/* ========================================================================== ** * ubi_Cache.c * * Copyright (C) 1997 by Christopher R. Hertel * * Email: crh@ubiqx.mn.org * -------------------------------------------------------------------------- ** * * This module implements a generic cache. * * -------------------------------------------------------------------------- ** * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Library General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * 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 * Library General Public License for more details. * * You should have received a copy of the GNU Library General Public * License along with this library; if not, write to the Free * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * * -------------------------------------------------------------------------- ** * * This module uses a splay tree to implement a simple cache. The cache * module adds a thin layer of functionality to the splay tree. In * particular: * * - The tree (cache) may be limited in size by the number of * entries permitted or the amount of memory used. When either * limit is exceeded cache entries are removed until the cache * conforms. * - Some statistical information is kept so that an approximate * "hit ratio" can be calculated. * - There are several functions available that provide access to * and management of cache size limits, hit ratio, and tree * trimming. * * The splay tree is used because recently accessed items tend toward the * top of the tree and less recently accessed items tend toward the bottom. * This makes it easy to purge less recently used items should the cache * exceed its limits. * * To use this module, you will need to supply a comparison function of * type ubi_trCompFunc and a node-freeing function of type * ubi_trKillNodeRtn. See ubi_BinTree.h for more information on * these. (This is all basic ubiqx tree management stuff.) * * Notes: * * - Cache performance will start to suffer dramatically if the * cache becomes large enough to force the OS to start swapping * memory to disk. This is because the nodes of the underlying tree * will be scattered across memory in an order that is completely * unrelated to their traversal order. As more and more of the * cache is placed into swap space, more and more swaps will be * required for a simple traversal (...and then there's the splay * operation). * * In one simple test under Linux, the load and dump of a cache of * 400,000 entries took only 1min, 40sec of real time. The same * test with 450,000 records took 2 *hours* and eight minutes. * * - In an effort to save memory, I considered using an unsigned * short to save the per-entry entry size. I would have tucked this * value into some unused space in the tree node structure. On * 32-bit word aligned systems this would have saved an additional * four bytes per entry. I may revisit this issue, but for now I've * decided against it. * * Using an unsigned short would limit the size of an entry to 64K * bytes. That's probably more than enough for most applications. * The key word in that last sentence, however, is "probably". I * really dislike imposing such limits on things. * * - Each entry keeps track of the amount of memory it used and the * cache header keeps the total. This information is provided via * the EntrySize parameter in ubi_cachePut(), so it is up to you to * make sure that the numbers are accurate. (The numbers don't even * have to represent bytes used.) * * As you consider this, note that the strdup() function--as an * example--will call malloc(). The latter generally allocates a * multiple of the system word size, which may be more than the * number of bytes needed to store the string. * * -------------------------------------------------------------------------- ** * * Log: ubi_Cache.c,v * Revision 0.4 1999/09/22 03:42:24 crh * Fixed a minor typo. * * Revision 0.3 1998/06/03 18:00:15 crh * Further fiddling with sys_include.h, which is no longer explicitly * included by this module since it is inherited from ubi_BinTree.h. * * Revision 0.2 1998/06/02 01:36:18 crh * Changed include name from ubi_null.h to sys_include.h to make it * more generic. * * Revision 0.1 1998/05/20 04:36:02 crh * The C file now includes ubi_null.h. See ubi_null.h for more info. * * Revision 0.0 1997/12/18 06:24:33 crh * Initial