CSEP 545: Cache Algorithm Implementation, Slides of Business Administration

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lastTrans = 1; ... int start() { if (lastTrans < 0) return - else { lastTrans = -(++lastTrans); return lastTrans; } }

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7/23/2013 CSEP 545 Docsity.com

int read(int blockAddr, int tId, int block) { / find the cache element e containing the block whose disk address is blockAddr / if (there is such a cache element e) { / the disk block at blockAddr is in cache / Cache(e).tId = tId; block = &Cache(e).newBlock; / &Cache(e).newBlock = address of Cache(e).newBlock / return 0; } else { / pick a cache entry e, where Cache(e).tId = 0. If there is no such entry, then return -1 */ diskRead(blockAddr, &Cache(e).oldBlock); Cache(e).newBlock = Cache(e).oldBlock; block = &Cache(e).newBlock; Cache(e).blockAddr = blockAddr Cache(e).tId = tId; return 0; }

}

int commit(int tId) { for (each cache entry e where Cache(e).tId == tId) { status = diskWrite(Cache(e).blockAddr, &Cache(e).newBlock); Cache(e).tId = - tId; if (status == -1) { Abort(tId); return -1; } Cache(e).oldBlock = Cache(e).newBlock }; for (each cache entry e where Cache(e).tId == -tId) Cache(e).tId = 0; lastTrans = -lastTrans;

return 0; }

int abort(int tId) { for (all cache entries e, where Cache(e).tId == -tId) { repeat { status = diskWrite(Cache(e).blockAddr, &Cache(e).oldBlock) }until (status == 0); /* Of course, this will not terminate if diskWrite keeps failing, but ignore that issue */

Cache(e).newBlock = Cache(e).oldBlock; }; for (all cache entries e) { Cache(e).tId = 0 }; lastTrans = -lastTrans; return 0; }