Example of a Windows Service, with a thread

Problem/Question/Abstract:

Delphi 5&6 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 servers as services.

Answer:

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.

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

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.

{*
  Windows Service Template
  ========================

  Author          Kim Sandell
                  emali: kim.sandell@nsftele.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.

{*
  A Windows NT Service Thread
  ===========================

  Author          Kim Sandell
                  Email: kim.sandell@nsftele.com
*}
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.