Spring transactions TransactionSynchronizationManager: isActualTransactionActive vs isSynchronizationActive

Question

I am a little bit confused about transaction resource management in Spring. Namely, I am confused about the usage of TransactionSynchronizationManager.isActualTransactionActive and TransactionSynchronizationManager.isSynchronizationActive.

Up to now, probably incorrectly, I assumed that isSynchronizationActive was used (also within the Spring codebase) to figure out whether there is an active transaction, initiated by TransactionSynchronizationManager.initSynchronization(). As far as I am concerned, when we suspend a transaction, the actual isSynchronizationActive is still true! I presume, therefore, the correct way of establishing a running transaction is by using isActualTransactionActive, correct?

If this is the case, what is the actual point of isSynchronizationActive method? I understand it tells you whether you can add synchronizations or not, but I am a bit lost about what it tells us about the transaction...

Answer 1

You will notice the following fields of TransactionSynchronizationManager

private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations =
        new NamedThreadLocal<Set<TransactionSynchronization>>("Transaction synchronizations");

private static final ThreadLocal<Boolean> actualTransactionActive =
        new NamedThreadLocal<Boolean>("Actual transaction active");

and the methods

public static boolean isSynchronizationActive() {
    return (synchronizations.get() != null);
}

public static boolean isActualTransactionActive() {
    return (actualTransactionActive.get() != null);
}

The TransactionSynchronizationManager basically acts as a registry for TransactionSynchronization. The javadoc states

If transaction synchronization isn't active, there is either no current transaction, or the transaction manager doesn't support transaction synchronization.

So you first init and register TransactionSynchronization with initSynchronization() and registerSynchronization(TransactionSynchronization). When these are registered, the TransactionManager can start a Transaction and tell the TransactionSynchronizationManager if it's active or not with setActualTransactionActive(boolean).

In conclusion, isSynchronizationActive() tells us if TransactionSynchronization has been enabled, even if no TransactionSynchronization instances have been registered.

isActualTransactionActive() tells us if there is an actual Transaction object active.

The TransactionSynchronizationManager javadoc states

Central helper that manages resources and transaction synchronizations per thread. To be used by resource management code but not by typical application code.

so don't ignore it.