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| -rw-r--r-- | src/rocksdb/util/aligned_buffer.h | 234 |
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diff --git a/src/rocksdb/util/aligned_buffer.h b/src/rocksdb/util/aligned_buffer.h new file mode 100644 index 000000000..95ee5dfe8 --- /dev/null +++ b/src/rocksdb/util/aligned_buffer.h @@ -0,0 +1,234 @@ +// Copyright (c) 2011-present, Facebook, Inc. All rights reserved. +// This source code is licensed under both the GPLv2 (found in the +// COPYING file in the root directory) and Apache 2.0 License +// (found in the LICENSE.Apache file in the root directory). +// +// Copyright (c) 2011 The LevelDB Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. See the AUTHORS file for names of contributors. +#pragma once + +#include <algorithm> + +#include "port/port.h" + +namespace ROCKSDB_NAMESPACE { + +// This file contains utilities to handle the alignment of pages and buffers. + +// Truncate to a multiple of page_size, which is also a page boundary. This +// helps to figuring out the right alignment. +// Example: +// TruncateToPageBoundary(4096, 5000) => 4096 +// TruncateToPageBoundary((4096, 10000) => 8192 +inline size_t TruncateToPageBoundary(size_t page_size, size_t s) { + s -= (s & (page_size - 1)); + assert((s % page_size) == 0); + return s; +} + +// Round up x to a multiple of y. +// Example: +// Roundup(13, 5) => 15 +// Roundup(201, 16) => 208 +inline size_t Roundup(size_t x, size_t y) { return ((x + y - 1) / y) * y; } + +// Round down x to a multiple of y. +// Example: +// Rounddown(13, 5) => 10 +// Rounddown(201, 16) => 192 +inline size_t Rounddown(size_t x, size_t y) { return (x / y) * y; } + +// AlignedBuffer manages a buffer by taking alignment into consideration, and +// aligns the buffer start and end positions. It is mainly used for direct I/O, +// though it can be used other purposes as well. +// It also supports expanding the managed buffer, and copying whole or part of +// the data from old buffer into the new expanded buffer. Such a copy especially +// helps in cases avoiding an IO to re-fetch the data from disk. +// +// Example: +// AlignedBuffer buf; +// buf.Alignment(alignment); +// buf.AllocateNewBuffer(user_requested_buf_size); +// ... +// buf.AllocateNewBuffer(2*user_requested_buf_size, /*copy_data*/ true, +// copy_offset, copy_len); +class AlignedBuffer { + size_t alignment_; + std::unique_ptr<char[]> buf_; + size_t capacity_; + size_t cursize_; + char* bufstart_; + + public: + AlignedBuffer() + : alignment_(), capacity_(0), cursize_(0), bufstart_(nullptr) {} + + AlignedBuffer(AlignedBuffer&& o) noexcept { *this = std::move(o); } + + AlignedBuffer& operator=(AlignedBuffer&& o) noexcept { + alignment_ = std::move(o.alignment_); + buf_ = std::move(o.buf_); + capacity_ = std::move(o.capacity_); + cursize_ = std::move(o.cursize_); + bufstart_ = std::move(o.bufstart_); + return *this; + } + + AlignedBuffer(const AlignedBuffer&) = delete; + + AlignedBuffer& operator=(const AlignedBuffer&) = delete; + + static bool isAligned(const void* ptr, size_t alignment) { + return reinterpret_cast<uintptr_t>(ptr) % alignment == 0; + } + + static bool isAligned(size_t n, size_t alignment) { + return n % alignment == 0; + } + + size_t Alignment() const { return alignment_; } + + size_t Capacity() const { return capacity_; } + + size_t CurrentSize() const { return cursize_; } + + const char* BufferStart() const { return bufstart_; } + + char* BufferStart() { return bufstart_; } + + void Clear() { cursize_ = 0; } + + char* Release() { + cursize_ = 0; + capacity_ = 0; + bufstart_ = nullptr; + return buf_.release(); + } + + void Alignment(size_t alignment) { + assert(alignment > 0); + assert((alignment & (alignment - 1)) == 0); + alignment_ = alignment; + } + + // Allocates a new buffer and sets the start position to the first aligned + // byte. + // + // requested_capacity: requested new buffer capacity. This