I have put together a .net winform application which consumes a wcf service exposed by another .net application running as a windows service.
Since the communication is within the same machine, I chose the NetNamedPipe as the communication channel, as it is the best choice suited for inter process communication in the same machine.
I want to know if I am using the correct property choices when defining the wcf service in the .net windows service.
The WCF service behaviour is defined as:
[ServiceBehavior(
ConcurrencyMode = ConcurrencyMode.Single,
InstanceContextMode = InstanceContextMode.Single)]
I chose the "InstanceContextMode" as Single so that I know objects in the wcf service are not recreated each time a wcf service method is called by the UI client.
However, while reading up the ConcurrencyMode property to choose on MSDN, I did get a little confused. At the basic level, I understand the ConcurrencyMode property dictates whether the wcf service supports a single, multiple or reentrant calls.
Does this mean, that if my UI client application is multithreaded and I call into the wcf service methods from those threads, I should choose "Concurrency" mode as "multiple" and if my UI client is not multi threaded, I should choose "Concurrency" mode as "single"? My UI client application is not running multiple threads. All operations are performed on the main UI thread through event handlers (through button clicks, combo box selections, etc...)
I am having situations where, after installing the application on a windows test machine, my UI client is sometimes not able to connect to the wcf service. It just keeps waiting on the call to the Connect method of the wcf client object and then eventually times out. I want to know if its related to the "ConcurrencyMode" choice I made. Or is this a "NetNamedPipe" communication channel problem?
Please advice.
Thanks in advance.
Subbu
Choose concurency mode as multiple only if your host object is thread safe i.e you have manually implemented locking on shared resource or your host object dont have any shared or class level objects at all. If host object is not thread safe use concurency mode as single as in this case wcf will automatically implement lock for you, only one request will be processed at a time on a context, parallel will be queued. So here decision should really depend on if your host object is thread safe or not.
Related
I have developed a WCF service for consumption within the organization's Ethernet.
The service is currently hosted on a windows-service and is using net.tcp binding.
There are 2 operation contracts defined in the service.
The client connecting to this service is a long running windows desktop application.
Employees(>30,000) usually have this client running throughout the week from Monday morning to Friday evening straight.
During this lifetime there might be a number of calls to the wcf service in question depending on a certain user action on the main desktop client.
Let us just say 1 in every 3 actions on the main desktop application would
trigger a call to our service.
Now we are planning to deploy this window service on each employee's desktop
I am also using `autofac` as the dependency resolver container.
My WCF service instance context is `PerSession`, but ideally speaking we have both the client and service running in the same desktop (for now) so I am planning to inject the same service instance for each new session using `autofac` container.
Now am not changing the `InstanceContext` attribute on the service implementation
because in future I might deploy the same service in a different hosting environment where I would like to have a new service object instance for each session.
Like mentioned earlier the client is a long running desktop application and I have read that it is a good practise to `Open` and `Close` the proxy for each call but if I leave the service to be PerSession it will create a new service instance for each call, which might not be required given the service and client have a 1-1 mapping. Another argument is that I am planning to inject the same instance for each session in this environment, so Open & Close for each service call shouldn't matter ?
So which approach should I take, make the service `Singleton` and Open Close for each call or
Open the client-side proxy when the desktop application loads/first service call and then Close it only when the desktop application is closed ?
My WCF service instance context is PerSession, but ideally speaking we have both the client and service running in the same desktop (for now) so I am planning to inject the same service instance for each new session using autofac container
Generally you want to avoid sharing a WCF client proxy because if it faults it becomes difficult to push (or in your case reinject) a new WCF to those parts of the code sharing the proxy. It is better to create a proxy per actor.
Now am not changing the InstanceContext attribute on the service implementation because in future I might deploy the same service in a different hosting environment where I would like to have a new service object instance for each session
I think there may be some confusion here. The InstanceContext.PerSession means that a server instance is created per WCF client proxy. That means one service instance each time you new MyClientProxy() even if you share it with 10 other objects being injected with the proxy singleton. This is irrespective of how you host it.
