Unable to create COM object in thread
lazarus / 34-Windows

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Eclipticon · 2012-09-02 18:08

Hi,

to access a COM object not only in my program's main thread but also
from a sub thread, I would like to create a new instance of it.

Unfortunately, creation of this new instance fails with a
CO_E_OBJNOTCONNECTED error (see comments in code below).

Can anyone hint me on what I am doing wrong? (Sorry, I can not give
too many details about this COM object or code, as this is subject to
a non-disclosure agreement!)

Thanks,

Paul

Code: [Select]unit threadtest2main;

{$mode objfpc}{$H+}

interface

uses
  Classes, Windows, SysUtils, FileUtil, Forms, Controls, Graphics,
  Instrument_TLB, Dialogs, StdCtrls, comobj, ActiveX;

type
  TTestThread = class(TThread)
  private
    SubThreadInstrument: Instrument;
  protected
    procedure Execute; override;
  end;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Label1: TLabel;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    MainThreadInstrument: Instrument;
  end;

var
  Form1: TForm1;
  ResultText: string;

implementation

{$R *.lfm}

procedure TTestThread.Execute;
var
  Success: HRESULT;
begin

  Success := CoInitializeEx(nil, COINIT_MULTITHREADED); // Tried with
COINIT_APARTMENTTHREADED, too
  if (Success <> S_OK) or (Success <> S_FALSE) then
    Exception.Create('Not s_ok or s_false');

  SubThreadInstrument := ComInstrument.Create;  // Calls
CreateComObject();
  // Code raises an EOleSysError here: CoCreateInstance() returns
CO_E_OBJNOTCONNECTED

  if SubThreadInstrument.SomeStatus then
    ResultText := ResultText + 'T'
  else
    ResultText := ResultText + 't';

  FreeAndNil(SubThreadInstrument);

  CoUninitialize;

end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MainThreadInstrument := ComInstrument.Create; // Calls
CreateComObject();
  // Creating a second instance of Instrument in the main thread works
well
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ATestThread: TTestThread;
  Success: HRESULT;
begin

  Success := CoInitializeEx(nil, COINIT_MULTITHREADED);
  if (Success <> S_OK) or (Success <> S_FALSE) then
    Exception.Create('Not s_ok or s_false');

  ATestThread := TTestThread.Create(False);

  if MainThreadInstrument.SomeStatus then
    ResultText := ResultText + 'B'
  else
    ResultText := ResultText + 'b';

  ATestThread.WaitFor;

  if Assigned(ATestThread.FatalException) then
    raise
Exception.Create(Exception(ATestThread.FatalException).Message);

  FreeAndNil(ATestThread);

  Label1.Caption := ResultText;

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeAndNil(MainThreadInstrument);
end;

end.

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ludob · 2012-09-03 09:22

Comobj does already a CoInitialize in its initialization section which
implies STA.  Try calling CoUninitialize in FormCreate followed by
CoInitializeEx(nil,COINIT_APARTMENTTHREADED)

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Eclipticon · 2012-09-03 19:18

Hi ludob,

thanks for the tip, unfortunately it did not do the job.

I am wondering though, isn't COINIT_APARTMENTTHREADED setting it to
STA? And shouldn't my CoInitializeEx return something different from
S_OK and S_FALSE if I specify a contradictory threading model?

Thanks!

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Eclipticon · 2012-09-03 19:38

Not added in proof: that should be twice

Code: [Select]if (Success <> S_OK) AND (Success <> S_FALSE) then
of course ...