diff options
author | Martin Leitner-Ankerl <martin.ankerl@gmail.com> | 2022-06-11 09:23:51 +0200 |
---|---|---|
committer | Martin Leitner-Ankerl <martin.ankerl@gmail.com> | 2023-03-23 19:38:38 +0100 |
commit | b8401c3281978beed6198b2f9782b6a8dd35cbd7 (patch) | |
tree | fb740536de54eb5bc056b52da7430c9137b0edd2 /src/support | |
parent | 23056436461a8b3af1a504b9638c48e8c8170652 (diff) | |
download | bitcoin-b8401c3281978beed6198b2f9782b6a8dd35cbd7.tar.xz |
Add pool based memory resource & allocator
A memory resource similar to std::pmr::unsynchronized_pool_resource, but
optimized for node-based containers.
Co-Authored-By: Pieter Wuille <pieter@wuille.net>
Diffstat (limited to 'src/support')
-rw-r--r-- | src/support/allocators/pool.h | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/src/support/allocators/pool.h b/src/support/allocators/pool.h new file mode 100644 index 0000000000..c8e70ebacf --- /dev/null +++ b/src/support/allocators/pool.h @@ -0,0 +1,349 @@ +// Copyright (c) 2022 The Bitcoin Core developers +// Distributed under the MIT software license, see the accompanying +// file COPYING or http://www.opensource.org/licenses/mit-license.php. + +#ifndef BITCOIN_SUPPORT_ALLOCATORS_POOL_H +#define BITCOIN_SUPPORT_ALLOCATORS_POOL_H + +#include <array> +#include <cassert> +#include <cstddef> +#include <list> +#include <memory> +#include <new> +#include <type_traits> +#include <utility> + +/** + * A memory resource similar to std::pmr::unsynchronized_pool_resource, but + * optimized for node-based containers. It has the following properties: + * + * * Owns the allocated memory and frees it on destruction, even when deallocate + * has not been called on the allocated blocks. + * + * * Consists of a number of pools, each one for a different block size. + * Each pool holds blocks of uniform size in a freelist. + * + * * Exhausting memory in a freelist causes a new allocation of a fixed size chunk. + * This chunk is used to carve out blocks. + * + * * Block sizes or alignments that can not be served by the pools are allocated + * and deallocated by operator new(). + * + * PoolResource is not thread-safe. It is intended to be used by PoolAllocator. + * + * @tparam MAX_BLOCK_SIZE_BYTES Maximum size to allocate with the pool. If larger + * sizes are requested, allocation falls back to new(). + * + * @tparam ALIGN_BYTES Required alignment for the allocations. + * + * An example: If you create a PoolResource<128, 8>(262144) and perform a bunch of + * allocations and deallocate 2 blocks with size 8 bytes, and 3 blocks with size 16, + * the members will look like this: + * + * m_free_lists m_allocated_chunks + * ┌───┐ ┌───┐ ┌────────────-------──────┐ + * │ │ blocks │ ├─►│ 262144 B │ + * │ │ ┌─────┐ ┌─────┐ └─┬─┘ └────────────-------──────┘ + * │ 1 ├─►│ 8 B ├─►│ 8 B │ │ + * │ │ └─────┘ └─────┘ : + * │ │ │ + * │ │ ┌─────┐ ┌─────┐ ┌─────┐ ▼ + * │ 2 ├─►│16 B ├─►│16 B ├─►│16 B │ ┌───┐ ┌─────────────────────────┐ + * │ │ └─────┘ └─────┘ └─────┘ │ ├─►│ ▲ │ ▲ + * │ │ └───┘ └──────────┬──────────────┘ │ + * │ . │ │ m_available_memory_end + * │ . │ m_available_memory_it + * │ . │ + * │ │ + * │ │ + * │16 │ + * └───┘ + * + * Here m_free_lists[1] holds the 2 blocks of size 8 bytes, and m_free_lists[2] + * holds the 3 blocks of size 16. The blocks came from the data stored in the + * m_allocated_chunks list. Each chunk has bytes 262144. The last chunk has still + * some memory available for the blocks, and when m_available_memory_it is at the + * end, a new chunk will be allocated and added to the list. + */ +template <std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES> +class PoolResource final +{ + static_assert(ALIGN_BYTES > 0, "ALIGN_BYTES must be nonzero"); + static_assert((ALIGN_BYTES & (ALIGN_BYTES - 1)) == 0, "ALIGN_BYTES must be a power of two"); + + /** + * In-place linked list of the allocations, used for the freelist. + */ + struct ListNode { + ListNode* m_next; + + explicit ListNode(ListNode* next) : m_next(next) {} + }; + static_assert(std::is_trivially_destructible_v<ListNode>, "Make sure we don't need to manually call a destructor"); + + /** + * Internal alignment value. The larger of the requested ALIGN_BYTES and alignof(FreeList). + */ + static constexpr std::size_t ELEM_ALIGN_BYTES = std::max(alignof(ListNode), ALIGN_BYTES); + static_assert((ELEM_ALIGN_BYTES & (ELEM_ALIGN_BYTES - 1)) == 