bkietz commented on a change in pull request #8716: URL: https://github.com/apache/arrow/pull/8716#discussion_r577713086
########## File path: cpp/src/arrow/util/cache_internal.h ########## @@ -0,0 +1,232 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <cassert> +#include <functional> +#include <list> +#include <memory> +#include <mutex> +#include <type_traits> +#include <unordered_map> +#include <utility> +#include <vector> + +#include "arrow/util/functional.h" +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +// A LRU (Least recently used) replacement cache +template <typename Key, typename Value> +class LRUCache { + public: + explicit LRUCache(int32_t capacity) : capacity_(capacity) { + // The map size can temporarily exceed the cache capacity, see Replace() + map_.reserve(capacity_ + 1); + } + + ARROW_DISALLOW_COPY_AND_ASSIGN(LRUCache); + ARROW_DEFAULT_MOVE_AND_ASSIGN(LRUCache); + + void Clear() { + items_.clear(); + map_.clear(); + // The C++ spec doesn't tell whether map_.clear() will shrink the map capacity + map_.reserve(capacity_ + 1); + } + + int32_t size() const { + assert(items_.size() == map_.size()); + return static_cast<int32_t>(items_.size()); + } + + template <typename K> + Value* Find(K&& key) { + const auto it = map_.find(key); + if (it == map_.end()) { + return NULLPTR; + } else { + // Found => move item at front of the list + auto list_it = it->second; + items_.splice(items_.begin(), items_, list_it); + return &list_it->value; + } + } + + template <typename K, typename V> + std::pair<bool, Value*> Replace(K&& key, V&& value) { + // Try to insert temporary iterator + auto pair = map_.emplace(std::forward<K>(key), ListIt{}); + const auto it = pair.first; + const bool inserted = pair.second; + if (inserted) { + // Inserted => push item at front of the list, and update iterator + items_.push_front(Item{&it->first, std::forward<V>(value)}); + it->second = items_.begin(); + // Did we exceed the cache capacity? If so, remove least recently used item + if (static_cast<int32_t>(items_.size()) > capacity_) { + const bool erased = map_.erase(*items_.back().key); + assert(erased); Review comment: Since this is an `_internal` header, it's fine to use `DCHECK` and `nullptr` here ########## File path: cpp/src/arrow/util/cache_internal.h ########## @@ -0,0 +1,232 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <cassert> +#include <functional> +#include <list> +#include <memory> +#include <mutex> +#include <type_traits> +#include <unordered_map> +#include <utility> +#include <vector> + +#include "arrow/util/functional.h" +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +// A LRU (Least recently used) replacement cache +template <typename Key, typename Value> +class LRUCache { + public: + explicit LRUCache(int32_t capacity) : capacity_(capacity) { + // The map size can temporarily exceed the cache capacity, see Replace() + map_.reserve(capacity_ + 1); + } + + ARROW_DISALLOW_COPY_AND_ASSIGN(LRUCache); + ARROW_DEFAULT_MOVE_AND_ASSIGN(LRUCache); + + void Clear() { + items_.clear(); + map_.clear(); + // The C++ spec doesn't tell whether map_.clear() will shrink the map capacity + map_.reserve(capacity_ + 1); + } + + int32_t size() const { + assert(items_.size() == map_.size()); + return static_cast<int32_t>(items_.size()); + } + + template <typename K> + Value* Find(K&& key) { + const auto it = map_.find(key); + if (it == map_.end()) { + return NULLPTR; + } else { + // Found => move item at front of the list + auto list_it = it->second; + items_.splice(items_.begin(), items_, list_it); + return &list_it->value; + } + } + + template <typename K, typename V> + std::pair<bool, Value*> Replace(K&& key, V&& value) { + // Try to insert temporary iterator + auto pair = map_.emplace(std::forward<K>(key), ListIt{}); + const auto it = pair.first; + const bool inserted = pair.second; + if (inserted) { + // Inserted => push item at front of the list, and update iterator + items_.push_front(Item{&it->first, std::forward<V>(value)}); + it->second = items_.begin(); + // Did we exceed the cache capacity? If so, remove least recently used item + if (static_cast<int32_t>(items_.size()) > capacity_) { + const bool erased = map_.erase(*items_.back().key); + assert(erased); + ARROW_UNUSED(erased); + items_.pop_back(); + } + return {true, &it->second->value}; + } else { + // Already exists => move item at front of the list, and update value + auto list_it = it->second; + items_.splice(items_.begin(), items_, list_it); + list_it->value = std::forward<V>(value); + return {false, &list_it->value}; + } + } + + private: + struct Item { + // Pointer to the key inside the unordered_map + const Key* key; + Value value; + }; + using List = std::list<Item>; + using ListIt = typename List::iterator; + + const int32_t capacity_; + // In most to least recently used order + std::list<Item> items_; + std::unordered_map<Key, ListIt> map_; +}; + +namespace detail { + +template <typename Key, typename Value, typename Cache, typename Func> +struct ThreadSafeMemoizer { + using RetType = Value; + + template <typename F> + ThreadSafeMemoizer(F&& func, int32_t cache_capacity) + : mutex_(new std::mutex), func_(std::forward<F>(func)), cache_(cache_capacity) {} + + // The memoizer can't return a pointer to the cached value, because + // the cache entry may be evicted by another thread. + + Value operator()(const Key& key) { + std::unique_lock<std::mutex> lock(*mutex_); + const Value* value_ptr; + value_ptr = cache_.Find(key); + if (ARROW_PREDICT_TRUE(value_ptr != NULLPTR)) { + return *value_ptr; + } + lock.unlock(); + Value v = func_(key); + lock.lock(); + return *cache_.Replace(key, std::move(v)).second; + } + + private: + std::unique_ptr<std::mutex> mutex_; + Func func_; + Cache cache_; +}; + +template <typename Key, typename Value, typename Cache, typename Func> +struct ThreadUnsafeMemoizer { + using RetType = const Value&; + + template <typename F> + ThreadUnsafeMemoizer(F&& func, int32_t cache_capacity) + : /*mutex_(new std::mutex), */ func_(std::forward<F>(func)), + cache_(cache_capacity) {} + + const Value& operator()(const Key& key) { + const Value* value_ptr; + value_ptr = cache_.Find(key); + if (ARROW_PREDICT_TRUE(value_ptr != NULLPTR)) { + return *value_ptr; + } + return *cache_.Replace(key, func_(key)).second; + } + + private: + Func func_; + Cache cache_; +}; + +// A copy-constructible callable wrapper, for std::function<> + +template <typename Callable, typename RetType = call_traits::return_type<Callable>, + typename Value = call_traits::argument_type<0, Callable>> +struct SharedCallable { + explicit SharedCallable(Callable callable) + : callable_(std::make_shared<Callable>(std::move(callable))) {} + + template <typename V> + RetType operator()(V&& v) { + return (*callable_)(std::forward<V>(v)); + } + + private: + const std::shared_ptr<Callable> callable_; +}; + +template <template <typename...> class Cache, + template <typename...> class MemoizerType = ThreadSafeMemoizer, typename Func, + typename Key = typename std::decay<call_traits::argument_type<0, Func>>::type, + typename Value = typename std::decay<call_traits::return_type<Func>>::type, + typename Memoizer = MemoizerType<Key, Value, Cache<Key, Value>, Func>, Review comment: This allows a memoizer to wrap the instance of `Func` by reference, which I think will be surprising. I've assembled an alternative in https://github.com/pitrou/arrow/pull/7 ########## File path: cpp/src/arrow/util/cache_benchmark.cc ########## @@ -0,0 +1,146 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#include "benchmark/benchmark.h" + +#include <cstdint> +#include <string> +#include <vector> + +#include "arrow/array.h" +#include "arrow/testing/random.h" +#include "arrow/util/cache_internal.h" +#include "arrow/util/checked_cast.h" +#include "arrow/util/logging.h" +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +static constexpr int32_t kCacheSize = 100; +static constexpr int32_t kSmallKeyLength = 8; +static constexpr int32_t kLargeKeyLength = 64; +static constexpr int32_t kSmallValueLength = 16; +static constexpr int32_t kLargeValueLength = 1024; + +static std::vector<std::string> MakeStrings(int64_t nvalues, int64_t min_length, + int64_t max_length) { + auto rng = ::arrow::random::RandomArrayGenerator(42); + auto arr = checked_pointer_cast<StringArray>(rng.String( + nvalues, static_cast<int32_t>(min_length), static_cast<int32_t>(max_length))); + std::vector<std::string> vec(nvalues); + for (int64_t i = 0; i < nvalues; ++i) { + vec[i] = arr->GetString(i); + } + return vec; +} + +static std::vector<std::string> MakeStrings(int64_t nvalues, int64_t length) { + return MakeStrings(nvalues, length, length); +} + +template <typename Cache, typename Key, typename Value> +static void BenchmarkCacheLookups(benchmark::State& state, const std::vector<Key>& keys, + const std::vector<Value>& values) { + const int32_t nitems = static_cast<int32_t>(keys.size()); + Cache cache(nitems); + for (int32_t i = 0; i < nitems; ++i) { + cache.Replace(keys[i], values[i]); + } + + for (auto _ : state) { + int64_t nfinds = 0; + for (const auto& key : keys) { + nfinds += (cache.Find(key) != nullptr); + } + benchmark::DoNotOptimize(nfinds); + ARROW_CHECK_EQ(nfinds, nitems); + } + state.SetItemsProcessed(state.iterations() * nitems); +} + +static void LRUCacheLookup(benchmark::State& state) { + const auto keys = MakeStrings(kCacheSize, state.range(0)); + const auto values = MakeStrings(kCacheSize, state.range(1)); + BenchmarkCacheLookups<LRUCache<std::string, std::string>>(state, keys, values); +} + +static void SetCacheArgs(benchmark::internal::Benchmark* bench) { + bench->Args({kSmallKeyLength, kSmallValueLength}); + bench->Args({kSmallKeyLength, kLargeValueLength}); + bench->Args({kLargeKeyLength, kSmallValueLength}); + bench->Args({kLargeKeyLength, kLargeValueLength}); +} + +BENCHMARK(LRUCacheLookup)->Apply(SetCacheArgs); + +struct Callable { + explicit Callable(std::vector<std::string> values) + : index_(0), values_(std::move(values)) {} + + std::string operator()(const std::string& key) { + // Return a value unrelated to the key + if (++index_ >= static_cast<int64_t>(values_.size())) { + index_ = 0; + } + return values_[index_]; + } + + private: + int64_t index_; + std::vector<std::string> values_; +}; + +template <typename Memoized> +static void BenchmarkMemoize(benchmark::State& state, Memoized&& mem, + const std::vector<std::string>& keys) { + // Prime memoization cache + for (const auto& key : keys) { + mem(key); + } + + for (auto _ : state) { + int64_t nbytes = 0; + for (const auto& key : keys) { + nbytes += static_cast<int64_t>(mem(key).length()); + } + benchmark::DoNotOptimize(nbytes); + } + state.SetItemsProcessed(state.iterations() * keys.size()); +} + +static void MemoizeLRUCached(benchmark::State& state) { + const auto keys = MakeStrings(kCacheSize, state.range(0)); + const auto values = MakeStrings(kCacheSize, state.range(1)); Review comment: I'd also be interested to see benchmarks where the size of the string set is `kCacheSize * [0.5, 0.9, 1.1, 2]` ########## File path: cpp/src/arrow/util/cache_internal.h ########## @@ -0,0 +1,232 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <cassert> +#include <functional> +#include <list> +#include <memory> +#include <mutex> +#include <type_traits> +#include <unordered_map> +#include <utility> +#include <vector> + +#include "arrow/util/functional.h" +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +// A LRU (Least recently used) replacement cache +template <typename Key, typename Value> +class LRUCache { + public: + explicit LRUCache(int32_t capacity) : capacity_(capacity) { + // The map size can temporarily exceed the cache capacity, see Replace() + map_.reserve(capacity_ + 1); + } + + ARROW_DISALLOW_COPY_AND_ASSIGN(LRUCache); + ARROW_DEFAULT_MOVE_AND_ASSIGN(LRUCache); + + void Clear() { + items_.clear(); + map_.clear(); + // The C++ spec doesn't tell whether map_.clear() will shrink the map capacity + map_.reserve(capacity_ + 1); + } + + int32_t size() const { + assert(items_.size() == map_.size()); + return static_cast<int32_t>(items_.size()); + } + + template <typename K> + Value* Find(K&& key) { + const auto it = map_.find(key); + if (it == map_.end()) { + return NULLPTR; + } else { + // Found => move item at front of the list + auto list_it = it->second; + items_.splice(items_.begin(), items_, list_it); + return &list_it->value; + } + } + + template <typename K, typename V> + std::pair<bool, Value*> Replace(K&& key, V&& value) { + // Try to insert temporary iterator + auto pair = map_.emplace(std::forward<K>(key), ListIt{}); + const auto it = pair.first; + const bool inserted = pair.second; + if (inserted) { + // Inserted => push item at front of the list, and update