mariadb/mysys/lf_hash.c

/* Copyright (C) 2006 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  extensible hash

  TODO
     try to get rid of dummy nodes ?
     for non-unique hash, count only _distinct_ values
     (but how to do it in lf_hash_delete ?)
*/
#include <my_global.h>
#include <m_string.h>
#include <my_sys.h>
#include <my_bit.h>
#include <lf.h>

LF_REQUIRE_PINS(3)

/* An element of the list */
typedef struct {
  intptr volatile link; /* a pointer to the next element in a listand a flag */
  uint32 hashnr;        /* reversed hash number, for sorting                 */
  const uchar *key;
  size_t keylen;
  /*
    data is stored here, directly after the keylen.
    thus the pointer to data is (void*)(slist_element_ptr+1)
  */
} LF_SLIST;

/*
  a structure to pass the context (pointers two the three successive elements
  in a list) from lfind to linsert/ldelete
*/
typedef struct {
  intptr volatile *prev;
  LF_SLIST *curr, *next;
} CURSOR;

/*
  the last bit in LF_SLIST::link is a "deleted" flag.
  the helper macros below convert it to a pure pointer or a pure flag
*/
#define PTR(V)      (LF_SLIST *)((V) & (~(intptr)1))
#define DELETED(V)  ((V) & 1)

/*
  DESCRIPTION
    Search for hashnr/key/keylen in the list starting from 'head' and
    position the cursor. The list is ORDER BY hashnr, key

  RETURN
    0 - not found
    1 - found

  NOTE
    cursor is positioned in either case
    pins[0..2] are used, they are NOT removed on return
*/
static int lfind(LF_SLIST * volatile *head, CHARSET_INFO *cs, uint32 hashnr,
                 const uchar *key, uint keylen, CURSOR *cursor, LF_PINS *pins)
{
  uint32       cur_hashnr;
  const uchar  *cur_key;
  uint         cur_keylen;
  intptr       link;

retry:
  cursor->prev= (intptr *)head;
  do { /* PTR() isn't necessary below, head is a dummy node */
    cursor->curr= (LF_SLIST *)(*cursor->prev);
    _lf_pin(pins, 1, cursor->curr);
  } while (*cursor->prev != (intptr)cursor->curr && LF_BACKOFF);
  for (;;)
  {
    if (unlikely(!cursor->curr))
      return 0; /* end of the list */
    do {
      /* QQ: XXX or goto retry ? */
      link= cursor->curr->link;
      cursor->next= PTR(link);
      _lf_pin(pins, 0, cursor->next);
    } while (link != cursor->curr->link && LF_BACKOFF);
    cur_hashnr= cursor->curr->hashnr;
    cur_key= cursor->curr->key;
    cur_keylen= cursor->curr->keylen;
    if (*cursor->prev != (intptr)cursor->curr)
    {
      (void)LF_BACKOFF;
      goto retry;
    }
    if (!DELETED(link))
    {
      if (cur_hashnr >= hashnr)
      {
        int r= 1;
        if (cur_hashnr > hashnr ||
            (r= my_strnncoll(cs, (uchar*) cur_key, cur_keylen, (uchar*) key,
                             keylen)) >= 0)
          return !r;
      }
      cursor->prev= &(cursor->curr->link);
      _lf_pin(pins, 2, cursor->curr);
    }
    else
    {
      /*
        we found a deleted node - be nice, help the other thread
        and remove this deleted node
      */
      if (my_atomic_casptr((void **)cursor->prev,
                           (void **)&cursor->curr, cursor->next))
        _lf_alloc_free(pins, cursor->curr);
      else
      {
        (void)LF_BACKOFF;
        goto retry;
      }
    }
    cursor->curr= cursor->next;
    _lf_pin(pins, 1, cursor->curr);
  }
}

/*
  DESCRIPTION
    insert a 'node' in the list that starts from 'head' in the correct
    position (as found by lfind)

