Question

How does ServiceStack handle concurrent calls? I’m looking for equivalent of ConcurrencyMode.Multiple in WCF.

My WCF services have this attribute set:

   [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Multiple, UseSynchronizationContext = false)]

Do I need to enable anything in ServiceStack to get it to use multiple threads for each call?

Answer 1

ServiceStack doesn’t have a configurable concurrency model per AppHost, it is dependent upon the AppHost you choose to host your ServiceStack services with:

ASP.NET Host (AppHostBase)

For ASP.NET web hosts, ServiceStack doesn’t create any new threads itself, the requests are simply handled on the same IIS/Nginx/etc ASP.NET HTTP WebWorker that handles the request.

HttpListener Self-Host (AppHostHttpListenerBase)

ServiceStack only creates a new thread on Startup when you call new AppHost().Start(url). There are no new threads created at run-time, i.e. the request is handled on the HttpListener async callback thread.

HttpListener Long Running Self-Host (AppHostHttpListenerLongRunningBase)

This is another Self-Host HttpListener option for ServiceStack that uses its own managed ThreadPool to execute the request on (free-ing up the HttpListener async callback thread). The default poolSize of the ThreadPool is 500 threads, though this is configurable in the AppHostHttpListenerLongRunningBase(poolSize) constructor.

RedisMQ Host (RedisMqServer)

A good option for managing long-running tasks is to delegate requests to a Redis MQ Host which is a light-weight MQ Server allowing you to defer and process requests in managed background threads. By default the RedisMqServer spawns a single background thread for each Message type (i.e. Request), though this is configurable on start-up, e.g: in the example below 2 background threads are used to handle PostTwitter requests, whilst only 1 background thread each is used to process CallFacebook and EmailMessage requests:

mq.RegisterHandler<PostTwitter>(ServiceController.ExecuteMessage, noOfThreads:2);
mq.RegisterHandler<CallFacebook>(ServiceController.ExecuteMessage);
mq.RegisterHandler<EmailMessage>(ServiceController.ExecuteMessage);