I "thought" it was not possible to use local procedure address as parameter
like in queue( @SyncOnPrint);
as Clecio showed ...
________________________________________
De: fpc-pascal-boun...@lists.freepascal.org
<fpc-pascal-boun...@lists.freepascal.org> em nome de Sven Barth
<pascaldra...@googlemail.com>
Enviado: segunda-feira, 23 de fevereiro de 2015 15:23
Para: fpc-pascal@lists.freepascal.org
Assunto: Re: [fpc-pascal] TThread.Queue vs TThread.Synchronize
On 23.02.2015 18:58, Graeme Geldenhuys wrote:
> Continuing on the TThread.Queue subject - is there any way to pass
> parameters (or record structure with basic types) to the Queue() call?
>
> That would be super useful instead of putting thread locking on
> variables (for example, reading a progress value to update a GUI
> progress bar).
Currently the only method is to use fields that belong to the TThread
instance.
> I understand that anonymous methods (something I again don't know much
> about) take a snapshot of local variables. So that could possibly be
> used with TThread.Queue() to send variable (simple data types)
> information? Please correct my if I am wrong - like I said, I don't
> really know anonymous methods or their real usage.
In Delphi both TThread.Queue() and TThread.Synchronize() have overloads
to accept anonymous functions. It would then work like this:
=== code begin ===
type
TPrintEvent = procedure(const aMsg: String) of object;
TMyThread = class(TThread)
private
fOnPrint: TPrintEvent;
protected
procedure Execute; override;
property OnPrint: TPrintEvent read fOnPrint write fOnPrint;
end;
procedure TMyThread.Execute;
var
s: String;
begin
s := 'Hello World';
Queue(procedure
begin
fOnPrint(s);
end);
end;
=== code end ===
In this example both "fOnPrint" and "s" would be captured by the
anonymous functions and will be available even after the thread has
terminated.
For FPC modes and those people that dislike the syntax of anonymous
functions (and yes, I can understand those people ;) ) I hope that we'll
get the following variation to work as well:
=== code begin ===
procedure TMyThread.Execute;
var
s: String;
procedure SyncOnPrint;
begin
fOnPrint(s);
end;
begin
s := 'Hello World';
Queue(@SyncOnPrint);
end;
=== code end ===
Regards,
Sven
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