mysql 插入前 锁表问题

$dbh = DBI->connect("dbi:mysql:database=$db_name;host=$ip;port=3306",$user,$passwd,{                          RaiseError => 1,                          AutoCommit => 0                        }) or die "can't connect to database ". DBI-errstr;     eval{    $dbh->do("select count(*) from t1 for update") ;    $dbh->do("insert into t1 values(87)") ;     $dbh->commit;        };    if( $@ ) {    #warn "Database error: $DBI::errstr\n";    $dbh->rollback(); #just die if rollback is failing      };  $dbh->disconnect;