JVM Crashes with a VM state:not at safepoint (normal execution) error

Question

Hello.
I have been battling with this error occasionally ocurring for months. There are many suggestions in various blogs and they all seem to think it's a JVM bug. I'm not so sure.
I am running JBOSS 4.0.5 on SuSE Linux 10. JVM is Java HotSpot(TM) Server VM (1.5.0_21-b01 mixed mode). The code is a servlet-based non-J2EE expanded WAR file. When my app starts, it instantiates a static object called ProductCache. This object has an inner class that extends Thread called RefreshThread which runs continually, sleeping for 60 minutes and then refreshing a java.util.Map in ProductCache called cache. It does this by calling a synchronized method addItem in the parent (ProductCache).
RefreshThread does this initial population of cache when it is instantiated and before start() is called by the instantiating class (ProductCache).
When I occasionally get the aforementioned JVM crash, it is always when this RefreshThread wakes up for the first time (60 minutes after instantiation). I immediately restart the JBOSS instance again, and the crash doesnt't happen again - until I stop JBOSS and replace the WAR with a new version. Once I restart JBOSS, there is a risk I may get the crash again. If I do, restarting JBOSS fixes it again!
I have tried stopping and starting JBOSS a second time immediately after updating the WAR file and this seems to mitigate the problem, but occasionally it still occurs. Restarting after the crash always stops the problem happening again even in this case.
Is there something about multithreading I am doing wrong? Are there special rules about instantiating threads from static objects? What about calling synchronized methods from threads instantiated by the object containing the synchronized method? Why would a restart after the crash always fix it?
Linux Info:
OS:SUSE Linux Enterprise Server 10 (i586)
VERSION = 10
uname:Linux 2.6.16.21-0.8-bigsmp #1 SMP Mon Jul 3 18:25:39 UTC 2006 i686
libc:glibc 2.4 NPTL 2.4
rlimit: STACK 8192k, CORE 0k, NPROC 71680, NOFILE 1024, AS infinity
load average:0.12 0.07 0.01
CPU:total 4 (cores per cpu 2, threads per core 1) family 6 model 15 stepping 6, cmov, cx8, fxsr, mmx, sse, sse2
Memory: 4k page, physical 8308300k(1178612k free), swap 2561k(2561k free)JVM command:
jvm_args: -Dprogram.name=run.sh -Xms512m -Xmx2048m -XX:-UseOnStackReplacement -Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000 -Djava.awt.headless=true -Duser.timezone=Pacific/Auckland -Djava.endorsed.dirs=/home/jboss/jboss-live-nz/lib/endorsed
java_command: org.jboss.Main -b webapp1-2 -c default -Dlog4j.configuration=file:///home/jboss/jboss-live-nz/bin/log4j.properties
Launcher Type: SUN_STANDARDRefreshThread code (partial):
     private class RefreshThread extends Thread implements RecordListener {
          private boolean die = false;
          private ProductCache parent;
          private DAOFactory factory;
          private CacheProductManager productManager;
          private AssortmentCache assortmentCache;
          private Map products;
          private RefreshThread( ProductCache caller ) throws Exception {
              this.setName( "CellnetProductCacheRefresh" );
              parent = caller;
                    factory = DAOFactory.getInstance( context );
                    productManager = (CacheProductManager)factory.createProductCacheLoader();
                    assortmentCache = AssortmentCache.getInstance( context );
              loadFromDatabase( true );
              loadV6Data();
          public void stopRefresh() {
               this.interrupt();
          public void run() {
               while( ! die ) {
                    try {
                         Thread.sleep( AppProperties.CACHE_PRODUCT_REFRESH_RATE * 60 * 1000 );
                         products = new HashMap();
                         productManager.loadAllItemsFromDatabase( this );
                         GregorianCalendar now = new GregorianCalendar();
                         if ( now.get( GregorianCalendar.HOUR_OF_DAY ) == 23 ) {
                             update( true, products );
                         } else
                             update( false, products );
                    } catch (CellnetWebException cwe) {
                        cwe.printStackTrace();
                    } catch (InterruptedException ie) {
                        die = true;
                    } catch (Exception e) {
                        e.printStackTrace();
         private void update( boolean fullReload, Map products ) throws Exception {
               int addedCount = 0;
               for( Iterator iter = products.keySet().iterator(); iter.hasNext(); ) {
                   ProductBean product = (ProductBean)products.get( iter.next() );
                   if ( fullReload || (! cache.containsKey( product.getId()) ) ) {
                       parent.setItem( product, null );
                       ++addedCount;
                       if ( ! fullReload ) {
                           try {
                             List productAssortments = productManager.findAssortments( product.getId() );
                             for( Iterator listIter = productAssortments.iterator(); listIter.hasNext(); ) {
                                 String assortmentId = (String)listIter.next();
                                 assortmentCache.addItem( assortmentId, product.getId() );
                         } catch (Exception e) {}
               if ( ! fullReload ) {
                   int deletedCount = 0;
                    for( Iterator iter = cache.keySet().iterator(); iter.hasNext(); ) {
                        String id = (String)iter.next();
                        if ( ! products.containsKey( id ) ) {
                            iter.remove();
                            ++deletedCount;
                            assortmentCache.removeItem( id );
               if ( fullReload ) {
                    assortmentCache.refresh();
         private void loadFromDatabase( boolean fullReload ) throws Exception {
             if ( productManager == null ) {
                 DAOFactory factory = DAOFactory.getInstance( context );
                 productManager = (CacheProductManager)factory.createProductCacheLoader();
             if ( fullReload ) {
                    System.out.println( "Full Product Cache upload commenced" );
                 cache = new HashMap();
             products = new HashMap();
               productManager.loadAllItemsFromDatabase( this );
               System.out.println( products.size() + " Products Loaded from the Database" );
               update( fullReload, products );
...

Answer 1

What do you mean by JVM crash? A core dump? Your code, shouldn't be able to cause a core dump even if you had a bug in it.
I did not read your code, and I don't know what you mean by static object, but you can start a thread from wherever you want, and where the thread was created doesn't matter. It should be able to invoke any methods. The only things that you have to think about is that you can get race conditions, deadlocks and all other issues that are related to concurrency.
Kaj