** This function is called after an CONCURRENT transaction is opened on the
** database. It allocates the BtreePtrmap structure used to track pointers
** to allocated pages and zeroes the nFree/iTrunk fields in the database 
** header on page 1.
*/
static int btreePtrmapAllocate(BtShared *pBt){
  int rc = SQLITE_OK;

  BtreePtrmap *pMap = sqlite3_malloc(sizeof(BtreePtrmap));
  assert( pBt->pMap==0 && sqlite3PagerIsConcurrent(pBt->pPager) );
  if( pMap==0 ){
    rc = SQLITE_NOMEM;
  }else{
    memset(&pBt->pPage1->aData[32], 0, sizeof(u32)*2);
    memset(pMap, 0, sizeof(BtreePtrmap));
    pMap->iFirst = pBt->nPage + 1;
    pBt->pMap = pMap;

  }
  return rc;
}

/*
** Free any BtreePtrmap structure allocated by an earlier call to
** btreePtrmapAllocate().
................................................................................
** when A already has a read lock, we encourage A to give up and let B
** proceed.
*/
int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
  sqlite3 *pBlock = 0;
  BtShared *pBt = p->pBt;
  int rc = SQLITE_OK;


  sqlite3BtreeEnter(p);
  btreeIntegrity(p);

  /* If the btree is already in a write-transaction, or it
  ** is already in a read-transaction and a read-transaction
  ** is requested, this is a no-op.
................................................................................
    */
    while( pBt->pPage1==0 && SQLITE_OK==(rc = lockBtree(pBt)) );

    if( rc==SQLITE_OK && wrflag ){
      if( (pBt->btsFlags & BTS_READ_ONLY)!=0 ){
        rc = SQLITE_READONLY;
      }else{
        int exFlag = (p->db->bConcurrent && !ISAUTOVACUUM) ? -1 : (wrflag>1);
        int bSubjInMem = sqlite3TempInMemory(p->db);
        assert( p->db->bConcurrent==0 || wrflag==1 );
        rc = sqlite3PagerBegin(pBt->pPager, exFlag, bSubjInMem);
        if( rc==SQLITE_OK ){
          rc = newDatabase(pBt);
        }
#ifdef SQLITE_ENABLE_CONCURRENT
        if( rc==SQLITE_OK && sqlite3PagerIsConcurrent(pBt->pPager) ){
          rc = btreePtrmapAllocate(pBt);
        }
#endif
      }
    }
  
    if( rc!=SQLITE_OK ){
      unlockBtreeIfUnused(pBt);
    }
  }while( (rc&0xFF)==SQLITE_BUSY && pBt->inTransaction==TRANS_NONE &&
................................................................................
        }
      }
    }
  }


trans_begun:









  if( rc==SQLITE_OK && wrflag ){
    /* This call makes sure that the pager has the correct number of
    ** open savepoints. If the second parameter is greater than 0 and
    ** the sub-journal is not already open, then it will be opened here.
    */
    int nSavepoint = p->db->nSavepoint;
    rc = sqlite3PagerOpenSavepoint(pBt->pPager, nSavepoint);
................................................................................
  ** or freed by this transaction. In this case no special handling is 
  ** required. Otherwise, if page 1 is dirty, proceed.  */
  BtreePtrmap *pMap = pBt->pMap;
  Pgno iTrunk = get4byte(&p1[32]);
  Pgno nPage = btreePagecount(pBt);
  u32 nFree = get4byte(&p1[36]);

  assert( sqlite3PagerIsConcurrent(pPager) );
  assert( pBt->pMap );
  rc = sqlite3PagerUpgradeSnapshot(pPager, pPage1->pDbPage);
  assert( p1==pPage1->aData );

  if( rc==SQLITE_OK ){
    Pgno nHPage = get4byte(&p1[28]);
    Pgno nFin = nHPage;         /* Size of db after transaction merge */
................................................................................