0, "ELEM_ALIGN_BYTES must be a power of two"); + static_assert(sizeof(ListNode) <= ELEM_ALIGN_BYTES, "Units of size ELEM_SIZE_ALIGN need to be able to store a ListNode"); + static_assert((MAX_BLOCK_SIZE_BYTES & (ELEM_ALIGN_BYTES - 1)) == 0, "MAX_BLOCK_SIZE_BYTES needs to be a multiple of the alignment."); + + /** + * Size in bytes to allocate per chunk + */ + const size_t m_chunk_size_bytes; + + /** + * Contains all allocated pools of memory, used to free the data in the destructor. + */ + std::list<std::byte*> m_allocated_chunks{}; + + /** + * Single linked lists of all data that came from deallocating. + * m_free_lists[n] will serve blocks of size n*ELEM_ALIGN_BYTES. + */ + std::array<ListNode*, MAX_BLOCK_SIZE_BYTES / ELEM_ALIGN_BYTES + 1> m_free_lists{}; + + /** + * Points to the beginning of available memory for carving out allocations. + */ + std::byte* m_available_memory_it = nullptr; + + /** + * Points to the end of available memory for carving out allocations. + * + * That member variable is redundant, and is always equal to `m_allocated_chunks.back() + m_chunk_size_bytes` + * whenever it is accessed, but `m_available_memory_end` caches this for clarity and efficiency. + */ + std::byte* m_available_memory_end = nullptr; + + /** + * How many multiple of ELEM_ALIGN_BYTES are necessary to fit bytes. We use that result directly as an index + * into m_free_lists. Round up for the special case when bytes==0. + */ + [[nodiscard]] static constexpr std::size_t NumElemAlignBytes(std::size_t bytes) + { + return (bytes + ELEM_ALIGN_BYTES - 1) / ELEM_ALIGN_BYTES + (bytes == 0); + } + + /** + * True when it is possible to make use of the freelist + */ + [[nodiscard]] static constexpr bool IsFreeListUsable(std::size_t bytes, std::size_t alignment) + { + return alignment <= ELEM_ALIGN_BYTES && bytes <= MAX_BLOCK_SIZE_BYTES; + } + + /** + * Replaces node with placement constructed ListNode that points to the previous node + */ + void PlacementAddToList(void* p, ListNode*& node) + { + node = new (p) ListNode{node}; + } + + /** + * Allocate one full memory chunk which will be used to carve out allocations. + * Also puts any leftover bytes into the freelist. + * + * Precondition: leftover bytes are either 0 or few enough to fit into a place in the freelist + */ + void AllocateChunk() + { + // if there is still any available memory left, put it into the freelist. + size_t remaining_available_bytes = std::distance(m_available_memory_it, m_available_memory_end); + if (0 != remaining_available_bytes) { + PlacementAddToList(m_available_memory_it, m_free_lists[remaining_available_bytes / ELEM_ALIGN_BYTES]); + } + + void* storage = ::operator new (m_chunk_size_bytes, std::align_val_t{ELEM_ALIGN_BYTES}); + m_available_memory_it = new (storage) std::byte[m_chunk_size_bytes]; + m_available_memory_end = m_available_memory_it + m_chunk_size_bytes; + m_allocated_chunks.emplace_back(m_available_memory_it); + } + + /** + * Access to internals for testing purpose only + */ + friend class PoolResourceTester; + +public: + /** + * Construct a new PoolResource object which allocates the first chunk. + * chunk_size_bytes will be rounded up to next multiple of ELEM_ALIGN_BYTES. + */ + explicit PoolResource(std::size_t chunk_size_bytes) + : m_chunk_size_bytes(NumElemAlignBytes(chunk_size_bytes) * ELEM_ALIGN_BYTES) + { + assert(m_chunk_size_bytes >= MAX_BLOCK_SIZE_BYTES); + AllocateChunk(); + } + + /** + * Construct a new Pool Resource object, defaults to 2^18=262144 chunk size. + */ + PoolResource() : PoolResource(262144) {} + + /** + * Disable copy & move semantics, these are not supported for the resource. + */ + PoolResource(const PoolResource&) = delete; + PoolResource& operator=(const PoolResource&) = delete; + PoolResource(PoolResource&&) = delete; + PoolResource& operator=(PoolResource&&) = delete; + + /** + * Deallocates all memory allocated associated with the memory resource. + */ + ~PoolResource() + { + for (std::byte* chunk : m_allocated_chunks) { + std::destroy(chunk, chunk + m_chunk_size_bytes); + ::operator delete ((void*)chunk, std::align_val_t{ELEM_ALIGN_BYTES}); + } + } + + /** + * Allocates a block of bytes. If possible the freelist is used, otherwise allocation + * is forwarded to ::operator new(). + */ + void* Allocate(std::size_t bytes, std::size_t alignment) + { + if (IsFreeListUsable(bytes, alignment)) { + const