[Proxool-developer] Bug 673073

[Bill H. <bi...@lo...>]

Hi all,

There has been a lot of activity on bug 673073 recently. It's all to do
with finalization of the house keeper and prototyper threads when the
application ends. This is the transcript:

---

Date: 2003-01-23 13:41
Sender: trex
Logged In: YES 
user_id=44856

First I must to say that the implementation of this pool  is very robust
and high quality. However I have encountered the following problems
using the pool. 

Connection c = DriverManager.getConnection(
  "proxool.alias:sun.jdbc.odbc.JdbcOdbcDriver:jdbc:odbc:test","",""); 

md = c.getMetaData(); 
// using metadata 
// getting the connection back to the pool 
md.getConnection().close() //!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 

the line above will not bring the connection up to the pool. It just
closes it messing the stuff. 

I know it is always possible to avoid this. Finally, I have solved this
problem but the listening to the real connection state would be really
nice feature to have. I mean if the pool would be able to listen to the
connection state and prevent it from misusinng. 

Andrew S. Budarevsky 

---

Date: 2003-01-24 10:06
Sender: billhorsman
Logged In: YES 
user_id=91747

Andrew,

Hmm, that's interesting. I see the problem, but I'm not sure of the best
way to solve it. I think the only way is to proxy the DatabaseMetaData
object and override the getConnection() method. 

The problem is that the Connection interface doesn't provide any hooks
with which to listen to a connection. Hmm. I will add a FAQ describing
this problem and schedule a task to fix this. Thanks for spotting such
an obscure problem!

Regards,
Bill

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Date: 2003-01-31 17:47
Sender: billhorsman
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I have fixed this by proxying DatabaseMetaData too. It is will be in
version 0.7 (due February 5th) or you can get the latest from CVS.

---

Date: 2003-02-03 12:38
Sender: trex
Logged In: YES 
user_id=44856

Hello Bill!

Good work! Though I won't change my framework to apply the newest stuff
for awhile I would suject that it might help to anybody else.

What I wanted to tell you more is that it seems the pool does not let
application quit by means of holding a running thread. But I am not sure
yet. At the moment  I have System.exit executed on QUIT event. Within
few days I am going to check that and inform you as soon as I have
something to tell you for sure.

Andrew

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Date: 2003-02-03 17:06
Sender: billhorsman
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Hi Andrew,

You should call ProxoolFacade.removeAllConnectionPools(delay) when you
quit. This will close all connections gracefully and kill all the
threads that are running. We can't think of a way of ensuring this
happens automatically. The delay is the amount of time (milliseconds)
that you are prepared to wait for connections to stop being active
before closing them anyway.

Hope this helps,
Bill

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Date: 2003-02-04 10:20
Sender: trex
Logged In: YES 
user_id=44856

Hello Bill!

Thank you for the advising. It is worth. However I would say that it
breaks the general concept of proxool to be a transparent driver's
proxy. I know it happens due to leak of virtual machine state events.
Oops... What about a finalize method? Could it be possible to close
pools on finalizing? I can explain why I am so concerned of the
trasparency. I am working on a framework that manages application data
flows, called streams. Database is one of data sources. In my case the
data source is not a driver of database or similar. It could be
something very very abstract entity resembling data source behaviour. I
don't think I even need to have a method closing the end point. I would
prefer to rely on system-wide finalization in case of Java. It's not
requirement, it's a feature. Few years ago I have implemented a pool of
tcp connections resided on servlet and connected to application server.
I don't remeber but it seems I closed connections by means of 
overriding finalize method.

What would you say?

Andrew. 

---

Date: 2003-02-04 12:14
Sender: billhorsman
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user_id=91747

Hi Andrew,

I take your point.  I don't like having code call the Proxool API
directly. I would really like to come up with a transparent solution to
this.

Actually, Proxool already overrides the finalize method, but in my
experience this doesn't always get called. I suspect that calling
System.exit() means that it doesn't get called. We really need to do
some more investigation into this to determine exactly what
circumstances cause what behaviour. I think we need to read the specs a
bit more closely and then do some testing. It would be nice to know
exactly what the problem is. 

We have not found any robust way of determining when the application has
ended.  Any suggestions are welcome. 

---

I have suggested to Andrew that he continues this discussion on this
list so that we can all get involved.

Regards,
-- 
  Bill Horsman
  Proxool
  http://proxool.sourceforge.net
  ICQ: 119577180