SQL> declare
   2    l_result number;
   3   begin
   4    l_result:=dbms_lock.request(
   5     id =>  1 ,
   6     lockmode => dbms_lock.x_mode,
   7     release_on_commit => false
   8    );
   9    dbms_output.put_line('result: '||to_char(l_result));
  10   end;
  11   /
result:  0 

PL/SQL procedure successfully completed.

--мы владеем блокировкой, поэтому следующий вызов вернёт 4
SQL> declare
   2    l_result number;
   3   begin
   4    l_result:=dbms_lock.request(
   5     id =>  1 ,
   6     lockmode => dbms_lock.x_mode,
   7     release_on_commit => false
   8    );
   9    dbms_output.put_line('result: '||to_char(l_result));
  10   end;
  11   /
result:  4 

PL/SQL procedure successfully completed.

--нам необходимо освободить блокировку
SQL> declare
   2    l_result number;
   3   begin
   4    l_result:=dbms_lock.release(id =>  1 );
   5   end;
   6   /

PL/SQL procedure successfully completed.

--теперь мы получим 0
SQL> declare
   2    l_result number;
   3   begin
   4    l_result:=dbms_lock.request(
   5     id =>  1 ,
   6     lockmode => dbms_lock.x_mode,
   7     release_on_commit => false
   8    );
   9    dbms_output.put_line('result: '||to_char(l_result));
  10   end;
  11   /
result:  0 

PL/SQL procedure successfully completed.