    /* Set the current transaction state to TRANS_NONE and unlock the 
    ** pager if this call closed the only read or write transaction.  */
    p->inTrans = TRANS_NONE;
    unlockBtreeIfUnused(pBt);
  }

  /* If this was an CONCURRENT transaction, delete the pBt->pMap object */


  btreePtrmapDelete(pBt);

  btreeIntegrity(p);
}

/*
** Commit the transaction currently in progress.
**
** This routine implements the second phase of a 2-phase commit.  The

** This function is called after an CONCURRENT transaction is opened on the
** database. It allocates the BtreePtrmap structure used to track pointers
** to allocated pages and zeroes the nFree/iTrunk fields in the database 
** header on page 1.
*/
static int btreePtrmapAllocate(BtShared *pBt){
  int rc = SQLITE_OK;
  if( pBt->pMap==0 ){
    BtreePtrmap *pMap = sqlite3_malloc(sizeof(BtreePtrmap));

    if( pMap==0 ){
      rc = SQLITE_NOMEM;
    }else{
      memset(&pBt->pPage1->aData[32], 0, sizeof(u32)*2);
      memset(pMap, 0, sizeof(BtreePtrmap));
      pMap->iFirst = pBt->nPage + 1;
      pBt->pMap = pMap;
    }
  }
  return rc;
}

/*
** Free any BtreePtrmap structure allocated by an earlier call to
** btreePtrmapAllocate().
................................................................................
** when A already has a read lock, we encourage A to give up and let B
** proceed.
*/
int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
  sqlite3 *pBlock = 0;
  BtShared *pBt = p->pBt;
  int rc = SQLITE_OK;
  int bConcurrent = (p->db->bConcurrent && !ISAUTOVACUUM);

  sqlite3BtreeEnter(p);
  btreeIntegrity(p);

  /* If the btree is already in a write-transaction, or it
  ** is already in a read-transaction and a read-transaction
  ** is requested, this is a no-op.
................................................................................
    */
    while( pBt->pPage1==0 && SQLITE_OK==(rc = lockBtree(pBt)) );

    if( rc==SQLITE_OK && wrflag ){
      if( (pBt->btsFlags & BTS_READ_ONLY)!=0 ){
        rc = SQLITE_READONLY;
      }else{
        int exFlag = bConcurrent ? -1 : (wrflag>1);


        rc = sqlite3PagerBegin(pBt->pPager, exFlag, sqlite3TempInMemory(p->db));
        if( rc==SQLITE_OK ){
          rc = newDatabase(pBt);
        }





      }
    }
  
    if( rc!=SQLITE_OK ){
      unlockBtreeIfUnused(pBt);
    }
  }while( (rc&0xFF)==SQLITE_BUSY && pBt->inTransaction==TRANS_NONE &&
................................................................................
        }
      }
    }
  }


trans_begun:
#ifdef SQLITE_ENABLE_CONCURRENT
  if( bConcurrent && rc==SQLITE_OK && sqlite3PagerIsWal(pBt->pPager) ){
    rc = sqlite3PagerBeginConcurrent(pBt->pPager);
    if( rc==SQLITE_OK && wrflag ){
      rc = btreePtrmapAllocate(pBt);
    }
  }
#endif

  if( rc==SQLITE_OK && wrflag ){
    /* This call makes sure that the pager has the correct number of
    ** open savepoints. If the second parameter is greater than 0 and
    ** the sub-journal is not already open, then it will be opened here.
    */
    int nSavepoint = p->db->nSavepoint;
    rc = sqlite3PagerOpenSavepoint(pBt->pPager, nSavepoint);
................................................................................
  ** or freed by this transaction. In this case no special handling is 
  ** required. Otherwise, if page 1 is dirty, proceed.  */
  BtreePtrmap *pMap = pBt->pMap;
  Pgno iTrunk = get4byte(&p1[32]);
  Pgno nPage = btreePagecount(pBt);
  u32 nFree = get4byte(&p1[36]);


  assert( pBt->pMap );
  rc = sqlite3PagerUpgradeSnapshot(pPager, pPage1->pDbPage);
  assert( p1==pPage1->aData );

  if( rc==SQLITE_OK ){
    Pgno nHPage = get4byte(&p1[28]);
    Pgno nFin = nHPage;         /* Size of db after transaction merge */
................................................................................

