How to I bind a Hibernate Session to a thread in Grails? - grails

Question

I'm writing a multi-threaded application in Grails and the additional threads need access to GORM/Hibernate. When they try to access GORM I get the error "org.hibernate.HibernateException: No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here".
OK fair enough, can someone guide me on the best way to set the threads up to have access? The error message almost sounds like you just need to change some config options yet I sense, it is not so simple...

Answer 1

There is a bean in Grails applications called “persistenceInterceptor” that can be used for this.
See this example from the JMS plugin on how to use it:
http://github.com/gpc/grails-jms/blob/master/src/groovy/grails/plugin/jms/listener/adapter/PersistenceContextAwareListenerAdapter.groovy#L21
Here is the interface:
https://github.com/grails/grails-core/blob/master/grails-core/src/main/groovy/grails/persistence/support/PersistenceContextInterceptor.java
And Hibernate impl:
https://github.com/grails/grails-data-mapping/blob/master/grails-datastore-gorm-support/src/main/groovy/org/grails/orm/hibernate4/support/HibernatePersistenceContextInterceptor.java

Answer 2

You need to put any GORM calls in a withTransaction closure. An example taken from a discussion of multi threading at
https://fbflex.wordpress.com/2010/06/11/writing-batch-import-scripts-with-grails-gsql-and-gpars/
Single threaded
user = User.findByUsername( photo.username )
multi threaded
User.withTransaction{
user = User.findByUsername( photo.username )
}

Answer 3

withNewSession will also work. In my case, I have low priority updates where the last update can always "win". version: false is also important here in order to avoid the StaleObjectException:
Thread.start {
try {
Widget.withNewSession {
xxx()
log.info "Asynchronously did some updates."
}
} catch (Exception ex) {
log.error "Failed to asynchronously do something...", ex
}
}

Answer 4

Luke Daley gave the right answer. Unfortunately, the links have changed. Thus, I'll update his answer and provide a code example to make this answer self-contained.
There is a bean in Grails applications called persistenceInterceptor that can be used for initializing the persistence context / session for Hibernate. You can inject the bean into one of your controller / service classes and start a new thread, e.g. using the following code snippet.
class YourControllerOrService {
PersistenceContextInterceptor persistenceInterceptor
def someOperation() {
...
Runnable yourTask = { ->
try {
if (persistenceInterceptor) {
persistenceInterceptor.init()
}
// execute the hibernate operations here in a transaction,
// e.g. call a method annotated with #Transactional
...
} catch (Exception e) {
log.error('Your error message', e)
} finally {
if (persistenceInterceptor) {
persistenceInterceptor.flush()
persistenceInterceptor.destroy()
}
}
}
Thread workerThread = new Thread(yourTask)
workerThread.start()
...
}
}
You'll find an exemplary implementation in the Grails JMS plug-in on GitHub.
The PersistenceContextInterceptor interface can be found on GitHub, too.