Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Concurrency and Transactions

The most basic operations for transactions are commit and rollback, but, in a distributed environment with concurrent processing, it can be difficult to guarantee that commit or rollback operations will be successfully processed, and the transaction can be spread among different threads, CPU cores, physical machines, and networks.

Ensuring that a rollback operation will successfully execute in such a scenario is crucial. Concurrency Utilities relies on the Java Transaction API (JTA) to implement and support transactions on its components through `javax.transaction.UserTransaction`, allowing application developers to explicitly manage transaction boundaries. More information is available in the JTA specification.

Optionally, context objects can begin, commit, or roll back transactions, but these objects cannot enlist in parent component transactions.

The following code snippet illustrates a `Runnable` task that obtains a `UserTransaction` and then starts and commits a transaction while interacting with other transactional components, such as an enterprise bean and a database:

    public class MyTransactionalTask implements Runnable {

       UserTransaction ut = ... // obtained through JNDI or injection

       public void run() {

           // Start a transaction
           ut.begin();

           // Invoke a Service or an EJB
           myEJB.businessMethod();

           // Update a database entity using an XA JDBC driver
           myEJB.updateCustomer(customer);

           // Commit the transaction
           ut.commit();

       }
    }

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