Branch data Line data Source code
1 : : // Copyright (c) 2022-present The Bitcoin Core developers
2 : : // Distributed under the MIT software license, see the accompanying
3 : : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 : :
5 : : #ifndef BITCOIN_SUPPORT_ALLOCATORS_POOL_H
6 : : #define BITCOIN_SUPPORT_ALLOCATORS_POOL_H
7 : :
8 : : #include <array>
9 : : #include <cassert>
10 : : #include <cstddef>
11 : : #include <list>
12 : : #include <memory>
13 : : #include <new>
14 : : #include <type_traits>
15 : : #include <utility>
16 : :
17 : : #include <util/check.h>
18 : : #include <util/overflow.h>
19 : :
20 : : /**
21 : : * A memory resource similar to std::pmr::unsynchronized_pool_resource, but
22 : : * optimized for node-based containers. It has the following properties:
23 : : *
24 : : * * Owns the allocated memory and frees it on destruction, even when deallocate
25 : : * has not been called on the allocated blocks.
26 : : *
27 : : * * Consists of a number of pools, each one for a different block size.
28 : : * Each pool holds blocks of uniform size in a freelist.
29 : : *
30 : : * * Exhausting memory in a freelist causes a new allocation of a fixed size chunk.
31 : : * This chunk is used to carve out blocks.
32 : : *
33 : : * * Block sizes or alignments that can not be served by the pools are allocated
34 : : * and deallocated by operator new().
35 : : *
36 : : * PoolResource is not thread-safe. It is intended to be used by PoolAllocator.
37 : : *
38 : : * @tparam MAX_BLOCK_SIZE_BYTES Maximum size to allocate with the pool. If larger
39 : : * sizes are requested, allocation falls back to new().
40 : : *
41 : : * @tparam ALIGN_BYTES Required alignment for the allocations.
42 : : *
43 : : * An example: If you create a PoolResource<128, 8>(262144) and perform a bunch of
44 : : * allocations and deallocate 2 blocks with size 8 bytes, and 3 blocks with size 16,
45 : : * the members will look like this:
46 : : *
47 : : * m_free_lists m_allocated_chunks
48 : : * ┌───┐ ┌───┐ ┌────────────-------──────┐
49 : : * │ │ blocks │ ├─►│ 262144 B │
50 : : * │ │ ┌─────┐ ┌─────┐ └─┬─┘ └────────────-------──────┘
51 : : * │ 1 ├─►│ 8 B ├─►│ 8 B │ │
52 : : * │ │ └─────┘ └─────┘ :
53 : : * │ │ │
54 : : * │ │ ┌─────┐ ┌─────┐ ┌─────┐ ▼
55 : : * │ 2 ├─►│16 B ├─►│16 B ├─►│16 B │ ┌───┐ ┌─────────────────────────┐
56 : : * │ │ └─────┘ └─────┘ └─────┘ │ ├─►│ ▲ │ ▲
57 : : * │ │ └───┘ └──────────┬──────────────┘ │
58 : : * │ . │ │ m_available_memory_end
59 : : * │ . │ m_available_memory_it
60 : : * │ . │
61 : : * │ │
62 : : * │ │
63 : : * │16 │
64 : : * └───┘
65 : : *
66 : : * Here m_free_lists[1] holds the 2 blocks of size 8 bytes, and m_free_lists[2]
67 : : * holds the 3 blocks of size 16. The blocks came from the data stored in the
68 : : * m_allocated_chunks list. Each chunk has bytes 262144. The last chunk has still
69 : : * some memory available for the blocks, and when m_available_memory_it is at the
70 : : * end, a new chunk will be allocated and added to the list.
71 : : */
72 : : template <std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES>
73 : : class PoolResource final
74 : : {
75 : : static_assert(ALIGN_BYTES > 0, "ALIGN_BYTES must be nonzero");
76 : : static_assert((ALIGN_BYTES & (ALIGN_BYTES - 1)) == 0, "ALIGN_BYTES must be a power of two");
77 : :
78 : : /**
79 : : * In-place linked list of the allocations, used for the freelist.
80 : : */
81 : : struct ListNode {
82 : : ListNode* m_next;
83 : :
84 : 42054051 : explicit ListNode(ListNode* next) : m_next(next) {}
85 : : };
86 : : static_assert(std::is_trivially_destructible_v<ListNode>, "Make sure we don't need to manually call a destructor");
87 : :
88 : : /**
89 : : * Internal alignment value. The larger of the requested ALIGN_BYTES and alignof(FreeList).