std::size_t num_alignments = NumElemAlignBytes(bytes); + if (nullptr != m_free_lists[num_alignments]) { + // we've already got data in the pool's freelist, unlink one element and return the pointer + // to the unlinked memory. Since FreeList is trivially destructible we can just treat it as + // uninitialized memory. + return std::exchange(m_free_lists[num_alignments], m_free_lists[num_alignments]->m_next); + } + + // freelist is empty: get one allocation from allocated chunk memory. + const std::ptrdiff_t round_bytes = static_cast<std::ptrdiff_t>(num_alignments * ELEM_ALIGN_BYTES); + if (round_bytes > m_available_memory_end - m_available_memory_it) { + // slow path, only happens when a new chunk needs to be allocated + AllocateChunk(); + } + + // Make sure we use the right amount of bytes for that freelist (might be rounded up), + return std::exchange(m_available_memory_it, m_available_memory_it + round_bytes); + } + + // Can't use the pool => use operator new() + return ::operator new (bytes, std::align_val_t{alignment}); + } + + /** + * Returns a block to the freelists, or deletes the block when it did not come from the chunks. + */ + void Deallocate(void* p, std::size_t bytes, std::size_t alignment) noexcept + { + if (IsFreeListUsable(bytes, alignment)) { + const std::size_t num_alignments = NumElemAlignBytes(bytes); + // put the memory block into the linked list. We can placement construct the FreeList + // into the memory since we can be sure the alignment is correct. + PlacementAddToList(p, m_free_lists[num_alignments]); + } else { + // Can't use the pool => forward deallocation to ::operator delete(). + ::operator delete (p, std::align_val_t{alignment}); + } + } + + /** + * Number of allocated chunks + */ + [[nodiscard]] std::size_t NumAllocatedChunks() const + { + return m_allocated_chunks.size(); + } + + /** + * Size in bytes to allocate per chunk, currently hardcoded to a fixed size. + */ + [[nodiscard]] size_t ChunkSizeBytes() const + { + return m_chunk_size_bytes; + } +}; + + +/** + * Forwards all allocations/deallocations to the PoolResource. + */ +template <class T, std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES> +class PoolAllocator +{ + PoolResource<MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>* m_resource; + + template <typename U, std::size_t M, std::size_t A> + friend class PoolAllocator; + +public: + using value_type = T; + using ResourceType = PoolResource<MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>; + + /** + * Not explicit so we can easily construct it with the correct resource + */ + PoolAllocator(ResourceType* resource) noexcept + : m_resource(resource) + { + } + + PoolAllocator(const PoolAllocator& other) noexcept = default; + PoolAllocator& operator=(const PoolAllocator& other) noexcept = default; + + template <class U> + PoolAllocator(const PoolAllocator<U, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& other) noexcept + : m_resource(other.resource()) + { + } + + /** + * The rebind struct here is mandatory because we use non type template arguments for + * PoolAllocator. See https://en.cppreference.com/w/cpp/named_req/Allocator#cite_note-2 + */ + template <typename U> + struct rebind { + using other = PoolAllocator<U, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>; + }; + + /** + * Forwards each call to the resource. + */ + T* allocate(size_t n) + { + return static_cast<T*>(m_resource->Allocate(n * sizeof(T), alignof(T))); + } + + /** + * Forwards each call to the resource. + */ + void deallocate(T* p, size_t n) noexcept + { + m_resource->Deallocate(p, n * sizeof(T), alignof(T)); + } + + ResourceType* resource() const noexcept + { + return m_resource; + } +}; + +template <class T1, class T2, std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES> +bool operator==(const PoolAllocator<T1, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& a, + const PoolAllocator<T2, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& b) noexcept +{ + return a.resource() == b.resource(); +} + +template <class T1, class T2, std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES> +bool operator!=(const PoolAllocator<T1, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& a, + const PoolAllocator<T2, MAX_BLOCK_SIZE_BYTES, ALIGN_BYTES>& b) noexcept +{ + return !(a == b); +} + +#endif // BITCOIN_SUPPORT_ALLOCATORS_POOL_H |