DLL Load/Unload

Hi, i have an application that use a DLL, and it is working for a long time.
DLL file resides in the same folder as EXE file.
Application has ShareMem (in a future will be FastShareMem, but "one step at a time") as its first uses unit.
The application shares data through BDE Alias thats is located in the server.
All works fine.
I have multiple users accessing the same application in different pcs, each of them has a link for executing the application with this data:
- it points to the exe file in the server
- working folder is a local folder, in which resides the copy of the DLL
So, when a user starts the application in his workstation, the exe is executed locally, and inmediatelly loads the DLL.
This works great as if i need to update the application, i am only need to change the exe file in the server.

Here is the problem & question:
How can i update the DLL file in each workstation, dinamically (by now, i am doing this by hand!!!)?
I think on this solution:
- put the new DLL version in data folder in server (this folder is acceded from all application running in all workstations).
- if date of local DLL file is older that server DLL file, i replace the local file with that on the server.

This seems to be a ratherly good solution, but, as my application loads the DLL file inmediatelly, i cannot do this.
I think this has to be related to load/unload of the dll at entry point or something like this, but i has no experience at all in here. My DLL has only a few functions, and my application uses an interface unit that declares all function and define them as externals.

Thanks to you all!!!
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spk2000arAsked:
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spk2000arConnect With a Mentor Author Commented:
That's not work for me. I understand what you mean, but i want to keep all the stuff running besides my application. In every workstation as the application run, itself has to verify if there is a new version of the dll and replace the local version.
I found a first step of a solution googling the problem... and that is load DLL dynamically. By now, i am using an static approach.
http://www.scalabium.com/faq/dct0130.htm
http://www.delphi3000.com/articles/article_1138.asp?SK=
I should try, as it is the solution
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spk2000arAuthor Commented:
Unit uImpresionInterfaz, is what i uses in my application.
unit uImpresionInterfaz;
 
interface
 
uses uGeneral, uImpresiones, Printers;
 
{$IFNDEF IMPRESION}
procedure ImprimirReciboFantasma(PuestoCaja: string;
                                 ParametrosImpresora: TParametrosImpresora;
                                 Fecha: TDateTime;
                                 Inmobiliaria, Renglon1, Renglon2, Renglon3, Nom: string;
                                 var Pun: real; Concepto: string; Adicionales: boolean); StdCall;
 
procedure ImprimirReciboGeneral(PuestoCaja: string;
                                ParametrosImpresora: TParametrosImpresora;
                                Fecha: TDateTime;
                                Inmobiliaria, Renglon1, Renglon2, Renglon3, Nom, Concepto, Firmante: string;
                                Adicionales: boolean); StdCall;
 
procedure ImprimirRecibo(PuestoCaja: string;
                         ParametrosImpresora: TParametrosImpresora;
                         PuntoVenta, Nro: string; Fecha: TDateTime;
                         Nom, Dom, NomProp: string;
                         SitIVA: integer; Cuit: string;
                         var SItems: TItems;
                         Total: real; Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirReciboHonorarios(PuestoCaja: string;
                                   ParametrosImpresora: TParametrosImpresora;
                                   PuntoVenta, Nro: string; Fecha: TDateTime;
                                   Nom, Dom: string;
                                   SitIVA: integer; Cuit: string;
                                   var SItems: TItems;
                                   var Hon: real;
                                   Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirReciboHonAdm(PuestoCaja: string;
                               ParametrosImpresora: TParametrosImpresora;
                               PuntoVenta, Nro: string; Fecha: TDateTime;
                               Nom, Dom: string;
                               SitIVA: integer; Cuit: string;
                               var SItems: TItems;
                               var Hon: real;
                               Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirReciboVarios(PuestoCaja: string;
                               ParametrosImpresora: TParametrosImpresora;
                               PuntoVenta, Nro: string; Fecha: TDateTime;
                               Nom, Dom: string;
                               SitIVA: integer; Cuit: string;
                               var SItems: TItems;
                               var Total: real; Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirLiquid(PuestoCaja: string;
                         ParametrosImpresora: TParametrosImpresora;
                         Inmobiliaria, PuntoVenta, Nro: string;
                         Fecha: TDateTime; Nom, Dom: string;
                         SitIVA: integer; Cuit: string;
                         var SItemsAlq, SItemsOtros: TItems;
                         Comision, Total: real; Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirFacturaA(PuestoCaja: string;
                           ParametrosImpresora: TParametrosImpresora;
                           PuntoVenta, Nro: string; Fecha: TDateTime;
                           Nom, Dom: string;
                           SitIVA: integer; Cuit: string;
                           var SItems: TItems;
                           var Hon, TasaIVA: real;
                           Comentarios: string; Adicionales: boolean); StdCall;
 