90 : : */
91 : : static constexpr std::size_t ELEM_ALIGN_BYTES = std::max(alignof(ListNode), ALIGN_BYTES);
92 : : static_assert((ELEM_ALIGN_BYTES & (ELEM_ALIGN_BYTES - 1)) == 0, "ELEM_ALIGN_BYTES must be a power of two");
93 : : static_assert(sizeof(ListNode) <= ELEM_ALIGN_BYTES, "Units of size ELEM_SIZE_ALIGN need to be able to store a ListNode");
94 : : static_assert((MAX_BLOCK_SIZE_BYTES & (ELEM_ALIGN_BYTES - 1)) == 0, "MAX_BLOCK_SIZE_BYTES needs to be a multiple of the alignment.");
95 : :
96 : : /**
97 : : * Size in bytes to allocate per chunk
98 : : */
99 : : const size_t m_chunk_size_bytes;
100 : :
101 : : /**
102 : : * Contains all allocated pools of memory, used to free the data in the destructor.
103 : : */
104 : : std::list<std::byte*> m_allocated_chunks{};
105 : :
106 : : /**
107 : : * Single linked lists of all data that came from deallocating.
108 : : * m_free_lists[n] will serve blocks of size n*ELEM_ALIGN_BYTES.
109 : : */
110 : : std::array<ListNode*, MAX_BLOCK_SIZE_BYTES / ELEM_ALIGN_BYTES + 1> m_free_lists{};
111 : :
112 : : /**
113 : : * Points to the beginning of available memory for carving out allocations.
114 : : */
115 : : std::byte* m_available_memory_it = nullptr;
116 : :
117 : : /**
118 : : * Points to the end of available memory for carving out allocations.
119 : : *
120 : : * That member variable is redundant, and is always equal to `m_allocated_chunks.back() + m_chunk_size_bytes`
121 : : * whenever it is accessed, but `m_available_memory_end` caches this for clarity and efficiency.
122 : : */
123 : : std::byte* m_available_memory_end = nullptr;
124 : :
125 : : /**
126 : : * How many multiple of ELEM_ALIGN_BYTES are necessary to fit bytes. We use that result directly as an index
127 : : * into m_free_lists. Round up for the special case when bytes==0.
128 : : */
129 [ + + ][ - + : 60012163 : [[nodiscard]] static constexpr std::size_t NumElemAlignBytes(std::size_t bytes)
+ + + + ]
130 : : {
131 : 84504754 : return CeilDiv(bytes, ELEM_ALIGN_BYTES) + (bytes == 0);
132 : : }
133 : :
134 : : /**
135 : : * True when it is possible to make use of the freelist
136 : : */
137 : 84318821 : [[nodiscard]] static constexpr bool IsFreeListUsable(std::size_t bytes, std::size_t alignment)
138 : : {
139 : 84318821 : return alignment <= ELEM_ALIGN_BYTES && bytes <= MAX_BLOCK_SIZE_BYTES;
140 : : }
141 : :
142 : : /**
143 : : * Replaces node with placement constructed ListNode that points to the previous node
144 : : */
145 : 42054051 : void PlacementAddToList(void* p, ListNode*& node)
146 : : {
147 : 42054051 : node = new (p) ListNode{node};
148 : 3322 : }
149 : :
150 : : /**
151 : : * Allocate one full memory chunk which will be used to carve out allocations.
152 : : * Also puts any leftover bytes into the freelist.
153 : : *
154 : : * Precondition: leftover bytes are either 0 or few enough to fit into a place in the freelist
155 : : */
156 : 406690 : void AllocateChunk()
157 : : {
158 : : // if there is still any available memory left, put it into the freelist.
159 : 406690 : size_t remaining_available_bytes = m_available_memory_end - m_available_memory_it;
160 [ + + ]: 406690 : if (0 != remaining_available_bytes) {
161 : : ASAN_UNPOISON_MEMORY_REGION(m_available_memory_it, sizeof(ListNode));
162 : 3322 : PlacementAddToList(m_available_memory_it, m_free_lists[remaining_available_bytes / ELEM_ALIGN_BYTES]);
163 : : ASAN_POISON_MEMORY_REGION(m_available_memory_it, sizeof(ListNode));
164 : : }
165 : :
166 : 406690 : void* storage = ::operator new (m_chunk_size_bytes, std::align_val_t{ELEM_ALIGN_BYTES});
167 : 406690 : m_available_memory_it = new (storage) std::byte[m_chunk_size_bytes];
168 : 406690 : m_available_memory_end = m_available_memory_it + m_chunk_size_bytes;
169 : : ASAN_POISON_MEMORY_REGION(m_available_memory_it, m_chunk_size_bytes);
170 : 406690 : m_allocated_chunks.emplace_back(m_available_memory_it);
171 : 406690 : }
172 : :
173 : : /**
174 : : * Access to internals for testing purpose only
175 : : */
176 : : friend class PoolResourceTester;
177 : :
178 : : public:
179 : : /**
180 : : * Construct a new PoolResource object which allocates the first chunk.
