java NIO select() call does not block

[cthiebot]

On HP-UX 11.11, PA-RISC server, with Java JVM greater than 1.4.1, the Java NIO select() call does not block leading to 100% cpu utilization.

I created a non-blocking SocketChannel and registered it with OP_CONNECT and OP_READ.

The following select() returns 0 without ever blocking:
java.nio.channels.Selector mxChannelsSelector;
int selectReturn = mxChannelsSelector.select(lTimeout);

The same code works with Java 1.4.1 on HP-UX 11.11. It works on Linux RedHat 5 + Java 1.6.

How to make it work on HP-UX with the latest Java JVM (1.6)?

Chris

[cthiebot]

Here is a sample of my Java NIO code using the select() statement. The select() does not block on HP-UX 11.11 as well as HP-UX 11.31 (with Java 1.6).

import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.Iterator;
import java.util.Set;


public class Test {

/**
* @param args
*/
public static void main(String[] args) {
SocketChannel mxSocketChannel = null;
Selector mxChannelsSelector = null;
try
{
mxSocketChannel = SocketChannel.open();
mxSocketChannel.configureBlocking(false);
InetSocketAddress mxRemoteAddress = new InetSocketAddress("localhost", 51421);
boolean t_connect = mxSocketChannel.connect(mxRemoteAddress);
int mnInterestOps = SelectionKey.OP_CONNECT;
//int mnInterestOps = SelectionKey.OP_CONNECT | SelectionKey.OP_READ;

//create the selector
mxChannelsSelector= SelectorProvider.provider().openSelector();

//register the channel with the selector indicating an interest in
// accepting new connections
SelectionKey x_key = mxSocketChannel.register(mxChannelsSelector, mnInterestOps);

//select loop
while(true)
{

//block until connect response is received
int selectReturn = mxChannelsSelector.select(0);

if (selectReturn == 0)
{
System.out.println("select returned 0");
}

} //end while(true)

} //end try block
catch (Exception ex)
{
System.out.println("exception " + ex);
}

}
}

[Dennis Handly]

If nobody else has an answer here, you should contact the Response Center for java support.

You could also use tusc to see what system calls are being made.

[cthiebot]

Actually, I noticed that the channel was already connected just after the connect() call. By testing the connect() return status and not setting the OP_CONNECT flag is the connection was already established, the select() call was behaving properly.

Here is the woking code sample:

public static void main(String[] args) {
SocketChannel mxSocketChannel = null;
Selector mxChannelsSelector = null;
int mnInterestOps = 0;
try
{
mxSocketChannel = SocketChannel.open();
mxSocketChannel.configureBlocking(false);
InetSocketAddress mxRemoteAddress = new InetSocketAddress("localhost", 51421);
boolean t_connect = mxSocketChannel.connect(mxRemoteAddress);

if (t_connect)
{
System.out.println("connected");
mnInterestOps = SelectionKey.OP_WRITE | SelectionKey.OP_READ ;
}
else
{
mnInterestOps = SelectionKey.OP_CONNECT;
}


//create the selector
mxChannelsSelector= SelectorProvider.provider().openSelector();

//register the channel with the selector indicating an interest
SelectionKey x_key = mxSocketChannel.register(mxChannelsSelector, mnInterestOps);


//select loop
while(true)
{

//block until connect response is received
int selectReturn = mxChannelsSelector.select(0);

if (selectReturn == 0)
{
System.out.println("select returned 0");
}

Set myKeys = mxChannelsSelector.selectedKeys();

if (!myKeys.isEmpty())
{
Iterator x_readyKeysIterator = myKeys.iterator();
// Iterate over the set of keys for which events are available
while (x_readyKeysIterator.hasNext())
{
SelectionKey x_selectionKey = (SelectionKey) x_readyKeysIterator.next();

// Remove selected key
x_readyKeysIterator.remove();

if (x_selectionKey.isValid())
{
if (x_selectionKey.isConnectable()) {
mxSocketChannel.finishConnect();
System.out.println("connection 2 accepted");

}
else if (x_selectionKey.isWritable()) {
System.out.println("writable channel, select return =" + selectReturn);
x_selectionKey.cancel();

}
else if (x_selectionKey.isReadable()) {
System.out.println("readable channel" + selectReturn);


}
}
else
{
//cancel the channel registration with this selector
x_selectionKey.cancel();
System.out.println("key not valid");
}

}
}
} //end while(true)

} //end try block
catch (Exception ex)
{
System.out.println("exception " + ex);
}

}

Chris

[cthiebot]

See my reply above.
Chris