Creating Windows Services
It's not uncommon for an enterprise application to need some form of background processes to do continuous work. These could be tasks such as
- Cleanup abandoned shopping carts
- Delete temporary files left behind by some report or image generation feature
- Send email notifications
- Create daily reports and send them out
- Check an email inbox
- Pull messages from a queue
- Perform daily or monthly archiving
- etc
For many of these things there are dedicated tools that provide that feature, like a reporting service (SSRS or BO,) scripts that run in the email server, or even simple executables that are fired by the Windows Task Scheduler. When you have only one or two background tasks, using something like the task scheduler may be OK, but administration quickly becomes painful when the number of tasks grows. The dedicated services like SSRS or BO can be overkill depending on the size of your application or organization.
One approach I like to take is to create a Windows Service for the application, grouping all the different background tasks under a single project, a single .exe, and a single configuration file. Visual Studio has always had a Windows Service project type, but the process of creating a working service is not as simple as you would hope, especially when your service performs more than one independent task.
After creating a couple of services, I realized that I definitely needed to stash all that monkey work somewhere I could just reuse later. I decided to create a helper library to assist creating and maintaining Windows services.
The library doesn't help with all kinds of Windows services, but has helped me a lot with the type of tasks I explained above. The key to the library is the ITask interface.
public interface ITask: IDisposable
{
bool Started { get; }
string Name { get; }
void Start();
void Stop();
void Execute();
}
This interface shown all that is needed to create a task that can be started, stopped, and invoked by the service process. But this interface has too many members and many tasks are common enough that these members will be implemented almost identically. For example, tasks that execute on a regular interval will be almost identical, the only different member will be the Execute method. That's why the library comes with some handy base classes as shown in this diagram.
Now when I need to implement a task that runs repeatedly I simply inherit a task from PeriodicalTask or ScheduledTask as seen below. These classes will be part of my service project, from which I remove all the other classes that were added by default.
class CleanupTask : PeriodicalTask
{
readonly static log4net.ILog Log =
log4net.LogManager.GetLogger(
System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
public override void Execute()
{
//time to run....
//TODO: write the actual code here
// ShoppingCart.DeleteAbandonedCarts();
Log.InfoFormat("Executed: {0}", this.GetType().Name);
}
}
class DailyReportTask : ScheduledTask
{
readonly static log4net.ILog Log =
log4net.LogManager.GetLogger(
System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
protected override void Execute(DateTime scheduledDate)
{
//time to run....
//TODO: write the actual code here
// SalesReport.SendDailySummary();
Log.InfoFormat("Executed: {0}", this.GetType().Name);
}
}
Instead of hard coding the interval or the scheduled time of the above tasks, we use the service's .config file for that:
<WindowsService>
<tasks>
<task name="CleanupTask" interval="600" />
<task name="DailyReportTask" time="21:30" />
</tasks>
</WindowsService>
There are only a few more things we need to do to get this service ready. First we need to add a new WindowsService item. Here we are naming it MyAppService and making it inherit from from SPServiceBase.
partial class MyAppService : SPServiceBase
{
public const string MyAppSvcName = "MyAppSVC";
public MyAppService()
{
InitializeComponent();
//Important.. use the constant here AFTER
// the call to InitializeComponent()
this.ServiceName = MyAppSvcName;
}
}
We also need to add an Installer Class, which I'll name simply Installer and which will be invoked during the service installation phase to add the appropriate registry entries to make the service be listed in the Services applet. Here's how this class looks like. Note that it inherits from another base class from the library.
[RunInstaller(true)]
public class Installer : SergioPereira.WindowsService.ServiceInstaller
{
//That's all we need. Hooray!
}
I mentioned that the installer will add the necessary registry information. Some of that are the name and description of the service. We provide that with an assembly attribute that you can put in the AssemblyInfo.cs or anywhere you like in a .cs file (outside any class or namespace.)
[assembly: ServiceRegistration(
SampleService.MyAppService.MyAppSvcName, // <-- just a string constant
"MyApp Support Service",
"Supports the MyApp application performing several " +
"critical background tasks.")
]
A Windows service is compiled as an .exe, so it needs an en entry point, a static Main function. Let's add a Program.cs like this:
class Program
{
static void Main(string[] args)
{
if (!SelfInstaller.ProcessIntallationRequest(args))
{
MyAppService svc = new MyAppService();
svc.AddTask(new CleanupTask());
svc.AddTask(new DailyReportTask());
//add more tasks if you have them
svc.Run();
}
}
}
The code above is pretty simple, we are creating the tasks and telling our service to take care of them. Then we start the service. The interesting thing is the call to ProcessIntallationRequest. This is where we added the self-installing capability of the service. If you wrote a service in the past, you know that they get installed by using InstallUtil.exe. One potential problem is that InstallUtil.exe may not be present on the server or not in the PATH, making an scripted installation a little more complicated. Instead, by using the that call from SelfInstaller, we enabled our service to be invoked like the following to install or uninstall it (remember to execute as an Administrator).
SampleService.exe -i[nstall] SampleService.exe -u[ninstall]
After installing it, you should see the service in the Services applet.
Here's the final structure of our project.
If you want, download the library source code along with a sample service project. There's more in the library than I have time to explain here, including an auto-update task and extra configuration properties for each task.