RE: re[2]: [Jdbm-developer] A preview of how thread local works o ut...

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Kevin,

If one transaction is suspended and another waits on it then there 
is no deadlock -- assuming that the suspended transaction will 
eventually release its locks.  If the suspended transaction never
results then this is still not a deadlock.  Transactions are required
to run and terminate and a suspended transaction which does not resume
is violating that requirement.

-bryan

-----Original Message-----
From: jdb...@li...
To: JDBM Developer listserv
Sent: 4/4/2006 10:47 AM
Subject: re[2]: [Jdbm-developer] A preview of how thread local works out...

Bryan-

The issue you describe only arises if the developer is using 2PL, and
even then deadlock detection should kick in and blow one of the
transactions.

My opinion on this is that if a developer is using suspend and resume,
then they are doing it in the context of a much larger
synchronization/concurrency implementation (e.g. Alex's processing
pools, non blocking IO, etc...).

As for having a library to support this kind of concurrency, I think
that this is a fantastic idea - but for a different OSS project.  JDBM's
primary responsibility in this arena is to provide a mechansim to allow
developers to interact with the database in this manner - and I'm pretty
sure that suspend and resume is really all that's needed to do that.

- K

	> Kevin,

This looks simple enough.  However, leaving a tx paused can cause grief
since any tx that blocks on the paused tx will never run.  This will
make
the actual use of start/suspend/resume much more complex.  Perhaps we
should
create some utility classes, e.g., thread pools, oriented at
facilitating
such concurrency processing?  We could also use a timeout on suspend
that
started ticking once another tx blocks on a suspended tx -- otherwise
the
active threads could become easily absorbed. 

-bryan

-----Original Message-----
From:  <mailto:jdb...@li...>
jdb...@li...
 <mailto:jdb...@li...>
[mailto:jdb...@li...] On Behalf Of Kevin
Day
Sent: Tuesday, April 04, 2006 1:57 AM
To: JDBM Developer listserv
Subject: [Jdbm-developer] A preview of how thread local works out...

I put together some sample code to show the impact of the threadlocal
decision, and wanted to share it...  

I'm quite happy with how it works out...

Cheers!

- K

package jdbm2test;
/**
* A simple example to show how an application would interact with the
record
manager
* @author kevin
*
*/
public class BasicUsage {
public BasicUsage() {
}
public static void main(String[] args) {
// TODO: Replace the TestDB calls with a record manager provider of some
sort
TestDB db = TestDB.getCleanDB();
RecordManager recman = db.recMgr;

recman.startNewTransaction();
int recid1 = recman.insert(new byte[]{1, 2, 3, 4, 5});
int recid2 = recman.insert(new byte[]{2, 3, 4, 5, 6});
recman.commitTransaction();

recman.startNewTransaction();
byte[] retrieved1 = recman.fetch(recid1).data;
byte[] retrieved2 = recman.fetch(recid2).data;
retrieved1[3] = retrieved2[3];
recman.update(recid1, retrieved1);
recman.commitTransaction();
recman.startNewTransaction();
int recid3 = recman.insert(new byte[]{3, 4, 5, 6, 7});
Transaction suspendedTx = recman.suspendTransaction();

recman.startNewTransaction();
int recid4 = recman.insert(new byte[]{4, 5, 6, 7, 8});
Row r1 = recman.fetch(recid3); // note : this will return null
System.out.println("r1 is " + r1);
recman.commitTransaction();

recman.resumeTransaction(suspendedTx);
Row r2 = recman.fetch(recid3); // note: this will return a valid value
System.out.println("r2 is " + r2.data[0] + ", " + r2.data[1] + "...");
recman.commitTransaction();
}
}

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