program onerror (output);
    DATABASE PERS = FILENAME 'PERSONNEL';

    var
        RDB$_LOCK_CONFLICT : [value,external] integer;
        i     : integer;
        error : boolean;

    procedure handle_error;
    begin
        if RDB$STATUS = RDB$_LOCK_CONFLICT
        then
            writeln ('database unavailable right now')
        else
            begin
            writeln ('Unexpected Error, Application Terminating');
            RDML$SIGNAL_ERROR(RDB$MESSAGE_VECTOR)
            end;
    end;

    begin
    for i := 1 to 100 do
        begin
        error := FALSE;
        READY PERS;
        START_TRANSACTION READ_WRITE NOWAIT
            RESERVING EMPLOYEES FOR EXCLUSIVE WRITE
            ON ERROR
              handle_error;
              error := TRUE;
            END_ERROR;

        if not error then
          begin
          {perform some read_write operation on the EMPLOYEES relation}
          writeln ('Accessing EMPLOYEES...');

          COMMIT;
          FINISH;
                           end;
        end;
    end.