Passing Object References

You must ensure that MTS object references are only exchanged in the following ways:

• Through return from an object creation interface, such as CoCreateInstance (or its equivalent), ITransactionContext::CreateInstance, or IObjectContext::CreateInstance.
• Through a call to QueryInterface.
• Through a method that has called SafeRef to obtain the object reference.

An object reference that is obtained in these ways is called a safe reference. MTS ensures that methods invoked using safe references execute within the correct context.

Using SafeRef to pass a reference to an object

Note It is not safe to exchange references by any other means. In particular, do not pass interfaces outside the object by using global variables. These restrictions are similar to those imposed by COM for references passed between apartments.

Calls that use safe references always pass through the MTS run-time environment. This allows MTS to manage context switches and allows MTS objects to have lifetimes that are independent of client references. For more information, see Deactivating Objects.

Callbacks

It is possible to make callbacks to clients and to other MTS components. For example, you can have an object that creates another object. The creating object can pass a reference to itself to the created object; the created object can then use this reference to call the creating object.

If you choose to use callbacks, note the following restrictions:

• Calling back to the base client or another package requires Access-level security on the client. Additionally, the client must be a DCOM server.
• Intervening firewalls may block calls back to the client.
• Work done on the callback executes in the environment of the object being called. It may be part of the same transaction, a different transaction, or no transaction.
• The creating object must call SafeRef and pass the returned reference to the created object in order to call back to itself.

See Also

SafeRef