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Problem with LoadLibrary   Найти похожие ветки 

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Jon ©   (2007-10-17 17:44) [0]

I have a problem using the Ghostscript API in my KOL application.

The process works correctly on the first iteration of the loop, but memory is corrupted in subsequent operations.

Here is a simplified demonstration of the problem:


program Test;

uses
 Windows, KOL;

var
 Button, FileList: PControl;

procedure ProcessPDF(PDFFileName, ImageFileName: String);
var
 libGSdll: HMODULE;
 GSinstance: Pointer;
 ErrorCode: Integer;
 Args: array of PChar;
 gsapi_new_instance: function (pinstance: Pointer; caller_handle: Pointer): Integer; stdcall;
 gsapi_init_with_args: function (pinstance:Pointer; argc: Integer; argv: array of PChar): Integer; stdcall;
 gsapi_exit: function (pinstance: Pointer): Integer; stdcall;
 gsapi_delete_instance: procedure (pinstance: Pointer); stdcall;
begin
 MsgOK("Source = " + PDFFileName + #$0D#$0A + "Destination = " + ImageFileName);
 if FileExists(PDFFileName) then
 begin
   libGSdll := LoadLibrary(PChar("c:\Program Files\gs\gs8.60\bin\gsdll32.dll"));
   if libGSdll <> 0 then
   begin
     @gsapi_new_instance := GetProcAddress(libGSdll,"gsapi_new_instance");
     @gsapi_init_with_args := GetProcAddress(libGSdll,"gsapi_init_with_args");
     @gsapi_exit := GetProcAddress(libGSdll,"gsapi_exit");
     @gsapi_delete_instance := GetProcAddress(libGSdll,"gsapi_delete_instance");
     New(GSinstance);
     ErrorCode := gsapi_new_instance(@GSinstance,nil);
     if ErrorCode <> 0 then
       MsgOK("Impossible to open an instance of Ghostscript. Error code: " + Int2Str(ErrorCode));
     try
       SetLength(Args,11);
       Args[0] := "-q";
       Args[1] := "-dNOPAUSE";
       Args[2] := "-dBATCH";
       Args[3] := "-dSAFER";
       Args[4] := "-sDEVICE=png16m";
       Args[5] := "-r300";
       Args[6] := "-dGraphicsAlphaBits=4";
       Args[7] := "-dFirstPage=1";
       Args[8] := "-dLastPage=1";
       Args[9] := PChar("-sOutputFile=" + ImageFileName);
       Args[10] := PChar(ExtractShortPathName(PDFFileName));
       ErrorCode := gsapi_init_with_args(GSinstance,Length(Args),Args);
       if ErrorCode <> 0 then
         MsgOK("Error printing document: " + ImageFileName);
       gsapi_exit(GSinstance);
     finally
       gsapi_delete_instance(GSinstance);
     end;
     GSinstance := nil;
     FreeLibrary(libGSdll);
   end;
 end;
end;

procedure ButtonClick(Dummy: Pointer; Sender: PControl);
var
 Counter: Integer;
begin
 for Counter := 0 to FileList.Count -1 do
   ProcessPDF(FileList.Items[Counter],ChangeFileExt(FileList.Items[Counter],".png") );
end;

begin
 Applet := NewForm(nil,"");
 FileList := NewEditbox(Applet,[eoMultiline,eoReadonly]);
 FileList.Color := clWhite;
 FileList.Add("c:\1.pdf" + #$0D#$0A);
 FileList.Add("c:\2.pdf" + #$0D#$0A);
 FileList.Add("c:\3.pdf" + #$0D#$0A);
 Button := NewButton(Applet,"Convert").PlaceRight;
 Button.OnClick := TOnEvent(MakeMethod(nil,@ButtonClick));
 Run(Applet);
end.


On first loop:

MsgOK("Source = " + PDFFileName + #$0D#$0A + "Destination = " + ImageFileName);

Source = c:\1.pdf  Destination = c:\1.png

Afterwards:

Source =   Destination = .png

All variables - including Counter - no longer contain valid data.

Can anyone offer any advice. Thanks in advance.

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← →
Vladimir Kladov ©   (2007-10-17 18:19) [1]

OleInit? Don"t know, I did not work with it.

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← →
Jon ©   (2007-10-17 20:46) [2]

Thank you but OleInit does not work.

The above code works once, but not again.
I assume that it is a memory management issue.
Is there a better way to load a library?

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← →
Vladimir Kladov ©   (2007-10-18 15:41) [3]

If the DLL contains bugs, it is still possible to use it this way:
- you run another instance of your app, passing some parameters to it via command line + memory mapped file,
- there it run silently and hidden and terminates as usual. In this case all loaded DLL"s are killed freeing all the allocated resources and w/o touching the main application any way.

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← →
Jon ©   (2007-10-18 16:10) [4]

Thank you very much for the suggestion- shall try it.
What do you mean by "memory mapped file"?

---

← →
Vladimir Kladov ©   (2007-10-18 16:22) [5]

If you don"t know what is it, then you don"t need it, just forget it :)
(But in MSDN you can read all about it. Shortly: the fastest way to 1) handle giant files 2) to exchange large data between separate processes).

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← →
Jon ©   (2007-10-18 16:43) [6]

Understood - researching it now. Thank you :-)

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