Hi Kyley
There is another option. The double check locking pattern. Once instantiated
the critical section is no longer used.
var
SingletonInstance : TSingletonObject;
function GetSingletonInstance : TSingletonObject;
begin
if (SingletonInstance= nil) then
begin
CriticalSection.Enter;
try
if (SingletonInstance= nil) then
begin
SingletonInstance:= TSingletonObject.Create;
end;
finally
CriticalSection.Leave;
end;
end;
Result := SingletonInstance;
end;
----- Original Message -----
From: "Kyley Harris" <[EMAIL PROTECTED]>
To: "NZ Borland Developers Group - Delphi List" <[email protected]>
Sent: Friday, May 19, 2006 4:52 PM
Subject: RE: [DUG] Usage - initialization and finalization
> Thanks. Hadn't thought of that before. It is of course quite possible
> for it to be constructed 2 times. Going back to that code sample I
> posted for observation I use this method for creating a Critical
> Section. This would probably be a good place to use that seeing as I use
> that in a very threaded environment.
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> On Behalf Of Jeremy North
> Sent: Friday, 19 May 2006 2:29 p.m.
> To: NZ Borland Developers Group - Delphi List
> Subject: Re: [DUG] Usage - initialization and finalization
>
> 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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