Deadlock while syncronizing Spring entity manager query - spring

Question

I'm developing an application using Spring which directs the DB using entity manager with #PersistenceContext injection. the application is executed in multiple threads, each in its own #Transactional scope.
As part of the thread process it should go and call :
entityManager.createQuery("some statement").getResultList()
This should return if an object exists on the DB and if not it will persist it. because i am using multiple threads i have put the call in a syncronized block on a shared object like this:
synchronized (getLock())
{
List<SomeObject> listOfObjects = entityManager.createQuery("some statement").getResultList();
if(listOfObjects == null || listOfObjects.size() < 1)
{
createObject();
}
}
The problem is that when I'm running this the process get stuck on the call to the getResultList and never released. Moreover, when i run the code and creating only one thread I get the same behavior.
if i change the flushMode to COMMIT the process is released but the results are not reflected well because the different threads could end at different times and the one creating the object will not necessarily be the one to end first.
my persistence xml is:
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">
<persistence-unit name="syncAdapterUnit"
transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>
<property name="hibernate.max_fetch_depth" value="3"/>
<property name="hibernate.connection.pool_size" value="10"/>
<property name="format_sql" value="false"/>
<property name="hibernate.jdbc.batch_size" value="50" />
<property name="hibernate.cache.use_query_cache" value="false" />
<property name="hibernate.cache.use_second_level_cache" value="false" />
</properties>
</persistence-unit>
</persistence>
The spring bean xml:
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.springframework.org/schema/beans"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
<tx:annotation-driven transaction-manager="transactionManager"/>
<bean id="managerFactoryBean" class="com.amdocs.dim.ManagerFactory" />
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory"/>
</bean>
<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean" destroy-method="destroy">
<property name="dataSource" ref="myDataSource"/>
<property name="jpaVendorAdapter" ref="hibernateVendorAdapter"/>
<property name="persistenceUnitName" value="syncAdapterUnit"/>
</bean>
<bean id="hibernateVendorAdapter"
class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="showSql" value="true"/>
<property name="generateDdl" value="false"/>
<property name="databasePlatform" value="org.hibernate.dialect.Oracle10gDialect"/>
<property name="database" value="ORACLE"/>
</bean>
<bean id="cifDBProperties" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="ignoreUnresolvablePlaceholders" value="true" />
<property name="location" value="classpath:APP-INF/conf/database.properties"/>
<property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_FALLBACK"/>
</bean>
<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" scope="singleton">
<property name="driverClassName" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</bean>
</beans>
I believe that the flush process is the one which blocks the app but didn't manage to understand why.