Crash in Serialization + Multiple Threads

I encounter NullPointerExceptions when I use Java-Serialization in multiple threads (.NET v1.1.4322, vjslib 1.0.5000.0). Here my test program:

package SerializationCrash;

import java.io.*;

public class Program
{
public static class Transfer implements java.io.Serializable
{
public int _a;
public String _b;
public double _c;

public Transfer()
{}

public Transfer(int a, String b, double c)
{
_a = a;
_b = b;
_c = c;
}
}

public static class Runner implements Runnable
{
private int _no;
public Runner(int no)
{
_no = no;
}

public void run()
{
try
{
Transfer[] t = new Transfer[100];

for(int j = 0; j < t.length; j++)
t[j] = new Transfer(j, "Transfer " + j, j + 0.5);

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(t);
oos.flush();
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
System.out.println("Thread " + _no + " finished");
}
}
}

/** @attribute System.STAThread() */
public static void main(String[] args) throws Exception, RuntimeException
{
Transfer tr = new Transfer();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(tr);

Thread[] t = new Thread[100];

for(int j = 0; j < t.length; j++)
{
t[j] = new Thread(new Runner(j));
t[j].start();
}

for(int j = 0; j < t.length; j++)
{
if(t[j].isAlive())
t[j].join();
}
}
}

Most of the threads crash with the following stack trace:

java.lang.NullPointerException: Object reference not set to an instance of an object.
at java.io.ObjectOutputStream.defaultWriteObject()
at java.io.ObjectOutputStream.writeObject(Object obj)
at java.io.ObjectOutputStream.writeArrayElements(Object obj, Int32 len, Class elemType)
at java.io.ObjectOutputStream.writeObject(Object obj)
at SerializationCrash.Runner.run()

When I run this program with only a bunch of threads (say 5) then it seems to work seamlessly. Another thing I recognized: when I serialize a Transfer-Object once before I start the threads, the error doesn't seem to happen:

public static void main(String[] args) throws Exception, RuntimeException
{
Transfer tr = new Transfer();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(tr);

Thread[] t = new Thread[100];
....

Do you know anything about issues concerning using Java-Serialization in multiple threads concurrently Perhaps the threads share serialization information about the Transfer-Class which is not synchronized.

Any hints would be welcome !

Best regards,

Michael

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Crash in Serialization + Multiple Threads

S Collins
Yes it runs nice under .NET 2.0 but sadly I have to support .NET 1.1 in the near future. So are there any hints why this is happening with the specified .NET version

Best regards,

Mike
guru13
Your application is working perfectly with .NET 2.0 (Visual Studio 2005).

Thread 0 finished
Thread 1 finished
Thread 2 finished
Thread 3 finished
Thread 4 finished
Thread 5 finished
Thread 6 finished
Thread 7 finished
Thread 8 finished
Thread 9 finished
Thread 10 finished
Thread 11 finished
Thread 12 finished
Thread 13 finished

.

.

.

Thread 99 finished
Crash in Serialization + Multiple Threads

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