Hi,
I am not sure why, but in many organisation, there is allot of unnecessary complexity when looking at source code. From Programmers using try/catch blocks all over the show to unnecessary synchronous service calls with multiple threads, causing deadlocks on SQL Server.
I would like to give a simple example, consider this code
static ProcessOrder()
{
const int workerCount = 4;
WorkQueue = new ConcurrentQueue();
Workers = new List();
for (var index = 0; index; workerCount; index++)
{
Worker = new BackgroundWorker();
Workers.Add(Worker);
Worker.DoWork += Worker_DoWork;
Worker.RunWorkerAsync();
}
}
The above code is extremely dangerous. You have no control over the load it will cause to backend calls, especially when it is calling Stored Procs etc. Secondly, it is not durable.
The above code, can easily be replaced by a NServiceBus Saga or handler, in the above, a Saga is appropriate, as this message is a Root Aggregate, we have an order to process. Sagas will provide an environment to preserve state and all the threading and correlation is all handled for you.
partial void HandleImplementation(ProcessOrder message)
{
Logger.Info("ProcessOrder received, Saga Instance: {0} for OrderId: {1}", Data.Id, Data.OrderId);
RunOnlyOncePerInstance(message);
AlwaysRunForEveryMessage(message); //counts and extracts new order items.
if (Data.OrderCount == 1)
{
SendSaveOrder(message);
return;
}
if (Data.InitialDelayPassed) //Expired workflow
SendUpdateOrderItem();
}
From the above, you can see state is preserved for each unique OrderId. This Saga processes multiple order items for an OrderId. Which can be submitted at any time during the day. We do not have to worry about multiple threads, correlation is dealt with automatically, well we set the correlation id to the OrderId, so order items coming in can be matched to the correct Saga instance.
We can now get rid of the unreliable issues with in memory worker threads, and uncontrolled pounding of the database.
By using a MSMQ infrastructure and leveraging NServiceBus, these sort of issues, you find in code, can be easily mitigated.
Romiko Derbynew 