Implementing a multithreaded queue with Berkeley DB JE edition

Hello guys,
I am implementing a queue using JE.
The Queue can have several threads pushing new entries and several threads consuming from it.
I have created one database with one string field as Key and another in the data.
The pushing thread creates a transaction cursor and just runs a put to write new entries in the queue. The consuming threads read from the queue trying and retrying with cursor.getFirst with a separated transactional cursor. Once the getFirst is successful, the thread deletes the entry.
The problem I have are the deadlocks. Multiple threads reach the very same record. So, to avoid the threads to read the same entry, I run the getFirst with a write lock until I delete the entry. It sounds good in theory, but in practice the threads are always in deadlock and the pushing thread cannot write only one row and the queue stays always empty.
Any ideas?
Thanks,

Thanks Koiaka.
This is something we haven't seen before. I have several questions.
1) Is the documentQueue Database empty (no records) at the time this occurs?
2) Please send the complete stack trace for the exception.
3) It looks like you have configured Serializable Isolation. I don't understand why this is needed for queue processing. Is there something that caused you to use this isolation mode?
4) Please send your complete Database (or EntityStore) and Environment configuration.
5) If you can send a small test (complete runnable program with a main) that reproduces this problem, it will speed up this process. If that is not possible, please send code snippets for the reader and writer threads, showing the JE calls they are making.
If the database is empty, you may need to throttle the reader threads to allow the writer to do some work. Having the readers sleep for a short interval if the queue is empty may work.
However, even without doing this, the deadlock you're seeing doesn't make sense, and I would like to get to the bottom of this. I am hoping that you can send a reproducible test program and would appreciate your help on that.
Thanks,
--mark

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And register it as follows:
reginfo := sys.aq$_reg_info(
'SOA_JMS.RJMTESTQ:SUBSCRIP1',
DBMS_AQ.NAMESPACE_AQ,
'plsql://SOA_JMS.EXCEPTION_QUEUE_NOFIFYCB_1?PR=0',
--utl_raw.cast_to_raw('STANDARDJMS')
HEXTORAW('FF')
reg_list := sys.aq$_reg_info_list(reginfo);
dbms_aq.register(reg_list,1);
The problem is the notifications are not firing as they should be.
I have done some tracing and found an error:
Error in PLSQL notification of msgid:BA964334E5A057A4E040C69BAF397075
Queue :"SOA_JMS"."RJMTESTQ"
Consumer Name :SUBSCRIP1
PLSQL function :SOA_JMS.EXCEPTION_QUEUE_NOFIFYCB_1
: Exception Occured, Error msg:
ORA-00604: error occurred at recursive SQL level 2
ORA-06550: line 1, column 7:
PLS-00306: wrong number or types of arguments in call to 'EXCEPTION_QUEUE_NOFIFYCB_1'
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored
This says that the parameters I have for my procedure is wrong. Looking through the documents I think it is something to do with the ?PR=0 used in the register call, but I can’t find any documentation telling me what the required parameters are.
Does anyone here know?
Thanks
Robert

Hi,
I have found the solution and I am posting here in case it helps anyone else.
The paramater names must match the callback not just the types and in/out.
So the following works:
create or replace procedure SOA_JMS.EXCEPTION_QUEUE_NOFIFYCB_2(
context in raw,
reginfo in sys.aq$_reg_info,
descr in sys.aq$_descriptor,
payload in raw,
payloadl in number
Robert

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