I need to call ProcThreadPool.DoParallel with "local" procedure as a parameter. Does DoParallel allow local procedures to pass a procedural parameters ? I get err: Error:
Incompatible type for arg no. 1: Got "<address of local procedure(Int64,Pointer,TMultiThreadProcItem);Register>", expected "<procedure variable type of
procedure(Int64,Pointer,TMultiThreadProcItem);Register>"

Best regards
Tomek

Zitat von Jan Kowalski :

That would be really helpful.
But I don't know how to define a local procedure type:

type
   TMTLocalProcedure = procedure(Index: PtrInt; Data: Pointer;
                                 Item: Pointer); ?
var
   p: TMTLocalProcedure;
procedure TestWithLocalProc;
   procedure LocalProc(Index: PtrInt; Data: Pointer; Item:
TMultiThreadProcItem);
   begin
   end;
begin
   ;
end;

Mattias

I wouldn't be sure it's possible. It makes no sense.

My guess:
A local (nested) procedure has access to the outer(parent or grand-parent if recursive) procedures variables (stackframe). Therefore a local procedure must expect to be somewhere below this parent.

If it was given as a pointer to some other procedure/object, and then called later, this may happen outside the parent. Then no such stackframe does exist, and the local procedure can not work.

Martin

And therefore such a local procedure type must be a combination of local scope and address: http://wiki.freepascal.org/Mac_Local_Procedure_Parameters

This feature is not yet implemented:
http://wiki.freepascal.org/Language_related_articles#Ideas_for_new_stuff

Vincent

Zitat von Vincent Snijders :

It makes enough sense in this case.
For example when you want to execute a loop in parallel, then you extract the loop into a procedure. With a local procedure you can keep the variables, which would make the process quite easy. If you can not use a local procedure, then you must define a record and move the local variables there.
Of course nested local procedures creates a whole bunch of problems, so maybe the record approach is much safer.
Maybe the extract procedure tool can be extended to do some of the monotone work automatically.
I will explain the process in more detail on the wiki.

Mattias

Sorry badly worded on my behalf.

It makes no sense, should have been: it can not be used the same way like normal procedure references, because it is limited to the scope. the way described on the link by Vincent indeed makes sense

You can create a thread call for local procedures, it needs some hacking though: no type checking is possible, you've to work with pointers and pass the context explicitly.

Can you give an example?

Mattias

See http://www.freepascal.org/docs-html/rtl/objects/callpointerlocal.html

and e.g. the comment of Jonas:
(0014130)
Jonas Maebe (manager)
2007-08-13 15:02
at http://bugs.freepascal.org/view.php?id=9432

It would be great if it can be done.
Thanks in advance

Tomek

Cool. It really works, at least under linux 32bit. I wonder on what other platforms this will work.

I added it to mtprocs. Now you can do:

procedure DoSomething(Value: PtrInt);
var
  p: array[1..2] of Pointer;
  procedure SubProc(Index: PtrInt; Data: Pointer; Item: TMultiThreadProcItem);
  begin
    p[Index]:=Pointer(Value);
  end;
var
  i: Integer;
begin
  ProcThreadPool.DoParallelLocalProc(@SubProc,1,2);
end;

This avoids splitting and produces much more readable code.

Mattias

objects.pp of FPC uses the same trick (see
http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/rtl/inc/objects.pp?revision=7964&view=markup around line 790) so it can be considered as officially supported and should work on most platforms.

2009/8/20 Mattias Gaertner :

... Cool. It really works, at least under linux 32bit. I wonder on what other platforms this will work. ...

Tested with two threads on dual core:
Linux 64bit - works great
Vista 32bit - works great
and XP 32bit with two threads on single core (virtualbox) - works ok :)

Great job ;)