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// 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.
//
#include "util/compression_context_cache.h"
#include "util/compression.h"
#include "util/core_local.h"
#include <atomic>
namespace ROCKSDB_NAMESPACE {
namespace compression_cache {
void* const SentinelValue = nullptr;
// Cache ZSTD uncompression contexts for reads
// if needed we can add ZSTD compression context caching
// which is currently is not done since BlockBasedTableBuilder
// simply creates one compression context per new SST file.
struct ZSTDCachedData {
// We choose to cache the below structure instead of a ptr
// because we want to avoid a) native types leak b) make
// cache use transparent for the user
ZSTDUncompressCachedData uncomp_cached_data_;
std::atomic<void*> zstd_uncomp_sentinel_;
char
padding[(CACHE_LINE_SIZE -
(sizeof(ZSTDUncompressCachedData) + sizeof(std::atomic<void*>)) %
CACHE_LINE_SIZE)]; // unused padding field
ZSTDCachedData() : zstd_uncomp_sentinel_(&uncomp_cached_data_) {}
ZSTDCachedData(const ZSTDCachedData&) = delete;
ZSTDCachedData& operator=(const ZSTDCachedData&) = delete;
ZSTDUncompressCachedData GetUncompressData(int64_t idx) {
ZSTDUncompressCachedData result;
void* expected = &uncomp_cached_data_;
if (zstd_uncomp_sentinel_.compare_exchange_strong(expected,
SentinelValue)) {
uncomp_cached_data_.CreateIfNeeded();
result.InitFromCache(uncomp_cached_data_, idx);
} else {
// Creates one time use data
result.CreateIfNeeded();
}
return result;
}
// Return the entry back into circulation
// This is executed only when we successfully obtained
// in the first place
void ReturnUncompressData() {
if (zstd_uncomp_sentinel_.exchange(&uncomp_cached_data_) != SentinelValue) {
// Means we are returning while not having it acquired.
assert(false);
}
}
};
static_assert(sizeof(ZSTDCachedData) % CACHE_LINE_SIZE == 0,
"Expected CACHE_LINE_SIZE alignment");
} // namespace compression_cache
using namespace compression_cache;
class CompressionContextCache::Rep {
public:
Rep() {}
ZSTDUncompressCachedData GetZSTDUncompressData() {
auto p = per_core_uncompr_.AccessElementAndIndex();
int64_t idx = static_cast<int64_t>(p.second);
return p.first->GetUncompressData(idx);
}
void ReturnZSTDUncompressData(int64_t idx) {
assert(idx >= 0);
auto* cn = per_core_uncompr_.AccessAtCore(static_cast<size_t>(idx));
cn->ReturnUncompressData();
}
private:
CoreLocalArray<ZSTDCachedData> per_core_uncompr_;
};
CompressionContextCache::CompressionContextCache() : rep_(new Rep()) {}
CompressionContextCache* CompressionContextCache::Instance() {
static CompressionContextCache instance;
return &instance;
}
void CompressionContextCache::InitSingleton() { Instance(); }
ZSTDUncompressCachedData
CompressionContextCache::GetCachedZSTDUncompressData() {
return rep_->GetZSTDUncompressData();
}
void CompressionContextCache::ReturnCachedZSTDUncompressData(int64_t idx) {
rep_->ReturnZSTDUncompressData(idx);
}
CompressionContextCache::~CompressionContextCache() { delete rep_; }
} // namespace ROCKSDB_NAMESPACE
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