. /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   10646 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   29409 void push_back(T* w) noexcept 72   36280 void push_back(T* w) noexcept
73   { 73   {
HITCBC 74   29409 auto* n = static_cast<node*>(w); 74   36280 auto* n = static_cast<node*>(w);
HITCBC 75   29409 n->next_ = nullptr; 75   36280 n->next_ = nullptr;
HITCBC 76   29409 n->prev_ = tail_; 76   36280 n->prev_ = tail_;
HITCBC 77   29409 if (tail_) 77   36280 if (tail_)
HITCBC 78   16520 static_cast<node*>(tail_)->next_ = w; 78   20636 static_cast<node*>(tail_)->next_ = w;
79   else 79   else
HITCBC 80   12889 head_ = w; 80   15644 head_ = w;
HITCBC 81   29409 tail_ = w; 81   36280 tail_ = w;
HITCBC 82   29409 } 82   36280 }
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   254967 T* pop_front() noexcept 103   284180 T* pop_front() noexcept
104   { 104   {
HITCBC 105   254967 if (!head_) 105   284180 if (!head_)
HITCBC 106   243129 return nullptr; 106   269596 return nullptr;
HITCBC 107   11838 T* w = head_; 107   14584 T* w = head_;
HITCBC 108   11838 head_ = static_cast<node*>(head_)->next_; 108   14584 head_ = static_cast<node*>(head_)->next_;
HITCBC 109   11838 if (head_) 109   14584 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   11797 tail_ = nullptr; 112   14544 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   11838 auto* n = static_cast<node*>(w); 115   14584 auto* n = static_cast<node*>(w);
HITCBC 116   11838 n->next_ = nullptr; 116   14584 n->next_ = nullptr;
HITCBC 117   11838 n->prev_ = nullptr; 117   14584 n->prev_ = nullptr;
HITCBC 118   11838 return w; 118   14584 return w;
119   } 119   }
120   120  
HITCBC 121   17571 void remove(T* w) noexcept 121   21696 void remove(T* w) noexcept
122   { 122   {
HITCBC 123   17571 auto* n = static_cast<node*>(w); 123   21696 auto* n = static_cast<node*>(w);
124   // Already detached — nothing to do. 124   // Already detached — nothing to do.
HITCBC 125   17571 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w) 125   21696 if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
MISUBC 126   ✗ return; 126   ✗ return;
HITCBC 127   17571 if (n->prev_) 127   21696 if (n->prev_)
HITCBC 128   5496 static_cast<node*>(n->prev_)->next_ = n->next_; 128   6875 static_cast<node*>(n->prev_)->next_ = n->next_;
129   else 129   else
HITCBC 130   12075 head_ = n->next_; 130   14821 head_ = n->next_;
HITCBC 131   17571 if (n->next_) 131   21696 if (n->next_)
HITCBC 132   11030 static_cast<node*>(n->next_)->prev_ = n->prev_; 132   13772 static_cast<node*>(n->next_)->prev_ = n->prev_;
133   else 133   else
HITCBC 134   6541 tail_ = n->prev_; 134   7924 tail_ = n->prev_;
HITCBC 135   17571 n->next_ = nullptr; 135   21696 n->next_ = nullptr;
HITCBC 136   17571 n->prev_ = nullptr; 136   21696 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   2743 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   1990485 bool empty() const noexcept 197   2272991 bool empty() const noexcept
198   { 198   {
HITCBC 199   1990485 return head_ == nullptr; 199   2272991 return head_ == nullptr;
200   } 200   }
201   201  
HITCBC 202   608397 void push(T* w) noexcept 202   697643 void push(T* w) noexcept
203   { 203   {
HITCBC 204   608397 w->next_ = nullptr; 204   697643 w->next_ = nullptr;
HITCBC 205   608397 if (tail_) 205   697643 if (tail_)
HITCBC 206   269124 tail_->next_ = w; 206   303987 tail_->next_ = w;
207   else 207   else
HITCBC 208   339273 head_ = w; 208   393656 head_ = w;
HITCBC 209   608397 tail_ = w; 209   697643 tail_ = w;
HITCBC 210   608397 } 210   697643 }
211   211  
HITCBC 212   322577 void splice(intrusive_queue& other) noexcept 212   372977 void splice(intrusive_queue& other) noexcept
213   { 213   {
HITCBC 214   322577 if (other.empty()) 214   372977 if (other.empty())
MISUBC 215   ✗ return; 215   ✗ return;
HITCBC 216   322577 if (tail_) 216   372977 if (tail_)
HITCBC 217   118380 tail_->next_ = other.head_; 217   147692 tail_->next_ = other.head_;
218   else 218   else
HITCBC 219   204197 head_ = other.head_; 219   225285 head_ = other.head_;
HITCBC 220   322577 tail_ = other.tail_; 220   372977 tail_ = other.tail_;
HITCBC 221   322577 other.head_ = nullptr; 221   372977 other.head_ = nullptr;
HITCBC 222   322577 other.tail_ = nullptr; 222   372977 other.tail_ = nullptr;
223   } 223   }
224   224  
HITCBC 225   842596 T* pop() noexcept 225   957947 T* pop() noexcept
226   { 226   {
HITCBC 227   842596 if (!head_) 227   957947 if (!head_)
HITCBC 228   234199 return nullptr; 228   260304 return nullptr;
HITCBC 229   608397 T* w = head_; 229   697643 T* w = head_;
HITCBC 230   608397 head_ = head_->next_; 230   697643 head_ = head_->next_;
HITCBC 231   608397 if (!head_) 231   697643 if (!head_)
HITCBC 232   220893 tail_ = nullptr; 232   245964 tail_ = nullptr;
233   // Defensive: clear stale linkage on popped node. 233   // Defensive: clear stale linkage on popped node.
HITCBC 234   608397 w->next_ = nullptr; 234   697643 w->next_ = nullptr;
HITCBC 235   608397 return w; 235   697643 return w;
236   } 236   }
237   }; 237   };
238   238  
239   } // namespace boost::corosio::detail 239   } // namespace boost::corosio::detail
240   240  
241   #endif 241   #endif