Re: McKoi db error

[Geert Bevin <gbevin at uwyn dot com>]

Tom Tromey wrote:
> If readObject and writeObject aren't implemented, all serialization
> implementations are required to fall back on the default behavior.
> Are you saying that libgcj doesn't do this in some situation?

Yes, exactly. In certain cases when the writeObject method is not
implemented and the readObject method is. I've attached a testcase of
the bug.

> That would be a libgcj bug.

It feels like it.

> I don't know of any java.io bugs that would cause this behavior.
> It is possible that you've run into a serialization bug, however.
> The easiest way to tell would be to try to reduce it to a simple test

I'm communicating with the author, but it's extremely tedious to find
since there's a *lot* of code in between the writing and the reading
that fails. I'll keep you posted though.

> case.  You could also look through gnats to see if there are other
> serialization bugs; maybe you've run into a known one.  I'm afraid
> this is an area that hasn't gotten a lot of attention in the past.

Ok, thanks for the help.

Geert Bevin

--
Geert Bevin             Uwyn
"Use what you need"     Lambermontlaan 148
http://www.uwyn.com     1030 Brussels
gbevin at uwyn dot com         Tel & Fax +32 2 245 41 06

PGP Fingerprint : 4E21 6399 CD9E A384 6619  719A C8F4 D40D 309F D6A9
Public PGP key  : available at servers pgp.mit.edu, wwwkeys.pgp.net

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class SerializationBug
{
	public static class Expr implements java.io.Serializable
	{
		static final long serialVersionUID = 6981261114471924028L;
		private ArrayList elements = new ArrayList();
		private transient ArrayList eval_stack;
		private StringBuffer text;
		public Expr()
		{
			text = new StringBuffer();
		}
		private void writeObject(java.io.ObjectOutputStream out)
			throws IOException
		{
			out.defaultWriteObject();
		}
		private void readObject(ObjectInputStream in)
			throws IOException, ClassNotFoundException
		{
			in.defaultReadObject();
		}
	}
	
	public static class NodeType4 implements java.io.Serializable
	{
		static final long serialVersionUID = 7866310557831478639L;
		private long id;
		private final static Object GLOB_LOCK = new Object();
		private static int GLOB_ID = 0;
	
		public NodeType4()
		{
			synchronized (GLOB_LOCK)
			{
				id = (System.currentTimeMillis() << 16) | (GLOB_ID & 0x0FFFF);
				++GLOB_ID;
			}
		}
	}

	public static class NodeType3 implements java.io.Serializable
	{
		static final long serialVersionUID = -108747827391465748L;
		private Object first;
		private Object second;

		public NodeType3(Object first, Object second)
		{
			this.first = first;
			this.second = second;
		}
	}

	public static class NodeType2 implements java.io.Serializable
	{
		static final long serialVersionUID = -7783166856668779902L;
		private Object first;
		private Object second;

		public NodeType2(Object first, Object second)
		{
			this.first = first;
			this.second = second;
		}
	}

	public static class NodeType1 implements java.io.Serializable
	{
		static final long serialVersionUID = 4133205808616807832L;
		private Object first;
		private Object second;
		private Object third;

		public NodeType1(Object first, Object second, Object third)
		{
			this.first = first;
			this.second = second;
			this.third = third;
		}
	}

	private static Class c1 = com.mckoi.JDBCDriver.class;

	public static void main(String[] args)
	{
		System.out.println("testing");
		try
		{
			ByteArrayOutputStream byte_out = new ByteArrayOutputStream();
			ObjectOutputStream out = new ObjectOutputStream(byte_out);
			NodeType4 node6 = new NodeType4();
			NodeType3 node5 = new NodeType3(node6, null);
			NodeType4 node4 = new NodeType4();
			NodeType3 node3 = new NodeType3(node4, new Expr());
			NodeType2 node2 = new NodeType2(node3, node6);
			NodeType1 node1 = new NodeType1(node2, null, null);
			System.out.println("writing nodes");
			out.writeObject(node1);
			out.flush();
			out.close();
			out = null;
			System.out.println("reading nodes");
			byte[] buf = byte_out.toByteArray();
			ObjectInputStream in =
				new ObjectInputStream(new ByteArrayInputStream(buf));
			try
			{
				in.readObject();
			}
			catch (ClassNotFoundException e1)
			{
				e1.printStackTrace();
			}
		}
		catch (IOException e)
		{
			throw new Error("IO Error: " + e.getMessage());
		}
	}
}