[hibernate-issues] [Hibernate-JIRA] Created: (HHH-5945) Race condition in building query cache

[Luca Domenichini (JIRA)]

Race condition in building query cache
--------------------------------------

                 Key: HHH-5945
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5945
             Project: Hibernate Core
          Issue Type: Bug
          Components: caching (L2)
    Affects Versions: 3.6.1
         Environment: Hibernate 3.6.1, EhCache 2.3.0..2.3.2, MSSQL 2005 Developer Edition
            Reporter: Luca Domenichini


I have this sample program that creates 10 threads that executes the same cached query in a thread-local current session context. Entity ClasseAltezza is a READ_ONLY cached entity.

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	public static void main(String[] args) {
		List<Thread> threads = new ArrayList<Thread>();
		for (int i=0; i<10; i++) {
			Thread t = new Thread() {
				@Override
				public void run() {
					try {
						HibernateUtil.beginTransaction();
						HibernateUtil.getCurrentSession()
							.createCriteria(ClasseAltezza.class)
							.setCacheable(true)
							.setCacheRegion(ClasseAltezza.class.toString())
							.list();
						HibernateUtil.commitTransaction();
					}
					catch (Exception ex) {
						ex.printStackTrace();
						HibernateUtil.rollbackTransaction();
					}
				}
			};
			threads.add(t);
		}
		for (Thread t : threads)
			t.start();
	}
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This is the output:

{panel}{noformat}org.hibernate.cache.CacheException: net.sf.ehcache.ObjectExistsException: Cache class com.promag.wms.base.persistence.entities.ClasseAltezza already exists
	at org.hibernate.cache.EhCacheProvider.buildCache(EhCacheProvider.java:101)
	at org.hibernate.cache.impl.bridge.RegionFactoryCacheProviderBridge.buildQueryResultsRegion(RegionFactoryCacheProviderBridge.java:115)
	at org.hibernate.cache.StandardQueryCache.<init>(StandardQueryCache.java:78)
	at org.hibernate.cache.StandardQueryCacheFactory.getQueryCache(StandardQueryCacheFactory.java:44)
	at org.hibernate.impl.SessionFactoryImpl.getQueryCache(SessionFactoryImpl.java:1173)
	at org.hibernate.loader.Loader.listUsingQueryCache(Loader.java:2285)
	at org.hibernate.loader.Loader.list(Loader.java:2268)
	at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
	at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
	at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
	at com.promag.wms.base.persistence.methods.ClasseAltezzaMethods.getAll(ClasseAltezzaMethods.java:30)
	at Test$1.run(Test.java:20)
Caused by: net.sf.ehcache.ObjectExistsException: Cache class com.promag.wms.base.persistence.entities.ClasseAltezza already exists
	at net.sf.ehcache.CacheManager.addCache(CacheManager.java:888)
	at org.hibernate.cache.EhCacheProvider.buildCache(EhCacheProvider.java:94)
	... 11 more
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I see that in Hibernate 3.6.0 there were a synchronized block in method SessionFactory.getQueryCache(String regionName) the prevented the same query region to be built twice as it happens in Hibernate 3.6.1, were the synchronized block is missing..

This is the method in SessionFactoryImpl:

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	public QueryCache getQueryCache(String regionName) throws HibernateException {
		if ( regionName == null ) {
			return getQueryCache();
		}

		if ( !settings.isQueryCacheEnabled() ) {
			return null;
		}

		synchronized ( allCacheRegions ) { // THIS SYNCHRONIZED IS MISSING IN 3.6.1!!!!
			QueryCache currentQueryCache = ( QueryCache ) queryCaches.get( regionName );
			if ( currentQueryCache == null ) {
				currentQueryCache = settings.getQueryCacheFactory().getQueryCache( regionName, updateTimestampsCache, settings, properties );
				queryCaches.put( regionName, currentQueryCache );
				allCacheRegions.put( currentQueryCache.getRegion().getName(), currentQueryCache.getRegion() );
			}
			return currentQueryCache;
		}
	}
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