Question

When i have a file transfer and the device loses internet connection
the DataOutputStream.write is sometimes blocking almost indefinably.

i know this is kind of normal since the underlying socket layers are doing it’s job as fast as it can.

I was thinking to use the

registerReceiver(mConnRec,new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));

and catch when this happen and do a socket.close() or DataOutputStream.close()
to force the DataOutputStream.write to stop block and normal code flow would occur
faster.

Will this work or what can i do to control the blocking?

Another ide i had was to start a thread which job is to every 5 sec
test internet exist like this

public boolean haveNetworkConn(Context ctx)
{
    boolean HaveConnectedWifi = false;
    boolean HaveConnectedMobile = false;

    ConnectivityManager cm = (ConnectivityManager) ctx.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo[] netInfo = cm.getAllNetworkInfo();

    for (NetworkInfo ni : netInfo)
    {
        if (ni.getTypeName().equalsIgnoreCase("WIFI"))
            if (ni.isConnected())
                HaveConnectedWifi = true;
        if (ni.getTypeName().equalsIgnoreCase("MOBILE"))
            if (ni.isConnected())
                HaveConnectedMobile = true;
    }
    return HaveConnectedWifi || HaveConnectedMobile;
} 

If that return false i could force a socket.close maybe.

Would really like to have some feedback on this ideas

UPDATE
Running some tests using the registerReceiver BroadcastReceiver.
Nothing happens when i close the data in and OutputStream and the socket itself.
It keeps on blocking at out.write(buffer, 0, val);. This was most unexpected.
using Eclipse and placing breakpoints and stepping..

private BroadcastReceiver mConnReceiver = new BroadcastReceiver() {

@Override
public void onReceive(Context context, Intent intent) {

     String action = intent.getAction();

     if (!action.equals(ConnectivityManager.CONNECTIVITY_ACTION)){
         return;
     }

     boolean noConnectivity = intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, false); 
     NetworkInfo aNetworkInfo = (NetworkInfo) intent.getParcelableExtra(ConnectivityManager.EXTRA_NETWORK_INFO);                     

     if (!noConnectivity)
     {
         if ((aNetworkInfo.getType() == ConnectivityManager.TYPE_MOBILE) || (aNetworkInfo.getType() == ConnectivityManager.TYPE_WIFI))
         {
             //Handle connected case
         }
     }
     else
     {
        if ((aNetworkInfo.getType() == ConnectivityManager.TYPE_MOBILE) || (aNetworkInfo.getType() == ConnectivityManager.TYPE_WIFI))
        {
            //Handle disconnected case
            if(socket != null)
                try {
                    out.close();
                    in.close();
                    socket.close();

                } catch (IOException e) {

                }
        }
     }

}
};

Answer 1

Yes, closing a socket is a way to unblock all the method calls currently blocked on the socket. Quoting from the documentation for close():

Any thread currently blocked in an I/O operation upon this socket will
throw a SocketException.

See also section 7.1.6 in “Java Concurrency in Practice”.

Registering a receiver for CONNECTIVITY_ACTION is a better solution than polling every 5 seconds since it saves CPU cycles and potentially allows for better latency in your application’s reaction to connectivity change.