. /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   40354 void push_back(T* w) noexcept 72   37779 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   40354 auto* n = static_cast<node*>(w); 74   37779 auto* n = static_cast<node*>(w);
HITCBC 75   40354 n->next_ = nullptr; 75   37779 n->next_ = nullptr;
HITCBC 76   40354 n->prev_ = tail_; 76   37779 n->prev_ = tail_;
HITCBC 77   40354 if (tail_) 77   37779 if (tail_)
HITCBC 78   23081 static_cast<node*>(tail_)->next_ = w; 78   21544 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   17273 head_ = w; 80   16235 head_ = w;
HITCBC 81   40354 tail_ = w; 81   37779 tail_ = w;
HITCBC 82   40354 } 82   37779 }
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   267344 T* pop_front() noexcept 103   260257 T* pop_front() noexcept
104   { 104   {
HITCBC 105   267344 if (!head_) 105   260257 if (!head_)
HITCBC 106   251122 return nullptr; 106   245071 return nullptr;
HITCBC 107   16222 T* w = head_; 107   15186 T* w = head_;
HITCBC 108   16222 head_ = static_cast<node*>(head_)->next_; 108   15186 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   16222 if (head_) 109   15186 if (head_)
HITCBC 110   41 static_cast<node*>(head_)->prev_ = nullptr; 110   43 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   16181 tail_ = nullptr; 112   15143 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   16222 auto* n = static_cast<node*>(w); 115   15186 auto* n = static_cast<node*>(w);
HITCBC 116   16222 n->next_ = nullptr; 116   15186 n->next_ = nullptr;
HITCBC 117   16222 n->prev_ = nullptr; 117   15186 n->prev_ = nullptr;
HITCBC 118   16222 return w; 118   15186 return w;
119   } 119   }
120   120  
HITCBC 121   24132 void remove(T* w) noexcept 121   22593 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   24132 auto* n = static_cast<node*>(w); 123   22593 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   24132 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   22593 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   24132 if (n->prev_) 127   22593 if (n->prev_)
HITCBC 128   7683 static_cast<node*>(n->prev_)->next_ = n->next_; 128   7169 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   16449 head_ = n->next_; 130   15424 head_ = n->next_;
HITCBC 131   24132 if (n->next_) 131   22593 if (n->next_)
HITCBC 132   15404 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   14379 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   8728 tail_ = n->prev_; 134   8214 tail_ = n->prev_;
HITCBC 135   24132 n->next_ = nullptr; 135   22593 n->next_ = nullptr;
HITCBC 136   24132 n->prev_ = nullptr; 136   22593 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   2733 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   2107585 bool empty() const noexcept 197   2028474 bool empty() const noexcept
198   { 198   {
HITCBC 199   2107585 return head_ == nullptr; 199   2028474 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   649642 void push(T* w) noexcept 202   624079 void push(T* w) noexcept
203   { 203   {
HITCBC 204   649642 w->next_ = nullptr; 204   624079 w->next_ = nullptr;
HITCBC 205   649642 if (tail_) 205   624079 if (tail_)
HITCBC 206   283594 tail_->next_ = w; 206   274180 tail_->next_ = w;
207   else 207   else
HITCBC 208   366048 head_ = w; 208   349899 head_ = w;
HITCBC 209   649642 tail_ = w; 209   624079 tail_ = w;
HITCBC 210   649642 } 210   624079 }
211   211  
HITCBC 212   342933 void splice(intrusive_queue& other) noexcept 212   328583 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   342933 if (other.empty()) 214   328583 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   342933 if (tail_) 216   328583 if (tail_)
HITCBC 217   135276 tail_->next_ = other.head_; 217   125944 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   207657 head_ = other.head_; 219   202639 head_ = other.head_;
HITCBC 220   342933 tail_ = other.tail_; 220   328583 tail_ = other.tail_;
HITCBC 221   342933 other.head_ = nullptr; 221   328583 other.head_ = nullptr;
HITCBC 222   342933 other.tail_ = nullptr; 222   328583 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   887945 T* pop() noexcept 225   855504 T* pop() noexcept
226   { 226   {
HITCBC 227   887945 if (!head_) 227   855504 if (!head_)
HITCBC 228   238303 return nullptr; 228   231425 return nullptr;
HITCBC 229   649642 T* w = head_; 229   624079 T* w = head_;
HITCBC 230   649642 head_ = head_->next_; 230   624079 head_ = head_->next_;
HITCBC 231   649642 if (!head_) 231   624079 if (!head_)
HITCBC 232   230772 tail_ = nullptr; 232   223955 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   649642 w->next_ = nullptr; 234   624079 w->next_ = nullptr;
HITCBC 235   649642 return w; 235   624079 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif