. /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   10606 intrusive_list() = default; 47   10606 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   23647 void push_back(T* w) noexcept 72   11901 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   23647 auto* n = static_cast<node*>(w); 74   11901 auto* n = static_cast<node*>(w);
HITCBC 75   23647 n->next_ = nullptr; 75   11901 n->next_ = nullptr;
HITCBC 76   23647 n->prev_ = tail_; 76   11901 n->prev_ = tail_;
HITCBC 77   23647 if (tail_) 77   11901 if (tail_)
HITCBC 78   13082 static_cast<node*>(tail_)->next_ = w; 78   6040 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   10565 head_ = w; 80   5861 head_ = w;
HITCBC 81   23647 tail_ = w; 81   11901 tail_ = w;
HITCBC 82   23647 } 82   11901 }
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   217081 T* pop_front() noexcept 103   209939 T* pop_front() noexcept
104   { 104   {
HITCBC 105   217081 if (!head_) 105   209939 if (!head_)
HITCBC 106   207567 return nullptr; 106   205129 return nullptr;
HITCBC 107   9514 T* w = head_; 107   4810 T* w = head_;
HITCBC 108   9514 head_ = static_cast<node*>(head_)->next_; 108   4810 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   9514 if (head_) 109   4810 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   9473 tail_ = nullptr; 112   4769 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   9514 auto* n = static_cast<node*>(w); 115   4810 auto* n = static_cast<node*>(w);
HITCBC 116   9514 n->next_ = nullptr; 116   4810 n->next_ = nullptr;
HITCBC 117   9514 n->prev_ = nullptr; 117   4810 n->prev_ = nullptr;
HITCBC 118   9514 return w; 118   4810 return w;
119   } 119   }
120   120  
HITCBC 121   14133 void remove(T* w) noexcept 121   7091 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   14133 auto* n = static_cast<node*>(w); 123   7091 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   14133 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   7091 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   14133 if (n->prev_) 127   7091 if (n->prev_)
HITCBC 128   4350 static_cast<node*>(n->prev_)->next_ = n->next_; 128   2003 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   9783 head_ = n->next_; 130   5088 head_ = n->next_;
HITCBC 131   14133 if (n->next_) 131   7091 if (n->next_)
HITCBC 132   8738 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   4043 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   5395 tail_ = n->prev_; 134   3048 tail_ = n->prev_;
HITCBC 135   14133 n->next_ = nullptr; 135   7091 n->next_ = nullptr;
HITCBC 136   14133 n->prev_ = nullptr; 136   7091 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   122 void for_each(F f)
142   { 142   {
HITCBC 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_) 143   122 for (T* p = head_; p; p = static_cast<node*>(p)->next_)
MISUBC 144   ✗ f(p); 144   ✗ f(p);
HITCBC 145   122 } 145   122 }
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   2732 intrusive_queue() = default; 183   2734 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   1796453 bool empty() const noexcept 197   1715865 bool empty() const noexcept
198   { 198   {
HITCBC 199   1796453 return head_ == nullptr; 199   1715865 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   554966 void push(T* w) noexcept 202   522573 void push(T* w) noexcept
203   { 203   {
HITCBC 204   554966 w->next_ = nullptr; 204   522573 w->next_ = nullptr;
HITCBC 205   554966 if (tail_) 205   522573 if (tail_)
HITCBC 206   237556 tail_->next_ = w; 206   227507 tail_->next_ = w;
207   else 207   else
HITCBC 208   317410 head_ = w; 208   295066 head_ = w;
HITCBC 209   554966 tail_ = w; 209   522573 tail_ = w;
HITCBC 210   554966 } 210   522573 }
211   211  
HITCBC 212   303969 void splice(intrusive_queue& other) noexcept 212   288499 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   303969 if (other.empty()) 214   288499 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   303969 if (tail_) 216   288499 if (tail_)
HITCBC 217   136830 tail_->next_ = other.head_; 217   117377 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   167139 head_ = other.head_; 219   171122 head_ = other.head_;
HITCBC 220   303969 tail_ = other.tail_; 220   288499 tail_ = other.tail_;
HITCBC 221   303969 other.head_ = nullptr; 221   288499 other.head_ = nullptr;
HITCBC 222   303969 other.tail_ = nullptr; 222   288499 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   759941 T* pop() noexcept 225   728645 T* pop() noexcept
226   { 226   {
HITCBC 227   759941 if (!head_) 227   728645 if (!head_)
HITCBC 228   204975 return nullptr; 228   206072 return nullptr;
HITCBC 229   554966 T* w = head_; 229   522573 T* w = head_;
HITCBC 230   554966 head_ = head_->next_; 230   522573 head_ = head_->next_;
HITCBC 231   554966 if (!head_) 231   522573 if (!head_)
HITCBC 232   180580 tail_ = nullptr; 232   177689 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   554966 w->next_ = nullptr; 234   522573 w->next_ = nullptr;
HITCBC 235   554966 return w; 235   522573 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif