Experimental Physics and
Industrial Control System

I recently ported JCA/CAJ to android and came across the fact that
BroadcastConnector does not bind the underlying DatagramSocket
to a local address.

According to the java.nio.channels.DatagramChannel docs a channel
is open()ed and then the underlying socket can be bound. Under android
it apparently must be. openjdk is more forgiving and binds the socket
automatically. However, there might be a problem:

For openjdk I came across the following source code

http://cr.openjdk.java.net/~dxu/8000404/webrev/src/share/classes/sun/nio/ch/DatagramChannelImpl.java.html

other reason to believe it is the same implementation you are using than

(if the user has not done so already).

At first glance there seems to be a race condition which could explain what
you experience:

receive(ByteBuffer dst) [starting at line 317] contains the following code:

   synchronized( readLock ) {
      ...
      if ( localAddress() == null ) {
          bind(null);
      }
.     ...
   }

and bind(SocketAddress local) [starting at line 654] is coded:

  synchronized( readLock ) {
    synchronized ( writeLock ) {
        if ( localAddress != null ) {
           throw new AlreadyBoundException();
        }
        // do actual binding here
        localAddress = xxx;
    }
  }

  synchronized ( writeLock ) {
        ...
        if ( localAddress == null ) {
          localAddress = Net.localAddress( fd );
        }
  }

then it finds 'localAddress' non-null and throws the exception.

on this analysis).

at creation time:

@@ -58,6 +58,9 @@

             // use non-blocking channel (no need for soTimeout)
             socket.configureBlocking(false);
+
+            // bind to any local port
+            socket.socket().bind( null );

             // set SO_BROADCAST
             socket.socket().setBroadcast(true);


HTH
-- Till

On 12/04/2013 06:48 PM, Kasemir, Kay wrote:

Hello:

Does anybody else see these messages from CAJ, the pure java channel access client?

Thanks,
Kay

2013-12-04 14:44:27.667 SEVERE [Thread 25] com.cosylab.epics.caj.impl.reactor.Reactor (processInternal) -
java.nio.channels.AlreadyBoundException
         at sun.nio.ch.DatagramChannelImpl.bind(DatagramChannelImpl.java:661)
         at sun.nio.ch.DatagramChannelImpl.receive(DatagramChannelImpl.java:327)
         at com.cosylab.epics.caj.impl.BroadcastTransport.processRead(BroadcastTransport.java:178)
         at com.cosylab.epics.caj.impl.BroadcastTransport.handleEvent(BroadcastTransport.java:155)
         at com.cosylab.epics.caj.impl.reactor.lf.LeaderFollowersHandler.handleEvent(LeaderFollowersHandler.java:77)
         at com.cosylab.epics.caj.impl.reactor.Reactor.processInternal(Reactor.java:400)
         at com.cosylab.epics.caj.impl.reactor.Reactor.process(Reactor.java:284)
         at com.cosylab.epics.caj.CAJContext$2.run(CAJContext.java:708)
         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
         at java.lang.Thread.run(Thread.java:722)

References:

CAJ "AlreadyBoundException" Kasemir, Kay

Navigate by Date:

Prev: Re: CAJ "AlreadyBoundException" Mark Rivers

Next: Re: which time/timestamp format to use for an EPICS facility? Benoit

Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  <2013>  2014  2015  2016  2017  2018  2019  2020  2021  2022  2023  2024 

Navigate by Thread:

Prev: Re: CAJ "AlreadyBoundException" Mark Rivers

Next: StreamDevice "No reply from device" messages John Dobbins

Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  <2013>  2014  2015  2016  2017  2018  2019  2020  2021  2022  2023  2024