** This function returns SQLITE_OK if the caller may write to the database.
** Otherwise, if the caller is operating on a snapshot that has already
** been overwritten by another writer, SQLITE_BUSY is returned.
*/
int sqlite3WalWriteLock(Wal *pWal, int op){
  int rc = SQLITE_OK;
  if( op ){
    assert( pWal->lockState == SQLITE_SHM_READ );
    rc = walSetLock(pWal, SQLITE_SHM_WRITE);

    /* If this connection is not reading the most recent database snapshot,
    ** it is not possible to write to the database. In this case release
    ** the write locks and return SQLITE_BUSY.
    */
    if( rc==SQLITE_OK ){
................................................................................
  void *pBusyHandlerArg           /* Argument to pass to xBusyHandler */
){
  int rc;                         /* Return code */
  int isChanged = 0;              /* True if a new wal-index header is loaded */

  assert( pWal->pWiData==0 );

  /* Get the CHECKPOINT lock */
  if( pWal->lockState!=SQLITE_SHM_UNLOCK ){
    /* This can occur when locking_mode=EXCLUSIVE */
    assert( pWal->lockState==SQLITE_SHM_READ
         || pWal->lockState==SQLITE_SHM_READ_FULL );
    walSetLock(pWal, SQLITE_SHM_UNLOCK);
  }




  do {
    rc = walSetLock(pWal, SQLITE_SHM_CHECKPOINT);
  }while( rc==SQLITE_BUSY && xBusyHandler(pBusyHandlerArg) );
  if( rc!=SQLITE_OK ){
    walSetLock(pWal, SQLITE_SHM_UNLOCK);
    return rc;
  }

** This function returns SQLITE_OK if the caller may write to the database.
** Otherwise, if the caller is operating on a snapshot that has already
** been overwritten by another writer, SQLITE_BUSY is returned.
*/
int sqlite3WalWriteLock(Wal *pWal, int op){
  int rc = SQLITE_OK;
  if( op ){
    assert( pWal->lockState==SQLITE_SHM_READ );
    rc = walSetLock(pWal, SQLITE_SHM_WRITE);

    /* If this connection is not reading the most recent database snapshot,
    ** it is not possible to write to the database. In this case release
    ** the write locks and return SQLITE_BUSY.
    */
    if( rc==SQLITE_OK ){
................................................................................
  void *pBusyHandlerArg           /* Argument to pass to xBusyHandler */
){
  int rc;                         /* Return code */
  int isChanged = 0;              /* True if a new wal-index header is loaded */

  assert( pWal->pWiData==0 );

  /* Get the CHECKPOINT lock. 
  **
  ** Normally, the connection will be in UNLOCK state at this point. But
  ** if the connection is in exclusive-mode it may still be in READ state
  ** even though the upper layer has no active read-transaction (because
  ** WalCloseSnapshot() is not called in exclusive mode). The state will
  ** be set to UNLOCK when this function returns. This is Ok.
  */
  assert( (pWal->lockState==SQLITE_SHM_UNLOCK)
       || (pWal->exclusiveMode && pWal->lockState==SQLITE_SHM_READ)
  );
  do {
    rc = walSetLock(pWal, SQLITE_SHM_CHECKPOINT);
  }while( rc==SQLITE_BUSY && xBusyHandler(pBusyHandlerArg) );
  if( rc!=SQLITE_OK ){
    walSetLock(pWal, SQLITE_SHM_UNLOCK);
    return rc;
  }

} {READ UNLOCK}
do_test wal2-6.4.7 {
  set ::locks [list]
  execsql { INSERT INTO t1 VALUES('Karl') }
  set ::locks
} {READ WRITE READ UNLOCK}
db close















finish_test

} {READ UNLOCK}
do_test wal2-6.4.7 {
  set ::locks [list]
  execsql { INSERT INTO t1 VALUES('Karl') }
  set ::locks
} {READ WRITE READ UNLOCK}
db close
tvfs delete

do_test wal2-6.5.1 {
  sqlite3 db test.db
  execsql {
    PRAGMA journal_mode = wal;
    PRAGMA locking_mode = exclusive;
    CREATE TABLE t2(a, b);
    PRAGMA wal_checkpoint;
    INSERT INTO t2 VALUES('I', 'II');
    PRAGMA journal_mode;
  }
} {wal exclusive wal}
db close

finish_test