synchronized, notify, wait,sleep, how to work together

[John_Woo]

Hi,

let's look at the following:

class GetConnection extends Thread
{
Connection con = null;
boolean done = false;

public void run()
{
try{
con = DriverManager.getConnection(...);
//notifyAll();
done = true;
}
catch(Exception e){}
}

synchronized Connection getConnection()
{
return con;
}
synchronized boolean getDone()
{
return done;
}
}

questions:
supposed in some cases it may take up to 10-20 seconds to get the
connection while other cases just takes 1-3 seconds.
what can I code in caller method, so that
1. if in 5 seconds, interrupte GetConnection thread if it has not yet
finished;
2. preventing "done" being written while trying to interrupt this
thread.

 

[dsjoblom]

Hi,

let's look at the following:

class GetConnection extends Thread
{
Connection con = null;
boolean done = false;

public void run()
{
try{
con = DriverManager.getConnection(...);
//notifyAll();
done = true;
}
catch(Exception e){}
}

synchronized Connection getConnection()
{
return con;
}
synchronized boolean getDone()
{
return done;
}
}

questions:
supposed in some cases it may take up to 10-20 seconds to get the
connection while other cases just takes 1-3 seconds.
what can I code in caller method, so that
1. if in 5 seconds, interrupte GetConnection thread if it has not yet
finished;
2. preventing "done" being written while trying to interrupt this
thread.

This is a classical producer-consumer problem. Read
http://java.sun.com/docs/books/tutorial/essential/concurrency/index.html
to get familiar with the basics.

If you are using java 1.5 or later, it's easiest to implement this
using a BlockingQueue. See
http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/BlockingQueue.html

The producer thread that creates the Connection puts the connection
into the queue using the offer method, and the consumer thread that
desires to use the connection uses the poll method with desired
timeout. If the consumer doesn't get an object (poll returns null), it
can interrupt the producer thread.

You may wish to try to implement this from scratch though, to
familiarize yourself with the concepts. See the first link I posted for
more information.

Regards,
Daniel Sjöblom

 

[Ben_]

Did you think to use a connection pooling library to avoid writing such code
?

 

[John_Woo]

Did you think to use a connection pooling library to avoid writing such code
?

Yes, with localThread, in case connection dropper and can't get
re-connection soon, we have to use other connection .

Do you have more idea?

 

[Ben_]

Sorry, I don't undestand your reply.

I meant to say that you could use a DataSource's Connection Pooling facility
(J2EE application) or something like Jakarta Commons DBCP (J2SE
application).

These have all parameters you seem to expect like, max time to wait to
obtain a connection, what to do if a connection is broken (purge all pool
and get all new connection or replace only the broken one), etc.

I think writing a configurable and resistant connection pool is non-trivial.