Lesson 11: Case Scenario Answers in C#

Printing Data Matrix 2d barcode in C# Lesson 11: Case Scenario Answers

1. The client is not involved in this transaction at all, other than to initiate the call to the internal WCF service. Because the transaction originates with the service and not with the client application, no configuration or deployment issues arise. 2. To propagate transaction information across the Internet, the WS-AtomicTransaction (WS-AT) protocol must be used, which requires the Microsoft Distributed Transaction

Controller (MSDTC) to be running on the computer that hosts the internal WCF service. Also, WS-AT must be enabled within the MSDTC configuration. From a configuration perspective, the endpoint associated with the external WCF service must use a binding that is capable of supporting transactions, and that particular binding should be marked as allowing transaction information to flow from the client to the service because, in this instance, the internal WCF service is actually the client to the external WCF service. 3. As it turns out, using WCF as the transaction mechanism eliminates most of the technical challenges. Within WCF, it is already possible for transaction information to move easily from client to service and for all updates to complete within that structure. The real challenge is in configuring the external WCF service properly. It too must be running MSDTC with WS-AT enabled and using a data source that can participate in an MSDTC-driven transaction. In addition, an underlying assumption is that the service will act in a properly transactional way, so no data updates will take place on the external service that cannot be part of the transaction.

1. Correct Answers: B and D A. Incorrect: These options would cause a single instance of the service object to be created for all requests. The concurrency mode of Multiple means that more than one simultaneous request is possible. With multiple requests, the possibility of concurrency issues associated with updating the hitCounter variable exists. B. Correct: The use of a concurrency mode of Single ensures that only one request at a time can be processed. Even though more than one session could be active, the fact that the hitCounter variable is an instance variable means that it cannot be updated by more than one thread at a time. C. Incorrect: Even though the InstanceContextMode is set to PerSession, more than one request, even from the same session, can occur. This means that two requests can be processed in the same instance, which, in the case of the class, means that concurrency problems can occur. D. Correct: The Single concurrency mode ensures that only one request is processed at a time, and the Single instance context mode means that only one instance is ever created.

2. Correct Answer: D A. Incorrect: These options would cause a single instance of the service object to be created for all requests. The concurrency mode of Multiple means that more than one simultaneous request is possible and, with multiple requests, the possibility of concurrency issues associated with updating the hitCounter variable exists. B. Incorrect: Although a concurrency mode of Single ensures that each service object can process only one request at a time, this is not sufficient when a shared or static variable is being used. The fact that the instance context mode is PerSession means that multiple service objects can be instantiated, each of which could update hitCounter. This introduces the possibility of concurrency problems. C. Incorrect: Having a PerSession instance context means multiple service objects, and a concurrency mode of Multiple means that simultaneous requests in each object are possible. Either one of these is sufficient to open up the possibility of concurrency issues. D. Correct: The concurrency mode ensures that only one request is processed at a time, and the instance context mode means that only one instance is ever created. This combination is required for static or shared variables to be safe from concurrency violations.