Revision. * * ========================================================================== ** */ #include "ubi_Cache.h" /* Header for *this* module. */ /* -------------------------------------------------------------------------- ** * Static data... */ /* commented out until I make use of it... static char ModuleID[] = "ubi_Cache\n\ \tRevision: 0.4 \n\ \tDate: 1999/09/22 03:42:24 \n\ \tAuthor: crh \n"; */ /* -------------------------------------------------------------------------- ** * Internal functions... */ static void free_entry( ubi_cacheRootPtr CachePtr, ubi_cacheEntryPtr EntryPtr ) /* ------------------------------------------------------------------------ ** * Free a ubi_cacheEntry, and adjust the mem_used counter accordingly. * * Input: CachePtr - A pointer to the cache from which the entry has * been removed. * EntryPtr - A pointer to the already removed entry. * * Output: none. * * Notes: The entry must be removed from the cache *before* this function * is called!!!! * ------------------------------------------------------------------------ ** */ { CachePtr->mem_used -= EntryPtr->entry_size; (*CachePtr->free_func)( (void *)EntryPtr ); } /* free_entry */ static void cachetrim( ubi_cacheRootPtr crptr ) /* ------------------------------------------------------------------------ ** * Remove entries from the cache until the number of entries and the amount * of memory used are *both* below or at the maximum. * * Input: crptr - pointer to the cache to be trimmed. * * Output: None. * * ------------------------------------------------------------------------ ** */ { while( ( crptr->max_entries && (crptr->max_entries < crptr->root.count) ) || ( crptr->max_memory && (crptr->max_memory < crptr->mem_used) ) ) { if( !ubi_cacheReduce( crptr, 1 ) ) return; } } /* cachetrim */ /* -------------------------------------------------------------------------- ** * Exported functions... */ ubi_cacheRootPtr ubi_cacheInit( ubi_cacheRootPtr CachePtr, ubi_trCompFunc CompFunc, ubi_trKillNodeRtn FreeFunc, unsigned long MaxEntries, unsigned long MaxMemory ) /* ------------------------------------------------------------------------ ** * Initialize a cache header structure. * * Input: CachePtr - A pointer to a ubi_cacheRoot structure that is * to be initialized. * CompFunc - A pointer to the function that will be called * to compare two cache values. See the module * comments, above, for more information. * FreeFunc - A pointer to a function that will be called * to free a cache entry. If you allocated * the cache entry using malloc(), then this * will likely be free(). If you are allocating * cache entries from a free list, then this will * likely be a function that returns memory to the * free list, etc. * MaxEntries - The maximum number of entries that will be * allowed to exist in the cache. If this limit * is exceeded, then existing entries will be * removed from the cache. A value of zero * indicates that there is no limit on the number * of cache entries. See ubi_cachePut(). * MaxMemory - The maximum amount of memory, in bytes, to be * allocated to the cache (excluding the cache * header). If this is exceeded, existing entries * in the cache will be removed until enough memory * has been freed to meet the condition. See * ubi_cachePut(). * * Output: A pointer to the initialized cache (i.e., the same as CachePtr). * * Notes: Both MaxEntries and MaxMemory may be changed after the cache * has been created. See * ubi_cacheSetMaxEntries() * ubi_cacheSetMaxMemory() * ubi_cacheGetMaxEntries() * ubi_cacheGetMaxMemory() (the latter two are macros). * * - Memory is allocated in multiples of the word size. The * return value of the strlen() function does not reflect * this; it will allways be less than or equal to the amount * of memory actually allocated. Keep this in mind when * choosing a value for MaxMemory. * * ------------------------------------------------------------------------ ** */ { if( CachePtr ) { (void)ubi_trInitTree( CachePtr, CompFunc, ubi_trOVERWRITE ); CachePtr->free_func = FreeFunc; CachePtr->max_entries = MaxEntries; CachePtr->max_memory = MaxMemory; CachePtr->mem_used = 0; CachePtr->cache_hits = 0; CachePtr->cache_trys = 0; } return( CachePtr ); } /* ubi_cacheInit */ ubi_cacheRootPtr ubi_cacheClear( ubi_cacheRootPtr CachePtr ) /* ------------------------------------------------------------------------ ** * Remove and free all entries in an existing cache. * * Input: CachePtr - A pointer to