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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.
122 lines
3.4 KiB
C++
122 lines
3.4 KiB
C++
/**
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* =========================================================================
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* File : block_cache.h
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* Project : 0 A.D.
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* Description : cache for aligned I/O blocks.
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#ifndef INCLUDED_BLOCK_CACHE
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#define INCLUDED_BLOCK_CACHE
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#include "io_buf.h"
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/**
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* block := power-of-two sized chunk of a file.
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* all transfers are expanded to naturally aligned, whole blocks
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* (this makes caching parts of files feasible; it is also much faster
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* for some aio implementations, e.g. wposix).
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*
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* measurements show this value to yield best read throughput.
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**/
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static const size_t BLOCK_SIZE = 32*KiB;
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/**
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* ID that uniquely identifies a block within a file
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**/
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class BlockId
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{
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public:
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BlockId();
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BlockId(const char* atom_fn, off_t ofs);
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bool operator==(const BlockId& rhs) const;
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bool operator!=(const BlockId& rhs) const;
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private:
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const char* m_atom_fn;
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u32 m_blockIndex;
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};
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/**
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* cache of (aligned) file blocks with support for zero-copy IO.
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* absorbs the overhead of rounding up archive IOs to the nearest block
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* boundaries by keeping the last few blocks in memory.
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*
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* the interface is quite similar to FileCache; see the note there.
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**/
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class BlockCache
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{
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public:
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/**
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* @param cacheSize total size [bytes] that the cache is to manage.
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* the default value is enough to support temp buffers and
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* absorb the cost of unaligned reads from a few archives.
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**/
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BlockCache(size_t cacheSize = 16 * BLOCK_SIZE);
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/**
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* Reserve a block for use as an IO buffer.
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*
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* @return suitably aligned memory; never fails.
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*
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* no further operations with the same id are allowed to succeed
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* until MarkComplete has been called.
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**/
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IoBuf Reserve(BlockId id);
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/**
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* Indicate that IO into the block has completed.
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*
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* this allows the cache to satisfy subsequent Retrieve() calls by
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* returning this block; if CONFIG_READ_ONLY_CACHE, the block is
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* made read-only. if need be and no references are currently attached
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* to it, the memory can also be commandeered by Reserve().
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**/
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void MarkComplete(BlockId id);
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/**
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* Attempt to retrieve a block the file cache.
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*
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* @return false if not in cache or its IO is still pending,
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* otherwise true.
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*
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* if successful, a reference is added to the block and its
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* buffer is returned.
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**/
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bool Retrieve(BlockId id, IoBuf& buf);
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/**
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* Indicate the block contents are no longer needed.
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*
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* this decreases the reference count; the memory can only be reused
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* if it reaches 0. the block remains in cache until evicted by a
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* subsequent Reserve() call.
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*
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* note: fails (raises a warning) if called for a buffer that is
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* currently between Reserve and MarkComplete operations.
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**/
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void Release(BlockId id);
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/**
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* Invalidate the contents of the cache.
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*
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* this effectively discards the contents of existing blocks
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* (more specifically: prevents them from satisfying Retrieve() calls
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* until a subsequent Reserve/MarkComplete of that block).
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*
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* useful for self-tests: multiple independent IO tests run in the same
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* process and must not influence each other via the cache.
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**/
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void InvalidateAll();
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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_BLOCK_CACHE
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