This document provides guidance on creating and managing services in Delphi. It discusses how to create a new service project, implement key service events like OnStart and OnStop, and ensure the service remains running through the use of a loop. It also demonstrates how to pass service state changes to any worker threads, and how to install and uninstall the service. The full example code shows integrating all these elements into a complete Windows service application.

1. Draft: 1st
Date: 22 Jan. 08
Author: Niall Munro
Title: GS: Assistant Data Analyst
Address: Generation Scotland Office
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Medical Genetics (OPD2)
2nd Floor, Out Patients Department
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Email: niall.munro@ed.ac.uk
DELPHI HOWTO:
SERVICES

2. Delphi Howto: System Services
CONTENTS
Introduction 1
Creating a New Service 2
Service Events 3
Keeping it Alive 4
Passing Event Signals to Threads 5
Installing / Uninstalling Your Service 6
Full Example 7
Useful Links 9
Table 1: Service events 3
Example 1: Skeleton code 1
Example 2: Keep alive loop 4
Example 3: Passing state calls to worker threads 5
Example 4: Installing your service 6
Example 5: Service uninstall success 6
Example 6: Full example code 8

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INTRODUCTION
A service is an application that runs in the background of an operating system that waits for client connections,
does some processing and then returns information. Web, FTP and e-mail servers are common examples of
services; they all require little human interaction hence why they run in the background. Services are also
useful for starting mission critical applications at boot time in that they start with the system instead of waiting
for a user to log on and have it automatically or manually launch at that point. This means that if there is a
systems failure and the computer the application is installed on may start upon reboot without a user having
logged on.
unit main;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, SvcMgr,
Dialogs;
type
TMyService = class(TService)
private
{ Private declarations }
public
function GetServiceController: TServiceController; override;
{ Public declarations }
end;var
MyService: TMyService;
implementation
{$R *.DFM}
procedure ServiceController(CtrlCode: DWord); stdcall;
begin
MyService.Controller(CtrlCode);
end;
function TMyService.GetServiceController: TServiceController;
begin
Result := ServiceController;
end;
end.
Example 1: Skeleton code

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CREATING A NEW SERVICE
You can create a new Delphi service in the Borland IDE by going to File>New>Other and selecting Service. This
will create the skeleton code as seen in example 1 on the previous page as well as other service specific code
required to communicate properly with the Windows API.
Note that you are not recommended to add services to non-service applications as they will not include the
necessary additionally generated code to handle service specific errors or Windows calls.
Services have both Code and Design views so you may drag and drop components from the designer toolbox.
The easiest way to name your service is by renaming it in the designer context by changing the Name attribute
to the name you wish to give to your new service object. This is also the name the service will be known as to
the system and the DisplayName attribute will be what appears in the services console and TaskManager i.e.
Microsoft’s Internet Information Services is displayed as World Wide Web Publishing in the services console
yet its service name is W3SVC. The service name is what is called from the command line when starting or
stopping services, net start W3SVC and for our own service it would be net start MyService.
You should also make sure the following properties are set to your requirements:
 AllowPause and AllowStop should be set to true unless otherwise required
 Interactive should be set to false unless you require to communicate with the Desktop such as via the
ShowMessage command
 StartType defines at which point during system initialisation should the process start, this should be
set to stAuto if you want it to start at during the system startup or stManual which will allow users
and applications to start it when required

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SERVICE EVENTS
Services come with a set of events that can be used to initialise variables, spawn worker threads as well as
initiating clean up code when a service terminates.
The following is a list of important service events and there meanings:
Event Description
AfterInstall (published) Occurs immediately after the service is registered with the Windows Service Control
manager.
AfterUninstall (published) Occurs immediately after the service is removed from the Service Control manager's
database.
BeforeInstall (published) Occurs before the service is first registered with the Windows Service Control
manager.
BeforeUninstall
(published)
Occurs immediately before the service is removed from the Service Control
manager's database.
OnContinue (published) Occurs when the Service Control manager resumes the service after it has been
paused.
OnExecute (published) Occurs when the thread associated with the service starts up.
OnPause (published) Occurs when the Service Control manager pauses the service temporarily.
OnShutdown (published) Occurs when the system running the service application is about to shut down.
OnStart (published) OnStartup occurs when the service first starts up, before the OnExecute event.
OnStop (published) Occurs when the Service Control manager stops the service.
Table 1: Service events

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KEEPING IT ALIVE
Services, like threads, require a loop in order to stay alive otherwise once it reaches the end of its first run of
the OnExecute method, it will return and the service will exit. To add a method for the OnExecute method
simply double click on the OnExecute event in the design view of the Borland IDE and it will automatically
generate the required method. The following demonstrates a loop that will keep the service alive:
procedure TMyService.ServiceExecute(Sender: TService);
begin
while not Terminated do
begin
ServiceThread.ProcessRequests(True); // wait for termination
end;
end;
Example 2: Keep alive loop
What the ServiceThread.ProcessRequests(True) does is to keep the thread alive instead of
terminating once it reaches the end of the method. The functionality of the service can come from worker
threads initiated before the loop or from TCP, HTTP or Socket components added in the design view.

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PASSING EVENT SIGNALS TO THREADS
One thing to remember is that if you utilise the Start, Stop, Pause and Continue events and you have worker
threads, you should pass these calls on to them as there is no point pausing a service only for a worker thread
to ignore the request. The following example explains how this would be done:
procedure TMyService.ServiceStart(Sender: TService; var Started: Boolean);
begin
WorkerThread := TWorkerThread.Create(False); // initialise thread
Started := True;
end;
procedure TMyService.ServiceContinue(Sender: TService; var Continued:
Boolean);
begin
WorkerThread.Resume;
Continued := True;
end;
procedure TMyService.ServicePause(Sender: TService; var Paused: Boolean);
begin
WorkerThread.Suspend;
Paused := True;
end;
procedure TMyService.ServiceStop(Sender: TService; var Stopped: Boolean);
begin
WorkerThread.Terminate;
Stopped := True;
end;
Example 3: Passing state calls to worker threads

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INSTALLING / UNINSTALLING YOUR SERVICE
Services come with the necessary code to install and uninstall themselves through the use of switches on the
command line or through the Run box located in the start menu. To register a service on a system open a new
Run box, locate your service executable and add the /install switch.
Example 4: Installing your service
Depending on what you specified as the StartType the service will either start during the boot process of the
machine or it will be started manually by users or other applications. To uninstall the service repeat the
process above except instead of the /install switch use /uninstall instead.
Example 5: Service uninstall success

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FULL EXAMPLE
unit main;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, SvcMgr,
Dialogs, MyWorkerThread;
{ MyWorkerThread will be a unit that contains TWorkerThread }
type
TMyService = class(TService)
private
{ Private declarations }
public
function GetServiceController: TServiceController; override;
{ Public declarations }
end;var
MyService: TMyService;
implementation
{$R *.DFM}
procedure ServiceController(CtrlCode: DWord); stdcall;
begin
MyService.Controller(CtrlCode);
end;
function TMyService.GetServiceController: TServiceController;
begin
Result := ServiceController;
end;
procedure TMyService.ServiceStart(Sender: TService; var Started: Boolean);
begin
WorkerThread := TWorkerThread.Create(False); // initialise thread
Started := True;
end;

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procedure TMyService.ServiceContinue(Sender: TService; var Continued:
Boolean);
begin
WorkerThread.Resume;
Continued := True;
end;
procedure TMyService.ServiceExecute(Sender: TService);
begin
while not Terminated do
begin
ServiceThread.ProcessRequests(True); // wait for termination
end;
end;
procedure TMyService.ServicePause(Sender: TService; var Paused: Boolean);
begin
WorkerThread.Suspend;
Paused := True;
end;
procedure TMyService.ServiceStop(Sender: TService; var Stopped: Boolean);
begin
WorkerThread.Terminate;
Stopped := True;
end;
end.
Example 6: Full example code

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USEFUL LINKS
Creating a Windows Service in Delphi – http://www.devarticles.com/c/a/Delphi-Kylix/Creating-a-Windows-
Service-in-Delphi/