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From Thomas McKiernan <MCKIE...@uk.ibm.com>
Subject Re: Sandesha2 synchronization and dead lock handling.
Date Fri, 24 Oct 2008 14:24:25 GMT
I think Andrew was saying that there is already an implicit order for the 
beans.
The point is people keep changing the code and breaking that order.
Therefore this is not quite a hack but an attempt to make explicit what is 
already implied in the open src code.

It would not work for the distributed case but, assuming each distributed 
thread was behaving correctly i.e. obeying the correct locking order then 
this would not be an issue.
And this would catch any thread disobeying that ordering.


----------------------------------
Thomas McKiernan

WebSphere Messaging Development,
IBM United Kingdom Limited

Internal Phone: 248241 
External Phone: +44 (0)1962 818241
Mobile: +44 (0)789 1737497
Email: MCKIERNA@uk.ibm.com

Mail Point 211, IBM, Hursley Park, Winchester, Hampshire, England, SO21 
2JN


Caminante, no hay camino 
Se hace camino al andar.
("Walker, there is no path; the path is made by walking.")  Antonio 
Machado



From:
"Amila Suriarachchi" <amilasuriarachchi@gmail.com>
To:
Thomas McKiernan/UK/IBM@IBMGB
Cc:
Andrew K Gatford/UK/IBM@IBMGB, "sandesha-dev@ws.apache.org" 
<sandesha-dev@ws.apache.org>
Date:
24/10/2008 14:06
Subject:
Re: Sandesha2 synchronization and dead lock handling.





On Fri, Oct 24, 2008 at 3:55 PM, Thomas McKiernan <MCKIERNA@uk.ibm.com> 
wrote:
How about a lock manager impl independent of any particular store's impl.
It could be abstract if necessary.

Basically, this has a hierarchy of classes (beans) hard coded.
If you use a store to access a bean then the store impl's tran calls into
the independent lock manager.

I feel this is a kind hack for the problem. And also as Andrew has 
mentioned this won't work in a 
distributed environment.
For me the correct solution is to go through all the transactions and make 
an order of which
transactions access the beans. But apparently  this is also seems to be 
difficult since a lot
of transactions has start and commits. 
So have to think bit more.

thanks,
Amila.




Any attempt to enlist outside of the locking hierarchy results in a hard
runtime error and a rollback of the tran.

Is this too naive?

----------------------------------
Thomas McKiernan

WebSphere Messaging Development,
IBM United Kingdom Limited

Internal Phone: 248241
External Phone: +44 (0)1962 818241
Mobile: +44 (0)789 1737497
Email: MCKIERNA@uk.ibm.com

Mail Point 211, IBM, Hursley Park, Winchester, Hampshire, England, SO21
2JN


Caminante, no hay camino
Se hace camino al andar.
("Walker, there is no path; the path is made by walking.")  Antonio
Machado



From:
Andrew K Gatford/UK/IBM@IBMGB
To:
"Amila Suriarachchi" <amilasuriarachchi@gmail.com>
Cc:
"sandesha-dev@ws.apache.org" <sandesha-dev@ws.apache.org>
Date:
24/10/2008 11:07
Subject:
Re: Sandesha2 synchronization and dead lock handling.



I went through similar pain when implementing a StorageManager and
encountered a number of deadlocks similar to the ones that you describe.
What I have gradually done is eliminate these in both the InMemory store
and my store by changing the ordering the beans were taken in.

In general the beans are taken in this order.

RMSBean or RMDBean followed by
SenderBean or InvokerBean.

In cases where both the RMSBean and RMDBean are locked, they tend to be
taken in that order - RMS followed by RMD.
The one thing that I do know is that it is fairly easy to introduce new
deadlocks by slightly altering the order that beans are read.

The one question I have is how does the jdbc store handle multiple threads

accessing multiple sequences, or even a single sequence, but with multiple

threads sending multiple requests.  From my experience this is where we
have found a lot of problems in the InMemory store and I expect to be even

more painful with a jdbc store.

Andrew Gatford
Technical Project Lead
Websphere ESB Foundation Technologies
Hursley MP211
IBM United Kingdom Laboratories, Hursley Park, Winchester, SO21 2JN
Telephone :
Internal (7) 245743
External 01962 815743
Internet : gatfora@uk.ibm.com



From:
"Amila Suriarachchi" <amilasuriarachchi@gmail.com>
To:
"sandesha-dev@ws.apache.org" <sandesha-dev@ws.apache.org>
Date:
24/10/2008 10:30
Subject:
Sandesha2 synchronization and dead lock handling.



hi all,

This is regarding the issue [1].

First of all as I learned Sandesha2 uses different beans to keep the state

of the sequence and the messages. In a dual channel mode
different threads can access these beans and update them concurrently. So
the synchronization of these beans done by using the
storage level transactions. Therefore Sandesha2 needs an storage which
supports isolated transactions.

To synchronize these beans the transactions must be completely isolated.
i.e It should not allow simultaneous reads of
same record from different transactions. Therefore I think the problem I
saw on[1] because not isolating the transactions properly.

Then I increased the transaction isolation to fix the above problem. It
fixed that problem but results in dead locks.
The reason I believe for this dead locks is that different transactions
try to access the data base tables in different order.
But unfortunately I could not fix the issue.

Normally these types of dead locks are prevented by accessing resources in

same order. Does Sandesha2 follows such a order or any
other technique?

Or is there any other reason for this dead locks and synchronization
problems? Can someone
have a better idea of Sandesha2 Design shed some light on this?

thanks,
Amila.


[1] http://issues.apache.org/jira/browse/SANDESHA2-179
--
Amila Suriarachchi
WSO2 Inc.
blog: http://amilachinthaka.blogspot.com/






Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU







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Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU









-- 
Amila Suriarachchi
WSO2 Inc.
blog: http://amilachinthaka.blogspot.com/







Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU







---------------------------------------------------------------------
To unsubscribe, e-mail: sandesha-dev-unsubscribe@ws.apache.org
For additional commands, e-mail: sandesha-dev-help@ws.apache.org


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