include/boost/corosio/detail/object_ref.hpp

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object_ref.hpp

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1		//
2		// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3		// Copyright (c) 2026 Steve Gerbino
4		//
5		// Distributed under the Boost Software License, Version 1.0. (See accompanying
6		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7		//
8		// Official repository: https://github.com/cppalliance/corosio
9		//
10
11		#ifndef BOOST_COROSIO_DETAIL_OBJECT_REF_HPP
12		#define BOOST_COROSIO_DETAIL_OBJECT_REF_HPP
13
14		#include <boost/corosio/detail/platform.hpp>
15		#include <boost/corosio/io/io_object.hpp>
16		#include <atomic>
17		#include <utility>
18
19		namespace boost::corosio::detail {
20
21		/// Add one reference to `impl`. `impl` must be non-null.
22		inline void
23	105679x	acquire(io_object::implementation* impl) noexcept
24		{
25	105679x	impl->refs_.fetch_add(1, std::memory_order_relaxed);
26	105679x	}
27
28		/** Drop one reference; runs `retire()` at zero. `impl` must be
29		non-null.
30
31		Uses release on the decrement and an acquire fence before the
32		zero-action so writes made while holding a reference are visible
33		to the recycler. TSan cannot model a standalone fence, so under
34		it the decrement itself is acq_rel instead -- strictly stronger,
35		and TSan's happens-before tracking models the exchange directly.
36		*/
37		inline void
38	126004x	release(io_object::implementation* impl) noexcept
39		{
40		#if BOOST_COROSIO_TSAN
41		if (impl->refs_.fetch_sub(1, std::memory_order_acq_rel) == 1)
42		impl->retire();
43		#else
44	252008x	if (impl->refs_.fetch_sub(1, std::memory_order_release) == 1)
45		{
46		std::atomic_thread_fence(std::memory_order_acquire);
47	20325x	impl->retire();
48		}
49		#endif
50	126004x	}
51
52		/** Owning intrusive reference to an I/O implementation.
53
54		Replaces `std::shared_ptr<void>` op keepalives: copy acquires,
55		move steals, destruction releases. Kept deliberately minimal —
56		two words smaller than a shared_ptr and no control block.
57		*/
58		class object_ref
59		{
60		io_object::implementation* p_ = nullptr;
61
62		public:
63		/// Destroy the object_ref, releasing the held reference, if any.
64	950945x	~object_ref() { reset(); }
65
66		/// Construct an object_ref holding no reference.
67	30938x	object_ref() noexcept = default;
68
69		/// Construct an object_ref that acquires a new reference to `p`.
70	105659x	explicit object_ref(io_object::implementation* p) noexcept : p_(p)
71		{
72	105659x	if (p_)
73	105659x	acquire(p_);
74	105659x	}
75
76		/// Construct a copy, acquiring another reference to `other`'s target.
77	3x	object_ref(object_ref const& other) noexcept : p_(other.p_)
78		{
79	3x	if (p_)
80	3x	acquire(p_);
81	3x	}
82
83		/// Construct by transferring the reference out of `other`.
84	511944x	object_ref(object_ref&& other) noexcept
85	511944x	: p_(std::exchange(other.p_, nullptr))
86		{
87	511944x	}
88
89		/// Release the held reference, if any, and acquire `other`'s target.
90	2x	object_ref& operator=(object_ref const& other) noexcept
91		{
92	2x	object_ref(other).swap(*this);
93	2x	return *this;
94		}
95
96		/// Release the held reference, if any, and take ownership of `other`'s.
97	408367x	object_ref& operator=(object_ref&& other) noexcept
98		{
99	408367x	object_ref(std::move(other)).swap(*this);
100	408367x	return *this;
101		}
102
103		/// Release the held reference, if any.
104	1431925x	void reset() noexcept
105		{
106	1431925x	if (p_)
107	105662x	release(std::exchange(p_, nullptr));
108	1431925x	}
109
110		/// Return the held implementation pointer.
111	3x	io_object::implementation* get() const noexcept { return p_; }
112
113		/// Return true if a reference is held.
114	13452x	explicit operator bool() const noexcept { return p_ != nullptr; }
115
116		/// Exchange the implementation pointers held by `*this` and `other`.
117	408369x	void swap(object_ref& other) noexcept { std::swap(p_, other.p_); }
118		};
119
120		} // namespace boost::corosio::detail
121
122		#endif
123