procedure ImprimirFacturaB(PuestoCaja: string;
                           ParametrosImpresora: TParametrosImpresora;
                           PuntoVenta, Nro: string; Fecha: TDateTime;
                           Nom, Dom: string;
                           SitIVA: integer; Cuit: string;
                           var SItems: TItems;
                           var Hon: real;
                           Comentarios: string; Adicionales: boolean); StdCall;
{$ENDIF}
 
implementation
 
{$IFNDEF IMPRESION}
  procedure ImprimirReciboFantasma;    external 'Impresion.DLL' name 'ImprimirReciboFantasma';
  procedure ImprimirReciboGeneral;     external 'Impresion.DLL' name 'ImprimirReciboGeneral';
  procedure ImprimirRecibo;            external 'Impresion.DLL' name 'ImprimirRecibo';
  procedure ImprimirReciboHonorarios;  external 'Impresion.DLL' name 'ImprimirReciboHonorarios';
  procedure ImprimirReciboHonAdm;      external 'Impresion.DLL' name 'ImprimirReciboHonAdm';
  procedure ImprimirReciboVarios;      external 'Impresion.DLL' name 'ImprimirReciboVarios';
  procedure ImprimirLiquid;            external 'Impresion.DLL' name 'ImprimirLiquid';
  procedure ImprimirFacturaA;          external 'Impresion.DLL' name 'ImprimirFacturaA';
  procedure ImprimirFacturaB;          external 'Impresion.DLL' name 'ImprimirFacturaB';
{$ENDIF}
 
end.

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spk2000arAuthor Commented:
DLL code...
library Impresion;
{$DEFINE IMPRESION}
 
uses
  SysUtils,
  Graphics,
  Dialogs,
  Printers,
  uImpresionInterfaz in '..\..\..\Modulos\DLLImpresion;
 
procedure ImprimirLiquid(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                         Inmobiliaria, PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom: string;
                         SitIVA: integer; Cuit: string;
                         var SItemsAlq, SItemsOtros: TItems;
                         Comision, Total: real; Comentarios: string;
                         Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirReciboVarios(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                               PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom: string;
                               SitIVA: integer; Cuit: string;
                               var SItems: TItems; var Total: real;
                               Comentarios: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirRecibo(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                         PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom, NomProp: string;
                         SitIVA: integer; Cuit: string;
                         var SItems: TItems; Total: real; Comentarios: string;
                         Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirFacturaA(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                           PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom: string;
                           SitIVA: integer; Cuit: string;
                           var SItems: TItems; var Hon, TasaIVA: real;
                           Comentarios: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirFacturaB(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                           PuntoVenta, Nro: string; Fecha: TDateTime;
                           Nom, Dom: string; SitIVA: integer; Cuit: string;
                           var SItems: TItems; var Hon: real;
                           Comentarios: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirReciboHonorarios(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                                   PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom: string;
                                   SitIVA: integer; Cuit: string; var SItems: TItems;
                                   var Hon: real; Comentarios: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirReciboHonAdm(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                               PuntoVenta, Nro: string; Fecha: TDateTime; Nom, Dom: string;
                               SitIVA: integer; Cuit: string; var SItems: TItems;
                               var Hon: real; Comentarios: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirReciboFantasma(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora; Fecha: TDateTime;
                                 Inmobiliaria, Renglon1, Renglon2, Renglon3, Nom: string;
                                 var Pun: real; Concepto: string; Adicionales: boolean); StdCall;
begin
end;
 
procedure ImprimirReciboGeneral(PuestoCaja: string; ParametrosImpresora: TParametrosImpresora;
                                Fecha: TDateTime;
                                Inmobiliaria, Renglon1, Renglon2, Renglon3, Nom, Concepto, Firmante: string;
                                Adicionales: boolean); StdCall;
begin
end;
 
exports ImprimirReciboFantasma;
exports ImprimirRecibo;
exports ImprimirReciboGeneral;
exports ImprimirReciboHonorarios;
exports ImprimirReciboHonAdm;
exports ImprimirReciboVarios;
exports ImprimirLiquid;
exports ImprimirFacturaA;
exports ImprimirFacturaB;
 
end.

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BembiCEOCommented:
Just some ideas:

Write something like an update program. This can be used, to kick out the DLL out of memory. Usually windows controls memory by itself, this may be the reason, taht you cannot replace the DLL at once as still in memory. But you may be able to force windows to close it as long as initiated by a seperate application.
The more easier option may be, to put the update program into the RUN setion of the registry and replace the DLL during reboot or relogon.
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BembiCEOCommented:
You are welcome...
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