Building Windows Services In Vb

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

Designing & Building Windows Services with VB.NET  Wallace

B. McClure

 Scalable

Development, Inc.

.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.net  AspAdvice – www.aspadvice.com  Windows Forms – www.windowsforms.net  Architecture – 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  Inherit

namespace.

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 class  Events.  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 can You 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.

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

Questions?

 Scalable

Development, Inc.  Consulting & Development Services.  http://www.scalabledevelopment.com  865-693-3004.  [email protected]

END