Like mentioned earlier the client is a long running desktop application and I have read that it is a good practise to Open and Close the proxy for each call
Incorrect. For a PerSession service that is very expensive. There is measurable cost in establishing the link to the service not to mention the overhead of creating the factories. PerSession services are per-session for a reason, it implies that the service is to maintain state between calls. For example in my PerSession services, I like to establish an expensive DB connection in the constructor that can then be utilised very quickly in later service calls. Opening/closing in this example essentially means that a new service instance is created together with a new DB connection. Slow!
Plus sharing a client proxy that is injected elsewhere sort of defeats the purpose of an injected proxy anyway. Not to mention closing it in one thread will cause a potential fault in another thread. Again note that I dislike the idea of shared proxies.
Another argument is that I am planning to inject the same instance for each session in this environment, so Open & Close for each service call shouldn't matter ?
Yes, like I said if you are going to inject then you should not call open/close. Then again you should not share in a multi-threaded environment.
So which approach should I take
Follow these guidelines
Singleton? PerCall? PerSession? That entirely depends on the nature of your service. Does it share state between method calls? Make it PerSession otherwise you could use PerCall. Don't want to create a new service instance more than once and you want to optionally share globals/singletons between method calls? Make it a Singleton
Rather than inject a shared concrete instance of the WCF client proxy, instead inject a mechanism (a factory) that when called allows each recipient to create their own WCF client proxy when required.
Do not call open/close after each call, that will hurt performance regardless of service instance mode. Even if your service is essentially compute only, repeated open/close for each method call on a Singleton service is still slow due to the start-up costs of the client proxy
Dispose the client proxy ASAP when no longer required. PerSession service instances remain on the server eating up valuable resources throughout the lifetime of the client proxy or until timeout (whichever occurs sooner).
If your service is localmachine, then you consider the NetNamedPipeBinding for it runs in Kernel mode; does not use the Network Redirector and is faster than TCP. Later when you deploy a remote service, add the TCP binding
I recommend this awesome WCF tome
We have set of WCF services running on single computer which collectively serves an WPF application which could be on same machine or on remote machine (within same network only). We need failover mechanisum so whenver any of the service crashes or hangs - we want to restart the service and initialize it by calling appropriate method.
Since we are not aware of what is the industry standard for implementing failover for WCF service - we have implemented like this way. We start main WCF service hosted in console app along with one more secondary WCF service which constantly checks health of main WCF service by calling exposed method on given endpoint. If main WCF service fails, it takes role of main WCF service and launches another secondary WCF service.
The above approach is working fine but only problem we have seen is memory since we launch services in pair and every host requires 10MB of memory.
Can anyone help me what is the industry practice for implementing failover for this kind of scenario?
I have a WCF service that all clients connect to in order to get notifications \ reminders (using a CALLBACK interface they implement). Currently the WCF service is self-hosted, but the plan is to have it hosted in a Windows Service.
The WCF service has a 'Publish', 'Subscribe' and 'Unsubscribe' operations.
I need to have a background worker thread of some sort poll an SQL server database table constantly [every XXX minutes], and look for certain 'reminder' rows. Once it finds them - it should notify all the connected clients.
I thought of 2 ways of achieving this.
.
METHOD A :
Have a separate EXE project (don't want it to be a console, so what should it be - a Windows Service ?) that will start and run a background thread. The background thread will connect to the 'Reminder' service as one of its clients. The background thread will poll the database, and once it finds something - it will send a 'Publish' message to the WCF service, that will make the WCF service send the reminder to all the subscribed clients.
.
METHOD B :
Somehow make the background thread run within the WCF service project, and when it detects a new reminder row in the database, somehow make it 'signal' the WCF service with the info, and the WCF service will then send this info to all subscribed clients.
.
Which method is better ? Any other suggestions ?
If this is a long running process, a windows service is the perfect solution.
Your main Win Service thread will be polling the DB, queuing the results into some kind of supplier/consumer thread safe collection.
You can host a WCF service within the win service, which can then consume (remove) any results from the queue and pass them back to the client as requested (calls into the WCF will come in on their own thread)
This is a pretty common architecture, and not difficult to implement.
Method A:
If you were to create two separate hosts (i.e. one for the WCF service and one for the "Polling" service) then you really have only one option to make it all work nicely.
Windows Service communication is very limited (without the help of a service endpoint, e.g. WCF). Therefor, if you were to host your "Polling" service in a Windows Service, you must couple it with a WCF service anyway.
