[fpc-pascal] Where and Why is there a memory leak?

[Graeme Geldenhuys]

On 2017-09-06 09:37, Michael Van Canneyt wrote:
>> type
>>    TBaseClass = class(TInterfacedObject, IHook)
>>    private
>>      FHook: IHook;
>>      property Hook: IHook read FHook implements IHook;
>>    public
>>      constructor Create;
>>      destructor Destroy; override;
>>    end;
>>
>>    constructor TBaseClass.Create;
>>    begin
>>      FHook := THook.Create;  // FPC 2.6.4 reports a memory leak here
>>    end;
>>
>>    destructor TBaseClass.Destroy;
>>    begin
>>      // nothing to do here
>>    end;
> You must free FHook here, because you are keeping a reference to the object,
> not the interface.

I changed the destructor to the code shown below. Just so you know, I 
tried this before I posted the message, and it didn't make any 
difference. FHook is a IHook interface reference, not a object 
reference. I can't change it either, otherwise FPC gives me a compiler 
error on the property ... implements...; line.

   destructor TBaseClass.Destroy;
   begin
     inherited;
     FHook := nil;
   end;

And the program output gives:

[t1]$ ./project1
THook did it
Heap dump by heaptrc unit
4 memory blocks allocated : 115/120
2 memory blocks freed     : 51/56
2 unfreed memory blocks : 64
True heap size : 1114112 (32 used in System startup)
True free heap : 1113696
Should be : 1113760
Call trace for block $000000080072F180 size 32
   $0000000000400379 line 35 of project1.lpr
Call trace for block $000000080072F0C0 size 32


Still 2 memory leaks. :-(

Regards,
   Graeme

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