imay commented on a change in pull request #2782: Add file cache for v2 URL: https://github.com/apache/incubator-doris/pull/2782#discussion_r373994534
########## File path: be/src/util/file_cache.h ########## @@ -0,0 +1,129 @@ +// 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 <memory> +#include <string> + +#include "olap/lru_cache.h" + +namespace doris { + +class Env; + +// A "smart" retrieved LRU cache handle. +// +// The cache handle is released when this object goes out of scope, possibly +// closing the opened file if it is no longer in the cache. +template <class FileType> +class OpenedFileHandle { +public: + OpenedFileHandle() : _cache(nullptr), _handle(nullptr) { } + + // A opened file handle + explicit OpenedFileHandle(Cache* cache, Cache::Handle* handle) + : _cache(cache), _handle(handle) { } + + // release cache handle + ~OpenedFileHandle() { + if (_handle != nullptr) { + _cache->release(_handle); + } + } + + OpenedFileHandle(OpenedFileHandle&& other) noexcept { + std::swap(_cache, other._cache); + std::swap(_handle, other._handle); + } + + OpenedFileHandle& operator=(OpenedFileHandle&& other) noexcept { + std::swap(_cache, other._cache); + std::swap(_handle, other._handle); + return *this; + } + + FileType* file() const { + DCHECK(_handle != nullptr); + return reinterpret_cast<FileType*>(_cache->value(_handle)); + } + +private: + Cache* _cache; + Cache::Handle* _handle; +}; + +// Cache of open files. +// +// The purpose of this cache is to enforce an upper bound on the maximum number +// of files open at a time. Files opened through the cache may be closed at any +// time, only to be reopened upon next use. +// +// The file cache can be viewed as having two logical parts: the client-facing +// File handle and the LRU cache. +// +// Client-facing API +// ----------------- +// The core of the client-facing API is the cache descriptor. A descriptor + +// LRU cache +// --------- +// The lower half of the file cache is a standard LRU cache whose keys are file +// names and whose values are pointers to opened file objects allocated on the +// heap. Unlike the descriptor map, this cache has an upper bound on capacity, +// and handles are evicted (and closed) according to an LRU algorithm. +// +// Whenever a descriptor is used by a client in file I/O, its file name is used +// in an LRU cache lookup. If found, the underlying file is still open and the +// file access is performed. Otherwise, the file must have been evicted and +// closed, so it is reopened and reinserted (possibly evicting a different open +// file) before the file access is performed. +// +// Every public method in the file cache is thread safe. +template <class FileType> +class FileCache { Review comment: Is OpenedFileCache better? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@doris.apache.org For additional commands, e-mail: commits-h...@doris.apache.org
