Problem with WaitForSingleObject

Hello,

Please have a look at the code below.
What it should be doing is:

1. User clicks the SpawnButton
2. ('Calculation began...') info is displayed
3. Thread starts the execution- it calculates if the entered number is prime
4. Once it's finished it displays the result and SetEvent(hEvent)
5. Main Thread waits until Thread finishes the calculation. It uses WaitForSingleObject(hEvent, INFINITE).

the problem is that 'WaitForSingleObject(hEvent, INFINITE)' never returns the value. It looks like this function
just never finds out that SetEvent(hEvent) was ever called- and it should because it IS CALLED.

What do I do wrong?

Jack


unit PrimeForm;

interface

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

type
  TPrimeFrm = class(TForm)
    SpawnButton: TButton;
    NumEdit: TEdit;
    ResultsMemo: TMemo;
    procedure SpawnButtonClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  PrimeFrm: TPrimeFrm;

implementation

uses PrimeThread;

{$R *.dfm}

procedure TPrimeFrm.SpawnButtonClick(Sender: TObject);
var
  NewThread: TPrimeThrd;

begin
  ResultsMemo.Lines.Add('Calculation began...');

  NewThread := TPrimeThrd.Create(True);
  NewThread.FreeOnTerminate := True;
  try
    NewThread.TestNumber := StrToInt(Trim(NumEdit.Text));
    ResetEvent(hEvent);
    NewThread.Resume;  
  except
    on EConvertError do
    begin
      NewThread.Free;
      ShowMessage('That is not a valid number!');
    end;
  end;


  case WaitForSingleObject(hEvent, INFINITE) of   //***PROBLEM
    WAIT_TIMEOUT : ResultsMemo.Lines.Add('It takes too long');
    WAIT_OBJECT_0 : ResultsMemo.Lines.Add('OK');
    WAIT_FAILED : ResultsMemo.Lines.Add('Failed');
  end;

  //***it NEVER returns the value, looks like SetEvent(hEvent) was never executed- but it was in UpdateResults!

end;

end.


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unit PrimeThread;

interface

uses
  Classes, Windows;

type
  TPrimeThrd = class(TThread)
  private
    FTestNumber: integer;
    FResultString: string;
  protected
    function IsPrime: boolean;
    procedure Execute; override;
    procedure UpdateResults;
  public
    property TestNumber: integer write FTestNumber;
  end;

var
  hEvent : THandle;
implementation

uses SysUtils, Dialogs, PrimeForm;

function TPrimeThrd.IsPrime: boolean;
var iter: integer;
begin
  result := true;
  if FTestNumber < 0 then
  begin
    result := false;
    exit;
  end;
  if FTestNumber <= 2 then
    exit;
  for iter := 2 to FTestNumber - 1 do
  begin
    if (FTestNumber mod iter) = 0 then
    begin
      result := false;
      {exit;}
    end;
  end;
end;

procedure TPrimeThrd.Execute;
begin
  if IsPrime then
    FResultString := IntToStr(FTestNumber) + ' is prime.'
  else
    FResultString := IntToStr(FTestNumber) + ' is not prime.';
  Synchronize(UpdateResults);

end;

procedure TPrimeThrd.UpdateResults;
begin
  PrimeFrm.ResultsMemo.Lines.Add(FResultString);
  SetEvent(hEvent);  
end;

initialization
  hEvent := CreateEvent(nil, True, false, PChar('MCS_WFSO_ExampleEvent'));

finalization
  CloseHandle(hEvent);

end.