CODEWITHSUNDEEP
springtransactionsthread-safety
Mr Tea
Mr Tea

Reputation: 101

Accessing Spring @Transactional service from multiple threads

I would like to know if the following is considered safe.

Usual Spring service class that accesses a bunch of DAOS / hibernate entities:

@Transactional
public class MyService {
    ...
    public SomeObject readStuffFromDB(String key)  {
    ...
    //return some records from the DB via hibernate entity etc
}

A class in the application that has the service wired in:

public class ServiceHolder {
    private MyService myService;

    private SomeOtherObject multiThreadedMethod() {

        ...
        //calls myService.readStuffFromDB() and uses the results 
        //to return something useful
}

multiThreadedMethod will be called from multiple threadpool threads. I would like to know if the multiThreadedMethod is safe in its calls to myService. It is NOT making any modifications to the DB - only reading.

What happens if two threads call myService.readStuffFromDB() at exactly the same time? Will a concurrent modification exception be thrown from somewhere?

I've been running it with no issues but I'm not 100% sure it will always work.

Upvotes: 1

Views: 515

Answers (1)

Marek Raki
Marek Raki

Reputation: 3146

Yes you will call the same object in the same time as long as your service bean is defined as singleton (which is default and proper), but you should not rely on local variables in you services. So the methods should be written that way they can work independently (you don't need a mutual exclusion here). If you called db and tried do any operations nothing would happen because every thread would receive a new instance of entity manager. If you modified db in the same time and any type of db exception was thrown you would get a rollback exception which is perfectly fine.

entityManager.persist() will do more or less entityManager.getEntityManagerAssignedToCurrentThread().persist()

It is a proxy not real object. So you are safe :)

Upvotes: 1

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