Wallace B. McClure

Scalable Development, Inc.

Scalable Development, Inc.Building systems today that perform tomorrow.

Designing & BuildingWindows Services

with VB.NET

.NET Experiences

PDC 2000 Build (July 2000). Visual Studio 1.0 Beta 1 (November 2000). Book began (January 2001). Visual Studio 1.0 Beta 2 (June 2001). First Production ASP.NET App (July 2001). Production Windows Service (November 2001).

Runs today. 4 Production Applications by shipment. Multiple running applications.

.NET Resources

ASP.NET – www.asp.netAspAdvice – www.aspadvice.comWindows Forms – www.windowsforms.netArchitecture –

msdn.microsoft.com/architecture.NET News – www.dotnetwire.com

What are Windows Services? Applications (Database, Web Server, …). Good for long running / complicated operations. Run all the time. No User Interface. Run within their own security context.

Limited access to local resources.Limited access to remote resources.

Debugging. Non-interactive.

Design Guidelines

Consistency.

No popup messages.

Information/Errors need to be written to somewhere.EventLog.Database.

Be careful blocking.

Types of .NET Applications

ASP.NET.Web Services.WinForms.Components.Windows

Services.Others.

.NET Support for Services System.ServiceProcess namespace.

Inherit from the ServiceBase Class.

Installation.

ServiceController Class Allows communication from authorized user (WinForms, ASP.NET, or other) to a Service (thru SCM).

Languages Support

C++ (Managed & Unmanaged).

Visual Basic.

C#.

Other .NET Languages.

Parts of a .NET Windows Service

Service Control Manager (SCM).System.ServiceProcess.ServiceBase

classEvents.Installation.

Process Installation.Service Installation.

Events in ServiceBase

OnStart().OnStop().OnPause().OnContinue().OnShutdown().OnPowerEvent().OnCustomCommand().

OnStart() Event

Called when the Service is issued the start command.

VB Syntax:Protected Overridable Sub OnStart

( _ByVal args() as String )

Hard to Debug By Default.

Debugging the OnStart() Event

Create a dummy service that is a part of your process.

Start the dummy service to start the process.

Attach to running process.Place breakpoint.Start “real” service.

OnStop() Event

Called when the Service is issued the stop command.

Protected Overridable Sub OnStop().

OnPause() Event

Called when the Service is issued the pause command.

Protected Overrideable Sub OnPause().

OnContinue() Event

Called when the Service is issued the continue command.

Protected Overrideable Sub OnContinue().

OnShutdown() Event

Called when the System sends the shutdown command to all Applications specifying that a system shutdown is inprogress.

Similar to the OnStop() event.

Protected Overrideable Sub OnShutdown().

OnPowerEvent() Event

Called when the computer’s power status has changed. Typically, this applies to a laptop computer when it goes into a suspended state.

Not the same as a system shutdown. Protected Overrideable Function OnPowerEvent( ByVal

powerStatus as PowerBroadcastStatus ) as Boolean Boolean return value is a response to a QuerySuspend

broadcast. True = Application is in a state where a suspend is ok. False

= suspend is not ok. PowerBroadcastStatus is an enumertion with 9 values.

OnCustomCommand() Event

Executed when a custom command is passed from the SCM to the service.

Protected Overridable Sub OnCustomCommand( ByVal command as Integer )

Command values between 128 & 255.

Security Context Service runs within a defined security context

(UserId/PassWord). What you do not necessarily

have access to: Desktop. Remote Resources. Mapped Drives.

What you do have access to: Local FileSystem. Network Protocols (TCP/IP, …). Database (ODBC, OleDb, MP).

Custom Commands /ServiceController

Use the ServiceController class.ExecuteCommand( ByVal command as

Integer ) method.Start, Stop, Pause, Continue.MachineName, ServiceName, Status

properties.

Installation

Each executable must have a process installer.

Each service within a process must have a service installer.

Command line utility (installutil.exe)

App.Config

XML Format.

Excellent for read only information.

Great, Now What canYou do with a Service?

Listen for events to occur.Network requests.Timer countdown.Messages arriving in a message

queue.File system changes.Other.

Example

Timer.

When the Timer counts down to zero, an event fires and our application performs an operation.

No continual polling occurs, no blocking, and no extra processing occurs on the system.

What’s Not to Like?

Requires the .NET Framework.

If a framework exception occurs when the framework stops, the Windows Service stops…….and there is nothing within the framework to restart that Windows Service.

Problem is rare, but possible. (ODP.NET 9.2.0.2.100.0 users, problem has been resolved)

Monitoring a Windows Service

Need something that won’t stop. Can do it with .NET and a Console application. Drop back to COM/API. Use WMI & “Scheduled Tasks.” Use ServiceController class. Run every few days/hours/minutes to monitor the

status of your Service.

Things to look at / Last Thoughts

Event Processing vs. Blocking.EventLog.Multiple Threads of Execution.Weak References.Performance Monitor

Integration.Nothing wrong with Interop.

Questions?

Scalable Development, Inc.Consulting & Development Services.http://www.scalabledevelopment.com865-693-3004.wallym@scalabledevelopment.com

END

Scalable Development, Inc.Building systems today that perform tomorrow.