  RETURN
    0     - inserted
    not 0 - a pointer to a duplicate (not pinned and thus unusable)

  NOTE
    it uses pins[0..2], on return all pins are removed.
    if there're nodes with the same key value, a new node is added before them.
*/
static LF_SLIST *linsert(LF_SLIST * volatile *head, CHARSET_INFO *cs,
                         LF_SLIST *node, LF_PINS *pins, uint flags)
{
  CURSOR         cursor;
  int            res;

  for (;;)
  {
    if (lfind(head, cs, node->hashnr, node->key, node->keylen,
              &cursor, pins) &&
        (flags & LF_HASH_UNIQUE))
    {
      res= 0; /* duplicate found */
      break;
    }
    else
    {
      node->link= (intptr)cursor.curr;
      DBUG_ASSERT(node->link != (intptr)node); /* no circular references */
      DBUG_ASSERT(cursor.prev != &node->link); /* no circular references */
      if (my_atomic_casptr((void **)cursor.prev, (void **)&cursor.curr, node))
      {
        res= 1; /* inserted ok */
        break;
      }
    }
  }
  _lf_unpin(pins, 0);
  _lf_unpin(pins, 1);
  _lf_unpin(pins, 2);
  /*
    Note that cursor.curr is not pinned here and the pointer is unreliable,
    the object may dissapear anytime. But if it points to a dummy node, the
    pointer is safe, because dummy nodes are never freed - initialize_bucket()
    uses this fact.
  */
  return res ? 0 : cursor.curr;
}

/*
  DESCRIPTION
    deletes a node as identified by hashnr/keey/keylen from the list
    that starts from 'head'

  RETURN
    0 - ok
    1 - not found

  NOTE
    it uses pins[0..2], on return all pins are removed.
*/
static int ldelete(LF_SLIST * volatile *head, CHARSET_INFO *cs, uint32 hashnr,
                   const uchar *key, uint keylen, LF_PINS *pins)
{
  CURSOR cursor;
  int res;

  for (;;)
  {
    if (!lfind(head, cs, hashnr, key, keylen, &cursor, pins))
    {
      res= 1; /* not found */
      break;
    }
    else
    {
      /* mark the node deleted */
      if (my_atomic_casptr((void **)&(cursor.curr->link),
                           (void **)&cursor.next,
                           (void *)(((intptr)cursor.next) | 1)))
      {
        /* and remove it from the list */
        if (my_atomic_casptr((void **)cursor.prev,
                             (void **)&cursor.curr, cursor.next))
          _lf_alloc_free(pins, cursor.curr);
        else
        {
          /*
            somebody already "helped" us and removed the node ?
            Let's check if we need to help that someone too!
            (to ensure the number of "set DELETED flag" actions
            is equal to the number of "remove from the list" actions)
          */
          lfind(head, cs, hashnr, key, keylen, &cursor, pins);
        }
        res= 0;
        break;
      }
    }
  }
  _lf_unpin(pins, 0);
  _lf_unpin(pins, 1);
  _lf_unpin(pins, 2);
  return res;
}

/*
  DESCRIPTION
    searches for a node as identified by hashnr/keey/keylen in the list
    that starts from 'head'

  RETURN
    0 - not found
    node - found

  NOTE
    it uses pins[0..2], on return the pin[2] keeps the node found
    all other pins are removed.
*/
static LF_SLIST *lsearch(LF_SLIST * volatile *head, CHARSET_INFO *cs,
                         uint32 hashnr, const uchar *key, uint keylen,
                         LF_PINS *pins)
{
  CURSOR cursor;
  int res= lfind(head, cs, hashnr, key, keylen, &cursor, pins);
  if (res)
    _lf_pin(pins, 2, cursor.curr);
  _lf_unpin(pins, 0);
  _lf_unpin(pins, 1);
  return res ? cursor.curr : 0;
}

static inline const uchar* hash_key(const LF_HASH *hash,
                                    const uchar *record, size_t *length)
{
  if (hash->get_key)
    return (*hash->get_key)(record, length, 0);
  *length= hash->key_length;
  return record + hash->key_offset;
}

