Problem with LoadLibrary

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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"?

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).

Understood - researching it now. Thank you :-)

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