Memory leak with a TCSVDataset

[Hansvb]

Hi,

I've been looking for a memory leak all day. it seems that this is caused by a TCSVDataset. See below. This minimal code has a memory leak. I suspect that with the line

Code: Pascal  [Select][+][-]

1. fDataset.Active:= True;

something happens in the background that will not be released later. Because if I don't implement that line, I don't have a leak. If that line does execute, then there is a leak.

I can't trace this back. What am I forgetting?

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   csvdataset;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     procedure Button1Click(Sender: TObject);
18.     procedure FormDestroy(Sender: TObject);
19.   private
20.     fDataset: TCSVDataset;
21.   public
22.  
23.   end;
24.  
25. var
26.   Form1: TForm1;
27.  
28. implementation
29.  
30. {$R *.lfm}
31.  
32. { TForm1 }
33.  
34. procedure TForm1.Button1Click(Sender: TObject);
35. begin
36.   fDataset:= TCSVDataset.Create(Nil);  // Self geeft ook een gehuegenlek
37.   fDataset.CSVOptions.FirstLineAsFieldNames:= True;
38.   fDataset.CSVOptions.Delimiter:= ',';
39.   fDataset.CSVOptions.QuoteChar:= '"';
40.   fDataset.CSVOptions.IgnoreOuterWhitespace := True;
41.   fDataset.FileName:= 'C:\Users\Hans\AppData\Roaming\Gwsw-exporter\686_regels.csv';
42.   fDataset.Active:= True;  //<----------- Something happens here that is later not released. ?
43. end;
44.  
45. procedure TForm1.FormDestroy(Sender: TObject);
46. var
47.   i: Integer;
48. begin
49.   if fDataset.Active then begin
50.     i:= fDataset.FieldCount;
51.  
52. {    for i:= fDataset.Fields.Count - 1 downto 0 do
53.       fDataset.Fields[i].Free;
54.  
55.     fDataset.Fields.Clear;}  // --> doesn't help
56.  
57.     fDataset.Active:= False;
58.     fDataset.Close;
59.  
60.   //fDataset.Clear;
61.   //fDataset.Destroy;
62.   end;
63.  
64.   if assigned(fDataset) then FreeAndNil(fDataset);
65.   //fDataset.Free;
66. end;
67.  
68. end.
69.  

Edit: Windows 11, Lazarus 4.4

[paweld]

How many times do you press the button? - Each time you press the button, you create a new instance of the component, and in form destroy you release only the last instance created. Pressing the button more than once will cause memory leaks.
A good rule of thumb is: if you release a component in the OnDestroy event, create it in OnCreate.

[wp]

Found the attached little demo project on my HD. For testing, I am compiling the application, running it and closing it immediately after the form is shown, I am doing nothing else inside the application.

* When I use Laz/main + FPC 3.2.2 in this test, several memory leaks are reported.
* Switched to an installation of Laz/main + FPC 3.3.1 - no more memory leak.
* Laz/main + FPC/fixes - no more memory leak
* Laz 4.4 + FPC 3.2.4RC1 - no memory leak either.

Therefore I would conclude that TCSVDataset does have a memory leak in FPC 3.2.2, but it has been fixed in FPC 3.2.4RC1 and newer.

[Hansvb]

@Paweld, this was just short quick code with which I can repeat it. I only press the button once. But the example could have been better.

@wp, I thought I saw in csvdataset.pp in the destroy a free to few but because I can't test  that and I'm not very sure I didn't mention that. I'll see tomorrow or later this week if I can manage to use a newer pascal version. And otherwise I can probably use buffdataset as a workaround. (Not tried yet).

[paweld]

You can use TSdfDataset as a replacement for TCSVDataset.

[jamie]

I believe I located the issue.

Code: Pascal  [Select][+][-]

1. procedure TCSVDataPacketReader.StoreFieldDefs(AnAutoIncValue: integer);        
2.  

In that procedure there is this.

Code: Pascal  [Select][+][-]

1. FBuilder:=TCSVBuilder.Create;
2.  

Which in the destructor nor in the current procedure above dose it get freed from what I can see.

Code: Pascal  [Select][+][-]

1. destructor TCSVDataPacketReader.Destroy;
2. begin
3.   FreeAndNil(FCreateFieldDefs);
4.   If FOwnsOptions then
5.     FreeAndNil(FOPtions);
6.   FreeAndNil(Fline);
7.   FreeAndNil(FParser);
8.   inherited Destroy;
9. end;                      
10.  
11.  

Unless I am going blinder, I don't see a release of the FBuilder ?

Just an observation.

I did try out the bufdataSet, that seems to work just fine so it's totally related to the CVS thingy..

Jamie

[dsiders]

I believe I located the issue.

Code: Pascal  [Select][+][-]

1. procedure TCSVDataPacketReader.StoreFieldDefs(AnAutoIncValue: integer);        
2.  

In that procedure there is this.

Code: Pascal  [Select][+][-]

1. FBuilder:=TCSVBuilder.Create;
2.  

Which in the destructor nor in the current procedure above dose it get freed from what I can see.

Code: Pascal  [Select][+][-]

1. destructor TCSVDataPacketReader.Destroy;
2. begin
3.   FreeAndNil(FCreateFieldDefs);
4.   If FOwnsOptions then
5.     FreeAndNil(FOPtions);
6.   FreeAndNil(Fline);
7.   FreeAndNil(FParser);
8.   inherited Destroy;
9. end;                      
10.  
11.  

Unless I am going blinder, I don't see a release of the FBuilder ?

Just an observation.

I did try out the bufdataSet, that seems to work just fine so it's totally related to the CVS thingy..

Jamie

Yes, that's exactly what was done in commit 56acf11ec2 back in Mar of 2022.

[wp]

Indeed, this was an old bug report of mine which I forgot: https://gitlab.com/freepascal.org/fpc/source/-/issues/39607

[jamie]

Ok, so I wasted that much time finding what was already known about.

So, what's the solution for now, place a corrected copy in the project folder?

I would prefer a new release of the IDE with 3.2.4 in it.

Jamie

[wp]

Ok, so I wasted that much time finding what was already known about.

No, you did not waste any time. Your analysis reminded me of my earlier work, and I finally had the idea to search for "TCSVDataset" among the closed gitlab reports.

So, what's the solution for now, place a corrected copy in the project folder?

Yes, that's what I would do.

[egsuh]

I raised this issue last year.

https://forum.lazarus.freepascal.org/index.php/topic,58510.0.html

Not sure it is solved in FPC 3.2.2, which comes with Lazarus 4.4.

[Hansvb]

Not sure it is solved in FPC 3.2.2, which comes with Lazarus 4.4.

I just tested it. I downloaded FPCUPdeluxe and installed the combination of Lazarus 4.4 with "FPC fixes 3.2". then the bug is gone.
The

Code: Pascal  [Select][+][-]

1. destructor TCSVDataPacketReader.Destroy;

has an extra line in the 3.2 FPC fixes:

Code: Pascal  [Select][+][-]

1. FreeAndNil(FBuilder);

[Hansvb]

If I put csvdataset of FPC version 3.2.3 in my project folder structure and compile my application then I no longer have a memory leak when I use a tcsvdataset.

Is that allowed license technically?

[cdbc]

Hi Hans
I'd say __Yes__, being that it's the same /product/ and under the same license as the rest of the /older/ compiler modules.
As long as the units / modules keep their original license, you should be fine to intermix / use them... 
Regards Benny

[Hansvb]

I don't expect anyone, except myself, to use my little tool, but I do want to put it on codeberg.org hence better safe in terms of license than hassle.