/*
  compute the hash key value from the raw key.
  note, that the hash value is limited to 2^31, because we need one
  bit to distinguish between normal and dummy nodes.
*/
static inline uint calc_hash(LF_HASH *hash, const uchar *key, uint keylen)
{
  ulong nr1= 1, nr2= 4;
  hash->charset->coll->hash_sort(hash->charset, (uchar*) key, keylen,
                                 &nr1, &nr2);
  return nr1 & INT_MAX32;
}

#define MAX_LOAD 1.0    /* average number of elements in a bucket */

static int initialize_bucket(LF_HASH *, LF_SLIST * volatile*, uint, LF_PINS *);

/*
  Initializes lf_hash, the arguments are compatible with hash_init
*/
void lf_hash_init(LF_HASH *hash, uint element_size, uint flags,
                  uint key_offset, uint key_length, hash_get_key get_key,
                  CHARSET_INFO *charset)
{
  lf_alloc_init(&hash->alloc, sizeof(LF_SLIST)+element_size,
                offsetof(LF_SLIST, key));
  lf_dynarray_init(&hash->array, sizeof(LF_SLIST *));
  hash->size= 1;
  hash->count= 0;
  hash->element_size= element_size;
  hash->flags= flags;
  hash->charset= charset ? charset : &my_charset_bin;
  hash->key_offset= key_offset;
  hash->key_length= key_length;
  hash->get_key= get_key;
  DBUG_ASSERT(get_key ? !key_offset && !key_length : key_length);
}

void lf_hash_destroy(LF_HASH *hash)
{
  LF_SLIST *el, **head= (LF_SLIST **)_lf_dynarray_value(&hash->array, 0);

  if (unlikely(!head))
    return;
  el= *head;

  while (el)
  {
    intptr next= el->link;
    if (el->hashnr & 1)
      lf_alloc_direct_free(&hash->alloc, el); /* normal node */
    else
      my_free((void *)el, MYF(0)); /* dummy node */
    el= (LF_SLIST *)next;
  }
  lf_alloc_destroy(&hash->alloc);
  lf_dynarray_destroy(&hash->array);
}

/*
  DESCRIPTION
    inserts a new element to a hash. it will have a _copy_ of
    data, not a pointer to it.

  RETURN
    0 - inserted
    1 - didn't (unique key conflict)
   -1 - out of memory

  NOTE
    see linsert() for pin usage notes
*/
int lf_hash_insert(LF_HASH *hash, LF_PINS *pins, const void *data)
{
  int csize, bucket, hashnr;
  LF_SLIST *node, * volatile *el;

  lf_rwlock_by_pins(pins);
  node= (LF_SLIST *)_lf_alloc_new(pins);
  if (unlikely(!node))
    return -1;
  memcpy(node+1, data, hash->element_size);
  node->key= hash_key(hash, (uchar *)(node+1), &node->keylen);
  hashnr= calc_hash(hash, node->key, node->keylen);
  bucket= hashnr % hash->size;
  el= _lf_dynarray_lvalue(&hash->array, bucket);
  if (unlikely(!el))
    return -1;
  if (*el == NULL && unlikely(initialize_bucket(hash, el, bucket, pins)))
    return -1;
  node->hashnr= my_reverse_bits(hashnr) | 1; /* normal node */
  if (linsert(el, hash->charset, node, pins, hash->flags))
  {
    _lf_alloc_free(pins, node);
    lf_rwunlock_by_pins(pins);
    return 1;
  }
  csize= hash->size;
  if ((my_atomic_add32(&hash->count, 1)+1.0) / csize > MAX_LOAD)
    my_atomic_cas32(&hash->size, &csize, csize*2);
  lf_rwunlock_by_pins(pins);
  return 0;
}

