The code below should work but I get an AV when the program calls `Bar.Free`.

Do you know why?

Lazarus 1.8.1 r57299 FPC 3.0.4 i386-win32-win32/win64

===begin===
program Project1;
uses
  SysUtils;
type
  IBar = interface
  ['{C22FB8F4-1EC6-42C4-81E4-F2A52CC52258}']
    function Name: string;
  end;
  TBar = class(TInterfacedObject, IBar)
  public
    function Name: string;
  end;

{ TBar }

function TBar.Name: string;
begin
  Result := ClassName;
end;
var
  Bar: TBar;
begin
  Bar := TBar.Create;
  try
    if Supports(Bar, IBar) then
      Writeln('Bar supports...');
  finally
    Bar.Free;
  end;
end.
===end===

Regards,
Marcos Douglas

Hi,
 
Bar shoud be released by Interface, no need to call Free.

V.
______________________________________________________________

The code below should work but I get an AV when the program calls `Bar.Free`.Do you know why?Lazarus 1.8.1 r57299 FPC 3.0.4 i386-win32-win32/win64...Regards,Marcos Douglas

----------

Vojtěch Čihák wrote

Hi, Bar shoud be released by Interface, no need to call Free.

I'm sorry, but `Bar` was defined as `Bar: TBar` so, it's a class not an interface.

Marcos Douglas

Yes, TBar is TInterfacedObject and is reference counted therefore Free is not needed. Just comment the line //Bar.Free; compile with -gh and you will see no memory leak.  
V.
______________________________________________________________

Vojtěch Čihák wrote

Hi, Bar shoud be released by Interface, no need to call Free.

I'm sorry, but `Bar` was defined as `Bar: TBar` so, it's a class not an interface.

Marcos Douglas

You think this is the problem...
All right, try to change your copy like this:

===begin===
  Bar := TBar.Create;
  try
    if Supports(Bar, IBar) then
      Writeln(Bar.Name + ' supports...');
  finally
    ////Bar.Free;  << no Free
  end;
===end===

Are you still seeing an AV?

Marcos Douglas

With this modification and -gh it is alright:
 
Interface]$ ./test
Bar supports...
Heap dump by heaptrc unit
7 memory blocks allocated : 875/880
7 memory blocks freed     : 875/880
0 unfreed memory blocks : 0
True heap size : 360448
True free heap : 360448
Interface]$
 
V.
______________________________________________________________

===begin===
 Bar := TBar.Create;
 try
   if Supports(Bar, IBar) then
     Writeln(Bar.Name + ' supports...');
 finally
   ////Bar.Free;  << no Free
 end;
===end===

Are you still seeing an AV?

Marcos Douglas

Not here. I'm using FPC 3.0.4.
I've took a look at EMB documentation:
http://docwiki.embarcadero.com/Libraries/XE2/en/System.SysUtils.Supports Take a look at "Warning" section. That's the problem.

Marcos Douglas

Vojtěch Čihák wrote

With this modification and -gh it is alright:

Only if you declare `Bar` as `IBar` instead of `TBar`. Please, check your code again.

Regards,
Marcos Douglas

I only added {$mode objfpc} to be able compile, so I test this code:  
program Project1;
{$mode objfpc}
 
uses
  SysUtils;
 
type
  IBar = interface
  ['{C22FB8F4-1EC6-42C4-81E4-F2A52CC52258}']
    function Name: string;
  end;
 
  TBar = class(TInterfacedObject, IBar)
  public
    function Name: string;
  end;
 
{ TBar }
 
function TBar.Name: string;
begin
  Result := ClassName;
end;
 
var
  Bar: TBar;
 
begin
  Bar := TBar.Create;
  try
    if Supports(Bar, IBar) then
      Writeln('Bar supports...');
  finally
    //FreeAndNil(Bar);
  end;
 
end.           
 
My FPC is also 3.0.4, on 64-bit Linux.
Compiled with -gh I have no memory leak since this demo is about COM interfaces.  
V.
______________________________________________________________

Vojtěch Čihák wrote

With this modification and -gh it is alright:

Only if you declare `Bar` as `IBar` instead of `TBar`. Please, check your code again.

Regards,
Marcos Douglas