Delphi-使用IFuture从并行编程库中读取大文件

Question

I'm reading in some large(ish) excel file which take "ages" to load. I can load it in before I really need to access it. So I thought this would be a good use for an IFuture from the Parallel Programming Library. But I'm not sure how to go about it as all of the "Future" examples only cover simple types such as strings, integers etc.

Here's the non-parallel code:

xls := TsmXLSFile.Create;
xls.Open(s);

Where "xls" is the Excel object and "s" is a memory stream.

How would a "Future" go about this? Would I declare xls as...

xls := IFuture<TsmXLSFile>

Is this correct. If it is then do I need to free it like a normal TsmXLSFile since it's now an interface?

Steve

Answer 1

Declare a field to get hold of that interface:

FXlsFuture: IFuture<TsmXLSFile>;

Add a method to create that future and another one to handle the loaded file:

function TForm90.CreateXlsFuture: IFuture<TsmXLSFile>;
begin
  { starts loading }
  Result := TTask.Future<TsmXLSFile>(
    function: TsmXLSFile
    begin
      result := TsmXLSFile.Create;
      result.Open(s);
    end);
end;

procedure TForm90.HandleXlsFuture(AFuture: IFuture<TsmXLSFile>);
var
  xsl: TsmXLSFile;
begin
  xsl := AFuture.Value; { eventually blocks until the file is loaded }
  { do something with the file }
  xsl.Free;
end;

In addition you can query the Status of the future to check if the file is already loaded to avoid blocking.

Answer 2

No, you can't do that. You would do it more like this:

... // this must be a persistant object
  ismXLSFile : IFuture< TsmXLSFile >;
...

// Get started

ismXLSFile := TTask.Future< TsmXLFile > (function : TsmXLFile begin Result := TsmXLFile.Create ); end; );

ismXLSFile.Start;

// Then at some later point
xls := ismXLSFile.Value;

And yes, you do still need to free it. xls is not an interfaced object. (ismXLSFile is).