Dynamic arrays, SetLength and memory issues

[kittyyo]

Hi all,

I am wondering why my program needs more memory the longer it runs - well it should not. I assume that I am doing something wrong with the dynamic arrays I'm using...

I've got a fixed array of dynamic arrays holding records,
e.g.:

TReservation = record
  Directed: Boolean; 
  Source, Destination: TStationAddress; 
    // these are only pointers to already existing objects
  Priority: 0..15;
  TimeOfRequest: Cardinal;
end;

TReservations = array of TReservation;

TReservationTable = class(TObject)
private
  Items: array[0..99] of TReservations;
end;

My program starts at position 0 of the Items array and assigns to it a certain number of TReservation records (normally 1 to 4), and that way it continues until position 99, clearing the previous items. Then it starts to re-use position 0 and so on... just like a ring buffer.

I thought this could work that way (schematically):

var
  i, j, CurrentPosition: Integer;

for i := 0 to 99999 do
begin
  CurrentPosition := i mod 100;
  // clear the item before the current item
  Finalize(Items[(i-1) mod 100]); 
  // OR (which one is better?)
  SetLength(Items[(i-1) mod 100], 0);
  // save some data into the current item
  SetLength(Items[CurrentItem], RandomRange(1,5));
  for j := 0 to High(Items[CurrentItem]) do
  begin
    Items[CurrentItem][j].Directed := True;
    Items[CurrentItem][j].Priority := 12;
    // ...
  end;
end;

I know that I would not have to clear all the previous items right away in this code sample, but this is only a scheme and my 'real' program needs to really clear previous items.

I am assuming that Finalize() or SetLength(x,0) do not free the memory assigned to the dynamic array with the records.

Keep in mind that I could assign 5 records to position 0 at the first run, and when I return to position 0 I could assign zero records. Then the memory for the 5 previously assigned records should be freed.

What am I doing wrong, or am I doing everything right?

Thanks for any suggestions!

Anne

 

[whosrdaddy]

setting the length of a dyn array to 0 is not enough, assigning nil to it will actually release memory.

Setlength(Array,0);
Array:=nil;

By the way, why working with dynamic arrays if you have things like Tlist and TObjectList?

cheers

--------------------------------------
What You See Is What You Get

 

[kittyyo]

Thanks!

Think I'm either old-fashioned or insane ;-)

Do you know how much more memory would be used by TObjectLists (in comparison to dynamic arrays)... if I'd have 20000 of them? I think this was my first intention when I decided not to use lists... two years ago... ;-)

 

[kittyyo]

... and, BTW: Is there any tool that can point a programmer to code that assigns memory but doesn't free it?

 

[whosrdaddy]

look for memory sleuth for the memory leak hunt...

Objects are using a bit more memory in this case but even for 20000 items, this should be negligible nowadays...

--------------------------------------
What You See Is What You Get