Delphi 5 and up has a template project for services, but it is incomplete. This example builds on that template and completes the service. It also shows how to start a thread that beeps every 2 seconds. You can use this as a base when developing services.

This example shows how to use the service template in delphi, taking it a step further and making a complete example. The source for this is included in the ntservice.zip file.

Coded under D6, but works for D5 if you copy the source parts after creating a template service.

Below are all the source files listed one by one. The same files and the whole project is in the NTService.zip file (as soon as it is uploaded)

To test the source, create a Service with Delphi, and pase these sources
on top of the automatically generated source.

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program NTService;

uses
  SvcMgr,
  NTServiceMain in 'Units\NTServiceMain.pas' {ExampleService: TService},
  NTServiceThread in 'Units\NTServiceThread.pas';

{$R *.RES}

begin
  Application.Initialize;
  Application.CreateForm(TExampleService, ExampleService);
  Application.Run;
end.
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(*
  Windows Service Template
  ========================

  Author          Kim Sandell

  Email           kim.sandell@celarius.com  

  Disclaimer      Freeware. Use and abuse at your own risk.

  Description     A Windows NT Service skeleton with a thread.
                  Works in WinNT 4.0, Win 2K, and Win XP Pro

                  The NTServiceThread.pas contains the actual
                  thread that is started under the service.
                  When you want to code a service, put the code in
                  its Execute() method.

  Example         To test the service, install it into the SCM with
                  the InstallService.bat file. The go to the Service
                  Control Manager and start the service.

                  The Interval can be set to execute the Example
                  Beeping every x seconds. It depends on the
                  application if it needs a inerval or not.

  Notes           This example has the service startup options set to
                  MANUAL. If you want to make a service that starts
                  automatically with windows then you need to
                  change this.
                  BE CAREFULT ! If your application hangs when
                  running as a service THERE IS NO WAY to
                  terminate the application.

  History     Description
  ==========  =====================================================
  24.09.2002  Initial version

*)
unit NTServiceMain;

interface

uses
  Windows, Messages, SysUtils, Classes, SvcMgr,
  NTServiceThread;

type
  TExampleService = class(TService)
    procedure ServiceExecute(Sender: TService);
    procedure ServiceStart(Sender: TService; var Started: Boolean);
    procedure ServiceStop(Sender: TService; var Stopped: Boolean);
    procedure ServicePause(Sender: TService; var Paused: Boolean);
    procedure ServiceContinue(Sender: TService; var Continued: Boolean);
    procedure ServiceShutdown(Sender: TService);
  private
    { Private declarations }
    fServicePri            : Integer;
    fThreadPri             : Integer;

    { Internal Start & Stop methods }
    Function _StartThread( ThreadPri:Integer ): Boolean;
    Function _StopThread: Boolean;
  public
    { Public declarations }
    NTServiceThread       : TNTServiceThread;

    function GetServiceController: TServiceController; override;
  end;

var
  ExampleService: TExampleService;

implementation

{$R *.DFM}

procedure ServiceController(CtrlCode: DWord); stdcall;
begin
     ExampleService.Controller(CtrlCode);
end;

function TExampleService.GetServiceController: TServiceController;
begin
     Result := ServiceController;
end;

procedure TExampleService.ServiceExecute(Sender: TService);
begin
     { Loop while service is active in SCM }
     While NOT Terminated do
     Begin
          { Process Service Requests }
          ServiceThread.ProcessRequests( False );
          { Allow system some time }
          Sleep(1);
     End;
end;

procedure TExampleService.ServiceStart(Sender: TService; var Started: Boolean);
begin
     { Default Values }
     Started     := False;
     fServicePri := NORMAL_PRIORITY_CLASS;
     fThreadPri  := Integer(tpLower);

     { Set the Service Priority }
     Case fServicePri of
      0 : SetPriorityClass( GetCurrentProcess, IDLE_PRIORITY_CLASS );
      1 : SetPriorityClass( GetCurrentProcess, NORMAL_PRIORITY_CLASS );
      2 : SetPriorityClass( GetCurrentProcess, HIGH_PRIORITY_CLASS );
      3 : SetPriorityClass( GetCurrentProcess, REALTIME_PRIORITY_CLASS );
     End;

