I'm developing a UWP client project which need to consume some services of a WCF server. I uses the "add service reference" tool of Visual Studio to auto generate service clients(proxies). The binding type is NetTcpBinding. Below is some code snippet which create the service client:
NetTcpBinding tcpBinding = new NetTcpBinding();
tcpBinding.Security.Mode = SecurityMode.None;
tcpBinding.Security.Transport.ClientCredentialType = TcpClientCredentialType.None;
tcpBinding.Security.Message.ClientCredentialType = MessageCredentialType.None;
MainServiceClient = new MainServiceClient(tcpBinding, new EndpointAddress("net.tcp://localhost:8773/MyWCF/MainService/tcp"));
The question is do I need to call OpenAsync() method of MainServiceClient? It seems the service client can be auto opened when it is first called. But I read from this article that auto-opened service client would have some performance penalty. The article was written in 2007. I just wonder if this mechanism have changed today, especially in UWP project. Can anyone share more light on this topic? Thanks!
To explain this case, you should know three ways to do WCF instance management. WCF has provided three ways by which you can control WCF service instances:Per call, Per session, Single instance.
When we configure a WCF service as per call, new service instances are created for every method call you make via a WCF proxy client.
Very often we need to maintain state between method calls or for a particular session. For those kinds of scenarios, we will need to configure the service per session. In per session, only one instance of a WCF service object is created for a session interaction.
Often we would like to create one global WCF instance for all WCF clients. To create a single instance of a WCF service, we need to configure the WCF service as Single instance mode.
And there are three ways by which you can handle concurrency for each service instance in WCF :single, multiple, and reentrant.
Single: A single request has access to the WCF service object at a given moment of time. So only one request will be processed at any given moment of time. The other requests have to wait until the request processed by the WCF service is completed.
Multiple: In this scenario, multiple requests can be handled by the WCF service object at any given moment of time. In other words, requests are processed at the same time by spawning multiple threads on the WCF server object. So you have great throughput here but you need to ensure concurrency issues related to WCF server objects.
Reentrant: A single request thread has access to the WCF service object, but the thread can exit the WCF service to call another WCF service or can also call a WCF client through callback and reenter without deadlock.
In "Instance mode = Per Session and Concurrency = Single" combination, one WCF service instance is created for every WCF client session because the WCF instance mode is set to per session. All the method are executed in a sequential manner one by one. In other words, only one thread is available for all method calls for a particular service instance.
For the above scenario, you should always open WCF client proxy explicitly before you are making any calls. Because it will maintain service state between method calls and obtain high performance.
For more detail you could refer to "WCF Concurrency (Single, Multiple, and Reentrant) and Throttling" and "Three ways to do WCF instance management".
Related
I have a WCF service with duplex binding hosted within a windows service. The service has to continuously poll for changes in a datasource (Azure service bus to be specific, but type of datasource isn't really important). If there is any new change in the datasource, the service should immediately notify one or more clients.
I have gone through many different potential approaches of achieving this such as Broadcasting, Publish/Subscribe with WCF, and List based publish subscribe
But in all these approaches, the chain of events is initiated explicitly by a client/publisher. For example in case of Pub-Sub, the whole chain of events is initiated when a publisher publishes something.
But in my scenario, there is no publisher. Service must itself poll onto a datasource and look for any new changes.
How do I achieve this in my scenario? Where should I have the polling logic?
One option is to have the polling logic in hosting environment (windows service) and call the publish of service whenever there is new data.
I am not sure how we can have the polling logic within the WCF service itself! Any leads/thoughts regarding this would be very helpful.
I want to create a service which receives a request from the client, adds the request to a database and than calls another WWF service ASYNCRONOUS which does some time consuming job withthe data from the database.
How do I make a service to be asincronous in Windows Workflow service?
I use the second Windows Workflow service as a queue(as it can only be one instance of this service=I set canCreateInstance to false).
To make a Workflow Service behave asynchronously create a One Way contract by using a Receive activity without a correlated SendReply.
When another Workflow (or WCF client proxy) calls this service it will not wait for a reply from the service.
As for your comment about only one instance of a service you are mistaken. There is no way to have a singleton workflow service (as there is with WCF services) and CanCreateInstance has no effect on this behavior.
I have to create a WCF web service that proxies an IMAP service (so that it can be consumed by a SL application).
The IMAP service requires that first the Login(credentials) method is called, to authenticate with the IMAP server. After the Login method is called the connection is kept open and other operations can be performed.
Does anybody know how can achieve this with a WCF service?
One solution I want to avoid is the proxy to login for every operation it has to perform (as the login operation usually takes 1-2 seconds). And I would have to pass the credentials every time: GetMail(credentials), GetFolders(credentials), etc.
I know it is highly recommended that WCF services not to be stateful, but it seems I need to keep the state of IMAP connection for every client. How can I do this?
Thanks!
This is one of those rather rare cases where I think using WCF sessions makes sense:
your first call that calls the IMAP Login method starts a WCF session
any subsequent call will be using the same session
some final call (e.g. something like a Done or Logout) will terminate that session
With a session in WCF, your service class on the server stays in memory for the duration of the entire session, i.e. it's not constantly re-created, and thus you can keep the IMAP connection "live" inside your service class.
Resources:
Sessions, Instancing, and Concurrency (MSDN)
Using Sessions (MSDN)
WCF Sessions - a brief introduction
WCF Sessions
Per-Session Instance Management in WCF
Be aware: WCF sessions are NOT ASP.NET sessions - those are two totally different things! Just to be clear from the get-go.
Also: only a handful of WCF bindings support sessions - netTcpBinding, wsHttpBinding and netNamedPipeBinding (as far as I know)
I have a WCF service hosted as Windows Service with most of its methods currently defined as:
[OperationContract(IsOneWay = true)]
But, now I need to send response back to the calling Web application for these service methods.
Now, because service methods are bit heavy (FYI, they are reporting methods that needs to do mail merge for a no. of records), I am thinking to either queue them or to process asynchronously, so essentially when the request is sent to the service it should save the request to database/queue, returning Request-Id to calling Web application.
In the mean-time, WCF service can just process incompleted requests from the queue or database.
Then either calling Web application can ping WCF service for status of request because it has Request-Id or
WCF service can ping back to calling app when the process corresponding to a Request-Id is completed.
To achieve above, can anyone please guide what changes I need to make to my WCF service (which currently has all one way operation)?
Also, please guide me whether I need to go for Asynch operation or message queuing?
Thank you!
Of course, going Async is simple:
remove the OneWay on the OperationContract in question and regenerate your Service WITH Async methods. There's a reason why Silverlight forces you to use Async operations. They do force you to rethink your UI.
I am trying to create a number of WCF services. These services will expose certain public methods and require to consume each other (i.e. call WCF Service methods from another WCF Service)
Is there any good reference tutorial material that I can refer to for this?
Thanks all in advance!
Consuming a web service in another web service is no different to consuming it in any other client. You create a proxy and make your call so all the general WCF documentation and tutorials will apply.
However, this is usually not a good practice - although sometimes is unavoidable in an SOA. Services must be consumed by clients and they should not call each other unless they have to.
There are a host of problems that can happen. First of all, a service has to wait for the result of a synchronous call from one or more services to return and your service thread will be locked until those calls are finished. If one call takes long, the other service will take long as well and you will have scalability issues.
Let the client call these services. If a call requires data from another service, get the client to make the call and get the data and then make the call again.