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/* |
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======================================================================= |
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Cache for out-of-core octree. |
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Uses an LRU page replacement scheme. Page table nodes are stored in |
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order of reference in a doubly linked list, with the most recently used |
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(MRU) page at the head, and the least recently used (LRU) at the tail. |
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Nodes are referenced by the page's base address via a hashtable for |
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constant time access (in the absence of hash collisions). Hash |
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collisions can be limited by adjusting the hashtable load factor |
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OOC_CACHE_LOAD; this is the fraction of the number of pages that will |
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actually be cached. |
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Roland Schregle (roland.schregle@{hslu.ch, gmail.com}) |
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(c) Lucerne University of Applied Sciences and Arts, |
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supported by the Swiss National Science Foundation (SNSF, #147053) |
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======================================================================= |
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$Id: ooccache.h,v 1.13 2015/11/16 13:33:08 taschreg Exp taschreg $ |
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*/ |
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#ifndef OOC_CACHE_H |
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#define OOC_CACHE_H |
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#include <stdio.h> |
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#include <stdint.h> |
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/* Hashtable load factor to limit hash collisions */ |
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#define OOC_CACHE_LOAD 0.75 |
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/* Minimum number of cache pages */ |
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#define OOC_CACHE_MINPAGES 8 |
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/* Hashing function for key -> pagetable mapping (assumes n is prime) */ |
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#define OOC_CACHE_PRIME 19603 |
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#define OOC_CACHE_HASH(k,n) ((k) * OOC_CACHE_PRIME % (n)) |
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/* Next index in pagetable probe sequence for collision resolution */ |
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#define OOC_CACHE_NEXT(i,n) (((i) + 1) % (n)) |
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/* Cache key and index types */ |
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typedef uint32_t OOC_CacheKey; |
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typedef uint32_t OOC_CacheIdx; |
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/* Undefined value for cache index */ |
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#define OOC_CACHEIDX_NULL UINT32_MAX |
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typedef struct { |
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OOC_CacheKey key; /* Key to resolve hashing collisions */ |
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OOC_CacheIdx prev, next; /* Previous/next page in history */ |
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void *data; /* Start of page data */ |
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} OOC_CacheNode; |
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typedef struct { |
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unsigned recSize, /* Data record size in bytes */ |
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recPerPage; /* Page size in number of records */ |
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unsigned long pageSize; /* Page size in bytes (precomp) */ |
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OOC_CacheIdx pageCnt, /* Num pages used */ |
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numPages; /* Pagetable size */ |
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/* NOTE: The hashtable load factor limits the number of pages actually |
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* used, such that pageCnt <= OOC_CACHE_LOAD * numPages */ |
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OOC_CacheNode *pageTable; /* Pagetable with numPages nodes */ |
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OOC_CacheIdx mru, lru; /* Most/least recently used page |
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== head/tail of page history */ |
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OOC_CacheKey lastKey; /* Previous key to detect repeat lookups */ |
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OOC_CacheNode *lastPage; /* Previous page for repeat lookups */ |
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unsigned long numReads, /* Statistics counters */ |
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numHits, |
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numColl, |
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numRept; |
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} OOC_Cache; |
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/* Initialise cache containing up to numPages pages; this is rounded up |
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* the next prime number to reduce hash clustering and collisions. The |
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* page size recPerPage is specified in units of records of size recSize |
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* bytes. Returns 0 on success, else -1. */ |
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int OOC_CacheInit (OOC_Cache *cache, unsigned numPages, |
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unsigned recPerPage, unsigned recSize); |
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/* Return pointer to cached record with index recIdx, loading from file |
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* and possibly evicting the LRU page */ |
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void *OOC_CacheData (OOC_Cache *cache, FILE *file, unsigned long recIdx); |
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/* Delete cache and free allocated pages */ |
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void OOC_DeleteCache (OOC_Cache *cache); |
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#endif |
