , tail_(other.tail_) 187   1 , tail_(other.tail_)
188   { 188   {
HITCBC 189   1 other.head_ = nullptr; 189   1 other.head_ = nullptr;
HITCBC 190   1 other.tail_ = nullptr; 190   1 other.tail_ = nullptr;
HITCBC 191   1 } 191   1 }
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   705 bool empty() const noexcept 197   1126 bool empty() const noexcept
198   { 198   {
HITCBC 199   705 return head_ == nullptr; 199   1126 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   521 void push(T* w) noexcept 202   720 void push(T* w) noexcept
203   { 203   {
HITCBC 204   521 w->next_ = nullptr; 204   720 w->next_ = nullptr;
HITCBC 205   521 if (tail_) 205   720 if (tail_)
HITCBC 206   262 tail_->next_ = w; 206   262 tail_->next_ = w;
207   else 207   else
HITCBC 208   259 head_ = w; 208   458 head_ = w;
HITCBC 209   521 tail_ = w; 209   720 tail_ = w;
HITCBC 210   521 } 210   720 }
211   211  
HITCBC 212   3 void splice(intrusive_queue& other) noexcept 212   3 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   3 if (other.empty()) 214   3 if (other.empty())
HITCBC 215   1 return; 215   1 return;
HITCBC 216   2 if (tail_) 216   2 if (tail_)
HITCBC 217   1 tail_->next_ = other.head_; 217   1 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   1 head_ = other.head_; 219   1 head_ = other.head_;
HITCBC 220   2 tail_ = other.tail_; 220   2 tail_ = other.tail_;
HITCBC 221   2 other.head_ = nullptr; 221   2 other.head_ = nullptr;
HITCBC 222   2 other.tail_ = nullptr; 222   2 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   2825 T* pop() noexcept 225   3226 T* pop() noexcept
226   { 226   {
HITCBC 227   2825 if (!head_) 227   3226 if (!head_)
HITCBC 228   2304 return nullptr; 228   2506 return nullptr;
HITCBC 229   521 T* w = head_; 229   720 T* w = head_;
HITCBC 230   521 head_ = head_->next_; 230   720 head_ = head_->next_;
HITCBC 231   521 if (!head_) 231   720 if (!head_)
HITCBC 232   258 tail_ = nullptr; 232   457 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   521 w->next_ = nullptr; 234   720 w->next_ = nullptr;
HITCBC 235   521 return w; 235   720 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif