fis-gtm/sr_port/db_csh_get.c

/****************************************************************
 *								*
 *	Copyright 2001, 2011 Fidelity Information Services, Inc	*
 *								*
 *	This source code contains the intellectual property	*
 *	of its copyright holder(s), and is made available	*
 *	under a license.  If you do not know the terms of	*
 *	the license, please stop and do not read further.	*
 *								*
 ****************************************************************/

#include "mdef.h"
#include "gdsroot.h"
#include "gtm_facility.h"
#include "fileinfo.h"
#include "gdsbt.h"
#include "gdsfhead.h"
#include "gdsbgtr.h"
#include "cache.h"
#include "hashtab.h"		/* needed for cws_insert.h */
#include "hashtab_int4.h"	/* needed for cws_insert.h */
#include "longset.h"		/* needed for cws_insert.h */
#include "cws_insert.h"

GBLREF sgmnt_addrs	*cs_addrs;
GBLREF unsigned int	t_tries;
GBLREF boolean_t        mu_reorg_process;

#define ENOUGH_TRIES_TO_FALL_BACK 17

/* This function returns a pointer to the cache_rec entry, NULL if not found, or CR_INVALID if the hash table is corrupt */

cache_rec_ptr_t	db_csh_get(block_id block) /* block number to look up */
{
	register sgmnt_addrs		*csa;
	sgmnt_data_ptr_t		csd;
	cache_rec_ptr_t			cr, cr_hash_base;
	int				blk_hash, lcnt, ocnt, hmax;
	bool				is_mm;
#	ifdef DEBUG
	cache_rec_ptr_t			cr_low, cr_high;
#	endif

	csa = cs_addrs;
	csd = csa->hdr;
	is_mm = (dba_mm == csd->acc_meth);
	assert((FALSE == is_mm) || (csa->now_crit));	/* if MM you should be in crit */
	VMS_ONLY(assert(FALSE == is_mm);)	/* in VMS, MM should never call db_csh_get */
	hmax = csd->bt_buckets;
	blk_hash = (block % hmax);
	if (!is_mm)
	{
		DEBUG_ONLY(cr_low = &csa->acc_meth.bg.cache_state->cache_array[0];)
		DEBUG_ONLY(cr_high = cr_low + csd->bt_buckets + csd->n_bts;)
		cr_hash_base = csa->acc_meth.bg.cache_state->cache_array + blk_hash;
	} else
	{
		DEBUG_ONLY(cr_low = (cache_rec_ptr_t)(csa->acc_meth.mm.mmblk_state->mmblk_array);)
		DEBUG_ONLY(cr_high = (cache_rec_ptr_t)(csa->acc_meth.mm.mmblk_state->mmblk_array + csd->bt_buckets + csd->n_bts);)
		cr_hash_base = (cache_rec_ptr_t)(csa->acc_meth.mm.mmblk_state->mmblk_array + blk_hash);
	}
	ocnt = 0;
	do
	{
		cr = cr_hash_base;
		assert((0 == cr->blk) || (BT_QUEHEAD == cr->blk));
		lcnt = hmax;
		do
		{
			cr = (cache_rec_ptr_t)((sm_uc_ptr_t)cr + cr->blkque.fl);
			assert(!CR_NOT_ALIGNED(cr, cr_low) && !CR_NOT_IN_RANGE(cr, cr_low, cr_high)
				UNIX_ONLY(|| is_mm));
			if (BT_QUEHEAD == cr->blk)
			{	/* We have reached the end of the queue, validate we have run the queue
				 * back around to the same queue header or we'll need to retry because the
				 * queue changed on us.
				 */
				if (cr == cr_hash_base)
					return (cache_rec_ptr_t)NULL;
				break;			/* Retry - something changed */
			}
			if ((CR_BLKEMPTY != cr->blk) && ((cr->blk % hmax) != blk_hash))
				break;			/* Retry - something changed */
			assert(!csa->now_crit || (0 != cr->blkque.fl) && (0 != cr->blkque.bl));
			if (cr->blk == block)
			{
				if (!is_mm)
				{
					if (CDB_STAGNATE <= t_tries || mu_reorg_process)
						CWS_INSERT(block);
					/* setting refer outside of crit may not prevent its replacement, but that's an
					 * inefficiency, not a tragedy because of concurrency checks in t_end or tp_tend;
					 * the real problem is to ensure that the cache_rec layout is such that this
					 * assignment does not damage other fields.
					 */
					cr->refer = TRUE;
				}
				return cr;
			}
			lcnt--;
		} while (lcnt);
		ocnt++;
		/* We rarely expect to come here, hence it is considered better to recompute the maximum value of ocnt (for the
		 * termination check) instead of storing it in a local variable at the beginning of the do loop */
	} while (ocnt < (csa->now_crit ? 1 : ENOUGH_TRIES_TO_FALL_BACK));
	BG_TRACE_PRO_ANY(csa, db_csh_get_too_many_loops);
	return (TRUE == csa->now_crit ? (cache_rec_ptr_t)CR_NOTVALID : (cache_rec_ptr_t) NULL);
}