public final class Transactions

The transaction a @Transactional method runs in, bound to the calling thread.

The build rewrites every @Transactional method into a call to begin, the original body, then commit – or afterThrow with the rollback decision it worked out from the annotation. Propagation, isolation, read-only and timeout arrive as constants. This class binds the connection, completion hooks and scoped resources to the physical transaction on the calling thread.

Joining

Nothing has to be handed the transaction. DataSource.borrow asks this class first, and a thread inside a transaction gets the transaction’s connection back instead of a pooled one – so the pool’s own methods, an EntityManager’s daos and a managed session all join it. The connection is borrowed, and BEGIN sent, only when the transaction first needs it: a @Transactional method that returns before touching the database costs only an in-memory scope, with no database round trip.

A thread that has never begun a transaction does not even read the thread-local: used is set by the first begin of the process, on the thread that is then inside it, so every other thread reading a stale false is correct – none of them is in a transaction.

Propagation

Spring’s seven, one for one; the constants below are the ordinals of com.codename1.backend.annotations.Propagation. A method that joins a transaction and fails with a rollback-worthy exception marks the whole transaction rollback-only, and the method that began it then rolls back and throws TransactionException.UnexpectedRollback rather than reporting a commit that did not happen.