include/boost/corosio/detail/intrusive.hpp

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intrusive.hpp

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1		//
2		// Copyright (c) 2025 Vinnie Falco ([email protected])
3		//
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)
6		//
7		// Official repository: https://github.com/cppalliance/corosio
8		//
9
10		#ifndef BOOST_COROSIO_DETAIL_INTRUSIVE_HPP
11		#define BOOST_COROSIO_DETAIL_INTRUSIVE_HPP
12
13		namespace boost::corosio::detail {
14
15		/** An intrusive doubly linked list.
16
17		This container provides O(1) push and pop operations for
18		elements that derive from @ref node. Elements are not
19		copied or moved; they are linked directly into the list.
20
21		@tparam T The element type. Must derive from `intrusive_list<T>::node`.
22		*/
23		template<class T>
24		class intrusive_list
25		{
26		public:
27		/** Base class for list elements.
28
29		Derive from this class to make a type usable with
30		@ref intrusive_list. The `next_` and `prev_` pointers
31		are private and accessible only to the list.
32		*/
33		class node
34		{
35		friend class intrusive_list;
36
37		private:
38		T* next_;
39		T* prev_;
40		};
41
42		private:
43		T* head_ = nullptr;
44		T* tail_ = nullptr;
45
46		public:
47	13251x	intrusive_list() = default;
48
49		intrusive_list(intrusive_list&& other) noexcept
50		: head_(other.head_)
51		, tail_(other.tail_)
52		{
53		other.head_ = nullptr;
54		other.tail_ = nullptr;
55		}
56
57		intrusive_list(intrusive_list const&) = delete;
58		intrusive_list& operator=(intrusive_list const&) = delete;
59		intrusive_list& operator=(intrusive_list&&) = delete;
60
61	4011x	bool empty() const noexcept
62		{
63	4011x	return head_ == nullptr;
64		}
65
66		/// Peek at the head element without removing it.
67	3948x	T* front() const noexcept
68		{
69	3948x	return head_;
70		}
71
72	59165x	void push_back(T* w) noexcept
73		{
74	59165x	auto* n = static_cast<node*>(w);
75	59165x	n->next_ = nullptr;
76	59165x	n->prev_ = tail_;
77	59165x	if (tail_)
78	25638x	static_cast<node*>(tail_)->next_ = w;
79		else
80	33527x	head_ = w;
81	59165x	tail_ = w;
82	59165x	}
83
84		void splice_back(intrusive_list& other) noexcept
85		{
86		if (other.empty())
87		return;
88		if (tail_)
89		{
90		static_cast<node*>(tail_)->next_ = other.head_;
91		static_cast<node*>(other.head_)->prev_ = tail_;
92		tail_ = other.tail_;
93		}
94		else
95		{
96		head_ = other.head_;
97		tail_ = other.tail_;
98		}
99		other.head_ = nullptr;
100		other.tail_ = nullptr;
101		}
102
103	724178x	T* pop_front() noexcept
104		{
105	724178x	if (!head_)
106	693819x	return nullptr;
107	30359x	T* w = head_;
108	30359x	head_ = static_cast<node*>(head_)->next_;
109	30359x	if (head_)
110	62x	static_cast<node*>(head_)->prev_ = nullptr;
111		else
112	30297x	tail_ = nullptr;
113		// Defensive: clear stale linkage so remove() on a
114		// popped node cannot corrupt the list.
115	30359x	auto* n = static_cast<node*>(w);
116	30359x	n->next_ = nullptr;
117	30359x	n->prev_ = nullptr;
118	30359x	return w;
119		}
120
121	28806x	void remove(T* w) noexcept
122		{
123	28806x	auto* n = static_cast<node*>(w);
124		// Already detached — nothing to do.
125	28806x	if (!n->next_ && !n->prev_ && head_ != w && tail_ != w)
126	✗	return;
127	28806x	if (n->prev_)
128	7873x	static_cast<node*>(n->prev_)->next_ = n->next_;
129		else
130	20933x	head_ = n->next_;
131	28806x	if (n->next_)
132	17792x	static_cast<node*>(n->next_)->prev_ = n->prev_;
133		else
134	11014x	tail_ = n->prev_;
135	28806x	n->next_ = nullptr;
136	28806x	n->prev_ = nullptr;
137		}
138
139		/// Invoke @p f for each element in the list.
140		template<class F>
141	122x	void for_each(F f)
142		{
143	122x	for (T* p = head_; p; p = static_cast<node*>(p)->next_)
144	✗	f(p);
145	122x	}
146		};
147
148		/** An intrusive singly linked FIFO queue.
149
150		This container provides O(1) push and pop operations for
151		elements that derive from @ref node. Elements are not
152		copied or moved; they are linked directly into the queue.
153
154		Unlike @ref intrusive_list, this uses only a single `next_`
155		pointer per node, saving memory at the cost of not supporting
156		O(1) removal of arbitrary elements.
157
158		@tparam T The element type. Must derive from `intrusive_queue<T>::node`.
159		*/
160		template<class T>
161		class intrusive_queue
162		{
163		public:
164		/** Base class for queue elements.
165
166		Derive from this class to make a type usable with
167		@ref intrusive_queue. The `next_` pointer is private
168		and accessible only to the queue.
169		*/
170		class node
171		{
172		friend class intrusive_queue;
173
174		private:
175		T* next_;
176		};
177
178		private:
179		T* head_ = nullptr;
180		T* tail_ = nullptr;
181
182		public:
183	6060x	intrusive_queue() = default;
184
185		intrusive_queue(intrusive_queue&& other) noexcept
186		: head_(other.head_)
187		, tail_(other.tail_)
188		{
189		other.head_ = nullptr;
190		other.tail_ = nullptr;
191		}
192
193		intrusive_queue(intrusive_queue const&) = delete;
194		intrusive_queue& operator=(intrusive_queue const&) = delete;
195		intrusive_queue& operator=(intrusive_queue&&) = delete;
196
197	5251406x	bool empty() const noexcept
198		{
199	5251406x	return head_ == nullptr;
200		}
201
202	1598798x	void push(T* w) noexcept
203		{
204	1598798x	w->next_ = nullptr;
205	1598798x	if (tail_)
206	723862x	tail_->next_ = w;
207		else
208	874936x	head_ = w;
209	1598798x	tail_ = w;
210	1598798x	}
211
212	824309x	void splice(intrusive_queue& other) noexcept
213		{
214	824309x	if (other.empty())
215	✗	return;
216	824309x	if (tail_)
217	259122x	tail_->next_ = other.head_;
218		else
219	565187x	head_ = other.head_;
220	824309x	tail_ = other.tail_;
221	824309x	other.head_ = nullptr;
222	824309x	other.tail_ = nullptr;
223		}
224
225	2231464x	T* pop() noexcept
226		{
227	2231464x	if (!head_)
228	632666x	return nullptr;
229	1598798x	T* w = head_;
230	1598798x	head_ = head_->next_;
231	1598798x	if (!head_)
232	615814x	tail_ = nullptr;
233		// Defensive: clear stale linkage on popped node.
234	1598798x	w->next_ = nullptr;
235	1598798x	return w;
236		}
237		};
238
239		} // namespace boost::corosio::detail
240
241		#endif
242