[fpc-devel] Need patch for bugs : 0011503 / 0009472

[Jonas Maebe]

On 19 Jun 2008, at 15:20, Boian Mitov wrote:

>  never call Free() on interfaced object. I surely know that if I  
> have used interfaces for the last 10 years or so ;-) .
> What I need is a way to make sure that all the references are gone.  
> This is the first non garbage collected compiler that has prevented  
> me from releasing all the references so far. Delphi, the C++ COM  
> libraries VB etc. they all have behaved in a predictable way.

Delphi doesn't, look at this example:

***
uses
   SysUtils;

type
   imyintf = interface
     function getrefcount: longint;
   end;

   tmyclass = class(tinterfacedobject,imyintf)
     function getrefcount: longint;
   end;


   function tmyclass.getrefcount: longint;
     begin
       result:=refcount;
     end;

procedure test;
var
   i: imyintf;

   function test2: imyintf;
     begin
       result:=tmyclass.create;
       writeln(i.getrefcount);
     end;

begin
   i:=tmyclass.create;
   i:=test2;
   writeln(i.getrefcount);
end;

begin
   test;
end.
***

The output is (when compiled with Kylix 3):
refcount of i in test2: 1
refcount of i after calling test2: 2

If you comment out the "writeln" in test2, then the result is:
refcount of i after calling test2: 1

The reason is that if you access "i" inside test2, then Delphi cannot  
perform the optimisation of skipping the temp, and it also only frees  
the temp at the end of the function.

The behaviour you are counting on is a side effect of an optimisation,  
not a behaviour by design.


Jonas