/*
  DESCRIPTION
    deletes an element with the given key from the hash (if a hash is
    not unique and there're many elements with this key - the "first"
    matching element is deleted)
  RETURN
    0 - deleted
    1 - didn't (not found)
   -1 - out of memory
  NOTE
    see ldelete() for pin usage notes
*/
int lf_hash_delete(LF_HASH *hash, LF_PINS *pins, const void *key, uint keylen)
{
  LF_SLIST * volatile *el;
  uint bucket, hashnr= calc_hash(hash, (uchar *)key, keylen);

  bucket= hashnr % hash->size;
  lf_rwlock_by_pins(pins);
  el= _lf_dynarray_lvalue(&hash->array, bucket);
  if (unlikely(!el))
    return -1;
  /*
    note that we still need to initialize_bucket here,
    we cannot return "node not found", because an old bucket of that
    node may've been split and the node was assigned to a new bucket
    that was never accessed before and thus is not initialized.
  */
  if (*el == NULL && unlikely(initialize_bucket(hash, el, bucket, pins)))
    return -1;
  if (ldelete(el, hash->charset, my_reverse_bits(hashnr) | 1,
              (uchar *)key, keylen, pins))
  {
    lf_rwunlock_by_pins(pins);
    return 1;
  }
  my_atomic_add32(&hash->count, -1);
  lf_rwunlock_by_pins(pins);
  return 0;
}

/*
  RETURN
    a pointer to an element with the given key (if a hash is not unique and
    there're many elements with this key - the "first" matching element)
    NULL         if nothing is found
    MY_ERRPTR    if OOM

  NOTE
    see lsearch() for pin usage notes
*/
void *lf_hash_search(LF_HASH *hash, LF_PINS *pins, const void *key, uint keylen)
{
  LF_SLIST * volatile *el, *found;
  uint bucket, hashnr= calc_hash(hash, (uchar *)key, keylen);

  bucket= hashnr % hash->size;
  lf_rwlock_by_pins(pins);
  el= _lf_dynarray_lvalue(&hash->array, bucket);
  if (unlikely(!el))
    return MY_ERRPTR;
  if (*el == NULL && unlikely(initialize_bucket(hash, el, bucket, pins)))
    return MY_ERRPTR;
  found= lsearch(el, hash->charset, my_reverse_bits(hashnr) | 1,
                 (uchar *)key, keylen, pins);
  lf_rwunlock_by_pins(pins);
  return found ? found+1 : 0;
}

static const uchar *dummy_key= "";

/*
  RETURN
    0 - ok
   -1 - out of memory
*/
static int initialize_bucket(LF_HASH *hash, LF_SLIST * volatile *node,
                              uint bucket, LF_PINS *pins)
{
  uint parent= my_clear_highest_bit(bucket);
  LF_SLIST *dummy= (LF_SLIST *)my_malloc(sizeof(LF_SLIST), MYF(MY_WME));
  LF_SLIST **tmp= 0, *cur;
  LF_SLIST * volatile *el= _lf_dynarray_lvalue(&hash->array, parent);
  if (unlikely(!el || !dummy))
    return -1;
  if (*el == NULL && bucket &&
      unlikely(initialize_bucket(hash, el, parent, pins)))
    return -1;
  dummy->hashnr= my_reverse_bits(bucket) | 0; /* dummy node */
  dummy->key= (char*) dummy_key;
  dummy->keylen= 0;
  if ((cur= linsert(el, hash->charset, dummy, pins, LF_HASH_UNIQUE)))
  {
    my_free((void *)dummy, MYF(0));
    dummy= cur;
  }
  my_atomic_casptr((void **)node, (void **)&tmp, dummy);
  /*
    note that if the CAS above failed (after linsert() succeeded),
    it would mean that some other thread has executed linsert() for
    the same dummy node, its linsert() failed, it picked up our
    dummy node (in "dummy= cur") and executed the same CAS as above.
    Which means that even if CAS above failed we don't need to retry,
    and we should not free(dummy) - there's no memory leak here
  */
  return 0;
}