If you want a lock in oracle, you're going about it the entirely wrong (though viable of course) way. Use dbms_lock.request example

   v_lock_sucess:=dbms_lock.request(lockhandle=>v_temp_lockhandle,
                                     lockmode=>dbms_lock.x_mode,
                                     TIMEOUT=>5,
                                     release_on_commit=>TRUE);
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