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To: "Amila Suriarachchi" <amilasuriarachchi@gmail.com>
Cc: "sandesha-dev@ws.apache.org" <sandesha-dev@ws.apache.org>
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Subject: Re: Sandesha2 synchronization and dead lock handling.
From: Andrew K Gatford <GATFORA@uk.ibm.com>
Message-ID: 
 <OF640251D3.F625AB19-ON802574EC.00350439-802574EC.0037099B@uk.ibm.com>
Date: Fri, 24 Oct 2008 11:01:10 +0100
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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/


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