COM & .NET Component Services

Voting on a Transaction

As mentioned before, a transactional object votes whether to commit or abort the transaction by setting the value of a bit in the context object. That bit is called the consistency bit. The name is appropriate. Consistency is the only transaction property under the application’s objects control. COM+ can manage atomicity and the resource managers guarantee isolation and durability, but only the objects know whether the changes they make to the system state are consistent or if they encounter errors that merit aborting the transaction.

When COM+ creates a transactional object, it puts it in its own private context and sets the context object consistency bit to TRUE. As a result, if the object makes no explicit attempt to set the consistency bit to FALSE, the object’s votes to commit the transaction.

Tip

An object can actually share its context with other objects whose transaction setting is set to Disabled.

The object can set the value of the consistency bit by accessing the context object and getting hold of IContextState interface, defined as:

enum tagTransactionVote
{
   TxCommit= 0,
   TxAbort = TxCommit + 1
}TransactionVote;

interface IContextState : IUnknown 
{
   HRESULT SetDeactivateOnReturn([in] BOOL bDeactivate);
   HRESULT GetDeactivateOnReturn([out]BOOL* pbDeactivate);
   HRESULT SetMyTransactionVote ([in]TransactionVote txVote);
   HRESULT GetMyTransactionVote ([out]TransactionVote* ptxVote);
}

IContextState is also discussed in Chapter 3, in the context of deactivating ...