    /* Set the current transaction state to TRANS_NONE and unlock the 
    ** pager if this call closed the only read or write transaction.  */
    p->inTrans = TRANS_NONE;
    unlockBtreeIfUnused(pBt);
  }

  /* If this was an CONCURRENT transaction, delete the pBt->pMap object.
  ** Also call PagerEndConcurrent() to ensure that the pager has discarded
  ** the record of all pages read within the transaction.  */
  btreePtrmapDelete(pBt);
  sqlite3PagerEndConcurrent(pBt->pPager);
  btreeIntegrity(p);
}

/*
** Commit the transaction currently in progress.
**
** This routine implements the second phase of a 2-phase commit.  The

      testcase( rc==SQLITE_NOMEM );
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}























/*
** Free the Pager.pInJournal and Pager.pAllRead bitvec objects.
*/
static void pagerFreeBitvecs(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
#ifdef SQLITE_ENABLE_CONCURRENT
  sqlite3BitvecDestroy(pPager->pAllRead);
  pPager->pAllRead = 0;
#endif
}

/*
** This function is a no-op if the pager is in exclusive mode and not
** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
** state.
**
................................................................................

  if( pPager->errCode ) return pPager->errCode;
  assert( pPager->eState>=PAGER_READER && pPager->eState<PAGER_ERROR );
  pPager->subjInMemory = (u8)subjInMemory;

  if( ALWAYS(pPager->eState==PAGER_READER) ){
    assert( pPager->pInJournal==0 );
#ifdef SQLITE_ENABLE_CONCURRENT
    assert( pPager->pAllRead==0 );
#endif

    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
................................................................................
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
      ** PAGER_RESERVED state. Otherwise, return an error code to the caller.
      ** The busy-handler is not invoked if another connection already
      ** holds the write-lock. If possible, the upper layer will call it.
      */
#ifdef SQLITE_ENABLE_CONCURRENT
      if( exFlag<0 ){
        pPager->pAllRead = sqlite3BitvecCreate(pPager->dbSize);
        if( pPager->pAllRead==0 ){
          rc = SQLITE_NOMEM;
        }
      }else
#endif
      {
        rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
      }
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
................................................................................
/*
** Set the in-memory cache of the database file size to nSz pages.
*/
void sqlite3PagerSetDbsize(Pager *pPager, Pgno nSz){
  pPager->dbSize = nSz;
}

/*
** Return true if this pager is currently within an CONCURRENT transaction.
*/
int sqlite3PagerIsConcurrent(Pager *pPager){
  return pPager->pAllRead!=0;
}

/*
** If this is a WAL mode connection and the WRITER lock is currently held,
** relinquish it.
*/
void sqlite3PagerDropExclusiveLock(Pager *pPager){
  if( pagerUseWal(pPager) ){
    sqlite3WalEndWriteTransaction(pPager->pWal);

      testcase( rc==SQLITE_NOMEM );
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

#ifdef SQLITE_ENABLE_CONCURRENT
int sqlite3PagerBeginConcurrent(Pager *pPager){
  int rc = SQLITE_OK;
  if( pPager->pAllRead==0 ){
    pPager->pAllRead = sqlite3BitvecCreate(pPager->dbSize);
    if( pPager->pAllRead==0 ){
      rc = SQLITE_NOMEM;
    }
  }
  return rc;
}

void sqlite3PagerEndConcurrent(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pAllRead);
  pPager->pAllRead = 0;
}

int sqlite3PagerIsWal(Pager *pPager){
  return pPager->pWal!=0;
}
#endif

/*
** Free the Pager.pInJournal and Pager.pAllRead bitvec objects.
*/
static void pagerFreeBitvecs(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  sqlite3PagerEndConcurrent(pPager);



}

/*
** This function is a no-op if the pager is in exclusive mode and not
** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
** state.
**
................................................................................

