/*-------------------------------------------------------------------------
 *
 * dynahash.c
 *	  dynamic hash tables
 *
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.48.2.2 2007/04/26 23:25:40 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 *
 * Dynamic hashing, after CACM April 1988 pp 446-457, by Per-Ake Larson.
 * Coded into C, with minor code improvements, and with hsearch(3) interface,
 * by ejp@ausmelb.oz, Jul 26, 1988: 13:16;
 * also, hcreate/hdestroy routines added to simulate hsearch(3).
 *
 * These routines simulate hsearch(3) and family, with the important
 * difference that the hash table is dynamic - can grow indefinitely
 * beyond its original size (as supplied to hcreate()).
 *
 * Performance appears to be comparable to that of hsearch(3).
 * The 'source-code' options referred to in hsearch(3)'s 'man' page
 * are not implemented; otherwise functionality is identical.
 *
 * Compilation controls:
 * DEBUG controls some informative traces, mainly for debugging.
 * HASH_STATISTICS causes HashAccesses and HashCollisions to be maintained;
 * when combined with HASH_DEBUG, these are displayed by hdestroy().
 *
 * Problems & fixes to ejp@ausmelb.oz. WARNING: relies on pre-processor
 * concatenation property, in probably unnecessary code 'optimisation'.
 *
 * Modified margo@postgres.berkeley.edu February 1990
 *		added multiple table interface
 * Modified by sullivan@postgres.berkeley.edu April 1990
 *		changed ctl structure for shared memory
 */

#include "postgres.h"

#include "utils/dynahash.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"

/*
 * Key (also entry) part of a HASHELEMENT
 */
#define ELEMENTKEY(helem)  (((char *)(helem)) + MAXALIGN(sizeof(HASHELEMENT)))

/*
 * Fast MOD arithmetic, assuming that y is a power of 2 !
 */
#define MOD(x,y)			   ((x) & ((y)-1))

/*
 * Private function prototypes
 */
static void *DynaHashAlloc(Size size);
static HASHSEGMENT seg_alloc(HTAB *hashp);
static bool element_alloc(HTAB *hashp);
static bool dir_realloc(HTAB *hashp);
static bool expand_table(HTAB *hashp);
static bool hdefault(HTAB *hashp);
static bool init_htab(HTAB *hashp, long nelem);
static void hash_corrupted(HTAB *hashp);
static void register_seq_scan(HTAB *hashp);
static void deregister_seq_scan(HTAB *hashp);
static bool has_seq_scans(HTAB *hashp);


/*
 * memory allocation routines
 */
static MemoryContext DynaHashCxt = NULL;
static MemoryContext CurrentDynaHashCxt = NULL;

static void *
DynaHashAlloc(Size size)
{
	Assert(MemoryContextIsValid(CurrentDynaHashCxt));
	return MemoryContextAlloc(CurrentDynaHashCxt, size);
}

#define MEM_ALLOC		DynaHashAlloc
#define MEM_FREE		pfree


#if HASH_STATISTICS
static long hash_accesses,
			hash_collisions,
			hash_expansions;
#endif


/************************** CREATE ROUTINES **********************/

HTAB *
hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
{
	HTAB	   *hashp;
	HASHHDR    *hctl;

	/* First time through, create a memory context for hash tables */
	if (!DynaHashCxt)
		DynaHashCxt = AllocSetContextCreate(TopMemoryContext,
											"DynaHash",
											ALLOCSET_DEFAULT_MINSIZE,
											ALLOCSET_DEFAULT_INITSIZE,
											ALLOCSET_DEFAULT_MAXSIZE);

	/* Select allocation context for this hash table */
	if (flags & HASH_CONTEXT)
		CurrentDynaHashCxt = info->hcxt;
	else
		CurrentDynaHashCxt = DynaHashCxt;

	/* Initialize the hash header */
	hashp = (HTAB *) MEM_ALLOC(sizeof(HTAB));
	if (!hashp)
		return NULL;
	MemSet(hashp, 0, sizeof(HTAB));

	hashp->tabname = (char *) MEM_ALLOC(strlen(tabname) + 1);
	strcpy(hashp->tabname, tabname);

	if (flags & HASH_FUNCTION)
		hashp->hash = info->hash;
	else
		hashp->hash = string_hash;		/* default hash function */