181 : : * chunk_size_bytes will be rounded up to next multiple of ELEM_ALIGN_BYTES.
182 : : */
183 [ - + ]: 403296 : explicit PoolResource(std::size_t chunk_size_bytes)
184 [ - + ]: 403296 : : m_chunk_size_bytes(NumElemAlignBytes(chunk_size_bytes) * ELEM_ALIGN_BYTES)
185 : : {
186 [ - + ]: 403296 : assert(m_chunk_size_bytes >= MAX_BLOCK_SIZE_BYTES);
187 [ + - ]: 403296 : AllocateChunk();
188 : 403296 : }
189 : :
190 : : /**
191 : : * Construct a new Pool Resource object, defaults to 2^18=262144 chunk size.
192 : : */
193 [ + - ]: 403293 : PoolResource() : PoolResource(262144) {}
194 : :
195 : : /**
196 : : * Disable copy & move semantics, these are not supported for the resource.
197 : : */
198 : : PoolResource(const PoolResource&) = delete;
199 : : PoolResource& operator=(const PoolResource&) = delete;
200 : : PoolResource(PoolResource&&) = delete;
201 : : PoolResource& operator=(PoolResource&&) = delete;
202 : :
203 : : /**
204 : : * Deallocates all memory allocated associated with the memory resource.
205 : : */
206 : 403296 : ~PoolResource()
207 : : {
208 [ + + ]: 809986 : for (std::byte* chunk : m_allocated_chunks) {
209 : 406690 : std::destroy(chunk, chunk + m_chunk_size_bytes);
210 : 406690 : ::operator delete ((void*)chunk, std::align_val_t{ELEM_ALIGN_BYTES});
211 : : ASAN_UNPOISON_MEMORY_REGION(chunk, m_chunk_size_bytes);
212 : : }
213 : 403296 : }
214 : :
215 : : /**
216 : : * Allocates a block of bytes. If possible the freelist is used, otherwise allocation
217 : : * is forwarded to ::operator new().
218 : : */
219 : 42159413 : void* Allocate(std::size_t bytes, std::size_t alignment)
220 : : {
221 [ + + ]: 42159413 : if (IsFreeListUsable(bytes, alignment)) {
222 : 42050729 : const std::size_t num_alignments = NumElemAlignBytes(bytes);
223 [ + + ]: 42050729 : if (nullptr != m_free_lists[num_alignments]) {
224 : : // we've already got data in the pool's freelist, unlink one element and return the pointer
225 : : // to the unlinked memory. Since FreeList is trivially destructible we can just treat it as
226 : : // uninitialized memory.
227 : 25199468 : ASAN_UNPOISON_MEMORY_REGION(m_free_lists[num_alignments], sizeof(ListNode));
228 : 25199468 : auto* next{m_free_lists[num_alignments]->m_next};
229 : 25199468 : ASAN_POISON_MEMORY_REGION(m_free_lists[num_alignments], sizeof(ListNode));
230 : 25199468 : ASAN_UNPOISON_MEMORY_REGION(m_free_lists[num_alignments], bytes);
231 : 25199468 : return std::exchange(m_free_lists[num_alignments], next);
232 : : }
233 : :
234 : : // freelist is empty: get one allocation from allocated chunk memory.
235 : 16851261 : const std::ptrdiff_t round_bytes = static_cast<std::ptrdiff_t>(num_alignments * ELEM_ALIGN_BYTES);
236 [ + + ]: 16851261 : if (round_bytes > m_available_memory_end - m_available_memory_it) {
237 : : // slow path, only happens when a new chunk needs to be allocated
238 : 3394 : AllocateChunk();
239 : : }
240 : :
241 : : // Make sure we use the right amount of bytes for that freelist (might be rounded up),
242 : : ASAN_UNPOISON_MEMORY_REGION(m_available_memory_it, round_bytes);
243 : 16851261 : return std::exchange(m_available_memory_it, m_available_memory_it + round_bytes);
244 : : }
245 : :
246 : : // Can't use the pool => use operator new()
247 : 108684 : return ::operator new (bytes, std::align_val_t{alignment});
248 : : }
249 : :
250 : : /**
251 : : * Returns a block to the freelists, or deletes the block when it did not come from the chunks.