  if( pPager->errCode ) return pPager->errCode;
  assert( pPager->eState>=PAGER_READER && pPager->eState<PAGER_ERROR );
  pPager->subjInMemory = (u8)subjInMemory;

  if( ALWAYS(pPager->eState==PAGER_READER) ){
    assert( pPager->pInJournal==0 );




    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
................................................................................
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
      ** PAGER_RESERVED state. Otherwise, return an error code to the caller.
      ** The busy-handler is not invoked if another connection already
      ** holds the write-lock. If possible, the upper layer will call it.  */


      if( exFlag>=0 ){







        rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
      }
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
................................................................................
/*
** Set the in-memory cache of the database file size to nSz pages.
*/
void sqlite3PagerSetDbsize(Pager *pPager, Pgno nSz){
  pPager->dbSize = nSz;
}








/*
** If this is a WAL mode connection and the WRITER lock is currently held,
** relinquish it.
*/
void sqlite3PagerDropExclusiveLock(Pager *pPager){
  if( pagerUseWal(pPager) ){
    sqlite3WalEndWriteTransaction(pPager->pWal);

int sqlite3SectorSize(sqlite3_file *);

/* Functions used to truncate the database file. */
void sqlite3PagerTruncateImage(Pager*,Pgno);

void sqlite3PagerRekey(DbPage*, Pgno, u16);




void sqlite3PagerDropExclusiveLock(Pager*);
int sqlite3PagerIsConcurrent(Pager*);
int sqlite3PagerIswriteable(DbPage*);
int sqlite3PagerUpgradeSnapshot(Pager *pPager, DbPage*);
void sqlite3PagerSetDbsize(Pager *pPager, Pgno);






#if defined(SQLITE_HAS_CODEC) && !defined(SQLITE_OMIT_WAL)
void *sqlite3PagerCodec(DbPage *);
#endif

/* Functions to support testing and debugging. */
#if !defined(NDEBUG) || defined(SQLITE_TEST)

int sqlite3SectorSize(sqlite3_file *);

/* Functions used to truncate the database file. */
void sqlite3PagerTruncateImage(Pager*,Pgno);

void sqlite3PagerRekey(DbPage*, Pgno, u16);

#ifdef SQLITE_ENABLE_CONCURRENT
void sqlite3PagerEndConcurrent(Pager*);
int sqlite3PagerBeginConcurrent(Pager*);
void sqlite3PagerDropExclusiveLock(Pager*);


int sqlite3PagerUpgradeSnapshot(Pager *pPager, DbPage*);
void sqlite3PagerSetDbsize(Pager *pPager, Pgno);
#else
# define sqlite3PagerEndConcurrent(x)
#endif

int sqlite3PagerIswriteable(DbPage*);

#if defined(SQLITE_HAS_CODEC) && !defined(SQLITE_OMIT_WAL)
void *sqlite3PagerCodec(DbPage *);
#endif

/* Functions to support testing and debugging. */
#if !defined(NDEBUG) || defined(SQLITE_TEST)

    }
  } {}
  do_test 9.$tn.4.2 {
    sql2 { DELETE FROM pp WHERE i=1 }
    list [catch { sql1 COMMIT } msg] $msg
  } {0 {}}
}



























finish_test

    }
  } {}
  do_test 9.$tn.4.2 {
    sql2 { DELETE FROM pp WHERE i=1 }
    list [catch { sql1 COMMIT } msg] $msg
  } {0 {}}
}

do_multiclient_test tn {
  do_test 10.$tn.1 {
    sql1 {
      PRAGMA journal_mode = wal;
      CREATE TABLE t1(a);
      CREATE TABLE t2(b);
      INSERT INTO t1 VALUES(1), (2), (3);
      INSERT INTO t2 VALUES(1), (2), (3);
    }
  } {wal}

  do_test 10.$tn.2 {
    sql1 {
      BEGIN CONCURRENT;
        SELECT * FROM t1;
        INSERT INTO t2 VALUES(4);
    }
  } {1 2 3}

  do_test 10.$tn.3 {
    sql2 { INSERT INTO t1 VALUES(4) }
    list [catch {sql1 COMMIT} msg] $msg
  } {1 {database is locked}}
}


finish_test