Version used: Delphi 7.

I'm working on a program that does a simple for loop on a Virtual ListView. The data is stored in the following record:

type TList=record
  Item:Integer;
  SubItem1:String;
  SubItem2:String;
end;

Item is the index. SubItem1 the status of the operations (success or not). SubItem2 the path to the file. The for loop loads each file, does a few operations and then, save it. The operations take place in a TStringList. Files are about 2mb each.

Now, if I do the operations on the main form, it works perfectly.

Multi-threaded, there is a huge memory problem. Somehow, the TStringList doesn't seem to be freed completely. After 3-4k files, I get an EOutofMemory exception. Sometimes, the software is stuck to 500-600mb, sometimes not. In any case, the TStringList always return an EOutofMemory exception and no file can be loaded anymore. On computers with more memory, it takes longer to get the exception.

The same thing happens with other components. For instance, if I use THTTPSend from Synapse, well, after a while, the software cannot create any new threads because the memory consumption is too high. It's around 500-600mb while it should be, max, 100mb. On the main form, everything works fine.

I guess the mistake is on my side. Maybe I don't understand threads enough. I tried to free everything on the Destroy event. I tried FreeAndNil procedure. I tried with only one thread at a time. I tried freeing the thread manually (no FreeOnTerminate...)

No luck.

So here is the thread code. It's only the basic idea; not the full code with all the operations. If I remove the LoadFile prodecure, everything works good. A thread is created for each file, according to a thread pool.

unit OperationsFiles;

interface

uses Classes, SysUtils, Windows;

type
 TOperationFile = class(TThread)
 private
  Position : Integer;
  TPath, StatusMessage: String;
  FileStringList: TStringList;
  procedure UpdateStatus;
  procedure LoadFile;
 protected
  procedure Execute; override;
 public
  constructor Create(Path: String; LNumber: Integer);
 end;

implementation

uses Form1;

procedure TOperationFile.LoadFile;
begin
 try
  FileStringList.LoadFromFile(TPath);
  // Operations...
  StatusMessage := 'Success';
 except
  on E : Exception do StatusMessage := E.ClassName;
 end;
end;

constructor TOperationFile.Create(Path : String; LNumber: Integer);
begin
 inherited Create(False);
 TPath := Path;
 Position := LNumber;
 FreeOnTerminate := True;
end;

procedure TOperationFile.UpdateStatus;
begin
 FileList[Position].SubItem1 := StatusMessage;
 Form1.ListView4.UpdateItems(Position,Position);
end;

procedure TOperationFile.Execute;
begin
 FileStringList:= TStringList.Create;
 LoadFile;

 Synchronize(UpdateStatus);

 FileStringList.Free;
end;

end.

What could be the problem?

I thought at one point that, maybe, too many threads are created. If a user loads 1 million files, well, ultimately, 1 million threads is going to be created -- although, only 50 threads are created and running at the same time.

Thanks for your input.