. /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   12823 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   42926 void push_back(T* w) noexcept 72   44488 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   42926 auto* n = static_cast<node*>(w); 74   44488 auto* n = static_cast<node*>(w);
HITCBC 75   42926 n->next_ = nullptr; 75   44488 n->next_ = nullptr;
HITCBC 76   42926 n->prev_ = tail_; 76   44488 n->prev_ = tail_;
HITCBC 77   42926 if (tail_) 77   44488 if (tail_)
HITCBC 78   24532 static_cast<node*>(tail_)->next_ = w; 78   25467 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   18394 head_ = w; 80   19021 head_ = w;
HITCBC 81   42926 tail_ = w; 81   44488 tail_ = w;
HITCBC 82   42926 } 82   44488 }
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   291000 T* pop_front() noexcept 103   303445 T* pop_front() noexcept
104   { 104   {
HITCBC 105   291000 if (!head_) 105   303445 if (!head_)
HITCBC 106   273912 return nullptr; 106   285731 return nullptr;
HITCBC 107   17088 T* w = head_; 107   17714 T* w = head_;
HITCBC 108   17088 head_ = static_cast<node*>(head_)->next_; 108   17714 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   17088 if (head_) 109   17714 if (head_)
HITCBC 110   41 static_cast<node*>(head_)->prev_ = nullptr; 110   40 static_cast<node*>(head_)->prev_ = nullptr;
111   else 111   else
HITCBC 112   17047 tail_ = nullptr; 112   17674 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   17088 auto* n = static_cast<node*>(w); 115   17714 auto* n = static_cast<node*>(w);
HITCBC 116   17088 n->next_ = nullptr; 116   17714 n->next_ = nullptr;
HITCBC 117   17088 n->prev_ = nullptr; 117   17714 n->prev_ = nullptr;
HITCBC 118   17088 return w; 118   17714 return w;
119   } 119   }
120   120  
HITCBC 121   25838 void remove(T* w) noexcept 121   26774 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   25838 auto* n = static_cast<node*>(w); 123   26774 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   25838 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   26774 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   25838 if (n->prev_) 127   26774 if (n->prev_)
HITCBC 128   8158 static_cast<node*>(n->prev_)->next_ = n->next_; 128   8471 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   17680 head_ = n->next_; 130   18303 head_ = n->next_;
HITCBC 131   25838 if (n->next_) 131   26774 if (n->next_)
HITCBC 132   16399 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   17022 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   9439 tail_ = n->prev_; 134   9752 tail_ = n->prev_;
HITCBC 135   25838 n->next_ = nullptr; 135   26774 n->next_ = nullptr;
HITCBC 136   25838 n->prev_ = nullptr; 136   26774 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   3339 intrusive_queue() = default; 183   3352 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   2237880 bool empty() const noexcept 197   2331865 bool empty() const noexcept
198   { 198   {
HITCBC 199   2237880 return head_ == nullptr; 199   2331865 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   686913 void push(T* w) noexcept 202   715331 void push(T* w) noexcept
203   { 203   {
HITCBC 204   686913 w->next_ = nullptr; 204   715331 w->next_ = nullptr;
HITCBC 205   686913 if (tail_) 205   715331 if (tail_)
HITCBC 206   304922 tail_->next_ = w; 206   317746 tail_->next_ = w;
207   else 207   else
HITCBC 208   381991 head_ = w; 208   397585 head_ = w;
HITCBC 209   686913 tail_ = w; 209   715331 tail_ = w;
HITCBC 210   686913 } 210   715331 }
211   211  
HITCBC 212   357608 void splice(intrusive_queue& other) noexcept 212   373160 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   357608 if (other.empty()) 214   373160 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   357608 if (tail_) 216   373160 if (tail_)
HITCBC 217   128085 tail_->next_ = other.head_; 217   131506 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   229523 head_ = other.head_; 219   241654 head_ = other.head_;
HITCBC 220   357608 tail_ = other.tail_; 220   373160 tail_ = other.tail_;
HITCBC 221   357608 other.head_ = nullptr; 221   373160 other.head_ = nullptr;
HITCBC 222   357608 other.tail_ = nullptr; 222   373160 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   943595 T* pop() noexcept 225   983857 T* pop() noexcept
226   { 226   {
HITCBC 227   943595 if (!head_) 227   983857 if (!head_)
HITCBC 228   256682 return nullptr; 228   268526 return nullptr;
HITCBC 229   686913 T* w = head_; 229   715331 T* w = head_;
HITCBC 230   686913 head_ = head_->next_; 230   715331 head_ = head_->next_;
HITCBC 231   686913 if (!head_) 231   715331 if (!head_)
HITCBC 232   253906 tail_ = nullptr; 232   266079 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   686913 w->next_ = nullptr; 234   715331 w->next_ = nullptr;
HITCBC 235   686913 return w; 235   715331 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif