pager.c

sqlite 嵌入式数据库的源码

  if( pPager->noSync ) pPager->needSync = 0;
}
#endif

/*
** The following global variable is incremented whenever the library
** attempts to open a temporary file.  This information is used for
** testing and analysis only.  
*/
int sqlite3_opentemp_count = 0;

/*
** Open a temporary file.  Write the name of the file into zFile
** (zFile must be at least SQLITE_TEMPNAME_SIZE bytes long.)  Write
** the file descriptor into *fd.  Return SQLITE_OK on success or some
** other error code if we fail.
**
** The OS will automatically delete the temporary file when it is
** closed.
*/
static int sqlite3pager_opentemp(char *zFile, OsFile *fd){
  int cnt = 8;
  int rc;
  sqlite3_opentemp_count++;  /* Used for testing and analysis only */
  do{
    cnt--;
    sqlite3OsTempFileName(zFile);
    rc = sqlite3OsOpenExclusive(zFile, fd, 1);
  }while( cnt>0 && rc!=SQLITE_OK && rc!=SQLITE_NOMEM );
  return rc;
}

/*
** Create a new page cache and put a pointer to the page cache in *ppPager.
** The file to be cached need not exist.  The file is not locked until
** the first call to sqlite3pager_get() and is only held open until the
** last page is released using sqlite3pager_unref().
**
** If zFilename is NULL then a randomly-named temporary file is created
** and used as the file to be cached.  The file will be deleted
** automatically when it is closed.
**
** If zFilename is ":memory:" then all information is held in cache.
** It is never written to disk.  This can be used to implement an
** in-memory database.
*/
int sqlite3pager_open(
  Pager **ppPager,         /* Return the Pager structure here */
  const char *zFilename,   /* Name of the database file to open */
  int nExtra,              /* Extra bytes append to each in-memory page */
  int flags                /* flags controlling this file */
){
  Pager *pPager;
  char *zFullPathname = 0;
  int nameLen;
  OsFile fd;
  int rc = SQLITE_OK;
  int i;
  int tempFile = 0;
  int memDb = 0;
  int readOnly = 0;
  int useJournal = (flags & PAGER_OMIT_JOURNAL)==0;
  int noReadlock = (flags & PAGER_NO_READLOCK)!=0;
  char zTemp[SQLITE_TEMPNAME_SIZE];

  *ppPager = 0;
  memset(&fd, 0, sizeof(fd));
  if( sqlite3_malloc_failed ){
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){
#ifndef SQLITE_OMIT_MEMORYDB
    if( strcmp(zFilename,":memory:")==0 ){
      memDb = 1;
      zFullPathname = sqliteStrDup("");
      rc = SQLITE_OK;
    }else
#endif
    {
      zFullPathname = sqlite3OsFullPathname(zFilename);
      if( zFullPathname ){
        rc = sqlite3OsOpenReadWrite(zFullPathname, &fd, &readOnly);
      }
    }
  }else{
    rc = sqlite3pager_opentemp(zTemp, &fd);
    zFilename = zTemp;
    zFullPathname = sqlite3OsFullPathname(zFilename);
    if( rc==SQLITE_OK ){
      tempFile = 1;
    }
  }
  if( !zFullPathname ){
    sqlite3OsClose(&fd);
    return SQLITE_NOMEM;
  }
  if( rc!=SQLITE_OK ){
    sqlite3OsClose(&fd);
    sqliteFree(zFullPathname);
    return rc;
  }
  nameLen = strlen(zFullPathname);
  pPager = sqliteMalloc( sizeof(*pPager) + nameLen*3 + 30 );
  if( pPager==0 ){
    sqlite3OsClose(&fd);
    sqliteFree(zFullPathname);
    return SQLITE_NOMEM;
  }
  TRACE3("OPEN %d %s\n", FILEHANDLEID(fd), zFullPathname);
  pPager->zFilename = (char*)&pPager[1];
  pPager->zDirectory = &pPager->zFilename[nameLen+1];
  pPager->zJournal = &pPager->zDirectory[nameLen+1];
  strcpy(pPager->zFilename, zFullPathname);
  strcpy(pPager->zDirectory, zFullPathname);
  for(i=nameLen; i>0 && pPager->zDirectory[i-1]!='/'; i--){}
  if( i>0 ) pPager->zDirectory[i-1] = 0;
  strcpy(pPager->zJournal, zFullPathname);
  sqliteFree(zFullPathname);
  strcpy(&pPager->zJournal[nameLen], "-journal");
  pPager->fd = fd;
#if OS_UNIX
  pPager->fd.pPager = pPager;
#endif
  pPager->journalOpen = 0;
  pPager->useJournal = useJournal && !memDb;
  pPager->noReadlock = noReadlock && readOnly;
  pPager->stmtOpen = 0;
  pPager->stmtInUse = 0;
  pPager->nRef = 0;
  pPager->dbSize = memDb-1;
  pPager->pageSize = SQLITE_DEFAULT_PAGE_SIZE;
  pPager->stmtSize = 0;
  pPager->stmtJSize = 0;
  pPager->nPage = 0;
  pPager->nMaxPage = 0;
  pPager->mxPage = 100;
  pPager->state = PAGER_UNLOCK;
  pPager->errMask = 0;
  pPager->tempFile = tempFile;
  pPager->memDb = memDb;
  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->fullSync = (pPager->noSync?0:1);
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->nExtra = FORCE_ALIGNMENT(nExtra);
  pPager->sectorSize = PAGER_SECTOR_SIZE;
  pPager->pBusyHandler = 0;
  memset(pPager->aHash, 0, sizeof(pPager->aHash));
  *ppPager = pPager;
  return SQLITE_OK;
}

/*
** Set the busy handler function.
*/
void sqlite3pager_set_busyhandler(Pager *pPager, BusyHandler *pBusyHandler){
  pPager->pBusyHandler = pBusyHandler;
}

/*
** Set the destructor for this pager.  If not NULL, the destructor is called
** when the reference count on each page reaches zero.  The destructor can
** be used to clean up information in the extra segment appended to each page.
**
** The destructor is not called as a result sqlite3pager_close().  
** Destructors are only called by sqlite3pager_unref().
*/
void sqlite3pager_set_destructor(Pager *pPager, void (*xDesc)(void*,int)){
  pPager->xDestructor = xDesc;
}

/*
** Set the reinitializer for this pager.  If not NULL, the reinitializer
** is called when the content of a page in cache is restored to its original
** value as a result of a rollback.  The callback gives higher-level code
** an opportunity to restore the EXTRA section to agree with the restored
** page data.
*/
void sqlite3pager_set_reiniter(Pager *pPager, void (*xReinit)(void*,int)){
  pPager->xReiniter = xReinit;
}

/*
** Set the page size.  Return the new size.  If the suggest new page
** size is inappropriate, then an alternative page size is selected
** and returned.
*/
int sqlite3pager_set_pagesize(Pager *pPager, int pageSize){
  assert( pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE );
  if( !pPager->memDb ){
    pPager->pageSize = pageSize;
  }
  return pPager->pageSize;
}

/*
** Read the first N bytes from the beginning of the file into memory
** that pDest points to.  No error checking is done.
*/
void sqlite3pager_read_fileheader(Pager *pPager, int N, unsigned char *pDest){
  memset(pDest, 0, N);
  if( MEMDB==0 ){
    sqlite3OsSeek(&pPager->fd, 0);
    sqlite3OsRead(&pPager->fd, pDest, N);
  }
}

/*
** Return the total number of pages in the disk file associated with
** pPager.
*/
int sqlite3pager_pagecount(Pager *pPager){
  i64 n;
  assert( pPager!=0 );
  if( pPager->dbSize>=0 ){
    return pPager->dbSize;
  }
  if( sqlite3OsFileSize(&pPager->fd, &n)!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_DISK;
    return 0;
  }
  n /= pPager->pageSize;
  if( !MEMDB && n==PENDING_BYTE/pPager->pageSize ){
    n++;
  }
  if( pPager->state!=PAGER_UNLOCK ){
    pPager->dbSize = n;
  }
  return n;
}

/*
** Forward declaration
*/
static int syncJournal(Pager*);


/*
** Unlink pPg from it's hash chain. Also set the page number to 0 to indicate
** that the page is not part of any hash chain. This is required because the
** sqlite3pager_movepage() routine can leave a page in the 
** pNextFree/pPrevFree list that is not a part of any hash-chain.
*/
static void unlinkHashChain(Pager *pPager, PgHdr *pPg){
  if( pPg->pgno==0 ){
    /* If the page number is zero, then this page is not in any hash chain. */
    return;
  }
  if( pPg->pNextHash ){
    pPg->pNextHash->pPrevHash = pPg->pPrevHash;
  }
  if( pPg->pPrevHash ){
    assert( pPager->aHash[pager_hash(pPg->pgno)]!=pPg );
    pPg->pPrevHash->pNextHash = pPg->pNextHash;
  }else{
    int h = pager_hash(pPg->pgno);
    assert( pPager->aHash[h]==pPg );
    pPager->aHash[h] = pPg->pNextHash;
  }

  pPg->pgno = 0;
  pPg->pNextHash = pPg->pPrevHash = 0;
}

/*
** Unlink a page from the free list (the list of all pages where nRef==0)
** and from its hash collision chain.
*/
static void unlinkPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager;

  /* Keep the pFirstSynced pointer pointing at the first synchronized page */
  if( pPg==pPager->pFirstSynced ){
    PgHdr *p = pPg->pNextFree;
    while( p && p->needSync ){ p = p->pNextFree; }
    pPager->pFirstSynced = p;
  }

  /* Unlink from the freelist */
  if( pPg->pPrevFree ){
    pPg->pPrevFree->pNextFree = pPg->pNextFree;
  }else{
    assert( pPager->pFirst==pPg );
    pPager->pFirst = pPg->pNextFree;
  }
  if( pPg->pNextFree ){
    pPg->pNextFree->pPrevFree = pPg->pPrevFree;
  }else{
    assert( pPager->pLast==pPg );
    pPager->pLast = pPg->pPrevFree;
  }
  pPg->pNextFree = pPg->pPrevFree = 0;

  /* Unlink from the pgno hash table */
  unlinkHashChain(pPager, pPg);
}

#ifndef SQLITE_OMIT_MEMORYDB
/*
** This routine is used to truncate an in-memory database.  Delete
** all pages whose pgno is larger than pPager->dbSize and is unreferenced.
** Referenced pages larger than pPager->dbSize are zeroed.
*/
static void memoryTruncate(Pager *pPager){
  PgHdr *pPg;
  PgHdr **ppPg;
  int dbSize = pPager->dbSize;

  ppPg = &pPager->pAll;
  while( (pPg = *ppPg)!=0 ){
    if( pPg->pgno<=dbSize ){
      ppPg = &pPg->pNextAll;
    }else if( pPg->nRef>0 ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
      ppPg = &pPg->pNextAll;
    }else{
      *ppPg = pPg->pNextAll;
      unlinkPage(pPg);
      sqliteFree(pPg);
      pPager->nPage--;
    }
  }
}
#else
#define memoryTruncate(p)
#endif

/*
** Try to obtain a lock on a file.  Invoke the busy callback if the lock
** is currently not available.  Repeate until the busy callback returns
** false or until the lock succeeds.
**
** Return SQLITE_OK on success and an error code if we cannot obtain
** the lock.
*/
static int pager_wait_on_lock(Pager *pPager, int locktype){
  int rc;
  assert( PAGER_SHARED==SHARED_LOCK );
  assert( PAGER_RESERVED==RESERVED_LOCK );
  assert( PAGER_EXCLUSIVE==EXCLUSIVE_LOCK );
  if( pPager->state>=locktype ){
    rc = SQLITE_OK;
  }else{
    int busy = 1;
    BusyHandler *pH;
    do {
      rc = sqlite3OsLock(&pPager->fd, locktype);
    }while( rc==SQLITE_BUSY && 
        (pH = pPager->pBusyHandler)!=0 && 
        pH->xFunc && pH->xFunc(pH->pArg, busy++)
    );
    if( rc==SQLITE_OK ){
      pPager->state = locktype;
    }
  }
  return rc;
}

/*
** Truncate the file to the number of pages specified.
*/
int sqlite3pager_truncate(Pager *pPager, Pgno nPage){
  int rc;
  sqlite3pager_pagecount(pPager);
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( MEMDB ){
    pPager->dbSize = nPage;
    memoryTruncate(pPager);
    return SQLITE_OK;
  }
  rc = syncJournal(pPager);
  if( rc!=SQLITE_OK ){