	/*
	 * If you don't specify a match function, it defaults to strncmp() if
	 * you used string_hash (either explicitly or by default) and to
	 * memcmp() otherwise.  (Prior to PostgreSQL 7.4, memcmp() was always
	 * used.)
	 */
	if (flags & HASH_COMPARE)
		hashp->match = info->match;
	else if (hashp->hash == string_hash)
		hashp->match = (HashCompareFunc) strncmp;
	else
		hashp->match = memcmp;

	/*
	 * Similarly, the key-copying function defaults to strncpy() or memcpy().
	 */
	if (hashp->hash == string_hash)
		hashp->keycopy = (HashCopyFunc) strncpy;
	else
		hashp->keycopy = memcpy;

	if (flags & HASH_SHARED_MEM)
	{
		/*
		 * ctl structure is preallocated for shared memory tables. Note
		 * that HASH_DIRSIZE had better be set as well.
		 */
		hashp->hctl = info->hctl;
		hashp->dir = info->dir;
		hashp->alloc = info->alloc;
		hashp->hcxt = NULL;
		hashp->isshared = true;

		/* hash table already exists, we're just attaching to it */
		if (flags & HASH_ATTACH)
			return hashp;
	}
	else
	{
		/* setup hash table defaults */
		hashp->hctl = NULL;
		hashp->dir = NULL;
		hashp->alloc = MEM_ALLOC;
		hashp->hcxt = CurrentDynaHashCxt;
		hashp->isshared = false;
	}

	if (!hashp->hctl)
	{
		hashp->hctl = (HASHHDR *) hashp->alloc(sizeof(HASHHDR));
		if (!hashp->hctl)
			return NULL;
	}

	hashp->frozen = false;

	if (!hdefault(hashp))
		return NULL;

	hctl = hashp->hctl;
#ifdef HASH_STATISTICS
	hctl->accesses = hctl->collisions = 0;
#endif

	if (flags & HASH_SEGMENT)
	{
		hctl->ssize = info->ssize;
		hctl->sshift = my_log2(info->ssize);
		/* ssize had better be a power of 2 */
		Assert(hctl->ssize == (1L << hctl->sshift));
	}
	if (flags & HASH_FFACTOR)
		hctl->ffactor = info->ffactor;

	/*
	 * SHM hash tables have fixed directory size passed by the caller.
	 */
	if (flags & HASH_DIRSIZE)
	{
		hctl->max_dsize = info->max_dsize;
		hctl->dsize = info->dsize;
	}

	/*
	 * hash table now allocates space for key and data but you have to say
	 * how much space to allocate
	 */
	if (flags & HASH_ELEM)
	{
		hctl->keysize = info->keysize;
		hctl->entrysize = info->entrysize;
	}

	if (flags & HASH_ALLOC)
		hashp->alloc = info->alloc;
	else
	{
		/* remaining hash table structures live in child of given context */
		hashp->hcxt = AllocSetContextCreate(CurrentDynaHashCxt,
											"DynaHashTable",
											ALLOCSET_DEFAULT_MINSIZE,
											ALLOCSET_DEFAULT_INITSIZE,
											ALLOCSET_DEFAULT_MAXSIZE);
		CurrentDynaHashCxt = hashp->hcxt;
	}

	if (!init_htab(hashp, nelem))
	{
		hash_destroy(hashp);
		return NULL;
	}
	return hashp;
}

/*
 * Set default HASHHDR parameters.
 */
static bool
hdefault(HTAB *hashp)
{
	HASHHDR    *hctl = hashp->hctl;

	MemSet(hctl, 0, sizeof(HASHHDR));

	hctl->ssize = DEF_SEGSIZE;
	hctl->sshift = DEF_SEGSIZE_SHIFT;
	hctl->dsize = DEF_DIRSIZE;
	hctl->ffactor = DEF_FFACTOR;
	hctl->nentries = 0;
	hctl->nsegs = 0;

	/* I added these MS. */

	/* rather pointless defaults for key & entry size */
	hctl->keysize = sizeof(char *);
	hctl->entrysize = 2 * sizeof(char *);

	/* table has no fixed maximum size */
	hctl->max_dsize = NO_MAX_DSIZE;

