Sudden exit of Thread without Exception or Error

Question

Hi @all,
I've got some strange problem.
Within my socket server I handle each request within a Thread. Inside this Thread, the whole code is surrounded by...
try
catch( Throwable th )
Sometimes a Thread dies without occurence of any Exception or Error.
Especially strage is, that (if it crashes) always objects of the same class and exactly the same line of code is executed last.
There is kind of logging, that is executed last, like ...
logLogger.debug( "" );
Next should be getting the instance of a Singleton, which is a database connection pool, and getting a database connection out of it.
DbConnectionPool.getInstance().getDbConnection();
Within "getInstance()", the first line of code is logging, as well as the first line of "getDbConnection()".
The logger that I use is log4j. The same code is used in many classes, but the error only occurs in few of them.
Do you have any idea, what this error could be about?
Could it be, that there is no Throwable risen in case of an error, but only the concerning Thread dies, but the whole virtual machine and other functionality works well, as before?
My system :
Suse Linux Enterprise Server Version 8 /
Suse Linux Enterprise Server Version 10
At least 4 CPUs and 8 GiB of RAM, as well as enough space on hard disk.
Java virtual machine :
Java(TM) SE Runtime Environment (build 1.6.0_20-b02), Java HotSpot(TM) Server VM (build 16.3-b01, mixed mode) /
Java(TM) SE Runtime Environment (build 1.6.0-b105), Java HotSpot(TM) Server VM (build 1.6.0-b105, mixed mode)
Many thanks in advance.
Bye ... Christian

Answer 1

The concerning code is as follows.
The Thread class :
try
// Get AddressCount parameter from configuration.
int iAddressCount = 0;
try
iAddressCount = Integer.parseInt( elmF1755.getAttributeValue( ATT_ADDRESSCOUNT ) );
logLogger.debug( "Received AddressCount from configuration : " + iAddressCount ); *// This is the last executed line of code.*
catch( Exception ex )
throw new Exception( String.format( "Invalid configuration attribute <%1$s : %2$s : %3$s>.", Constants.FUNCTIONPARAMETER, Constants.ELM_F1755, Constants.ATT_ADDRESSCOUNT ), ex );
// Get free database connection from the pool.
clsDB = DbConnectionPool.getInstance().getDbConnection();
if( clsDB == null )
throw new Exception( "No free database connection available." );
catch( Throwable th )
String strError = th.getClass().getSimpleName() + " occured. (" + th.getMessage() + ")";
logLogger.error( strError, th );
clsResponse.clear();
clsResponse.setTag( SSI_T002_FUNCID, GLF1755_ID );
clsResponse.setFuncOrRetVal( SSI_E999_SYSERROR, strError );          
return clsResponse.getResponseString();
finally
// Clean-up
if( result != null )
result.close();
logLogger.debug( "End execute." );
The DbConnectionPool code :
public static DbConnectionPool getInstance()
throws Exception
logLogger.debug( "Get instance of the DbConnectionPool." ); *// This should be executed next*
if( instance == null )
instance = new DbConnectionPool();
return ( instance );
public synchronized Connection getConnection()
logLogger.debug( "Start getConnection." ); *// This should be executed as well*
}