How to make a Windows Service listen for additional request while it is already processing the current request?

Question

I need to build a Windows Service in VB.net under Visual Studio 2003. This Windows service should read the flat file (Huge file of about a million records) from the local folder and upload it to the corresponding database table. This should be done in Rollback mode (Database transaction). While transferring data to table, the service should also be listening to additional client requests. So, if in between client requests for a cancel operation, then the service should rollback the transactions and give feedback to the client. This windows service also keeps writing continuously to two log files about the status and error records. My client is ASPX page (A website).

Can somebody help me explain how to organize and achieve this functionality in a windows service(Processing and listening for additional client requests simultaneously. Ex. Cancellation request).

Also could you suggest me the ideal way of achieving this (like if it is best to implement it as web service or windows service or just a remote object or some other way).

Thank you all for your help in advance!

Answer 1

You can architect your service to spawn "worker threads" that do the heavy lifting, while it simply listens for additional requests. Because future calls are likely to have to deal with the current worker, this may work better than, say, architecting it as a web service using IIS.

The way I would set it up is: service main thread is listening on a port or pipe for a communication. When it gets a call to process data, it spawns a worker thread, giving it some "status token" (could be as simple as a reference to a boolean variable) which it will check at regular intervals to make sure it should still be running. Thread kicks off, service goes back to listening (network classes maintain a buffer of received data so calls will only fail if they "time out").

If the service receives a call to abort, it will set the token to a "cancel" value. The worker thread will read this value on its next poll and get the message, rollback the transaction and die.

This can be set up to have multiple workers processing multiple files at once, belonging to callers keyed by their IP or some unique "session" identifier you pass back and forth.

Answer 2

You can design your work like what FTP do. FTP use two ports, one for commands and another for data transfer.

You can consider two classes, one for command parsing and another for data transfer, each one on separate threads.

Use a communication channel (like a privileged queue) between threads. You can use Syste.Collections.Concurrent if you move to .NET 4.0 and more threading features like CancellationTokens...

WCF has advantages over web service, but comparing it to windows service needs more details of your project. In general WCF is easier to implement in compare to windows service.