capacity will be + // rounded up based on alignment. + // copy_data: Copy data from old buffer to new buffer. If copy_offset and + // copy_len are not passed in and the new requested capacity is bigger + // than the existing buffer's capacity, the data in the exising buffer is + // fully copied over to the new buffer. + // copy_offset: Copy data from this offset in old buffer. + // copy_len: Number of bytes to copy. + // + // The function does nothing if the new requested_capacity is smaller than + // the current buffer capacity and copy_data is true i.e. the old buffer is + // retained as is. + void AllocateNewBuffer(size_t requested_capacity, bool copy_data = false, + uint64_t copy_offset = 0, size_t copy_len = 0) { + assert(alignment_ > 0); + assert((alignment_ & (alignment_ - 1)) == 0); + + copy_len = copy_len > 0 ? copy_len : cursize_; + if (copy_data && requested_capacity < copy_len) { + // If we are downsizing to a capacity that is smaller than the current + // data in the buffer -- Ignore the request. + return; + } + + size_t new_capacity = Roundup(requested_capacity, alignment_); + char* new_buf = new char[new_capacity + alignment_]; + char* new_bufstart = reinterpret_cast<char*>( + (reinterpret_cast<uintptr_t>(new_buf) + (alignment_ - 1)) & + ~static_cast<uintptr_t>(alignment_ - 1)); + + if (copy_data) { + assert(bufstart_ + copy_offset + copy_len <= bufstart_ + cursize_); + memcpy(new_bufstart, bufstart_ + copy_offset, copy_len); + cursize_ = copy_len; + } else { + cursize_ = 0; + } + + bufstart_ = new_bufstart; + capacity_ = new_capacity; + buf_.reset(new_buf); + } + + // Append to the buffer. + // + // src : source to copy the data from. + // append_size : number of bytes to copy from src. + // Returns the number of bytes appended. + // + // If append_size is more than the remaining buffer size only the + // remaining-size worth of bytes are copied. + size_t Append(const char* src, size_t append_size) { + size_t buffer_remaining = capacity_ - cursize_; + size_t to_copy = std::min(append_size, buffer_remaining); + + if (to_copy > 0) { + memcpy(bufstart_ + cursize_, src, to_copy); + cursize_ += to_copy; + } + return to_copy; + } + + // Read from the buffer. + // + // dest : destination buffer to copy the data to. + // offset : the buffer offset to start reading from. + // read_size : the number of bytes to copy from the buffer to dest. + // Returns the number of bytes read/copied to dest. + size_t Read(char* dest, size_t offset, size_t read_size) const { + assert(offset < cursize_); + + size_t to_read = 0; + if (offset < cursize_) { + to_read = std::min(cursize_ - offset, read_size); + } + if (to_read > 0) { + memcpy(dest, bufstart_ + offset, to_read); + } + return to_read; + } + + // Pad to the end of alignment with "padding" + void PadToAlignmentWith(int padding) { + size_t total_size = Roundup(cursize_, alignment_); + size_t pad_size = total_size - cursize_; + + if (pad_size > 0) { + assert((pad_size + cursize_) <= capacity_); + memset(bufstart_ + cursize_, padding, pad_size); + cursize_ += pad_size; + } + } + + void PadWith(size_t pad_size, int padding) { + assert((pad_size + cursize_) <= capacity_); + memset(bufstart_ + cursize_, padding, pad_size); + cursize_ += pad_size; + } + + // After a partial flush move the tail to the beginning of the buffer. + void RefitTail(size_t tail_offset, size_t tail_size) { + if (tail_size > 0) { + memmove(bufstart_, bufstart_ + tail_offset, tail_size); + } + cursize_ = tail_size; + } + + // Returns a place to start appending. + // WARNING: Note that it is possible to write past the end of the buffer if + // the buffer is modified without using the write APIs or encapsulation + // offered by AlignedBuffer. It is up to the user to guard against such + // errors. + char* Destination() { return bufstart_ + cursize_; } + + void Size(size_t cursize) { cursize_ = cursize; } +}; +} // namespace ROCKSDB_NAMESPACE |