the cache that is to be cleared. * * Output: A pointer to the cache header (i.e., the same as CachePtr). * This function re-initializes the cache header. * * ------------------------------------------------------------------------ ** */ { if( CachePtr ) { (void)ubi_trKillTree( CachePtr, CachePtr->free_func ); CachePtr->mem_used = 0; CachePtr->cache_hits = 0; CachePtr->cache_trys = 0; } return( CachePtr ); } /* ubi_cacheClear */ void ubi_cachePut( ubi_cacheRootPtr CachePtr, unsigned long EntrySize, ubi_cacheEntryPtr EntryPtr, ubi_trItemPtr Key ) /* ------------------------------------------------------------------------ ** * Add an entry to the cache. * * Input: CachePtr - A pointer to the cache into which the entry * will be added. * EntrySize - The size, in bytes, of the memory block indicated * by EntryPtr. This will be copied into the * EntryPtr->entry_size field. * EntryPtr - A pointer to a memory block that begins with a * ubi_cacheEntry structure. The entry structure * should be followed immediately by the data to be * cached (even if that is a pointer to yet more data). * Key - Pointer used to identify the lookup key within the * Entry. * * Output: None. * * Notes: After adding the new node, the cache is "trimmed". This * removes extra nodes if the tree has exceeded it's memory or * entry count limits. It is unlikely that the newly added node * will be purged from the cache (assuming a reasonably large * cache), since new nodes in a splay tree (which is what this * module was designed to use) are moved to the top of the tree * and the cache purge process removes nodes from the bottom of * the tree. * - The underlying splay tree is opened in OVERWRITE mode. If * the input key matches an existing key, the existing entry will * be politely removed from the tree and freed. * - Memory is allocated in multiples of the word size. The * return value of the strlen() function does not reflect * this; it will allways be less than or equal to the amount * of memory actually allocated. * * ------------------------------------------------------------------------ ** */ { ubi_trNodePtr OldNode; EntryPtr->entry_size = EntrySize; CachePtr->mem_used += EntrySize; (void)ubi_trInsert( CachePtr, EntryPtr, Key, &OldNode ); if( OldNode ) free_entry( CachePtr, (ubi_cacheEntryPtr)OldNode ); cachetrim( CachePtr ); } /* ubi_cachePut */ ubi_cacheEntryPtr ubi_cacheGet( ubi_cacheRootPtr CachePtr, ubi_trItemPtr FindMe ) /* ------------------------------------------------------------------------ ** * Attempt to retrieve an entry from the cache. * * Input: CachePtr - A ponter to the cache that is to be searched. * FindMe - A ubi_trItemPtr that indicates the key for which * to search. * * Output: A pointer to the cache entry that was found, or NULL if no * matching entry was found. * * Notes: This function also updates the hit ratio counters. * The counters are unsigned short. If the number of cache tries * reaches 32768, then both the number of tries and the number of * hits are divided by two. This prevents the counters from * overflowing. See the comments in ubi_cacheHitRatio() for * additional notes. * * ------------------------------------------------------------------------ ** */ { ubi_trNodePtr FoundPtr; FoundPtr = ubi_trFind( CachePtr, FindMe ); if( FoundPtr ) CachePtr->cache_hits++; CachePtr->cache_trys++; if( CachePtr->cache_trys & 0x8000 ) { CachePtr->cache_hits = CachePtr->cache_hits / 2; CachePtr->cache_trys = CachePtr->cache_trys / 2; } return( (ubi_cacheEntryPtr)FoundPtr ); } /* ubi_cacheGet */ ubi_trBool ubi_cacheDelete( ubi_cacheRootPtr CachePtr, ubi_trItemPtr DeleteMe ) /* ------------------------------------------------------------------------ ** * Find and delete the specified cache entry. * * Input: CachePtr - A pointer to the cache. * DeleteMe - The key of the entry to be deleted. * * Output: TRUE if the entry was found & freed, else FALSE. * * ------------------------------------------------------------------------ ** */ { ubi_trNodePtr FoundPtr; FoundPtr = ubi_trFind( CachePtr, DeleteMe ); if( FoundPtr ) { (void)ubi_trRemove( CachePtr, FoundPtr ); free_entry( CachePtr, (ubi_cacheEntryPtr)FoundPtr ); return( ubi_trTRUE ); } return( ubi_trFALSE ); } /* ubi_cacheDelete */ ubi_trBool ubi_cacheReduce( ubi_cacheRootPtr CachePtr, unsigned long count ) /* ------------------------------------------------------------------------ ** * Remove <count> entries from the bottom of the cache. * * Input: CachePtr - A pointer to the cache which is to be reduced in * size. * count - The number of entries to remove. * * Output: The function will return TRUE if <count> entries were removed, * else FALSE. A return value of FALSE should indicate that * there were less than <count> entries in the cache, and that the * cache is now empty. * * Notes: This function forces a reduction in the number of cache entries * without requiring that the MaxMemory or MaxEntries values be * changed. * * ------------------------------------------------------------------------ ** */ { ubi_trNodePtr NodePtr; while( count ) { NodePtr = ubi_trLeafNode( CachePtr->root.root ); if( NULL == NodePtr ) return( ubi_trFALSE ); else { (void)ubi_trRemove( CachePtr, NodePtr ); free_entry( CachePtr, (ubi_cacheEntryPtr)NodePtr ); } count--; } return( ubi_trTRUE ); } /* ubi_cacheReduce */ unsigned long ubi_cacheSetMaxEntries( ubi_cacheRootPtr CachePtr, unsigned long NewSize ) /* ------------------------------------------------------------------------ ** * Change the maximum number of entries allowed to exist in the cache. * * Input: CachePtr - A pointer to the cache to be modified. * NewSize - The new maximum number of cache entries. * * Output: The maximum number of entries previously allowed to exist in * the cache. * * Notes: If the new size is less than the old size, this function will * trim the cache (remove excess entries). * - A value of zero indicates an unlimited number of entries. * * ------------------------------------------------------------------------ ** */ { unsigned long oldsize = CachePtr->max_entries; /* Save the old value. */ CachePtr->max_entries = NewSize; /* Apply the new value. */ if( (NewSize < oldsize) || (NewSize && !oldsize) ) /* If size is smaller, */ cachetrim( CachePtr ); /* remove excess. */ return( oldsize ); } /* ubi_cacheSetMaxEntries */ unsigned long ubi_cacheSetMaxMemory( ubi_cacheRootPtr CachePtr, unsigned long NewSize ) /* ------------------------------------------------------------------------ ** * Change the maximum amount of memory to be used for storing cache * entries. * * Input: CachePtr - A pointer to the cache to be modified. * NewSize - The new cache memory size. * * Output: The previous maximum memory size. * * Notes: If the new size is less than the old size, this function will * trim the cache (remove excess entries). * - A value of zero indicates that the cache has no memory limit. * * ------------------------------------------------------------------------ ** */ { unsigned long oldsize = CachePtr->max_memory; /* Save the old value. */ CachePtr->max_memory = NewSize; /* Apply the new value. */ if( (NewSize < oldsize) || (NewSize && !oldsize) ) /* If size is smaller, */ cachetrim( CachePtr ); /* remove excess. */ return( oldsize ); } /* ubi_cacheSetMaxMemory */ int ubi_cacheHitRatio( ubi_cacheRootPtr CachePtr ) /* ------------------------------------------------------------------------ ** * Returns a value that is 10,000 times the slightly weighted average hit * ratio for the cache. * * Input: CachePtr - Pointer to the cache to be queried. * * Output: An integer that is 10,000 times the number of successful * cache hits divided by the number of cache lookups, or: * (10000 * hits) / trys * You can easily convert this to a float, or do something * like this (where i is the return value of this function): * * printf( "Hit rate : %d.%02d%%\n", (i/100), (i%100) ); * * Notes: I say "slightly-weighted", because the numerator and * denominator are both accumulated in locations of type * 'unsigned short'. If the number of cache trys becomes * large enough, both are divided by two. (See function * ubi_cacheGet().) * Dividing both numerator and denominator by two does not * change the ratio (much...it is an integer divide), but it * does mean that subsequent increments to either counter will * have twice as much significance as previous ones. * * - The value returned by this function will be in the range * [0..10000] because ( 0 <= cache_hits <= cache_trys ) will * always be true. * * ------------------------------------------------------------------------ ** */ { int tmp = 0; if( CachePtr->cache_trys ) tmp = (int)( (10000 * (long)(CachePtr->cache_hits) ) / (long)(CachePtr->cache_trys) ); return( tmp ); } /* ubi_cacheHitRatio */ /* -------------------------------------------------------------------------- */