	/* garbage collection for HASH_REMOVE */
	hctl->freeList = NULL;

	return true;
}


static bool
init_htab(HTAB *hashp, long nelem)
{
	HASHHDR    *hctl = hashp->hctl;
	HASHSEGMENT *segp;
	int			nbuckets;
	int			nsegs;

	/*
	 * Divide number of elements by the fill factor to determine a desired
	 * number of buckets.  Allocate space for the next greater power of
	 * two number of buckets
	 */
	nelem = (nelem - 1) / hctl->ffactor + 1;

	nbuckets = 1 << my_log2(nelem);

	hctl->max_bucket = hctl->low_mask = nbuckets - 1;
	hctl->high_mask = (nbuckets << 1) - 1;

	/*
	 * Figure number of directory segments needed, round up to a power of
	 * 2
	 */
	nsegs = (nbuckets - 1) / hctl->ssize + 1;
	nsegs = 1 << my_log2(nsegs);

	/*
	 * Make sure directory is big enough. If pre-allocated directory is
	 * too small, choke (caller screwed up).
	 */
	if (nsegs > hctl->dsize)
	{
		if (!(hashp->dir))
			hctl->dsize = nsegs;
		else
			return false;
	}

	/* Allocate a directory */
	if (!(hashp->dir))
	{
		CurrentDynaHashCxt = hashp->hcxt;
		hashp->dir = (HASHSEGMENT *)
			hashp->alloc(hctl->dsize * sizeof(HASHSEGMENT));
		if (!hashp->dir)
			return false;
	}

	/* Allocate initial segments */
	for (segp = hashp->dir; hctl->nsegs < nsegs; hctl->nsegs++, segp++)
	{
		*segp = seg_alloc(hashp);
		if (*segp == NULL)
			return false;
	}

#if HASH_DEBUG
	fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n%s%ld\n",
			"TABLE POINTER   ", hashp,
			"DIRECTORY SIZE  ", hctl->dsize,
			"SEGMENT SIZE    ", hctl->ssize,
			"SEGMENT SHIFT   ", hctl->sshift,
			"FILL FACTOR     ", hctl->ffactor,
			"MAX BUCKET      ", hctl->max_bucket,
			"HIGH MASK       ", hctl->high_mask,
			"LOW  MASK       ", hctl->low_mask,
			"NSEGS           ", hctl->nsegs,
			"NENTRIES        ", hctl->nentries);
#endif
	return true;
}

/*
 * Estimate the space needed for a hashtable containing the given number
 * of entries of given size.
 * NOTE: this is used to estimate the footprint of hashtables in shared
 * memory; therefore it does not count HTAB which is in local memory.
 * NB: assumes that all hash structure parameters have default values!
 */
long
hash_estimate_size(long num_entries, Size entrysize)
{
	long		size = 0;
	long		nBuckets,
				nSegments,
				nDirEntries,
				nElementAllocs,
				elementSize;

	/* estimate number of buckets wanted */
	nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
	/* # of segments needed for nBuckets */
	nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
	/* directory entries */
	nDirEntries = DEF_DIRSIZE;
	while (nDirEntries < nSegments)
		nDirEntries <<= 1;		/* dir_alloc doubles dsize at each call */

	/* fixed control info */
	size += MAXALIGN(sizeof(HASHHDR));	/* but not HTAB, per above */
	/* directory */
	size += MAXALIGN(nDirEntries * sizeof(HASHSEGMENT));
	/* segments */
	size += nSegments * MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET));
	/* elements --- allocated in groups of HASHELEMENT_ALLOC_INCR */
	elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
	nElementAllocs = (num_entries - 1) / HASHELEMENT_ALLOC_INCR + 1;
	size += nElementAllocs * HASHELEMENT_ALLOC_INCR * elementSize;

	return size;
}

/*
 * Select an appropriate directory size for a hashtable with the given
 * maximum number of entries.
 * This is only needed for hashtables in shared memory, whose directories
 * cannot be expanded dynamically.
 * NB: assumes that all hash structure parameters have default values!
 *
 * XXX this had better agree with the behavior of init_htab()...
 */
long
hash_select_dirsize(long num_entries)
{
	long		nBuckets,
				nSegments,
				nDirEntries;

	/* estimate number of buckets wanted */
	nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
	/* # of segments needed for nBuckets */
	nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
	/* directory entries */
	nDirEntries = DEF_DIRSIZE;
	while (nDirEntries < nSegments)
		nDirEntries <<= 1;		/* dir_alloc doubles dsize at each call */

	return nDirEntries;
}


/********************** DESTROY ROUTINES ************************/

void
hash_destroy(HTAB *hashp)
{
	if (hashp != NULL)
	{
		/* allocation method must be one we know how to free, too */
		Assert(hashp->alloc == MEM_ALLOC);
		/* so this hashtable must have it's own context */
		Assert(hashp->hcxt != NULL);

		hash_stats("destroy", hashp);

		/*
		 * Free buckets, dir etc. by destroying the hash table's memory
		 * context.
		 */
		MemoryContextDelete(hashp->hcxt);

		/*
		 * Free the HTAB and control structure, which are allocated in the
		 * parent context (DynaHashCxt or the context given by the caller
		 * of hash_create()).
		 */
		MEM_FREE(hashp->hctl);
		MEM_FREE(hashp->tabname);
		MEM_FREE(hashp);
	}
}

void
hash_stats(const char *where, HTAB *hashp)
{
#if HASH_STATISTICS
	fprintf(stderr, "%s: this HTAB -- accesses %ld collisions %ld\n",
			where, hashp->hctl->accesses, hashp->hctl->collisions);

	fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
			hashp->hctl->nentries, hashp->hctl->keysize,
			hashp->hctl->max_bucket, hashp->hctl->nsegs);
	fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
			where, hash_accesses, hash_collisions);
	fprintf(stderr, "hash_stats: total expansions %ld\n",
			hash_expansions);
#endif
}

/*******************************SEARCH ROUTINES *****************************/


/* Convert a hash value to a bucket number */
static inline uint32
calc_bucket(HASHHDR *hctl, uint32 hash_val)
{
	uint32		bucket;

	bucket = hash_val & hctl->high_mask;
	if (bucket > hctl->max_bucket)
		bucket = bucket & hctl->low_mask;

	return bucket;
}

/*----------
 * hash_search -- look up key in table and perform action
 *
 * action is one of:
 *		HASH_FIND: look up key in table
 *		HASH_ENTER: look up key in table, creating entry if not present
 *		HASH_REMOVE: look up key in table, remove entry if present
 *		HASH_FIND_SAVE: look up key in table, also save in static var
 *		HASH_REMOVE_SAVED: remove entry saved by HASH_FIND_SAVE
 *
 * Return value is a pointer to the element found/entered/removed if any,
 * or NULL if no match was found.  (NB: in the case of the REMOVE actions,
 * the result is a dangling pointer that shouldn't be dereferenced!)
 * A NULL result for HASH_ENTER implies we ran out of memory.
 *
 * If foundPtr isn't NULL, then *foundPtr is set TRUE if we found an
 * existing entry in the table, FALSE otherwise.  This is needed in the
 * HASH_ENTER case, but is redundant with the return value otherwise.
 *
 * The HASH_FIND_SAVE/HASH_REMOVE_SAVED interface is a hack to save one
 * table lookup in a find/process/remove scenario.	Note that no other
 * addition or removal in the table can safely happen in between.
 *----------
 */
void *
hash_search(HTAB *hashp,
			const void *keyPtr,
			HASHACTION action,
			bool *foundPtr)
{
	HASHHDR    *hctl = hashp->hctl;
	uint32		hashvalue = 0;
	uint32		bucket;
	long		segment_num;
	long		segment_ndx;
	HASHSEGMENT segp;
	HASHBUCKET	currBucket;
	HASHBUCKET *prevBucketPtr;

	static struct State
	{
		HASHBUCKET	currBucket;
		HASHBUCKET *prevBucketPtr;
	}			saveState;

#if HASH_STATISTICS
	hash_accesses++;
	hctl->accesses++;
#endif

	/*
	 * Do the initial lookup (or recall result of prior lookup)
	 */
	if (action == HASH_REMOVE_SAVED)
	{
		currBucket = saveState.currBucket;
		prevBucketPtr = saveState.prevBucketPtr;