It is then feasible to host both services together in one Windows Service and by manually instantiating the WCF host and passing into the constructor a "Polling" service.
protected override void OnStart(string[] args)
{
//...
// This would be you "polling" service that would start a background thread to poll the db.
var notificationHost = new PollingService();
// This is your WCF service which you will be "self hosted".
var serviceHost = new WcfService(notificationHost);
new ServiceHost(serviceHost).Open();
//...
}
This is far from ideal because you need to communicate via events between the two services, plus your WCF service must run on singleton mode for manual instantiation to work... So this leaves you with...
Method B:
If you were to host the "Polling" services inside your WCF service, you are going to run into a number of issues.
You need to be aware of the number of instances of the "Polling" services that gets created. If your WCF service has been configured to be instantiated for every session, you could end up with too many "Polling" services and that may end up killing your db/servers.
To avoid the first issue, you may need to set a singleton WCF service, which may lead to a scaling issue in the near future where one WCF service instance is not enough to handle the number of connection requests.
Method C:
Given the drawbacks in Method A and B, the best solution would be to host two independent WCF services.
This is your regular service where you have subscriber/unsubscribe/publish.
This is your polling singleton service with subscribe/unsubscribe.
The idea is that your regular service, upon receiving a subscriber will open a new connection to your polling service or use an existing one (depending on how you configure your session) and wait for a reply. Your polling service is a long running WCF service that polls your db and publish the notification to its subscribers (i.e. the other WCF host).
Pros:
You are assured that there will be only one polling service.
You could scale your solution to host the regular service in IIS and the polling service in Windows Service.
Communication limitations is minimal between the two services and no need for events.
Test each service interdependently through their interfaces.
Low coupling and high cohesion between the services (this is what we want!).
Cons:
More services means more interfaces and contracts to maintain.
Higher complexity.
I know that it is not a good idea to have timers inside a WCF service class that is hosted inside IIS since these are meant to have short lifetimes. And from the advice here it also sounds like having a service is the best way to go for that situation.
But has anyone tried using timers inside a self-hosted service in production? We have a windows service that acts as a client and uses timers to do periodic operations at the moment.
This is fine for most cases, but I am concerned about the robustness of the design: some of the operations are critical (financial system calculation triggers). Since the WCF service and the windows service are two components, ensuring both are running is difficult.
If I moved the critical operations to a timer inside the WCF Service I remove that problem, but what else should I be concerned about then?
If I understand correctly, your question is actually about IIS-hosted WCF services, is that right?
IIS controls the application pool that your WCF service runs in. That means that IIS may decide to recycle your application pool and all the apps/services in it. Then your service only gets activated again once it is called by a client. So, scheduling in WCF services or ASP.NET applications cannot be relied on.
The picture of course changes if you can self-host your WCF service. Then there is no IIS application pooling to take into account, and you can schedule at will. Therefore, if you need the combination of WCF + scheduling, it's best to create a Windows service that will include both.
Have a winform application and want to host a WCF service inside it. Do I need to host it in a seperate appdomain? Any recommendations?
You don't need to host it in separate domain but you must decide if you want service request to be processed by UI thread or different thread. It depends on the way you create ServiceHost instance or on ServiceBehavior applied to your service class.
When service is hosted in UI thread it can directly interact with UI but request processing is part of message loop and all service requests are processed by single thread (sequentially). When request is processed no other windows event (including UI events) can be processed = application freezes.
When service is hosted in different thread it behaves as in any other hosting environment but it can't directly interact with UI - you must use delegate invocation.
Ways to enforce service to run in own threads:
Create and open ServiceHost instance before you call Application.Run (start of Windows message loop)
Create and open ServiceHost instance in separate thread
Use [ServiceBehavior(UseSynchronizationContext = false)] on your service implementation
No, you don't have to host it in a separate AppDomain. Just host it. There's nothing terribly special about WinForms in this regard.
What's your app do? Is the service a part of the apps regular functions or a completly seperate logical entity?
If you want to be loading and unload resources (such as assemblies) related to your service without shutting your app down a seperate app domain would make this much easier, but otherwise I don't see much of a reason to complicate things.
Just my 2c. :-)
You can host in Win form but you have to keep it running throughout.
Also suggest you to host in IIS so any type of client avail your service.