Experimental Physics and
Industrial Control System

Kay-Uwe Kasemir <[email protected]> · Fri, 07 Jul 2006 12:30:18 -0400

On Jul 6, 2006, at 18:37 , Harley N wrote:

...

2. Is there something that needs to be done when shutting down a
Java program, so the client disconnects and reconnects cleanly?

Hi:
I've been wondering myself about that.

Here's what I use so far to start/stop CA connections when using JCA/
CAJ.

It seems to "work", meaning: I can start/stop CA connections from a
running

application, but I have no idea if it's the correct way to do this.

Maybe somebody has better ideas?
Thanks,
-Kay

 // Only once, reference-counted, as soon as the first PV is created:
 jca = JCALibrary.getInstance();
 jca_context = jca.createContext(JCALibrary.CHANNEL_ACCESS_JAVA);
 // For each new channel.

// ('this' implements the ConnectionListener and MonitorListener
interfaces)

channel = jca_context.createChannel(name, this);
 // Then, after all channels were created:

jca_context.flushIO();

// One can naively call flushIO() after each createChannel().

// That "works", but at least with the "C" version of the CA client
library

// that would be a performance hit.
 // If the channel is found on the network, the ConnectionListener
runs.

public void connectionChanged(ConnectionEvent ev)

{

if (ev.isConnected())

{

// Subscribe, but only once!

if (was_ever_connected == false)

{

was_ever_connected == true;

channel.addMonitor(1, this);

// Might be better to tell the application that a
"flush" is due,

// and run that from a timer, instead of flushing after
each addMonitor()

jca_context.flushIO();

}

}

else

{

// .. notify your application that we're disconnected;
schedule GUI update, ...

}

}
  // For each subscription update, this one gets invoked:
  public void monitorChanged(MonitorEvent ev)
  {
      if (ev.getStatus().isSuccessful())
      {
          DBR dbr = ev.getDBR();
          // decode the value, schedule GUI update, ....
        }
        else
        {
          // ...
        }
    }
  }
  // For each channel that we no longer want:
  channel.dispose();
  channel = null;
  // dispose() seems to "work" for me, but I'm unclear:
  // There's also a channel.destroy().
  // Finally, after the last PV was destroyed:
  jca_context.destroy();
  jca = null;

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System