		/*
		 * Try to catch subsequent errors
		 */
		Assert(currBucket);
		saveState.currBucket = NULL;
	}
	else
	{
		HashCompareFunc match;
		Size		keysize = hctl->keysize;

		hashvalue = hashp->hash(keyPtr, keysize);
		bucket = calc_bucket(hctl, hashvalue);

		segment_num = bucket >> hctl->sshift;
		segment_ndx = MOD(bucket, hctl->ssize);

		segp = hashp->dir[segment_num];

		if (segp == NULL)
			hash_corrupted(hashp);

		prevBucketPtr = &segp[segment_ndx];
		currBucket = *prevBucketPtr;

		/*
		 * Follow collision chain looking for matching key
		 */
		match = hashp->match;	/* save one fetch in inner loop */
		while (currBucket != NULL)
		{
			if (currBucket->hashvalue == hashvalue &&
				match(ELEMENTKEY(currBucket), keyPtr, keysize) == 0)
				break;
			prevBucketPtr = &(currBucket->link);
			currBucket = *prevBucketPtr;
#if HASH_STATISTICS
			hash_collisions++;
			hctl->collisions++;
#endif
		}
	}

	if (foundPtr)
		*foundPtr = (bool) (currBucket != NULL);

	/*
	 * OK, now what?
	 */
	switch (action)
	{
		case HASH_FIND:
			if (currBucket != NULL)
				return (void *) ELEMENTKEY(currBucket);
			return NULL;

		case HASH_FIND_SAVE:
			if (currBucket != NULL)
			{
				saveState.currBucket = currBucket;
				saveState.prevBucketPtr = prevBucketPtr;
				return (void *) ELEMENTKEY(currBucket);
			}
			return NULL;

		case HASH_REMOVE:
		case HASH_REMOVE_SAVED:
			if (currBucket != NULL)
			{
				Assert(hctl->nentries > 0);
				hctl->nentries--;

				/* remove record from hash bucket's chain. */
				*prevBucketPtr = currBucket->link;

				/* add the record to the freelist for this table.  */
				currBucket->link = hctl->freeList;
				hctl->freeList = currBucket;

				/*
				 * better hope the caller is synchronizing access to this
				 * element, because someone else is going to reuse it the
				 * next time something is added to the table
				 */
				return (void *) ELEMENTKEY(currBucket);
			}
			return NULL;

		case HASH_ENTER:
			/* Return existing element if found, else create one */
			if (currBucket != NULL)
				return (void *) ELEMENTKEY(currBucket);

			/* disallow inserts if frozen */
			if (hashp->frozen)
				elog(ERROR, "cannot insert into a frozen hashtable");

			/* get the next free element */
			currBucket = hctl->freeList;
			if (currBucket == NULL)
			{
				/* no free elements.  allocate another chunk of buckets */
				if (!element_alloc(hashp))
					return NULL;	/* out of memory */
				currBucket = hctl->freeList;
				Assert(currBucket != NULL);
			}

			hctl->freeList = currBucket->link;

			/* link into hashbucket chain */
			*prevBucketPtr = currBucket;
			currBucket->link = NULL;

			/* copy key into record */
			currBucket->hashvalue = hashvalue;
			hashp->keycopy(ELEMENTKEY(currBucket), keyPtr, hctl->keysize);

			/* caller is expected to fill the data field on return */

			/*
			 * Check if it is time to split a bucket.  Can't split if table
			 * is the subject of any active hash_seq_search scans.
			 */
			if (++hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
				!has_seq_scans(hashp))
			{
				/*
				 * NOTE: failure to expand table is not a fatal error, it
				 * just means we have to run at higher fill factor than we
				 * wanted.
				 */
				expand_table(hashp);
			}

			return (void *) ELEMENTKEY(currBucket);
	}

	elog(ERROR, "unrecognized hash action code: %d", (int) action);

