/** * @file lldiskcache.h * @brief The disk cache implementation declarations. * * @Description: * This code implements a disk cache using the following ideas: * 1/ The metadata for a file can be encapsulated in the filename. The filenames will be composed of the following fields: Prefix: Used to identify the file as a part of the cache. An additional reason for using a prefix is that it might be possible, either accidentally or maliciously to end up with the cache dir set to a non-cache location such as your OS system dir or a work folder. Purging files from that would obviously be a disaster so this is an extra step to help avoid that scenario. ID: Typically the asset ID (UUID) of the asset being saved but can be anything valid for a filename Extra Info: A field for use in the future that can be used to store extra identifiers - e.g. the discard level of a JPEG2000 file Asset Type: A text string created from the LLAssetType enum that identifies the type of asset being stored. .asset A file extension of .asset is used to help identify this as a Viewer asset file * 2/ The time of last access for a file can be updated instantly * for file reads and automatically as part of the file writes. * 3/ The purge algorithm collects a list of all files in the * directory, sorts them by date of last access (write) and then * deletes any files based on age until the total size of all * the files is less than the maximum size specified. * 4/ An LLSingleton idiom is used since there will only ever be * a single cache and we want to access it from numerous places. * 5/ Performance on my modest system seems very acceptable. For * example, in testing, I was able to purge a directory of * 10,000 files, deleting about half of them in ~ 1700ms. For * the same sized directory of files, writing the last updated * time to each took less than 600ms indicating that this * important part of the mechanism has almost no overhead. * * $LicenseInfo:firstyear=2009&license=viewerlgpl$ * Second Life Viewer Source Code * Copyright (C) 2020, Linden Research, Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; * version 2.1 of the License only. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA * * Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA * $/LicenseInfo$ */ #ifndef _LLDISKCACHE #define _LLDISKCACHE #include "llsingleton.h" class LLDiskCache : public LLParamSingleton { public: /** * Since this is using the LLSingleton pattern but we * want to allow the constructor to be called first * with various parameters, we also invoke the * LLParamSingleton idiom and use it to initialize * the class via a call in LLAppViewer. */ LLSINGLETON(LLDiskCache, /** * The full name of the cache folder - typically a * a child of the main Viewer cache directory. Defined * by the setting at 'DiskCacheDirName' */ const std::string cache_dir, /** * The maximum size of the cache in bytes - Based on the * setting at 'CacheSize' and 'DiskCachePercentOfTotal' */ const int max_size_bytes, /** * A flag that enables extra cache debugging so that * if there are bugs, we can ask uses to enable this * setting and send us their logs */ const bool enable_cache_debug_info); virtual ~LLDiskCache() = default; public: /** * Construct a filename and path to it based on the file meta data * (id, asset type, additional 'extra' info like discard level perhaps) * Worth pointing out that this function used to be in LLFileSystem but * so many things had to be pushed back there to accomodate it, that I * decided to move it here. Still not sure that's completely right. */ const std::string metaDataToFilepath(const std::string id, LLAssetType::EType at, const std::string extra_info); /** * Update the "last write time" of a file to "now". This must be called whenever a * file in the cache is read (not written) so that the last time the file was * accessed is up to date (This is used in the mechanism for purging the cache) */ void updateFileAccessTime(const std::string file_path); /** * Purge the oldest items in the cache so that the combined size of all files * is no bigger than mMaxSizeBytes. */ void purge(); /** * Clear the cache by removing all the files in the specified cache * directory individually. Only the files that contain a prefix defined * by mCacheFilenamePrefix will be removed. */ void clearCache(); /** * Return some information about the cache for use in About Box etc. */ const std::string getCacheInfo(); private: /** * Utility function to gather the total size the files in a given * directory. Primarily used here to determine the directory size * before and after the cache purge */ uintmax_t dirFileSize(const std::string dir); /** * Utility function to convert an LLAssetType enum into a * string that we use as part of the cache file filename */ const std::string assetTypeToString(LLAssetType::EType at); private: /** * The maximum size of the cache in bytes. After purge is called, the * total size of the cache files in the cache directory will be * less than this value */ uintmax_t mMaxSizeBytes; /** * The folder that holds the cached files. The consumer of this * class must avoid letting the user set this location as a malicious * setting could potentially point it at a non-cache directory (for example, * the Windows System dir) with disastrous results. */ std::string mCacheDir; /** * The prefix inserted at the start of a cache file filename to * help identify it as a cache file. It's probably not required * (just the presence in the cache folder is enough) but I am * paranoid about the cache folder being set to something bad * like the users' OS system dir by mistake or maliciously and * this will help to offset any damage if that happens. */ std::string mCacheFilenamePrefix; /** * When enabled, displays additional debugging information in * various parts of the code */ bool mEnableCacheDebugInfo; }; #endif // _LLDISKCACHE