342 lines
8.6 KiB
C
342 lines
8.6 KiB
C
/*-
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* See the file LICENSE for redistribution information.
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*
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* Copyright (c) 1996, 1997
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* Sleepycat Software. All rights reserved.
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*/
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#include "config.h"
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#ifndef lint
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static const char sccsid[] = "@(#)mp_fget.c 10.33 (Sleepycat) 12/2/97";
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#endif /* not lint */
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#ifndef NO_SYSTEM_INCLUDES
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <errno.h>
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#include <stdlib.h>
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#include <string.h>
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#endif
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#include "db_int.h"
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#include "shqueue.h"
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#include "db_shash.h"
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#include "mp.h"
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#include "common_ext.h"
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int __sleep_on_every_page_get; /* XXX: thread debugging option. */
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/*
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* memp_fget --
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* Get a page from the file.
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*/
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int
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memp_fget(dbmfp, pgnoaddr, flags, addrp)
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DB_MPOOLFILE *dbmfp;
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db_pgno_t *pgnoaddr;
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int flags;
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void *addrp;
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{
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BH *bhp;
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DB_MPOOL *dbmp;
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MPOOL *mp;
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MPOOLFILE *mfp;
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size_t bucket, mf_offset;
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u_long cnt;
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int b_incr, b_inserted, readonly_alloc, ret;
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void *addr;
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dbmp = dbmfp->dbmp;
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/*
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* Validate arguments.
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*
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* !!!
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* Don't test for DB_MPOOL_CREATE and DB_MPOOL_NEW flags for readonly
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* files here, and create non-existent pages in readonly files if the
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* flags are set, later. The reason is that the hash access method
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* wants to get empty pages that don't really exist in readonly files.
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* The only alternative is for hash to write the last "bucket" all the
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* time, which we don't want to do because one of our big goals in life
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* is to keep database files small. It's sleazy as hell, but we catch
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* any attempt to actually write the file in memp_fput().
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*/
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#define OKFLAGS (DB_MPOOL_CREATE | DB_MPOOL_LAST | DB_MPOOL_NEW)
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if (flags != 0) {
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if ((ret =
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__db_fchk(dbmp->dbenv, "memp_fget", flags, OKFLAGS)) != 0)
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return (ret);
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switch (flags) {
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case DB_MPOOL_CREATE:
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case DB_MPOOL_LAST:
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case DB_MPOOL_NEW:
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case 0:
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break;
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default:
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return (__db_ferr(dbmp->dbenv, "memp_fget", 1));
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}
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}
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#ifdef DEBUG
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/*
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* XXX
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* We want to switch threads as often as possible. Sleep every time
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* we get a new page to make it more likely.
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*/
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if (__sleep_on_every_page_get &&
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(__db_yield == NULL || __db_yield() != 0))
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__db_sleep(0, 1);
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#endif
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mp = dbmp->mp;
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mfp = dbmfp->mfp;
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mf_offset = R_OFFSET(dbmp, mfp);
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addr = NULL;
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bhp = NULL;
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b_incr = b_inserted = ret = 0;
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LOCKREGION(dbmp);
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/*
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* If mmap'ing the file, just return a pointer. However, if another
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* process has opened the file for writing since we mmap'd it, start
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* playing the game by their rules, i.e. everything goes through the
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* cache. All pages previously returned should be safe, as long as
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* a locking protocol was observed.
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*
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* XXX
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* We don't discard the map because we don't know when all of the
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* pages will have been discarded from the process' address space.
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* It would be possible to do so by reference counting the open
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* pages from the mmap, but it's unclear to me that it's worth it.
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*/
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if (dbmfp->addr != NULL && F_ISSET(dbmfp->mfp, MP_CAN_MMAP)) {
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readonly_alloc = 0;
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if (LF_ISSET(DB_MPOOL_LAST))
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*pgnoaddr = mfp->last_pgno;
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else {
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/*
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* !!!
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* Allocate a page that can never really exist. See
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* the comment above about non-existent pages and the
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* hash access method.
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*/
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if (LF_ISSET(DB_MPOOL_CREATE | DB_MPOOL_NEW))
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readonly_alloc = 1;
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else if (*pgnoaddr > mfp->last_pgno) {
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__db_err(dbmp->dbenv,
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"%s: page %lu doesn't exist",
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__memp_fn(dbmfp), (u_long)*pgnoaddr);
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ret = EINVAL;
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goto err;
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}
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}
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if (!readonly_alloc) {
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addr = R_ADDR(dbmfp, *pgnoaddr * mfp->stat.st_pagesize);
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++mp->stat.st_map;
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++mfp->stat.st_map;
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goto mapret;
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}
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}
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/* Check if requesting the last page or a new page. */
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if (LF_ISSET(DB_MPOOL_LAST))
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*pgnoaddr = mfp->last_pgno;
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if (LF_ISSET(DB_MPOOL_NEW)) {
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*pgnoaddr = mfp->last_pgno + 1;
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goto alloc;
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}
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/* Check the BH hash bucket queue. */
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bucket = BUCKET(mp, mf_offset, *pgnoaddr);
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for (cnt = 0,
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bhp = SH_TAILQ_FIRST(&dbmp->htab[bucket], __bh);
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bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, hq, __bh)) {
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++cnt;
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if (bhp->pgno == *pgnoaddr && bhp->mf_offset == mf_offset) {
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addr = bhp->buf;
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++mp->stat.st_hash_searches;
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if (cnt > mp->stat.st_hash_longest)
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mp->stat.st_hash_longest = cnt;
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mp->stat.st_hash_examined += cnt;
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goto found;
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}
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}
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if (cnt != 0) {
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++mp->stat.st_hash_searches;
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if (cnt > mp->stat.st_hash_longest)
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mp->stat.st_hash_longest = cnt;
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mp->stat.st_hash_examined += cnt;
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}
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alloc: /*
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* Allocate a new buffer header and data space, and mark the contents
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* as useless.
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*/
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if ((ret = __memp_ralloc(dbmp, sizeof(BH) -
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sizeof(u_int8_t) + mfp->stat.st_pagesize, NULL, &bhp)) != 0)
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goto err;
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addr = bhp->buf;
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#ifdef DEBUG
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if ((ALIGNTYPE)addr & (sizeof(size_t) - 1)) {
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__db_err(dbmp->dbenv,
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"Internal error: BH data NOT size_t aligned.");
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abort();
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}
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#endif
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memset(bhp, 0, sizeof(BH));
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LOCKINIT(dbmp, &bhp->mutex);
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/*
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* Prepend the bucket header to the head of the appropriate MPOOL
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* bucket hash list. Append the bucket header to the tail of the
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* MPOOL LRU chain.
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*
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* We have to do this before we read in the page so we can discard
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* our region lock without screwing up the world.
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*/
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bucket = BUCKET(mp, mf_offset, *pgnoaddr);
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SH_TAILQ_INSERT_HEAD(&dbmp->htab[bucket], bhp, hq, __bh);
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SH_TAILQ_INSERT_TAIL(&mp->bhq, bhp, q);
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++mp->stat.st_page_clean;
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b_inserted = 1;
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/* Set the page number, and associated MPOOLFILE. */
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bhp->mf_offset = mf_offset;
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bhp->pgno = *pgnoaddr;
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/*
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* If we know we created the page, zero it out and continue.
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*
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* !!!
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* Note: DB_MPOOL_NEW deliberately doesn't call the pgin function.
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* If DB_MPOOL_CREATE is used, then the application's pgin function
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* has to be able to handle pages of 0's -- if it uses DB_MPOOL_NEW,
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* it can detect all of its page creates, and not bother.
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*
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* Otherwise, read the page into memory, optionally creating it if
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* DB_MPOOL_CREATE is set.
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*
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* Increment the reference count for created buffers, but importantly,
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* increment the reference count for buffers we're about to read so
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* that the buffer can't move.
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*/
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++bhp->ref;
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b_incr = 1;
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if (LF_ISSET(DB_MPOOL_NEW))
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memset(addr, 0, mfp->stat.st_pagesize);
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else {
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/*
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* It's possible for the read function to fail, which means
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* that we fail as well.
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*/
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reread: if ((ret = __memp_pgread(dbmfp,
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bhp, LF_ISSET(DB_MPOOL_CREATE | DB_MPOOL_NEW))) != 0)
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goto err;
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/*
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* !!!
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* The __memp_pgread call discarded and reacquired the region
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* lock. Because the buffer reference count was incremented
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* before the region lock was discarded the buffer can't move
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* and its contents can't change.
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*/
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++mp->stat.st_cache_miss;
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++mfp->stat.st_cache_miss;
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}
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if (0) {
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found: /* Increment the reference count. */
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if (bhp->ref == UINT16_T_MAX) {
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__db_err(dbmp->dbenv,
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"%s: too many references to page %lu",
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__memp_fn(dbmfp), bhp->pgno);
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ret = EINVAL;
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goto err;
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}
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++bhp->ref;
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b_incr = 1;
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/*
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* Any found buffer might be trouble.
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*
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* BH_LOCKED --
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* I/O in progress, wait for it to finish. Because the buffer
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* reference count was incremented before the region lock was
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* discarded we know the buffer can't move and its contents
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* can't change.
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*/
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for (cnt = 0; F_ISSET(bhp, BH_LOCKED); ++cnt) {
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UNLOCKREGION(dbmp);
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/*
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* Sleep so that we don't simply spin, switching locks.
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* (See the comment in include/mp.h.)
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*/
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if (cnt != 0 &&
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(__db_yield == NULL || __db_yield() != 0))
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__db_sleep(0, 1);
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LOCKBUFFER(dbmp, bhp);
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/* Waiting for I/O to finish... */
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UNLOCKBUFFER(dbmp, bhp);
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LOCKREGION(dbmp);
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}
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/*
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* BH_TRASH --
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* The buffer is garbage.
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*/
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if (F_ISSET(bhp, BH_TRASH))
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goto reread;
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/*
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* BH_CALLPGIN --
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* The buffer was written, and the contents need to be
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* converted again.
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*/
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if (F_ISSET(bhp, BH_CALLPGIN)) {
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if ((ret = __memp_pg(dbmfp, bhp, 1)) != 0)
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goto err;
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F_CLR(bhp, BH_CALLPGIN);
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}
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++mp->stat.st_cache_hit;
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++mfp->stat.st_cache_hit;
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}
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/*
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* If we're returning a page after our current notion of the last-page,
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* update our information. Note, there's no way to un-instantiate this
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* page, it's going to exist whether it's returned to us dirty or not.
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*/
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if (bhp->pgno > mfp->last_pgno)
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mfp->last_pgno = bhp->pgno;
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mapret: LOCKHANDLE(dbmp, dbmfp->mutexp);
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++dbmfp->pinref;
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UNLOCKHANDLE(dbmp, dbmfp->mutexp);
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if (0) {
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err: /*
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* If no other process is already waiting on a created buffer,
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* go ahead and discard it, it's not useful.
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*/
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if (b_incr)
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--bhp->ref;
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if (b_inserted && bhp->ref == 0)
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__memp_bhfree(dbmp, mfp, bhp, 1);
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}
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UNLOCKREGION(dbmp);
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*(void **)addrp = addr;
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return (ret);
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}
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