	return NULL;				/* keep compiler quiet */
}

/*
 * hash_seq_init/_search/_term
 *			Sequentially search through hash table and return
 *			all the elements one by one, return NULL when no more.
 *
 * hash_seq_term should be called if and only if the scan is abandoned before
 * completion; if hash_seq_search returns NULL then it has already done the
 * end-of-scan cleanup.
 *
 * NOTE: caller may delete the returned element before continuing the scan.
 * However, deleting any other element while the scan is in progress is
 * UNDEFINED (it might be the one that curIndex is pointing at!).  Also,
 * if elements are added to the table while the scan is in progress, it is
 * unspecified whether they will be visited by the scan or not.
 *
 * NOTE: it is possible to use hash_seq_init/hash_seq_search without any
 * worry about hash_seq_term cleanup, if the hashtable is first locked against
 * further insertions by calling hash_freeze.  This is used by nodeAgg.c,
 * wherein it is inconvenient to track whether a scan is still open, and
 * there's no possibility of further insertions after readout has begun.
 */
void
hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
{
	status->hashp = hashp;
	status->curBucket = 0;
	status->curEntry = NULL;
	if (!hashp->frozen)
		register_seq_scan(hashp);
}

void *
hash_seq_search(HASH_SEQ_STATUS *status)
{
	HTAB	   *hashp = status->hashp;
	HASHHDR    *hctl = hashp->hctl;

	while (status->curBucket <= hctl->max_bucket)
	{
		long		segment_num;
		long		segment_ndx;
		HASHSEGMENT segp;

		if (status->curEntry != NULL)
		{
			/* Continuing scan of curBucket... */
			HASHELEMENT *curElem;

			curElem = status->curEntry;
			status->curEntry = curElem->link;
			if (status->curEntry == NULL)		/* end of this bucket */
				++status->curBucket;
			return (void *) ELEMENTKEY(curElem);
		}

		/*
		 * initialize the search within this bucket.
		 */
		segment_num = status->curBucket >> hctl->sshift;
		segment_ndx = MOD(status->curBucket, hctl->ssize);

		/*
		 * first find the right segment in the table directory.
		 */
		segp = hashp->dir[segment_num];
		if (segp == NULL)
			hash_corrupted(hashp);

		/*
		 * now find the right index into the segment for the first item in
		 * this bucket's chain.  if the bucket is not empty (its entry in
		 * the dir is valid), we know this must correspond to a valid
		 * element and not a freed element because it came out of the
		 * directory of valid stuff.  if there are elements in the bucket
		 * chains that point to the freelist we're in big trouble.
		 */
		status->curEntry = segp[segment_ndx];

		if (status->curEntry == NULL)	/* empty bucket */
			++status->curBucket;
	}

	hash_seq_term(status);
	return NULL;				/* out of buckets */
}

void
hash_seq_term(HASH_SEQ_STATUS *status)
{
	if (!status->hashp->frozen)
		deregister_seq_scan(status->hashp);
}

/*
 * hash_freeze
 *			Freeze a hashtable against future insertions (deletions are
 *			still allowed)
 *
 * The reason for doing this is that by preventing any more bucket splits,
 * we no longer need to worry about registering hash_seq_search scans,
 * and thus caller need not be careful about ensuring hash_seq_term gets
 * called at the right times.
 *
 * Multiple calls to hash_freeze() are allowed, but you can't freeze a table
 * with active scans (since hash_seq_term would then do the wrong thing).
 */
void
hash_freeze(HTAB *hashp)
{
	if (hashp->isshared)
		elog(ERROR, "cannot freeze shared hashtable");
	if (!hashp->frozen && has_seq_scans(hashp))
		elog(ERROR, "cannot freeze hashtable with active scans");
	hashp->frozen = true;
}


/********************************* UTILITIES ************************/

/*
 * Expand the table by adding one more hash bucket.
 */
static bool
expand_table(HTAB *hashp)
{
	HASHHDR    *hctl = hashp->hctl;
	HASHSEGMENT old_seg,
				new_seg;
	long		old_bucket,
				new_bucket;
	long		new_segnum,
				new_segndx;
	long		old_segnum,
				old_segndx;
	HASHBUCKET *oldlink,
			   *newlink;
	HASHBUCKET	currElement,
				nextElement;

#ifdef HASH_STATISTICS
	hash_expansions++;
#endif

	new_bucket = hctl->max_bucket + 1;
	new_segnum = new_bucket >> hctl->sshift;
	new_segndx = MOD(new_bucket, hctl->ssize);

	if (new_segnum >= hctl->nsegs)
	{
		/* Allocate new segment if necessary -- could fail if dir full */
		if (new_segnum >= hctl->dsize)
			if (!dir_realloc(hashp))
				return false;
		if (!(hashp->dir[new_segnum] = seg_alloc(hashp)))
			return false;
		hctl->nsegs++;
	}

	/* OK, we created a new bucket */
	hctl->max_bucket++;

	/*
	 * *Before* changing masks, find old bucket corresponding to same hash
	 * values; values in that bucket may need to be relocated to new
	 * bucket. Note that new_bucket is certainly larger than low_mask at
	 * this point, so we can skip the first step of the regular hash mask
	 * calc.
	 */
	old_bucket = (new_bucket & hctl->low_mask);

	/*
	 * If we crossed a power of 2, readjust masks.
	 */
	if ((uint32) new_bucket > hctl->high_mask)
	{
		hctl->low_mask = hctl->high_mask;
		hctl->high_mask = (uint32) new_bucket | hctl->low_mask;
	}

	/*
	 * Relocate records to the new bucket.	NOTE: because of the way the
	 * hash masking is done in calc_bucket, only one old bucket can need to
	 * be split at this point.	With a different way of reducing the hash
	 * value, that might not be true!
	 */
	old_segnum = old_bucket >> hctl->sshift;
	old_segndx = MOD(old_bucket, hctl->ssize);

	old_seg = hashp->dir[old_segnum];
	new_seg = hashp->dir[new_segnum];

	oldlink = &old_seg[old_segndx];
	newlink = &new_seg[new_segndx];

	for (currElement = *oldlink;
		 currElement != NULL;
		 currElement = nextElement)
	{
		nextElement = currElement->link;
		if ((long) calc_bucket(hctl, currElement->hashvalue) == old_bucket)
		{
			*oldlink = currElement;
			oldlink = &currElement->link;
		}
		else
		{
			*newlink = currElement;
			newlink = &currElement->link;
		}
	}
	/* don't forget to terminate the rebuilt hash chains... */
	*oldlink = NULL;
	*newlink = NULL;

	return true;
}


static bool
dir_realloc(HTAB *hashp)
{
	HASHSEGMENT *p;
	HASHSEGMENT *old_p;
	long		new_dsize;
	long		old_dirsize;
	long		new_dirsize;

	if (hashp->hctl->max_dsize != NO_MAX_DSIZE)
		return false;

	/* Reallocate directory */
	new_dsize = hashp->hctl->dsize << 1;
	old_dirsize = hashp->hctl->dsize * sizeof(HASHSEGMENT);
	new_dirsize = new_dsize * sizeof(HASHSEGMENT);

	old_p = hashp->dir;
	CurrentDynaHashCxt = hashp->hcxt;
	p = (HASHSEGMENT *) hashp->alloc((Size) new_dirsize);

	if (p != NULL)
	{
		memcpy(p, old_p, old_dirsize);
		MemSet(((char *) p) + old_dirsize, 0, new_dirsize - old_dirsize);
		MEM_FREE((char *) old_p);
		hashp->dir = p;
		hashp->hctl->dsize = new_dsize;
		return true;
	}

	return false;
}


static HASHSEGMENT
seg_alloc(HTAB *hashp)
{
	HASHSEGMENT segp;

	CurrentDynaHashCxt = hashp->hcxt;
	segp = (HASHSEGMENT) hashp->alloc(sizeof(HASHBUCKET) * hashp->hctl->ssize);

	if (!segp)
		return NULL;

	MemSet(segp, 0, sizeof(HASHBUCKET) * hashp->hctl->ssize);

	return segp;
}

/*
 * allocate some new elements and link them into the free list
 */
static bool
element_alloc(HTAB *hashp)
{
	HASHHDR    *hctl = hashp->hctl;
	Size		elementSize;
	HASHELEMENT *tmpElement;
	int			i;

	/* Each element has a HASHELEMENT header plus user data. */
	elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctl->entrysize);

	CurrentDynaHashCxt = hashp->hcxt;
	tmpElement = (HASHELEMENT *)
		hashp->alloc(HASHELEMENT_ALLOC_INCR * elementSize);

	if (!tmpElement)
		return false;

