I'm having problems acquiring an EntityManager in a multi-threaded application. Each time an EntityManager is needed it is obtained by calling the following SpiderConfig.getNewEntityManager() method:


public static EntityManager getNewEntityManager() {
EntityManagerFactory emf =
Persistence.createEntityManagerFactory("spider");
EntityManager lEm = emf.createEntityManager();
emf.close();
return lEm;
}

I'm getting the exception below when a thread tries to get an EntityManager.

How should the EntityManagerFactory be used? Should a single shared factory instance be used in all the threads or should a new instance be created for each thread?


Exception in thread "Converter" javax.persistence.PersistenceException: org.hibernate.cache.CacheException: Attempt to restart an already started EhCacheProvider. Use sessionFactory.close() between repeated calls to buildSessionFactory. Consider using net.sf.ehcache.hibernate.SingletonEhCacheProvider. Error from ehcache was: Cannot parseConfiguration CacheManager. Attempt to create a new instance of CacheManager using the diskStorePath "/tmp" which is already used by an existing CacheManager. The source of the configuration was classpath.
at org.hibernate.ejb.Ejb3Configuration.createEntityManagerFactory(Ejb3Configuration.java:217)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:114)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:37)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:27)
at fi.kvanttisofta.spider2.config.SpiderConfig.getNewEntityManager(SpiderConfig.java:54)
at fi.kvanttisofta.spider2.Converter.runOnce(Converter.java:38)
at fi.kvanttisofta.spider2.Worker.run(Worker.java:69)
at java.lang.Thread.run(Thread.java:613)
Caused by: org.hibernate.cache.CacheException: Attempt to restart an already started EhCacheProvider. Use sessionFactory.close() between repeated calls to buildSessionFactory. Consider using net.sf.ehcache.hibernate.SingletonEhCacheProvider. Error from ehcache was: Cannot parseConfiguration CacheManager. Attempt to create a new instance of CacheManager using the diskStorePath "/tmp" which is already used by an existing CacheManager. The source of the configuration was classpath.
at org.hibernate.cache.EhCacheProvider.start(EhCacheProvider.java:133)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:180)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1213)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:631)
at org.hibernate.ejb.Ejb3Configuration.createEntityManagerFactory(Ejb3Configuration.java:760)
at org.hibernate.ejb.Ejb3Configuration.createFactory(Ejb3Configuration.java:151)
at org.hibernate.ejb.Ejb3Configuration.createEntityManagerFactory(Ejb3Configuration.java:205)
... 7 more

Single instance.