How to avoid deadlock - ORA-00060 in trigger

Question

Hi,
We are using 11.2.0.3 and have a trigger which acts upon a mutex table.
Trying to catch when value from other program has changed locked value from 0 to 1 to indicate they have finished.
Once they finished we need to lock the mutex table by updating locked value.
Code below gives error ORA-00060 - deadlock.
Any idea how to avoid but allow us to updat ethe mutex table in trigger at star t to say we are locking and at end to indicate we are finished.
Thanks
CREATE OR REPLACE TRIGGER example_trg AFTER UPDATE
ON por_zic_flags
FOR EACH ROW
when (NEW.locked = '0' and old.locked = '1')
declare
PRAGMA AUTONOMOUS_TRANSACTION;
I INTEGER;
v_locked por_zic_flags.locked%type;
begin
select locked
into v_locked
from por_zic_flags
--where tabname = ‘table name’
  for update;
update por_zic_flags set locked = '2';--, guid = '100'; -- unique seq#
commit;
-- call procedure do processing on other tables
-- Now indicate finished processing
select locked
into v_locked
from por_zic_flags
  for update;
update por_zic_flags set locked = '0';--, guid = '100'; -- unique seq#
commit;
end;

Answer 1

>
Trying to catch when value from other program has changed locked value from 0 to 1 to indicate they have finished.
Once they finished we need to lock the mutex table by updating locked value.
Code below gives error ORA-00060 - deadlock.
Any idea how to avoid but allow us to updat ethe mutex table in trigger at star t to say we are locking and at end to indicate we are finished.
>
Triggers should not be used for non-transactional purposes like this.
A simple SELECT . . . WHERE (myLock = 'UNLOCKED') FOR UPDATE can be used to query the record and lock it if the lock is not already set. Then your code can update the lock value and that will prevent the same query by other users from being successful.
But you haven't really provided any information about what you are trying to do.
If you want to prevent two processes from executing at the same time you can use Oracle's LOCK functionality.
See this thread for how to use DBMS_LOCK to create your own locks that can serialize access to your procedures.
Re: possible to lock stored procedure so only one session may run it at a time?