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102 рядки
2.7 KiB
102 рядки
2.7 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "db/log_writer.h"
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#include <stdint.h>
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#include "leveldb/env.h"
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#include "util/coding.h"
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#include "util/crc32c.h"
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namespace leveldb {
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namespace log {
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Writer::Writer(WritableFile* dest)
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: dest_(dest),
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block_offset_(0) {
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for (int i = 0; i <= kMaxRecordType; i++) {
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char t = static_cast<char>(i);
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type_crc_[i] = crc32c::Value(&t, 1);
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}
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}
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Writer::~Writer() {
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}
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Status Writer::AddRecord(const Slice& slice) {
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const char* ptr = slice.data();
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size_t left = slice.size();
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// Fragment the record if necessary and emit it. Note that if slice
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// is empty, we still want to iterate once to emit a single
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// zero-length record
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Status s;
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do {
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const int leftover = kBlockSize - block_offset_;
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assert(leftover >= 0);
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if (leftover < kHeaderSize) {
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// Switch to a new block
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if (leftover > 0) {
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// Fill the trailer (literal below relies on kHeaderSize being 7)
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assert(kHeaderSize == 7);
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dest_->Append(Slice("\x00\x00\x00\x00\x00\x00", leftover));
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}
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block_offset_ = 0;
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}
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// Invariant: we never leave < kHeaderSize bytes in a block.
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const int avail = kBlockSize - block_offset_ - kHeaderSize;
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assert(avail >= 0);
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const size_t fragment_length = (left < avail) ? left : avail;
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RecordType type;
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const bool begin = (ptr == slice.data());
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const bool end = (left == fragment_length);
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if (begin && end) {
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type = kFullType;
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} else if (begin) {
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type = kFirstType;
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} else if (end) {
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type = kLastType;
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} else {
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type = kMiddleType;
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}
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s = EmitPhysicalRecord(type, ptr, fragment_length);
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ptr += fragment_length;
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left -= fragment_length;
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} while (s.ok() && left > 0);
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return s;
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}
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Status Writer::EmitPhysicalRecord(RecordType t, const char* ptr, size_t n) {
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assert(n <= 0xffff); // Must fit in two bytes
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assert(block_offset_ + kHeaderSize + n <= kBlockSize);
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// Format the header
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char buf[kHeaderSize];
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buf[4] = static_cast<char>(n & 0xff);
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buf[5] = static_cast<char>(n >> 8);
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buf[6] = static_cast<char>(t);
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// Compute the crc of the record type and the payload.
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uint32_t crc = crc32c::Extend(type_crc_[t], ptr, n);
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crc = crc32c::Mask(crc); // Adjust for storage
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EncodeFixed32(buf, crc);
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// Write the header and the payload
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Status s = dest_->Append(Slice(buf, kHeaderSize));
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if (s.ok()) {
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s = dest_->Append(Slice(ptr, n));
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if (s.ok()) {
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s = dest_->Flush();
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}
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}
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block_offset_ += kHeaderSize + n;
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return s;
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}
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}
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}
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