     { Attempt to start the thread, if it fails free it }
     If _StartThread( fThreadPri ) then
     Begin
          { Signal success back }
          Started := True;
     End Else
     Begin
          { Signal Error back }
          Started := False;
          { Stop all activity }
          _StopThread;
     End;
end;

procedure TExampleService.ServiceStop(Sender: TService;
  var Stopped: Boolean);
begin
     { Try to stop the thread - signal results back }
     Stopped := _StopThread;
end;

procedure TExampleService.ServicePause(Sender: TService; var Paused: Boolean);
begin
     { Attempt to PAUSE the thread }
     If Assigned(NTServiceThread) AND (NOT NTServiceThread.Suspended) then
     Begin
          { Suspend the thread }
          NTServiceThread.Suspend;
          { Return results }
          Paused := (NTServiceThread.Suspended = True);
     End Else Paused := False;
end;

procedure TExampleService.ServiceContinue(Sender: TService;
  var Continued: Boolean);
begin
     { Attempt to RESUME the thread }
     If Assigned(NTServiceThread) AND (NTServiceThread.Suspended) then
     BEGIN
          { Suspend the thread }
          If NTServiceThread.Suspended then NTServiceThread.Resume;
          { Return results }
          Continued := (NTServiceThread.Suspended = False);
     END Else Continued := False;
end;

procedure TExampleService.ServiceShutdown(Sender: TService);
begin
     { Attempt to STOP (Terminate) the thread }
     _StopThread;
end;

function TExampleService._StartThread( ThreadPri: Integer ): Boolean;
begin
     { Default result }
     Result := False;
     { Create Thread and Set Default Values }
     If NOT Assigned(NTServiceThread) then
     Try
        { Create the Thread object }
        NTServiceThread := TNTServiceThread.Create( True );
        { Set the Thread Priority }
        Case ThreadPri of
         0 : NTServiceThread.Priority := tpIdle;
         1 : NTServiceThread.Priority := tpLowest;
         2 : NTServiceThread.Priority := tpLower;
         3 : NTServiceThread.Priority := tpNormal;
         4 : NTServiceThread.Priority := tpHigher;
         5 : NTServiceThread.Priority := tpHighest;
        End;
        { Set the Execution Interval of the Thread }
        NTServiceThread.Interval := 2;
        
        { Start the Thread }
        NTServiceThread.Resume;
        { Return success }
        If NOT NTServiceThread.Suspended then Result := True;
     Except
        On E:Exception do ; // TODO: Exception Logging
     End;
end;

function TExampleService._StopThread: Boolean;
begin
     { Default result }
     Result := False;
     { Stop and Free Thread }
     If Assigned(NTServiceThread) then
     Try
        { Terminate thread }
        NTServiceThread.Terminate;
        { If it is suspended - Restart it }
        If NTServiceThread.Suspended then NTServiceThread.Resume;
        { Wait for it to finish }
        NTServiceThread.WaitFor;
        { Free & NIL it }
        NTServiceThread.Free;
        NTServiceThread := NIL;
        { Return results }
        Result := True;
     Except
        On E:Exception do ; // TODO: Exception Logging
     End Else
     Begin
          { Return success - Nothing was ever started ! }
          Result := True;
     End;
end;

end.
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(*
  A Windows NT Service Thread
  ===========================

  Author          Kim Sandell
*)
unit NTServiceThread;

interface

uses
  Windows, Messages, SysUtils, Classes;
  
type
  TNTServiceThread = Class(TThread)
  private
    { Private declarations }
  Public
    { Public declarations }
    Interval              : Integer;

    Procedure Execute; Override;
  Published
    { Published declarations }
  End;

implementation

{ TNTServiceThread }

procedure TNTServiceThread.Execute;
Var
   TimeOut      : Integer;
begin
     { Do NOT free on termination - The Serivce frees the Thread }
     FreeOnTerminate := False;

     { Set Interval }
     TimeOut := Interval * 4;

     { Main Loop }
     Try
        While Not Terminated do
        Begin
             { Decrement timeout }
             Dec( TimeOut );

             If (TimeOut=0) then
             Begin
                  { Reset timer }
                  TimeOut := Interval * 4;

                  { Beep once per x seconds }
                  Beep;
             End;
             { Wait 1/4th of a second }
             Sleep(250);
        End;
     Except
        On E:Exception do ; // TODO: Exception logging...
     End;
     { Terminate the Thread - This signals Terminated=True }
     Terminate;
end;

end.
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