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https://gitea.wildfiregames.com/0ad/0ad.git
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janwas
317f98a6c0
archive: pretty much done except for trace and archive_builder IO: io_manager still needs to be fixed/revised (especially WRT buffer and alignment management) posix: done vfs: need to complete vfs_mount and tie it in to vfs.cpp dir_util: needs further revisions (VFS interface changed since then) This was SVN commit r5475.
92 lines
3.2 KiB
C++
92 lines
3.2 KiB
C++
/**
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* =========================================================================
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* File : file_cache.h
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* Project : 0 A.D.
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* Description : cache of file contents (supports zero-copy IO)
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#ifndef INCLUDED_FILE_CACHE
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#define INCLUDED_FILE_CACHE
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typedef boost::shared_ptr<const u8> FileCacheData;
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/**
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* cache of file contents with support for zero-copy IO.
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* this works by reserving a region of the cache, using it as the IO buffer,
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* and returning the memory directly to users. optional write-protection
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* via MMU ensures that the shared contents aren't inadvertently changed.
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*
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* (unique copies of) VFS pathnames are used as lookup key and owner tag.
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*
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* to ensure efficient operation and prevent fragmentation, only one
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* reference should be active at a time. in other words, read a file,
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* process it, and only then start reading the next file.
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*
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* rationale: this is rather similar to BlockCache; however, the differences
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* (Reserve's size parameter, Add vs. MarkComplete, different eviction
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* policies) are enough to warrant separate implementations.
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**/
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class FileCache
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{
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public:
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/**
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* @param size maximum amount [bytes] of memory to use for the cache.
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* (managed as a virtual memory region that's committed on-demand)
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**/
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FileCache(size_t size);
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/**
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* Reserve a chunk of the cache's memory region.
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*
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* @param vfsPathname pathname of the file that is to be read; this is
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* the key that will be used to Retrieve the file contents.
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* @param size required number of bytes (more may be allocated due to
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* alignment and/or internal fragmentation)
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* @return memory suitably aligned for IO; never fails.
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*
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* it is expected that this data will be Add()-ed once its IO completes.
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**/
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FileCacheData Reserve(const char* vfsPathname, size_t size);
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/**
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* Add a file's contents to the cache.
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*
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* the cache will be able to satisfy subsequent Retrieve() calls by
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* returning this data; if CONFIG_READ_ONLY_CACHE, the buffer is made
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* read-only. if need be and no references are currently attached to it,
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* the memory can also be commandeered by Reserve().
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*
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* @param cost is the expected cost of retrieving the file again and
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* influences how/when it is evicted from the cache.
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**/
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void Add(const char* vfsPathname, FileCacheData data, size_t size, uint cost = 1);
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/**
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* Remove a file's contents from the cache (if it exists).
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*
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* this ensures subsequent reads of the files see the current, presumably
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* recently changed, contents of the file.
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*
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* this would typically be called in response to a notification that a
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* file has changed.
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**/
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void Remove(const char* vfsPathname);
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/**
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* Attempt to retrieve a file's contents from the file cache.
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*
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* @return whether the contents were successfully retrieved; if so,
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* data references the read-only file contents.
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**/
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bool Retrieve(const char* vfsPathname, FileCacheData& data, size_t& size);
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private:
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class Impl;
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boost::shared_ptr<Impl> impl;
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};
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#endif // #ifndef INCLUDED_FILE_CACHE
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