. /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   12913 intrusive_list() = default; 47   12913 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   39269 void push_back(T* w) noexcept 72   41300 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   39269 auto* n = static_cast<node*>(w); 74   41300 auto* n = static_cast<node*>(w);
HITCBC 75   39269 n->next_ = nullptr; 75   41300 n->next_ = nullptr;
HITCBC 76   39269 n->prev_ = tail_; 76   41300 n->prev_ = tail_;
HITCBC 77   39269 if (tail_) 77   41300 if (tail_)
HITCBC 78   22340 static_cast<node*>(tail_)->next_ = w; 78   23564 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   16929 head_ = w; 80   17736 head_ = w;
HITCBC 81   39269 tail_ = w; 81   41300 tail_ = w;
HITCBC 82   39269 } 82   41300 }
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   268677 T* pop_front() noexcept 103   275984 T* pop_front() noexcept
104   { 104   {
HITCBC 105   268677 if (!head_) 105   275984 if (!head_)
HITCBC 106   253053 return nullptr; 106   259554 return nullptr;
HITCBC 107   15624 T* w = head_; 107   16430 T* w = head_;
HITCBC 108   15624 head_ = static_cast<node*>(head_)->next_; 108   16430 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   15624 if (head_) 109   16430 if (head_)
HITCBC 110   42 static_cast<node*>(head_)->prev_ = nullptr; 110   41 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   15582 tail_ = nullptr; 112   16389 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   15624 auto* n = static_cast<node*>(w); 115   16430 auto* n = static_cast<node*>(w);
HITCBC 116   15624 n->next_ = nullptr; 116   16430 n->next_ = nullptr;
HITCBC 117   15624 n->prev_ = nullptr; 117   16430 n->prev_ = nullptr;
HITCBC 118   15624 return w; 118   16430 return w;
119   } 119   }
120   120  
HITCBC 121   23645 void remove(T* w) noexcept 121   24870 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   23645 auto* n = static_cast<node*>(w); 123   24870 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   23645 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   24870 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   23645 if (n->prev_) 127   24870 if (n->prev_)
HITCBC 128   7427 static_cast<node*>(n->prev_)->next_ = n->next_; 128   7835 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   16218 head_ = n->next_; 130   17035 head_ = n->next_;
HITCBC 131   23645 if (n->next_) 131   24870 if (n->next_)
HITCBC 132   14937 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   15754 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   8708 tail_ = n->prev_; 134   9116 tail_ = n->prev_;
HITCBC 135   23645 n->next_ = nullptr; 135   24870 n->next_ = nullptr;
HITCBC 136   23645 n->prev_ = nullptr; 136   24870 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   3352 intrusive_queue() = default; 183   3360 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   2071783 bool empty() const noexcept 197   2133109 bool empty() const noexcept
198   { 198   {
HITCBC 199   2071783 return head_ == nullptr; 199   2133109 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   637808 void push(T* w) noexcept 202   655840 void push(T* w) noexcept
203   { 203   {
HITCBC 204   637808 w->next_ = nullptr; 204   655840 w->next_ = nullptr;
HITCBC 205   637808 if (tail_) 205   655840 if (tail_)
HITCBC 206   281937 tail_->next_ = w; 206   290224 tail_->next_ = w;
207   else 207   else
HITCBC 208   355871 head_ = w; 208   365616 head_ = w;
HITCBC 209   637808 tail_ = w; 209   655840 tail_ = w;
HITCBC 210   637808 } 210   655840 }
211   211  
HITCBC 212   333109 void splice(intrusive_queue& other) noexcept 212   341807 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   333109 if (other.empty()) 214   341807 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   333109 if (tail_) 216   341807 if (tail_)
HITCBC 217   124271 tail_->next_ = other.head_; 217   124471 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   208838 head_ = other.head_; 219   217336 head_ = other.head_;
HITCBC 220   333109 tail_ = other.tail_; 220   341807 tail_ = other.tail_;
HITCBC 221   333109 other.head_ = nullptr; 221   341807 other.head_ = nullptr;
HITCBC 222   333109 other.tail_ = nullptr; 222   341807 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   874306 T* pop() noexcept 225   900160 T* pop() noexcept
226   { 226   {
HITCBC 227   874306 if (!head_) 227   900160 if (!head_)
HITCBC 228   236498 return nullptr; 228   244320 return nullptr;
HITCBC 229   637808 T* w = head_; 229   655840 T* w = head_;
HITCBC 230   637808 head_ = head_->next_; 230   655840 head_ = head_->next_;
HITCBC 231   637808 if (!head_) 231   655840 if (!head_)
HITCBC 232   231600 tail_ = nullptr; 232   241145 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   637808 w->next_ = nullptr; 234   655840 w->next_ = nullptr;
HITCBC 235   637808 return w; 235   655840 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif