Mercurial > hg > memcached
diff assoc.c @ 0:30782bb1fc04 MEMCACHED_1_2_3
memcached-1.2.3
author | Maxim Dounin <mdounin@mdounin.ru> |
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date | Sun, 23 Sep 2007 03:58:34 +0400 |
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new file mode 100644 --- /dev/null +++ b/assoc.c @@ -0,0 +1,616 @@ +/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */ +/* + * Hash table + * + * The hash function used here is by Bob Jenkins, 1996: + * <http://burtleburtle.net/bob/hash/doobs.html> + * "By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. + * You may use this code any way you wish, private, educational, + * or commercial. It's free." + * + * The rest of the file is licensed under the BSD license. See LICENSE. + * + * $Id: assoc.c 551 2007-05-07 21:24:31Z plindner $ + */ + +#include "memcached.h" +#include <sys/stat.h> +#include <sys/socket.h> +#include <sys/signal.h> +#include <sys/resource.h> +#include <fcntl.h> +#include <netinet/in.h> +#include <errno.h> +#include <stdlib.h> +#include <stdio.h> +#include <string.h> +#include <assert.h> + +/* + * Since the hash function does bit manipulation, it needs to know + * whether it's big or little-endian. ENDIAN_LITTLE and ENDIAN_BIG + * are set in the configure script. + */ +#if ENDIAN_BIG == 1 +# define HASH_LITTLE_ENDIAN 0 +# define HASH_BIG_ENDIAN 1 +#else +# if ENDIAN_LITTLE == 1 +# define HASH_LITTLE_ENDIAN 1 +# define HASH_BIG_ENDIAN 0 +# else +# define HASH_LITTLE_ENDIAN 0 +# define HASH_BIG_ENDIAN 0 +# endif +#endif + +#define rot(x,k) (((x)<<(k)) ^ ((x)>>(32-(k)))) + +/* +------------------------------------------------------------------------------- +mix -- mix 3 32-bit values reversibly. + +This is reversible, so any information in (a,b,c) before mix() is +still in (a,b,c) after mix(). + +If four pairs of (a,b,c) inputs are run through mix(), or through +mix() in reverse, there are at least 32 bits of the output that +are sometimes the same for one pair and different for another pair. +This was tested for: +* pairs that differed by one bit, by two bits, in any combination + of top bits of (a,b,c), or in any combination of bottom bits of + (a,b,c). +* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed + the output delta to a Gray code (a^(a>>1)) so a string of 1's (as + is commonly produced by subtraction) look like a single 1-bit + difference. +* the base values were pseudorandom, all zero but one bit set, or + all zero plus a counter that starts at zero. + +Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that +satisfy this are + 4 6 8 16 19 4 + 9 15 3 18 27 15 + 14 9 3 7 17 3 +Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing +for "differ" defined as + with a one-bit base and a two-bit delta. I +used http://burtleburtle.net/bob/hash/avalanche.html to choose +the operations, constants, and arrangements of the variables. + +This does not achieve avalanche. There are input bits of (a,b,c) +that fail to affect some output bits of (a,b,c), especially of a. The +most thoroughly mixed value is c, but it doesn't really even achieve +avalanche in c. + +This allows some parallelism. Read-after-writes are good at doubling +the number of bits affected, so the goal of mixing pulls in the opposite +direction as the goal of parallelism. I did what I could. Rotates +seem to cost as much as shifts on every machine I could lay my hands +on, and rotates are much kinder to the top and bottom bits, so I used +rotates. +------------------------------------------------------------------------------- +*/ +#define mix(a,b,c) \ +{ \ + a -= c; a ^= rot(c, 4); c += b; \ + b -= a; b ^= rot(a, 6); a += c; \ + c -= b; c ^= rot(b, 8); b += a; \ + a -= c; a ^= rot(c,16); c += b; \ + b -= a; b ^= rot(a,19); a += c; \ + c -= b; c ^= rot(b, 4); b += a; \ +} + +/* +------------------------------------------------------------------------------- +final -- final mixing of 3 32-bit values (a,b,c) into c + +Pairs of (a,b,c) values differing in only a few bits will usually +produce values of c that look totally different. This was tested for +* pairs that differed by one bit, by two bits, in any combination + of top bits of (a,b,c), or in any combination of bottom bits of + (a,b,c). +* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed + the output delta to a Gray code (a^(a>>1)) so a string of 1's (as + is commonly produced by subtraction) look like a single 1-bit + difference. +* the base values were pseudorandom, all zero but one bit set, or + all zero plus a counter that starts at zero. + +These constants passed: + 14 11 25 16 4 14 24 + 12 14 25 16 4 14 24 +and these came close: + 4 8 15 26 3 22 24 + 10 8 15 26 3 22 24 + 11 8 15 26 3 22 24 +------------------------------------------------------------------------------- +*/ +#define final(a,b,c) \ +{ \ + c ^= b; c -= rot(b,14); \ + a ^= c; a -= rot(c,11); \ + b ^= a; b -= rot(a,25); \ + c ^= b; c -= rot(b,16); \ + a ^= c; a -= rot(c,4); \ + b ^= a; b -= rot(a,14); \ + c ^= b; c -= rot(b,24); \ +} + +#if HASH_LITTLE_ENDIAN == 1 +uint32_t hash( + const void *key, /* the key to hash */ + size_t length, /* length of the key */ + const uint32_t initval) /* initval */ +{ + uint32_t a,b,c; /* internal state */ + union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */ + + /* Set up the internal state */ + a = b = c = 0xdeadbeef + ((uint32_t)length) + initval; + + u.ptr = key; + if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) { + const uint32_t *k = key; /* read 32-bit chunks */ +#ifdef VALGRIND + const uint8_t *k8; +#endif // ifdef VALGRIND + + /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */ + while (length > 12) + { + a += k[0]; + b += k[1]; + c += k[2]; + mix(a,b,c); + length -= 12; + k += 3; + } + + /*----------------------------- handle the last (probably partial) block */ + /* + * "k[2]&0xffffff" actually reads beyond the end of the string, but + * then masks off the part it's not allowed to read. Because the + * string is aligned, the masked-off tail is in the same word as the + * rest of the string. Every machine with memory protection I've seen + * does it on word boundaries, so is OK with this. But VALGRIND will + * still catch it and complain. The masking trick does make the hash + * noticably faster for short strings (like English words). + */ +#ifndef VALGRIND + + switch(length) + { + case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; + case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break; + case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break; + case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break; + case 8 : b+=k[1]; a+=k[0]; break; + case 7 : b+=k[1]&0xffffff; a+=k[0]; break; + case 6 : b+=k[1]&0xffff; a+=k[0]; break; + case 5 : b+=k[1]&0xff; a+=k[0]; break; + case 4 : a+=k[0]; break; + case 3 : a+=k[0]&0xffffff; break; + case 2 : a+=k[0]&0xffff; break; + case 1 : a+=k[0]&0xff; break; + case 0 : return c; /* zero length strings require no mixing */ + } + +#else /* make valgrind happy */ + + k8 = (const uint8_t *)k; + switch(length) + { + case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; + case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ + case 10: c+=((uint32_t)k8[9])<<8; /* fall through */ + case 9 : c+=k8[8]; /* fall through */ + case 8 : b+=k[1]; a+=k[0]; break; + case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ + case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */ + case 5 : b+=k8[4]; /* fall through */ + case 4 : a+=k[0]; break; + case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ + case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */ + case 1 : a+=k8[0]; break; + case 0 : return c; /* zero length strings require no mixing */ + } + +#endif /* !valgrind */ + + } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) { + const uint16_t *k = key; /* read 16-bit chunks */ + const uint8_t *k8; + + /*--------------- all but last block: aligned reads and different mixing */ + while (length > 12) + { + a += k[0] + (((uint32_t)k[1])<<16); + b += k[2] + (((uint32_t)k[3])<<16); + c += k[4] + (((uint32_t)k[5])<<16); + mix(a,b,c); + length -= 12; + k += 6; + } + + /*----------------------------- handle the last (probably partial) block */ + k8 = (const uint8_t *)k; + switch(length) + { + case 12: c+=k[4]+(((uint32_t)k[5])<<16); + b+=k[2]+(((uint32_t)k[3])<<16); + a+=k[0]+(((uint32_t)k[1])<<16); + break; + case 11: c+=((uint32_t)k8[10])<<16; /* @fallthrough */ + case 10: c+=k[4]; /* @fallthrough@ */ + b+=k[2]+(((uint32_t)k[3])<<16); + a+=k[0]+(((uint32_t)k[1])<<16); + break; + case 9 : c+=k8[8]; /* @fallthrough */ + case 8 : b+=k[2]+(((uint32_t)k[3])<<16); + a+=k[0]+(((uint32_t)k[1])<<16); + break; + case 7 : b+=((uint32_t)k8[6])<<16; /* @fallthrough */ + case 6 : b+=k[2]; + a+=k[0]+(((uint32_t)k[1])<<16); + break; + case 5 : b+=k8[4]; /* @fallthrough */ + case 4 : a+=k[0]+(((uint32_t)k[1])<<16); + break; + case 3 : a+=((uint32_t)k8[2])<<16; /* @fallthrough */ + case 2 : a+=k[0]; + break; + case 1 : a+=k8[0]; + break; + case 0 : return c; /* zero length strings require no mixing */ + } + + } else { /* need to read the key one byte at a time */ + const uint8_t *k = key; + + /*--------------- all but the last block: affect some 32 bits of (a,b,c) */ + while (length > 12) + { + a += k[0]; + a += ((uint32_t)k[1])<<8; + a += ((uint32_t)k[2])<<16; + a += ((uint32_t)k[3])<<24; + b += k[4]; + b += ((uint32_t)k[5])<<8; + b += ((uint32_t)k[6])<<16; + b += ((uint32_t)k[7])<<24; + c += k[8]; + c += ((uint32_t)k[9])<<8; + c += ((uint32_t)k[10])<<16; + c += ((uint32_t)k[11])<<24; + mix(a,b,c); + length -= 12; + k += 12; + } + + /*-------------------------------- last block: affect all 32 bits of (c) */ + switch(length) /* all the case statements fall through */ + { + case 12: c+=((uint32_t)k[11])<<24; + case 11: c+=((uint32_t)k[10])<<16; + case 10: c+=((uint32_t)k[9])<<8; + case 9 : c+=k[8]; + case 8 : b+=((uint32_t)k[7])<<24; + case 7 : b+=((uint32_t)k[6])<<16; + case 6 : b+=((uint32_t)k[5])<<8; + case 5 : b+=k[4]; + case 4 : a+=((uint32_t)k[3])<<24; + case 3 : a+=((uint32_t)k[2])<<16; + case 2 : a+=((uint32_t)k[1])<<8; + case 1 : a+=k[0]; + break; + case 0 : return c; /* zero length strings require no mixing */ + } + } + + final(a,b,c); + return c; /* zero length strings require no mixing */ +} + +#elif HASH_BIG_ENDIAN == 1 +/* + * hashbig(): + * This is the same as hashword() on big-endian machines. It is different + * from hashlittle() on all machines. hashbig() takes advantage of + * big-endian byte ordering. + */ +uint32_t hash( const void *key, size_t length, const uint32_t initval) +{ + uint32_t a,b,c; + union { const void *ptr; size_t i; } u; /* to cast key to (size_t) happily */ + + /* Set up the internal state */ + a = b = c = 0xdeadbeef + ((uint32_t)length) + initval; + + u.ptr = key; + if (HASH_BIG_ENDIAN && ((u.i & 0x3) == 0)) { + const uint32_t *k = key; /* read 32-bit chunks */ +#ifdef VALGRIND + const uint8_t *k8; +#endif // ifdef VALGRIND + + /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */ + while (length > 12) + { + a += k[0]; + b += k[1]; + c += k[2]; + mix(a,b,c); + length -= 12; + k += 3; + } + + /*----------------------------- handle the last (probably partial) block */ + /* + * "k[2]<<8" actually reads beyond the end of the string, but + * then shifts out the part it's