For a typical use case triggered by a HTTP request and involving a database query this works as follows. The request thread handles the request that goes into the boundary; for example, a JAX-RS UsersResource, by the inversion of control principle, the JAX-RS resource method is called by the container. The resource injects and uses a UserManagement EJB, which is also invoked indirectly by the container. All operations executed by the proxies happen in synchronous terms. The EJB will use an entity manager to store a new User entity and as soon as the business method that initiated the currently active transaction returns, the container will try to commit the transaction to the database. Depending on the transaction result, the boundary resource method resumes and constructs the client response. All this happens synchronously while the client call blocks and waits for the response.

Synchronous execution includes the handling of synchronous CDI events. Events decouple firing domain events from handling them; however, the event handling is performed synchronously. There are several kinds of transactional observer methods. By specifying the transaction phase, the event will be handled at transaction commit time, either before completion, after completion, only after a failed transaction, or after a successful transaction, respectively. By default, or when no transaction is active, CDI events are handled immediately when they are fired. This enables engineers to implement sophisticated solutions; for example, involving events that happen only after entities have been added to the database successfully. Again, in all cases, this handling is executed synchronously.