Question

Dynamic arrays are reference counted, and so the memory is freed automatically by the compiler. My question is, when exactly does this automatic freeing occur? Does it happen immediately, or at the end of the containing procedure?

Here is a concrete example

procedure DoStuff;
var data:TBytes;
begin
  data:=GetData; // lets say data now contains 1 Gig of data.
  DoStuffWithData(data);
  // I now want to free up this 1Gig of memory before continuing.
  // Is this call needed, or would the memory be freed in the next line anyway?
  Finalize(data); 

  data:=GetMoreData; // The first array now has no remaining references
  DoStuffWithData(data);
end

Is the call to Finalize() redundant?

Answer 1

The call to Finalize isn’t quite redundant. It’s true that the dynamic array’s reference count will be decremented on the next line (therefore destroying the array, probably), but that will only happen after the new dynamic array is allocated. Just before the return of GetMoreData, but before the assignment takes place, there will be two dynamic arrays in memory. If you destroy the first one manually in advance, then you’ll only have one array in memory at a time.

The second array that you store in data will get destroyed as DoStuff returns (assuming DoStuffWithData doesn’t store a copy of the dynamic-array reference elsewhere, increasing its reference count).