Case Study: 2
Scenario 2
Background
You are developing an ASP.NET MVC application in Visual Studio 2012 that will be used to process orders.
Business Requirements
The application contains the following three pages.
A page that queries an external database for orders that are ready to be processed. The user can then
process the order.
A page to view processed orders.
A page to view vendor information.
The application consumes three WCF services to retrieve external data.
Technical Requirements
Visual Studio Solution:
The solution contains the following four projects.
ExternalQueue: A WCF service project used to communicate with the external order database.
OrderProcessor: An ASP.NET MVC project used for order processing and logging order metadata.
OrderUpload: A WCF service project used to submitorder data to an external data source.
Shipping: A WCF service project used to acquire shipping information.
ExternalQueue Project:
Entity Framework is used for data access. The entities are defined in the ExternalOrders.edmx file as shown in
the following diagram.
The project contains two services defined in the following files.
IExternalQueueService.cs
ExternalQueueService.svc.
The ExternalQueue.Helpers namespace contains a definition for a class named OrderNotFound Exception.
OrderProcessor Project:
Entity Framework is used for data access. The entities are defined in the ProcessedOrders.edmx file asshown
in the following diagram.
The classes are contained in the OrderProcessor.Entities namespace. The project contains the followingtwo
controllers.
InboundQueueController.cs
ProcessedOrderController.cs
WCF service proxies to the ExternalQueue, Shipping and OrderUpload services have been generated by using
the command prompt. The ExecuteCommandProcedure() method in the ExternalQueueService.svc file must
run asynchronously.
The ProcessedOrderController controller has the following requirements.
The GetVendorPolicy() method must enforce a 10 minute absolute cache expiration policy.
The GetProcessedOrders() method must return a view of the 10 most recently processed orders.
OrderUpload Project:
The project contains two services defined in the following files.
IUploadCallbackService.cs
UploadCallbackService.svc
Data Access is maintained in a file named UploadOrder.es.
Shipping Project:
Entity Framework is used for data access. The entities are defined in the ExternalOrders.edmx file as shown in
the following diagram.
The Custom Tool property for ExternalOrders.edmx has been removed. POCO classes for the Entity Model are
located in the ShippingAddress.cs file. The POCO entity must be loaded by using lazy loading. The project
contains two services defined in the following files.
IShippingService.cs
ShippingService.svc.
The IShippingService contract must contain an operation that receives an order number as a parameter. The
operation must return a class named ShippingInfo that inherits from a class named State.
Application Structure
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DRAG DROP
The UploadOrder() method in the UploadCallbackService service is not implementing the callback behavior
defined in the IUploadCallBackService interface. You need to modify the class to implement the required
callback behavior. What should you do? (To answer, drag the appropriate code segments to the
correct location or locations in the answer area. Each code segments may be used once, more than once,or
not at all. You may need to drag the split bar between panes or scroll to view content.)
Answer:
the answer should be multiple. that is single?
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No that’s should be Single. because it involves in Callback and it is better to do this in single thread.
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correct response concurrencyMode.Multiple
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why?
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yes Multiple
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why multiple?
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Why is it multiple?
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see http://wcftutorial.net/How-to-Create-Callback-Service-in-WCF.aspx
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it depends of binding type. See
http://stackoverflow.com/questions/6065379/understanding-wcf-servicebehaviorproperty-concurrencymode
“default value is PerCall for bindings not supporting sessions (basicHttpBinding, webHttpBinding, wsHttpBinding without security context or reliable session) or PerSession for bindings supporting sessions (netTcpBinding, netNamedPipeBinding, wsHttpBinding in default configuration using security context).
ConcurrencyMode defines how can an instance of the service be used if multiple requests want to access it. For example PerCall instancing with Multiple concurrency is the same as Single concurrency because each instance is used to serve exactly one request regardless the concurrency setting”
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WCF Instancing mode default is InstanceContextMode.PerSession
https://blogs.msdn.microsoft.com/edpinto/2006/10/16/wcf-instancing-mode-default-is-instancecontextmode-persession/
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If we set Multiple… should not need some synchronization on UploadDB.UploadOrder?
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Single! Wich Multiple you get a deadlock
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As you can see at code is no lock implemented, so assuming concurrency is what service handles itself.
For that reason Single seems to be the right answer. (Multiple if no lock needed)
Deadlock can happen while two calls accessing same resource, its hard to tell as I am not sure what Upload method does in behind the scenes.
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