src/ex/recycling_memory_resource.cpp

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recycling_memory_resource.cpp

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1		//
2		// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
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/capy
8		//
9
10		#include <boost/capy/ex/recycling_memory_resource.hpp>
11
12		#include <new>
13		#include <tuple>
14
15		namespace boost {
16		namespace capy {
17
18		// Instance destruction does nothing: the resource is stateless (all pools
19		// are static). Global-pool cleanup is owned by global()'s holder, exactly
20		// as in the original where the global pool's own destructor drained it,
21		// independent of any instance lifetime.
22	307x	recycling_memory_resource::~recycling_memory_resource() = default;
23
24		#if (defined(BOOST_CAPY_DYN_LINK) \|\| defined(BOOST_ALL_DYN_LINK)) && \
25		!defined(BOOST_CAPY_STATIC_LINK)
26
27		recycling_memory_resource::pool&
28	644349x	recycling_memory_resource::local() noexcept
29		{
30		static thread_local pool p;
31	644349x	return p;
32		}
33
34		bool&
35	216943x	recycling_memory_resource::thread_armed() noexcept
36		{
37		static thread_local bool armed = false;
38	216943x	return armed;
39		}
40
41		#endif
42
43		namespace {
44
45		// Set once this thread's pool was drained at exit. Another thread_local
46		// destroyed later can still free frames; they must not be cached.
47		thread_local bool pool_drained = false;
48
49		} // namespace
50
51		bool
52	211195x	recycling_memory_resource::arm_thread_cleanup() noexcept
53		{
54		struct janitor
55		{
56	365x	~janitor()
57		{
58		// Return this thread's cached blocks to the OS so nothing
59		// leaks at thread exit. The pool has a trivial dtor, so its
60		// thread-local storage is still valid here.
61	365x	auto& lp = local();
62	2555x	for(auto& b : lp.buckets)
63	6728x	while(b.count > 0)
64	4538x	::operator delete(b.pop());
65	365x	pool_drained = true;
66	365x	thread_armed() = false;
67	365x	}
68		};
69	211195x	if(pool_drained)
70	5x	return false;
71	211190x	static thread_local janitor j;
72	211190x	std::ignore = j;
73	211190x	return true;
74		}
75
76		recycling_memory_resource::pool&
77	420498x	recycling_memory_resource::global() noexcept
78		{
79		// Holder gives the global pool a destructor (the trivial-dtor pool type
80		// itself must stay guard-free for local()). Runs unconditionally at
81		// process exit, mirroring the original global pool destructor, and is
82		// locked because a worker thread may still be in a slow path. This path
83		// is cold (slow paths only), so the holder's guard costs nothing hot.
84		struct holder
85		{
86		pool p;
87
88	34x	~holder()
89		{
90	34x	std::lock_guard<std::mutex> lock(global_mutex());
91	238x	for(auto& b : p.buckets)
92	327x	while(b.count > 0)
93	123x	::operator delete(b.pop());
94	34x	}
95		};
96	420498x	static holder h;
97	420498x	return h.p;
98		}
99
100		std::mutex&
101	420532x	recycling_memory_resource::global_mutex() noexcept
102		{
103		// Never destroyed: it is locked during process-exit teardown (in
104		// global()'s holder destructor), after a function-local `static
105		// std::mutex` could itself have been destroyed. Placement-new into
106		// static storage owns no heap allocation, so there is nothing to leak.
107		alignas(std::mutex) static unsigned char storage[sizeof(std::mutex)];
108		static std::mutex* const mtx =
109	420532x	::new(static_cast<void*>(storage)) std::mutex();
110	420532x	return *mtx;
111		}
112
113		void*
114	210833x	recycling_memory_resource::allocate_slow(
115		std::size_t rounded, std::size_t idx)
116		{
117		// Once this thread's pool was drained at exit, take one block and
118		// leave the pool empty: nothing would release a refill.
119	210833x	bool const cache = arm_thread_cleanup();
120		{
121	210833x	std::lock_guard<std::mutex> lock(global_mutex());
122	210833x	auto& b = global().buckets[idx];
123	210833x	if(auto* p = cache ? b.pop(local().buckets[idx]) : b.pop())
124	716x	return p;
125	210833x	}
126	210117x	return ::operator new(rounded);
127		}
128
129		void
130	209665x	recycling_memory_resource::deallocate_slow(
131		void* p, std::size_t idx)
132		{
133		{
134	209665x	std::lock_guard<std::mutex> lock(global_mutex());
135	209665x	if(global().buckets[idx].push(p))
136	4209x	return;
137	209665x	}
138	205456x	::operator delete(p);
139		}
140
141		void*
142	102470x	recycling_memory_resource::do_allocate(std::size_t bytes, std::size_t alignment)
143		{
144	102470x	return allocate_fast(bytes, alignment);
145		}
146
147		void
148	102470x	recycling_memory_resource::do_deallocate(void* p, std::size_t bytes, std::size_t alignment)
149		{
150	102470x	deallocate_fast(p, bytes, alignment);
151	102470x	}
152
153		std::pmr::memory_resource*
154	4555x	get_recycling_memory_resource() noexcept
155		{
156	4555x	static recycling_memory_resource instance;
157	4555x	return &instance;
158		}
159
160		} // namespace capy
161		} // namespace boost
162