	/* link all the new entries into the freelist */
	for (i = 0; i < HASHELEMENT_ALLOC_INCR; i++)
	{
		tmpElement->link = hctl->freeList;
		hctl->freeList = tmpElement;
		tmpElement = (HASHELEMENT *) (((char *) tmpElement) + elementSize);
	}

	return true;
}

/* complain when we have detected a corrupted hashtable */
static void
hash_corrupted(HTAB *hashp)
{
	/*
	 * If the corruption is in a shared hashtable, we'd better force a
	 * systemwide restart.	Otherwise, just shut down this one backend.
	 */
	if (hashp->isshared)
		elog(PANIC, "hash table \"%s\" corrupted", hashp->tabname);
	else
		elog(FATAL, "hash table \"%s\" corrupted", hashp->tabname);
}

/* calculate ceil(log base 2) of num */
int
my_log2(long num)
{
	int			i;
	long		limit;

	for (i = 0, limit = 1; limit < num; i++, limit <<= 1)
		;
	return i;
}


/************************* SEQ SCAN TRACKING ************************/

/*
 * We track active hash_seq_search scans here.  The need for this mechanism
 * comes from the fact that a scan will get confused if a bucket split occurs
 * while it's in progress: it might visit entries twice, or even miss some
 * entirely (if it's partway through the same bucket that splits).  Hence
 * we want to inhibit bucket splits if there are any active scans on the
 * table being inserted into.  This is a fairly rare case in current usage,
 * so just postponing the split until the next insertion seems sufficient.
 *
 * Given present usages of the function, only a few scans are likely to be
 * open concurrently; so a finite-size stack of open scans seems sufficient,
 * and we don't worry that linear search is too slow.  Note that we do
 * allow multiple scans of the same hashtable to be open concurrently.
 *
 * This mechanism can support concurrent scan and insertion in a shared
 * hashtable if it's the same backend doing both.  It would fail otherwise,
 * but locking reasons seem to preclude any such scenario anyway, so we don't
 * worry.
 *
 * This arrangement is reasonably robust if a transient hashtable is deleted
 * without notifying us.  The absolute worst case is we might inhibit splits
 * in another table created later at exactly the same address.  We will give
 * a warning at transaction end for reference leaks, so any bugs leading to
 * lack of notification should be easy to catch.
 */

#define MAX_SEQ_SCANS 100

static HTAB *seq_scan_tables[MAX_SEQ_SCANS];	/* tables being scanned */
static int	num_seq_scans = 0;


/* Register a table as having an active hash_seq_search scan */
static void
register_seq_scan(HTAB *hashp)
{
	if (num_seq_scans >= MAX_SEQ_SCANS)
		elog(ERROR, "too many active hash_seq_search scans");
	seq_scan_tables[num_seq_scans] = hashp;
	num_seq_scans++;
}

/* Deregister an active scan */
static void
deregister_seq_scan(HTAB *hashp)
{
	int		i;

	/* Search backward since it's most likely at the stack top */
	for (i = num_seq_scans - 1; i >= 0; i--)
	{
		if (seq_scan_tables[i] == hashp)
		{
			seq_scan_tables[i] = seq_scan_tables[num_seq_scans - 1];
			num_seq_scans--;
			return;
		}
	}
	elog(ERROR, "no hash_seq_search scan for hash table \"%s\"",
		 hashp->tabname);
}

/* Check if a table has any active scan */
static bool
has_seq_scans(HTAB *hashp)
{
	int		i;

	for (i = 0; i < num_seq_scans; i++)
	{
		if (seq_scan_tables[i] == hashp)
			return true;
	}
	return false;
}

/* Clean up any open scans at end of transaction */
void
AtEOXact_HashTables(bool isCommit)
{
	/*
	 * During abort cleanup, open scans are expected; just silently clean 'em
	 * out.  An open scan at commit means someone forgot a hash_seq_term()
	 * call, so complain.
	 *
	 * Note: it's tempting to try to print the tabname here, but refrain for
	 * fear of touching deallocated memory.  This isn't a user-facing message
	 * anyway, so it needn't be pretty.
	 */
	if (isCommit)
	{
		int		i;

		for (i = 0; i < num_seq_scans; i++)
		{
			elog(WARNING, "leaked hash_seq_search scan for hash table %p",
				 seq_scan_tables[i]);
		}
	}
	num_seq_scans = 0;
}
