Creating a Superior Transaction Manager
In KTM, a superior transaction manager is a resource manager that creates superior enlistments for the transactions that it participates in. A superior enlistment is an enlistment that grants the resource manager the ability to coordinate the commit operation for the enlistment's transaction. In other words, either a transactional client or the superior transaction manager can start the pre-prepare/prepare/commit sequence for the transaction.
After a resource manager has created a superior enlistment for a transaction, KTM rejects all calls to ZwCommitTransaction for the transaction. Therefore, transactional clients cannot commit such a transaction. Instead, the resource manager that created the superior enlistment must call ZwPrePrepareEnlistment, ZwPrepareEnlistment, and ZwCommitEnlistment.
When to Create a Superior Transaction Manager
Suppose that you want to integrate a transaction processing system (TPS) component with KTM, but the component contains its own non-KTM transaction management capabilities that clients can call. In such a situation, you might have to create a superior transaction manager.
For example, suppose that your component provides its own interfaces that clients use to create and commit transactions. Because your component's clients do not call KTM to create or commit transactions, your component must become a superior transaction manager when you integrate it into a KTM-based TPS.
How to Create a Superior Transaction Manager
If you want your component to be a superior transaction manager, it must do the following:
Call ZwCreateResourceManager to register as a resource manager.
Call ZwCreateTransaction every time that a client of your component creates a transaction by using your component's client interface.
Call ZwCreateEnlistment, setting the ENLISTMENT_SUPERIOR flag, and specifying both the ENLISTMENT_SUPERIOR_RIGHTS and ENLISTMENT_SUBORDINATE_RIGHTS access flags.
KTM permits only one superior enlistment per transaction. Other resource managers can create additional enlistments. These enlistments are called subordinate enlistments because they cannot initiate the commit operation.
To roll back a superior enlistment, your superior transaction manager calls ZwRollbackEnlistment.
To recover a superior enlistment, your superior transaction manager calls ZwRecoverEnlistment.
When a superior transaction manager commits, rolls back, or recovers a transaction, KTM sends transaction notifications to all subordinate enlistments so that they can participate.
A TPS that includes a superior transaction manager cannot use single-phase commit operations.
During a recovery operation, if KTM cannot determine the outcome of a transaction, it sends a TRANSACTION_NOTIFY_RECOVER_QUERY notification to the superior transaction manager. In response, the superior transaction manager must call ZwCommitEnlistment if the transaction can be committed or ZwRollbackEnlistment if the transaction should be rolled back. If the superior transaction manager cannot determine the outcome of a transaction, it should not respond to the TRANSACTION_NOTIFY_RECOVER_QUERY notification until it can determine an outcome.