[DUG] Usage - initialization and finalization

[Paul A Norman]

Thanks for all of that everybody.

Kyely, the information on scope, and also the non-existance yet of the
Application object during *Initialization* is very helpful thanks.

"You don't always have to use initialization to create and finalize to
destroy. That would be very resource hungry."

I was thinking of it as an alternative, like *Initialization *as the point
to create gloabl UNIT wide VAR .TstringLists etc .. instead of during
.onFormCreate, and for freeing stringlists etc .. during
*Finalization*instead of during .
*onDestroy*

Reason being . .

I was wondering whether there are any circumstances where using Finilization
to .*free* objects is more reliable than .*ondestroy *?
Is Finalization called after Tform.*onDestroy*, or does it failsafe even if
onDestroy fails for some system reason?

Paul

On 19/05/06, Jeremy North <jeremy.north at gmail.com> wrote:
>
> An alternate and thread safe way to perform this operation is to use
> InterlockedCompareExchange.
>
> It is possible (although not very probable) to have FList created
> twice without using InterlockedCompareExchange. Probably not worth the
> extra effort though.
>
> ms-help://borland.bds4/dllproc/base/interlockedcompareexchange.htm
>
> This technique is implemented in the TPrivateHeap class in the
> PrivateHeap unit. It was originally written by Hallvard Vassbotn. If
> you are interested in the inner workings of Delphi and the Compiler,
> you should read his blog (http://hallvards.blogspot.com/).
>
> For the OP I would minimize the use of the Initialization section to
> cases where you really need it. Otherwise your unit cannot be smart
> linked out.
>
> /// code below
>
> unit Unit4;
>
> interface
>
> uses
>    Windows
> , Classes
> , SysUtils
> ;
>
> function GetList: TList;
>
> implementation
>
> var
> FList: TList;
>
> function GetList: TList;
> var
> lList: TList;
> begin
> if FList = nil then
> begin
>    lList := TList.Create;
>    if InterlockedCompareExchange(Integer(FList), Integer(lList), 0) <> 0
> then
>      lList.Free;
> end;
> result := FList;
> end;
>
> initialization
>
> finalization
> FreeAndNil(FList);
>
> end.
>
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