. /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   12783 intrusive_list() = default; 47   12823 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   38439 void push_back(T* w) noexcept 72   41878 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   38439 auto* n = static_cast<node*>(w); 74   41878 auto* n = static_cast<node*>(w);
HITCBC 75   38439 n->next_ = nullptr; 75   41878 n->next_ = nullptr;
HITCBC 76   38439 n->prev_ = tail_; 76   41878 n->prev_ = tail_;
HITCBC 77   38439 if (tail_) 77   41878 if (tail_)
HITCBC 78   21858 static_cast<node*>(tail_)->next_ = w; 78   23882 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   16581 head_ = w; 80   17996 head_ = w;
HITCBC 81   38439 tail_ = w; 81   41878 tail_ = w;
HITCBC 82   38439 } 82   41878 }
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   275534 T* pop_front() noexcept 103   410970 T* pop_front() noexcept
104   { 104   {
HITCBC 105   275534 if (!head_) 105   410970 if (!head_)
HITCBC 106   260256 return nullptr; 106   394280 return nullptr;
HITCBC 107   15278 T* w = head_; 107   16690 T* w = head_;
HITCBC 108   15278 head_ = static_cast<node*>(head_)->next_; 108   16690 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   15278 if (head_) 109   16690 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   15238 tail_ = nullptr; 112   16649 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   15278 auto* n = static_cast<node*>(w); 115   16690 auto* n = static_cast<node*>(w);
HITCBC 116   15278 n->next_ = nullptr; 116   16690 n->next_ = nullptr;
HITCBC 117   15278 n->prev_ = nullptr; 117   16690 n->prev_ = nullptr;
HITCBC 118   15278 return w; 118   16690 return w;
119   } 119   }
120   120  
HITCBC 121   23161 void remove(T* w) noexcept 121   25188 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   23161 auto* n = static_cast<node*>(w); 123   25188 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   23161 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   25188 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   23161 if (n->prev_) 127   25188 if (n->prev_)
HITCBC 128   7268 static_cast<node*>(n->prev_)->next_ = n->next_; 128   7941 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   15893 head_ = n->next_; 130   17247 head_ = n->next_;
HITCBC 131   23161 if (n->next_) 131   25188 if (n->next_)
HITCBC 132   14616 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   15966 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   8545 tail_ = n->prev_; 134   9222 tail_ = n->prev_;
HITCBC 135   23161 n->next_ = nullptr; 135   25188 n->next_ = nullptr;
HITCBC 136   23161 n->prev_ = nullptr; 136   25188 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_; 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   3323 intrusive_queue() = default; 183   3387 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   2136047 bool empty() const noexcept 197   3243085 bool empty() const noexcept
198   { 198   {
HITCBC 199   2136047 return head_ == nullptr; 199   3243085 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   656118 void push(T* w) noexcept 202   985575 void push(T* w) noexcept
203   { 203   {
HITCBC 204   656118 w->next_ = nullptr; 204   985575 w->next_ = nullptr;
HITCBC 205   656118 if (tail_) 205   985575 if (tail_)
HITCBC 206   291223 tail_->next_ = w; 206   439298 tail_->next_ = w;
207   else 207   else
HITCBC 208   364895 head_ = w; 208   546277 head_ = w;
HITCBC 209   656118 tail_ = w; 209   985575 tail_ = w;
HITCBC 210   656118 } 210   985575 }
211   211  
HITCBC 212   342711 void splice(intrusive_queue& other) noexcept 212   522015 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   342711 if (other.empty()) 214   522015 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   342711 if (tail_) 216   522015 if (tail_)
HITCBC 217   125280 tail_->next_ = other.head_; 217   182040 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   217431 head_ = other.head_; 219   339975 head_ = other.head_;
HITCBC 220   342711 tail_ = other.tail_; 220   522015 tail_ = other.tail_;
HITCBC 221   342711 other.head_ = nullptr; 221   522015 other.head_ = nullptr;
HITCBC 222   342711 other.tail_ = nullptr; 222   522015 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   903728 T* pop() noexcept 225   1371652 T* pop() noexcept
226   { 226   {
HITCBC 227   903728 if (!head_) 227   1371652 if (!head_)
HITCBC 228   247610 return nullptr; 228   386077 return nullptr;
HITCBC 229   656118 T* w = head_; 229   985575 T* w = head_;
HITCBC 230   656118 head_ = head_->next_; 230   985575 head_ = head_->next_;
HITCBC 231   656118 if (!head_) 231   985575 if (!head_)
HITCBC 232   239615 tail_ = nullptr; 232   364237 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   656118 w->next_ = nullptr; 234   985575 w->next_ = nullptr;
HITCBC 235   656118 return w; 235   985575 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif