Arief Sujatmiko on Blogspot: Desember 2025

Selasa, 16 Desember 2025

Creating Expert System for Database Application Development

In the year 2016, my friend show me he create a desktop application using Delphi that he create very fast. I think I cannot compete with him with that software development skill. I am thinking what if I create an expert system to help create desktop application for me. Then I create this application and name it Gampang Builder.

The design of Gampang Builder is very simple, it get input from the user about the application design and generate softwaer project for it, not a complete software but only:

Main form and main menu of the application.
Navigation system to access facilities in the application and limiting access by application user.
Data service for create, edit and delete for entities and relations.
Editing form for the entites and relations.
Printable report for the entities.

When we create an application first we have to define the backgroud of the problem to solve and the target to be achieved by the application.

Then we choose the technology for the to be generated application.

To make our code more reusable I split the code into few modules.

In each module we can define the class name for the data service and access right than can be used to limit user access because not every user will have the same access level.

After we define the modules we can define the entities by the data table and relations between entities in the applications.

In the data tabel we can define field name, data type, its characteristic, and relation with other table such as look up or master-detail.

If we need the printed design for documentation, Gampang Builder can print it.

The last thing to do is generate the application but because this application is too old and many changes to the library change the package file reader, I will repair the code and update when it completed. I created a few application with this program, one of the application is a medical laboratory database application and is still running today from 2016. I dont have time yet to improve this program but maybe someday.

That's all in this article, I hope it's usefull.

Creating Simple Web Server with Lazarus

Web server is a program or sub program that provide data to client program not limited to web browser using HTTP or HTTPS (HTTP over SSL) protocol. HTTP is a simple, fast and robust protocol for client-server application. The HTTP protocol works by having the client send a request to the server, then the server processes the request and sends back a response to the client.

Example of HTTP Client's Request:

GET / HTTP/1.1
Host: www.example.com

The first line of a HTTP request consist of a command, a url and the protocol version. Followed by header lines and terminated by empty line. Each header line consist of header name and value separated by colon and one space. After the header data is the content data that contain n bytes where n is the value of Content-Length header.

Example of HTTP Server's Response:

HTTP/1.1 200 OK
Date: Mon, 23 May 2005 22:38:34 GMT
Content-Type: text/html; charset=UTF-8
Content-Length: 155
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux)
ETag: "3f80f-1b6-3e1cb03b"
Accept-Ranges: bytes
Connection: close

<html>
  <head>
    <title>An Example Page</title>
  </head>
  <body>
    <p>Hello World, this is a very simple HTML document.</p>
  </body>
</html>

The first line of a HTTP response consist of protocol version and result code followed by error message. Followed by header lines and terminated by empty line. Each header line consist of header name and value separated by colon and one space. After the header data is the content data that contain n bytes where n is the value of Content-Length header.

Free Pascal, Delphi and Lazarus share the same programming language the Object Pascal with little differentiation. So many Delphi component can be used in Lazarus and vice versa because it only requires minor changes in the source code to support both programming. If you don't want to use visual component you can use operating system API like winsock (Windows Socket) for Windows or unisock (Unix Socket) for Linux. I will use synapse for Free Pascal library in this example.

To help parsing input data I create TStringSplitter :

type
{ TStringSplitter }
TStringSplitter = class(TObject)
private
FLine: String;
FCol: Integer;
procedure SetCol(AValue: Integer);
procedure SetLine(AValue: String);
public
constructor Create;
function Fetch(const ATerminator: String=''): String;
property Line: String read FLine write SetLine;
property Col: Integer read FCol write SetCol;
end;
function PosAfter(const SubText, Text: String; StartAt: Integer): Integer;
var
I, L1, L2: Integer;
begin
Result := -1;
L1 := Length(SubText);
L2 := Length(Text);
if ((L1 > L2) or (StartAt < 1)) then exit;
for I := StartAt to L2-L1+1 do
if (CompareMem(@SubText[1], @Text[I], L1)) then
begin
Result := I;
exit;
end;
end;
procedure TStringSplitter.SetCol(AValue: Integer);
begin
FCol := AValue;
end;
procedure TStringSplitter.SetLine(AValue: String);
begin
FLine := AValue;
FCol := 1;
end;
constructor TStringSplitter.Create;
begin
FLine := '';
FCol := 1;
end;
function TStringSplitter.Fetch(const ATerminator: String): String;
var
I, J: Integer;
begin
Result := '';
I := FCol;
if (I > Length(FLine)) then exit;
if (ATerminator <> '') then
begin
J := PosAfter(ATerminator, FLine, I);
if (J > 0) then
begin
Result := Copy(FLine, I, J-I);
FCol := J + Length(ATerminator);
exit;
end;
end;
Result := Copy(FLine, FCol, MaxInt);
FCol := Length(FLine) + 1;
end;

When the server is started it initialize the socket to listen to the specified port. Then it repeatly check for incoming connection and start HTTP handler worker thread until the server is terminated.

procedure TDaemon1.WorkServerListener(Thread: TWorkerThread);
var
sock: TTCPBlockSocket;
h: TSocket;
begin
try
sock := TTCPBlockSocket.Create;
try
sock.Bind('0.0.0.0',IntToStr(Port));
if (sock.LastError <> 0) then
raise ENetworkError.Create('Cannot bind to port '+IntToStr(Port));
sock.Listen;
if (sock.LastError <> 0) then
raise ENetworkError.Create('Cannot listen to port '+IntToStr(Port));
while (not Thread.Terminated) do
begin
if (sock.CanRead(0)) then
begin
h := sock.Accept;
{$HINTS OFF}
if (h <> INVALID_SOCKET) then
WorkerThreads.AddNew(@WorkRequestHandler,Pointer(h));
{$HINTS ON}
end
else
Sleep(1);
end;
finally
sock.Free; // close and free socket object
end;
except
on E: Exception do
// DebugLog('HTTP Server terminated by error '+E.ClassName+': '+
// E.Message);
end;
end;

The HTTP handler worker thread read HTTP request from incoming connection and send back HTTP Respond.

procedure TDaemon1.WorkRequestHandler(Thread: TWorkerThread);
var
sock: TTCPBlockSocket;
S1: TStringSplitter;
s, cmd, url, http_ver, nm, vl, error_msg, respond_text, respond_data: AnsiString;
I, result_code: Integer;
close_socket, can_read: Boolean;
headers, gets, respond_headers: TStrings;
begin
result_code := 500;
close_socket := True;
sock := TTCPBlockSocket.Create;
S1 := TStringSplitter.Create;
headers := TStringList.Create;
gets := TStringList.Create;
respond_headers := TStringList.Create;
try
{$HINTS OFF}
sock.Socket := TSocket(Thread.Param);
{$HINTS ON}
repeat
can_read := sock.CanRead(0);
if (sock.LastError <> 0) then exit;
if (can_read) then
begin
I := Pos('?',url);
if (I >= 1) then
begin
S1.Line := Copy(url, I+1, MaxInt);
repeat
nm := S1.Fetch('=');
if (nm <> '') then
begin
vl := S1.Fetch('&');
gets.Values[nm] := vl;
end;
until (nm = '');
Delete(url,I,MaxInt);
end;
S1.Line := sock.RecvString(ReadTimeout);
if (sock.LastError <> 0) then exit;
cmd := S1.Fetch(' ');
url := S1.Fetch(' ');
http_ver := S1.Fetch;
if ((cmd = 'GET') or (cmd = 'POST')) then
begin
close_socket := (http_ver = 'HTTP/0.9') or (http_ver = 'HTTP/1.0');
S1.Line := sock.RecvString(ReadTimeout);
if (sock.LastError <> 0) then exit;
while (S1.Line <> '') do
begin
nm := S1.Fetch(': ');
vl := S1.Fetch;
headers.Values[nm] := vl;
end;
//
// .. do some processing here
//
respond_data :=
'<head><title>Welcome</title></head><body><h1>Welcome to my Web Server</h1><p>You are in here: '+HttpEncode(url)+'</body>';
respond_headers.Values['Content-Type'] := 'html/text';
respond_headers.Values['Content-Length'] := IntToStr(Length(respond_data));
result_code := 200;
end
else begin
result_code := 501;
close_socket := True;
end;
if((result_code < 200) or (result_code > 499)) then close_socket := True;
case result_code of
200: error_msg := 'OK';
400: error_msg := 'Bad Reqeust';
500: error_msg := 'Internal Server Error';
501: error_msg := 'Not Implemented';
end;
respond_text :=
http_ver + ' ' + IntToStr(result_code) + ' ' + error_msg + #13#10;
for I := 0 to respond_headers.Count do
respond_text := respond_text + respond_headers.Names[I] + ': ' +
respond_headers.ValueFromIndex[I] + #13#10;
respond_text := respond_text + #13#10 + respond_data;
sock.SendBuffer(@respond_text[1], Length(respond_text));
headers.Clear;
respond_headers.Clear;
respond_text := '';
end
else
Sleep(1);
until (Thread.Terminated or close_socket);
finally
respond_headers.Free;
gets.Free;
headers.Free;
S1.Free;
sock.Free;
end;
end;

You can send and receive data using easy to parse data like JSON, XML, BSON or binary data for data service, it is very flexible.

That's all for this article and I hope it's useful.

Kamis, 04 Desember 2025

Creating Thread from Procedure to simplify thread programming in Free Pascal and Delphi

Thread in Free Pascal and Delphi is a process that run simutanously with main program. This is very useful when we need to process data in background while user doing his own work. And is needed to maximize processing in multicore processor because a process including main process can only use 1 core and a quad core processor require a minimum of 4 threads to use all 4 cores.

Basically to create a thread we need to create the thread class and override the execute procedure with the thread code. To minimize work I create WorkerThreadList class, a very simple class to run a procedure of object as a thread.

First the class definition:

type
{ TSemaphore }
TSemaphore = class(TObject)
private
FSem: Integer;
public
constructor Create;
destructor Destroy; override;
procedure Lock;
procedure Unlock;
end;
{ WorkerThreads Routines }
TWorkerThread = class;
TWorkerThreadList = class;
TWorkEvent = procedure(WT: TWorkerThread) of object;
{ TWorkerThread }
TWorkerThread = class(TThread)
private
FOwner: TWorkerThreadList;
FOnWork: TWorkEvent;
FParam: Pointer;
protected
procedure Execute; override;
public
constructor Create(AOwner: TWorkerThreadList; AOnWork: TWorkEvent;
AParam: Pointer);
destructor Destroy; override;
property OnWork: TWorkEvent read FOnWork write FOnWork;
property Param: Pointer read FParam;
property Terminated;
end;
{ TWorkerThreadList }
TWorkerThreadList = class(TObject)
private
FWorkers: TObjectList;
FSem: TSemaphore;
function GetItems(Index: Integer): TWorkerThread;
public
constructor Create;
destructor Destroy; override;
function AddNew(AOnWork: TWorkEvent; AParam: Pointer=nil): TWorkerThread;
procedure TerminateWait(Thread: TWorkerThread);
procedure UnregisterWorkerThread(AThread: TWorkerThread);
procedure TerminateWorkerThreads(Wait: Boolean);
property Items[Index: Integer]: TWorkerThread read GetItems; default;
end;

Then I create the class definition like this:

{ TWorkerThreadList }
function TWorkerThreadList.GetItems(Index: Integer): TWorkerThread;
begin
Result := TWorkerThread(FWorkers[Index]);
end;
constructor TWorkerThreadList.Create;
begin
inherited;
FWorkers := TObjectList.Create(False);
FSem := TSemaphore.Create;
end;
destructor TWorkerThreadList.Destroy;
begin
TerminateWorkerThreads(True);
FWorkers.Free;
FSem.Free;
inherited Destroy;
end;
function TWorkerThreadList.AddNew(AOnWork: TWorkEvent;
AParam: Pointer): TWorkerThread;
var
N: TWorkerThread;
begin
N := TWorkerThread.Create(Self, AOnWork, AParam);
try
FSem.Lock;
try
FWorkers.Add(N);
finally
FSem.Unlock;
end;
Result := N;
N.Start;
except
N.Free;
raise;
end;
end;
procedure TWorkerThreadList.TerminateWait(Thread: TWorkerThread);
begin
if (Thread = nil) then exit;
FSem.Lock;
try
if (FWorkers.IndexOf(Thread) < 0) then
exit
else begin
if (not Thread.Terminated) then Thread.Terminate;
if (Thread.Suspended) then Thread.Start;
end;
finally
FSem.Unlock;
end;
repeat
FSem.Lock;
try
if (FWorkers.IndexOf(Thread) < 0) then exit;
finally
FSem.Unlock;
end;
Sleep(1);
until (False);
end;
procedure TWorkerThreadList.UnregisterWorkerThread(AThread: TWorkerThread);
begin
if ((AThread = nil) or (AThread.FOwner <> Self)) then
exit;
FSem.Lock;
try
FWorkers.Remove(AThread);
AThread.FOwner := nil;
finally
FSem.Unlock;
end;
end;
procedure TWorkerThreadList.TerminateWorkerThreads(Wait: Boolean);
var
I, J: Integer;
begin
repeat
FSem.Lock;
try
J := FWorkers.Count;
for I := 0 to J-1 do
begin
with TWorkerThread(FWorkers[I]) do
begin
if (not Terminated) then Terminate;
if (Suspended) then Start;
end;
end;
finally
FSem.Unlock;
end;
Sleep(1);
until ((J = 0) or not Wait);
end;
{ TWorkerThread }
procedure TWorkerThread.Execute;
begin
try
if (Assigned(FOnWork)) then FOnWork(Self);
except
end;
if (FOwner <> nil) then FOwner.UnregisterWorkerThread(Self);
end;
constructor TWorkerThread.Create(AOwner: TWorkerThreadList; AOnWork: TWorkEvent;
AParam: Pointer);
begin
inherited Create(True);
FreeOnTerminate := True;
Priority := tpIdle;
FOwner := AOwner;
FOnWork := AOnWork;
FParam := AParam;
end;
destructor TWorkerThread.Destroy;
begin
if (FOwner <> nil) then FOwner.UnregisterWorkerThread(Self);
inherited Destroy;
end;
{ TSemaphore }
constructor TSemaphore.Create;
begin
FSem := 0;
end;
destructor TSemaphore.Destroy;
begin
Unlock;
inherited Destroy;
end;
procedure TSemaphore.Lock;
begin
while (InterLockedExchange(FSem, 1) = 1) do Sleep(1);
end;
procedure TSemaphore.Unlock;
begin
InterLockedExchange(FSem, 0);
end;

Using this class I can run a procedure of object with this parameter using TWorkerThreadList object:

TWorkEvent = procedure(WT: TWorkerThread) of object;

How to use the TWorkerThreadList class:

Define WorkerThreads variable as global variable or in the data module:

WorkerThreads: TWorkerThreadList;
Add object create and free for the WorkerThreads object in the data module on create and on destroy:
1. procedure TDaemon1.DataModuleCreate(Sender: TObject);
2. begin
3. WorkerThreads := TWorkerThreadList.Create;
4. end;
6. procedure TDaemon1.DataModuleDestroy(Sender: TObject);
7. begin
8. WorkerThreads.Free;
9. end;
Create the thread procedure:
1. procedure TDaemon1.WorkServerListener(Thread: TWorkerThread);
2. begin
3. try
4. { do something }
5. except
6. { do handle exceptions }
7. end;
8. end;
Create thread for the procedure:
1. procedure TDaemon1.DataModuleStart(Sender: TCustomDaemon; var OK: Boolean
2. );
3. begin
4. WorkerThreads.AddNew(@WorkServerListener, nil);
5. OK := True;
6. end;

WorkerThreadList object can be created and destroyed as needed. A WorkerThreadList object can run alot of procedures.

Working with thread can be tricky, You have to be carefull with race condition, some objects that is not thread safe you need to put semaphore so that only one thread can access it at a time. Memory leak is not the only bugs.

Thats all for the WorkerThreadList object, and I hope this article can be useful.