library DLLEntryLib;
uses
 SysUtils,
 Windows,
 Dialogs,
 Classes;

procedure DLLEntryPoint(dwReason: DWord);
begin
 case dwReason of
 DLL_PROCESS_ATTACH: ShowMessage('Attaching to process');
 DLL_PROCESS_DETACH: ShowMessage('Detaching from process');
 DLL_THREAD_ATTACH: MessageBeep(0);
 DLL_THREAD_DETACH: MessageBeep(0);
 end;
end;

begin
 { First, assign the procedure to the DLLProc variable }
 DllProc := @DLLEntryPoint;
 { Now invoke the procedure to reflect that the DLL is attaching to the
 process }
 DLLEntryPoint(DLL_PROCESS_ATTACH);
end.

{
Copyright © 1999 by Delphi 5 Developer's Guide - Xavier Pacheco and Steve Teixeira
}

unit MainFrm;

interface

uses
 Windows, Messages, SysUtils, Classes, Graphics, Controls,
 Forms, Dialogs, StdCtrls, ComCtrls, Gauges;

type

 { Define a TThread descendant }
 TTestThread = class(TThread)
 procedure Execute; override;
 procedure SetCaptionData;
 end;

 TMainForm = class(TForm)
 btnLoadLib: TButton;
 btnFreeLib: TButton;
 btnCreateThread: TButton;
 btnFreeThread: TButton;
 lblCount: TLabel;
 procedure btnLoadLibClick(Sender: TObject);
 procedure btnFreeLibClick(Sender: TObject);
 procedure btnCreateThreadClick(Sender: TObject);
 procedure btnFreeThreadClick(Sender: TObject);
 procedure FormCreate(Sender: TObject);
 private
 LibHandle: THandle;
 TestThread: TTestThread;
 Counter: Integer;
 GoThread: Boolean;
 end;

var
 MainForm: TMainForm;

implementation

{$R *.DFM}

procedure TTestThread.Execute;
begin
 while MainForm.GoThread do
 begin
 Synchronize(SetCaptionData);
 Inc(MainForm.Counter);
 end;
end;

procedure TTestThread.SetCaptionData;
begin
 MainForm.lblCount.Caption := IntToStr(MainForm.Counter);
end;

procedure TMainForm.btnLoadLibClick(Sender: TObject);
{ This procedure loads the library DllEntryLib.DLL }
begin
 if LibHandle = 0 then
 begin
 LibHandle := LoadLibrary('DLLENTRYLIB.DLL');
 if LibHandle = 0 then
 raise Exception.Create('Unable to Load DLL');
 end
 else
 MessageDlg('Library already loaded', mtWarning, [mbok], 0);
end;

procedure TMainForm.btnFreeLibClick(Sender: TObject);
{ This procedure frees the library }
begin
 if not (LibHandle = 0) then
 begin
 FreeLibrary(LibHandle);
 LibHandle := 0;
 end;
end;

procedure TMainForm.btnCreateThreadClick(Sender: TObject);
{ This procedure creates the TThread instance. If the DLL is loaded a
 message beep will occur. }
begin
 if TestThread = nil then
 begin
 GoThread := True;
 TestThread := TTestThread.Create(False);
 end;
end;

procedure TMainForm.btnFreeThreadClick(Sender: TObject);
{ In freeing the TThread a message beep will occur if the DLL is loaded. }
begin
 if not (TestThread = nil) then
 begin
 GoThread := False;
 TestThread.Free;
 TestThread := nil;
 Counter := 0;
 end;

end;

procedure TMainForm.FormCreate(Sender: TObject);
begin
 LibHandle := 0;
 TestThread := nil;
end;

end.