252 : : */
253 : 42159413 : void Deallocate(void* p, std::size_t bytes, std::size_t alignment) noexcept
254 : : {
255 [ + + ]: 42159413 : if (IsFreeListUsable(bytes, alignment)) {
256 : 42050729 : const std::size_t num_alignments = NumElemAlignBytes(bytes);
257 : : // put the memory block into the linked list. We can placement construct the FreeList
258 : : // into the memory since we can be sure the alignment is correct.
259 : : ASAN_UNPOISON_MEMORY_REGION(p, sizeof(ListNode));
260 [ + - + - : 42050729 : PlacementAddToList(p, m_free_lists[num_alignments]);
+ - ]
261 [ + - + - : 42050729 : ASAN_POISON_MEMORY_REGION(p, std::max(bytes, sizeof(ListNode)));
+ - ]
262 : : } else {
263 : : // Can't use the pool => forward deallocation to ::operator delete().
264 : 108684 : ::operator delete (p, std::align_val_t{alignment});
265 : : }
266 : 42159408 : }
267 : :
268 : : /**
269 : : * Number of allocated chunks
270 : : */
271 : 1160910 : [[nodiscard]] std::size_t NumAllocatedChunks() const
272 : : {
273 [ + - + - ]: 2321819 : return m_allocated_chunks.size();
[ + - + -
+ - ]
274 : : }
275 : :
276 : : /**
277 : : * Size in bytes to allocate per chunk, currently hardcoded to a fixed size.
278 : : */
279 : 1161172 : [[nodiscard]] size_t ChunkSizeBytes() const
280 : : {
281 [ + - ][ + - : 1161172 : return m_chunk_size_bytes;
+ - + - #
# # # #
# ][ + - +
- + - + -
+ - + - ]
282 : : }
283 : : };
284 : :
285 : :
286 : : /**
287 : : * Forwards all allocations/deallocations to the PoolResource.
288 : : */
289 : : template <class T, std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES = alignof(T)>
290 : : class PoolAllocator
291 : : {
292 : : PoolResource<MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>* m_resource;
293 : :
294 : : template <typename U, std::size_t M, std::size_t A>
295 : : friend class PoolAllocator;
296 : :
297 : : public:
298 : : using value_type = T;
299 : : using ResourceType = PoolResource<MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>;
300 : :
301 : : /**
302 : : * Not explicit so we can easily construct it with the correct resource
303 : : */
304 : 403293 : PoolAllocator(ResourceType* resource) noexcept
305 [ + - ]: 403293 : : m_resource(resource)
[ + - + - ]
306 : : {
307 : : }
308 : :
309 : : PoolAllocator(const PoolAllocator& other) noexcept = default;
310 : : PoolAllocator& operator=(const PoolAllocator& other) noexcept = default;
311 : :
312 : : template <class U>
313 : 2033668 : PoolAllocator(const PoolAllocator<U, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& other) noexcept
314 : 2033668 : : m_resource(other.resource())
315 : : {
316 : : }
317 : :
318 : : /**
319 : : * The rebind struct here is mandatory because we use non type template arguments for
320 : : * PoolAllocator. See https://en.cppreference.com/w/cpp/named_req/Allocator#cite_note-2
321 : : */
322 : : template <typename U>
323 : : struct rebind {
324 : : using other = PoolAllocator<U, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>;
325 : : };
326 : :
327 : : /**
328 : : * Forwards each call to the resource.
329 : : */
330 : 42158458 : T* allocate(size_t n)
331 : : {
332 : 42158458 : return static_cast<T*>(m_resource->Allocate(n * sizeof(T), alignof(T)));
333 : : }
334 : :
335 : : /**
336 : : * Forwards each call to the resource.
337 : : */
338 : 42158458 : void deallocate(T* p, size_t n) noexcept
339 : : {
340 : 42158458 : m_resource->Deallocate(p, n * sizeof(T), alignof(T));
341 : : }
342 : :
343 : 2033668 : ResourceType* resource() const noexcept
344 : : {
345 [ + - + - ]: 2033668 : return m_resource;
346 : : }
347 : : };
348 : :
349 : : template <class T1, class T2, std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES>
350 : : bool operator==(const PoolAllocator<T1, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& a,
351 : : const PoolAllocator<T2, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& b) noexcept
352 : : {
353 : : return a.resource() == b.resource();
354 : : }
355 : :
356 : : #endif // BITCOIN_SUPPORT_ALLOCATORS_POOL_H
|