iterator + items_.push_front(Item{&it->first, std::forward<V>(value)}); + it->second = items_.begin(); + // Did we exceed the cache capacity? If so, remove least recently used item + if (static_cast<int32_t>(items_.size()) > capacity_) { + const bool erased = map_.erase(*items_.back().key); + assert(erased); + ARROW_UNUSED(erased); + items_.pop_back(); + } + return {true, &it->second->value}; + } else { + // Already exists => move item at front of the list, and update value + auto list_it = it->second; + items_.splice(items_.begin(), items_, list_it); + list_it->value = std::forward<V>(value); + return {false, &list_it->value}; + } + } + + private: + struct Item { + // Pointer to the key inside the unordered_map + const Key* key; + Value value; + }; + using List = std::list<Item>; + using ListIt = typename List::iterator; + + const int32_t capacity_; + // In most to least recently used order + std::list<Item> items_; + std::unordered_map<Key, ListIt> map_; +}; + +namespace detail { + +template <typename Key, typename Value, typename Cache, typename Func> +struct ThreadSafeMemoizer { + using RetType = Value; + + template <typename F> + ThreadSafeMemoizer(F&& func, int32_t cache_capacity) + : mutex_(new std::mutex), func_(std::forward<F>(func)), cache_(cache_capacity) {} + + // The memoizer can't return a pointer to the cached value, because + // the cache entry may be evicted by another thread. + + Value operator()(const Key& key) { + std::unique_lock<std::mutex> lock(*mutex_); + const Value* value_ptr; + value_ptr = cache_.Find(key); + if (ARROW_PREDICT_TRUE(value_ptr != NULLPTR)) { + return *value_ptr; + } + lock.unlock(); + Value v = func_(key); + lock.lock(); + return *cache_.Replace(key, std::move(v)).second; + } + + private: + std::unique_ptr<std::mutex> mutex_; + Func func_; + Cache cache_; +}; + +template <typename Key, typename Value, typename Cache, typename Func> +struct ThreadUnsafeMemoizer { + using RetType = const Value&; + + template <typename F> + ThreadUnsafeMemoizer(F&& func, int32_t cache_capacity) + : /*mutex_(new std::mutex), */ func_(std::forward<F>(func)), + cache_(cache_capacity) {} + + const Value& operator()(const Key& key) { + const Value* value_ptr; + value_ptr = cache_.Find(key); + if (ARROW_PREDICT_TRUE(value_ptr != NULLPTR)) { + return *value_ptr; + } + return *cache_.Replace(key, func_(key)).second; + } + + private: + Func func_; + Cache cache_; +}; + +// A copy-constructible callable wrapper, for std::function<> + +template <typename Callable, typename RetType = call_traits::return_type<Callable>, + typename Value = call_traits::argument_type<0, Callable>> +struct SharedCallable { + explicit SharedCallable(Callable callable) + : callable_(std::make_shared<Callable>(std::move(callable))) {} + + template <typename V> + RetType operator()(V&& v) { + return (*callable_)(std::forward<V>(v)); + } + + private: + const std::shared_ptr<Callable> callable_; +}; + +template <template <typename...> class Cache, + template <typename...> class MemoizerType = ThreadSafeMemoizer, typename Func, + typename Key = typename std::decay<call_traits::argument_type<0, Func>>::type, + typename Value = typename std::decay<call_traits::return_type<Func>>::type, + typename Memoizer = MemoizerType<Key, Value, Cache<Key, Value>, Func>, + typename RetFunc = std::function<typename Memoizer::RetType(const Key&)>> +static RetFunc Memoize(Func&& func, int32_t cache_capacity) { + return SharedCallable<Memoizer>(Memoizer(std::forward<Func>(func), cache_capacity)); +} + +// template <template <typename K, typename V> class Cache, +// template <typename K, typename V, typename C, typename F> +// class MemoizerType = ThreadSafeMemoizer, +// typename Func, +// typename Key = typename std::decay<call_traits::argument_type<0, +// Func>>::type, typename Value = typename +// std::decay<call_traits::return_type<Func>>::type, typename Memoizer = +// MemoizerType<Key, Value, Cache<Key, Value>, Func>, typename RetFunc = +// Memoizer> +// static RetFunc Memoize(Func&& func, int32_t cache_capacity) { +// return Memoizer(std::forward<Func>(func), cache_capacity); +// } Review comment: ```suggestion ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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