not allowed to read. Because the + * string is aligned, the illegal read is in the same word as the + * rest of the string. Every machine with memory protection I've seen + * does it on word boundaries, so is OK with this. But VALGRIND will + * still catch it and complain. The masking trick does make the hash + * noticably faster for short strings (like English words). + */ +#ifndef VALGRIND + + switch(length) + { + case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; + case 11: c+=k[2]&0xffffff00; b+=k[1]; a+=k[0]; break; + case 10: c+=k[2]&0xffff0000; b+=k[1]; a+=k[0]; break; + case 9 : c+=k[2]&0xff000000; b+=k[1]; a+=k[0]; break; + case 8 : b+=k[1]; a+=k[0]; break; + case 7 : b+=k[1]&0xffffff00; a+=k[0]; break; + case 6 : b+=k[1]&0xffff0000; a+=k[0]; break; + case 5 : b+=k[1]&0xff000000; a+=k[0]; break; + case 4 : a+=k[0]; break; + case 3 : a+=k[0]&0xffffff00; break; + case 2 : a+=k[0]&0xffff0000; break; + case 1 : a+=k[0]&0xff000000; break; + case 0 : return c; /* zero length strings require no mixing */ + } + +#else /* make valgrind happy */ + + k8 = (const uint8_t *)k; + switch(length) /* all the case statements fall through */ + { + case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; + case 11: c+=((uint32_t)k8[10])<<8; /* fall through */ + case 10: c+=((uint32_t)k8[9])<<16; /* fall through */ + case 9 : c+=((uint32_t)k8[8])<<24; /* fall through */ + case 8 : b+=k[1]; a+=k[0]; break; + case 7 : b+=((uint32_t)k8[6])<<8; /* fall through */ + case 6 : b+=((uint32_t)k8[5])<<16; /* fall through */ + case 5 : b+=((uint32_t)k8[4])<<24; /* fall through */ + case 4 : a+=k[0]; break; + case 3 : a+=((uint32_t)k8[2])<<8; /* fall through */ + case 2 : a+=((uint32_t)k8[1])<<16; /* fall through */ + case 1 : a+=((uint32_t)k8[0])<<24; break; + case 0 : return c; + } + +#endif /* !VALGRIND */ + + } else { /* need to read the key one byte at a time */ + const uint8_t *k = key; + + /*--------------- all but the last block: affect some 32 bits of (a,b,c) */ + while (length > 12) + { + a += ((uint32_t)k[0])<<24; + a += ((uint32_t)k[1])<<16; + a += ((uint32_t)k[2])<<8; + a += ((uint32_t)k[3]); + b += ((uint32_t)k[4])<<24; + b += ((uint32_t)k[5])<<16; + b += ((uint32_t)k[6])<<8; + b += ((uint32_t)k[7]); + c += ((uint32_t)k[8])<<24; + c += ((uint32_t)k[9])<<16; + c += ((uint32_t)k[10])<<8; + c += ((uint32_t)k[11]); + mix(a,b,c); + length -= 12; + k += 12; + } + + /*-------------------------------- last block: affect all 32 bits of (c) */ + switch(length) /* all the case statements fall through */ + { + case 12: c+=k[11]; + case 11: c+=((uint32_t)k[10])<<8; + case 10: c+=((uint32_t)k[9])<<16; + case 9 : c+=((uint32_t)k[8])<<24; + case 8 : b+=k[7]; + case 7 : b+=((uint32_t)k[6])<<8; + case 6 : b+=((uint32_t)k[5])<<16; + case 5 : b+=((uint32_t)k[4])<<24; + case 4 : a+=k[3]; + case 3 : a+=((uint32_t)k[2])<<8; + case 2 : a+=((uint32_t)k[1])<<16; + case 1 : a+=((uint32_t)k[0])<<24; + break; + case 0 : return c; + } + } + + final(a,b,c); + return c; +} +#else // HASH_XXX_ENDIAN == 1 +#error Must define HASH_BIG_ENDIAN or HASH_LITTLE_ENDIAN +#endif // hash_XXX_ENDIAN == 1 + +typedef unsigned long int ub4; /* unsigned 4-byte quantities */ +typedef unsigned char ub1; /* unsigned 1-byte quantities */ + +/* how many powers of 2's worth of buckets we use */ +static int hashpower = 16; + +#define hashsize(n) ((ub4)1<<(n)) +#define hashmask(n) (hashsize(n)-1) + +/* Main hash table. This is where we look except during expansion. */ +static item** primary_hashtable = 0; + +/* + * Previous hash table. During expansion, we look here for keys that haven't + * been moved over to the primary yet. + */ +static item** old_hashtable = 0; + +/* Number of items in the hash table. */ +static int hash_items = 0; + +/* Flag: Are we in the middle of expanding now? */ +static int expanding = 0; + +/* + * During expansion we migrate values with bucket granularity; this is how + * far we've gotten so far. Ranges from 0 .. hashsize(hashpower - 1) - 1. + */ +static int expand_bucket = 0; + +void assoc_init(void) { + unsigned int hash_size = hashsize(hashpower) * sizeof(void*); + primary_hashtable = malloc(hash_size); + if (! primary_hashtable) { + fprintf(stderr, "Failed to init hashtable.\n"); + exit(EXIT_FAILURE); + } + memset(primary_hashtable, 0, hash_size); +} + +item *assoc_find(const char *key, const size_t nkey) { + uint32_t hv = hash(key, nkey, 0); + item *it; + int oldbucket; + + if (expanding && + (oldbucket = (hv & hashmask(hashpower - 1))) >= expand_bucket) + { + it = old_hashtable[oldbucket]; + } else { + it = primary_hashtable[hv & hashmask(hashpower)]; + } + + while (it) { + if ((nkey == it->nkey) && + (memcmp(key, ITEM_key(it), nkey) == 0)) { + return it; + } + it = it->h_next; + } + return 0; +} + +/* returns the address of the item pointer before the key. if *item == 0, + the item wasn't found */ + +static item** _hashitem_before (const char *key, const size_t nkey) { + uint32_t hv = hash(key, nkey, 0); + item **pos; + int oldbucket; + + if (expanding && + (oldbucket = (hv & hashmask(hashpower - 1))) >= expand_bucket) + { + pos = &old_hashtable[oldbucket]; + } else { + pos = &primary_hashtable[hv & hashmask(hashpower)]; + } + + while (*pos && ((nkey != (*pos)->nkey) || memcmp(key, ITEM_key(*pos), nkey))) { + pos = &(*pos)->h_next; + } + return pos; +} + +/* grows the hashtable to the next power of 2. */ +static void assoc_expand(void) { + old_hashtable = primary_hashtable; + + primary_hashtable = calloc(hashsize(hashpower + 1), sizeof(void *)); + if (primary_hashtable) { + if (settings.verbose > 1) + fprintf(stderr, "Hash table expansion starting\n"); + hashpower++; + expanding = 1; + expand_bucket = 0; + do_assoc_move_next_bucket(); + } else { + primary_hashtable = old_hashtable; + /* Bad news, but we can keep running. */ + } +} + +/* migrates the next bucket to the primary hashtable if we're expanding. */ +void do_assoc_move_next_bucket(void) { + item *it, *next; + int bucket; + + if (expanding) { + for (it = old_hashtable[expand_bucket]; NULL != it; it = next) { + next = it->h_next; + + bucket = hash(ITEM_key(it), it->nkey, 0) & hashmask(hashpower); + it->h_next = primary_hashtable[bucket]; + primary_hashtable[bucket] = it; + } + + old_hashtable[expand_bucket] = NULL; + + expand_bucket++; + if (expand_bucket == hashsize(hashpower - 1)) { + expanding = 0; + free(old_hashtable); + if (settings.verbose > 1) + fprintf(stderr, "Hash table expansion done\n"); + } + } +} + +/* Note: this isn't an assoc_update. The key must not already exist to call this */ +int assoc_insert(item *it) { + uint32_t hv; + int oldbucket; + + assert(assoc_find(ITEM_key(it), it->nkey) == 0); /* shouldn't have duplicately named things defined */ + + hv = hash(ITEM_key(it), it->nkey, 0); + if (expanding && + (oldbucket = (hv & hashmask(hashpower - 1))) >= expand_bucket) + { + it->h_next = old_hashtable[oldbucket]; + old_hashtable[oldbucket] = it; + } else { + it->h_next = primary_hashtable[hv & hashmask(hashpower)]; + primary_hashtable[hv & hashmask(hashpower)] = it; + } + + hash_items++; + if (! expanding && hash_items > (hashsize(hashpower) * 3) / 2) { + assoc_expand(); + } + + return 1; +} + +void assoc_delete(const char *key, const size_t nkey) { + item **before = _hashitem_before(key, nkey); + + if (*before) { + item *nxt = (*before)->h_next; + (*before)->h_next = 0; /* probably pointless, but whatever. */ + *before = nxt; + hash_items--; + return; + } + /* Note: we never actually get here. the callers don't delete things + they can't find. */ + assert(*before != 0); +}