assoc.c

memcached是一个高性能的分布式的内存对象缓存系统

  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);
}