05709fb43e
This is not an API-breaking change, because it reduces the API that the leveldb embedder must implement. The project will build just fine against ports that still implement InitOnce. C++11 guarantees thread-safe initialization of static variables inside functions. This is a more restricted form of std::call_once or pthread_once_t (e.g., single call site), so the compiler might be able to generate better code [1]. Equally important, having less code in port_example.h makes it easier to port to other platforms. Due to the change above, this CL introduces a new approach for storing the singleton BytewiseComparatorImpl instance returned by BytewiseComparator(). The new approach avoids a dynamic memory allocation, which eliminates the false positive from LeakSanitizer reported in https://github.com/google/leveldb/issues/200 [1] https://stackoverflow.com/a/27206650/ ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=212348004
77 lines
2.0 KiB
C++
77 lines
2.0 KiB
C++
// 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 <algorithm>
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#include <cstdint>
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#include <string>
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#include "leveldb/comparator.h"
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#include "leveldb/slice.h"
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#include "util/logging.h"
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#include "util/no_destructor.h"
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namespace leveldb {
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Comparator::~Comparator() { }
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namespace {
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class BytewiseComparatorImpl : public Comparator {
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public:
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BytewiseComparatorImpl() { }
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virtual const char* Name() const {
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return "leveldb.BytewiseComparator";
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}
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virtual int Compare(const Slice& a, const Slice& b) const {
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return a.compare(b);
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}
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virtual void FindShortestSeparator(
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std::string* start,
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const Slice& limit) const {
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// Find length of common prefix
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size_t min_length = std::min(start->size(), limit.size());
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size_t diff_index = 0;
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while ((diff_index < min_length) &&
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((*start)[diff_index] == limit[diff_index])) {
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diff_index++;
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}
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if (diff_index >= min_length) {
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// Do not shorten if one string is a prefix of the other
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} else {
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uint8_t diff_byte = static_cast<uint8_t>((*start)[diff_index]);
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if (diff_byte < static_cast<uint8_t>(0xff) &&
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diff_byte + 1 < static_cast<uint8_t>(limit[diff_index])) {
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(*start)[diff_index]++;
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start->resize(diff_index + 1);
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assert(Compare(*start, limit) < 0);
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}
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}
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}
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virtual void FindShortSuccessor(std::string* key) const {
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// Find first character that can be incremented
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size_t n = key->size();
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for (size_t i = 0; i < n; i++) {
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const uint8_t byte = (*key)[i];
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if (byte != static_cast<uint8_t>(0xff)) {
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(*key)[i] = byte + 1;
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key->resize(i+1);
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return;
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}
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}
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// *key is a run of 0xffs. Leave it alone.
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}
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};
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} // namespace
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const Comparator* BytewiseComparator() {
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static NoDestructor<BytewiseComparatorImpl> singleton;
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return singleton.get();
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}
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} // namespace leveldb
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