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DLL Hell with COM modules 23 May 2022 14:52 #22577

  • wriedmann
  • wriedmann's Avatar
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  • Posts: 3154
  • Hello all,
    in one of my (VO) applications I'm using several COM modules, and with a new version of a used library I had the problem that I had a classic case of DLL hell: two libraries I used had dependencies on different versions of the System.Threading.Tasks.Extensions.dll library.
    After a few hours of searching I found a very interesting solution: put them in different subdirectories of the application directory and then use the AssemblyResolve event to redirect the load to the correct path:
    protected method AssemblyResolve( oSender as object, oArgs as ResolveEventArgs ) as Assembly
    local oAssembly as Assembly
    local cFileName as string
    local cAsmFile as string
    
    if oArgs:Name:Contains( ".resources")
    	return null
    endif
    
        // check for assemblies already loaded
    oAssembly := AppDomain.CurrentDomain.GetAssemblies():FirstOrDefault( { a => a:FullName == oArgs.Name } )
    if oAssembly != null
        return oAssembly
    endif
    cFileName := oArgs:Name:Split( ',') [1] + ".dll":ToLower()
    cAsmFile := Path.Combine ( ".\","AlpiComLib", cFileName )
    
    try
    
    return System.Reflection.Assembly.LoadFrom( cAsmFile )
    
    catch // oEx as Exception
    
    end try
    return null

    You have to register as follows:
    AppDomain.CurrentDomain.AssemblyResolve += AssemblyResolve

    That way you can also change the loading path for other runtime DLLs.

    Wolfgang
    Wolfgang Riedmann
    Meran, South Tyrol, Italy

    www.riedmann.it - docs.xsharp.it

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    DLL Hell with COM modules 23 May 2022 15:55 #22578

    • NickFriend
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  • Posts: 236
  • Hi Wolfgang,

    I've had similar issues at times. You can probably also use a binding redirect in an assemblyname.exe.cfg file, to avoid distrbuting multiple versions of the file. Something like this:
    <?xml version="1.0" encoding="utf-8"?>
    <configuration>
      <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
          <dependentAssembly>
            <assemblyIdentity name="System.Threading.Tasks.Extensions" publicKeyToken="cc7b13ffcd2ddd51" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-4.2.0.1" newVersion="4.2.0.1" />
          </dependentAssembly>
        </assemblyBinding>
      </runtime>
    </configuration>
    This makes any request to use the file redirect to the V4.2.0.1 file.

    Nick

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    DLL Hell with COM modules 23 May 2022 15:59 #22579

    • wriedmann
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  • Posts: 3154
  • Hi Nick,
    I saw that also, but since the DLLs that are loading the conflicting DLLs are not mine, I just preferred to to don't change the manifest.
    Wolfgang
    Wolfgang Riedmann
    Meran, South Tyrol, Italy

    www.riedmann.it - docs.xsharp.it

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    DLL Hell with COM modules 25 May 2022 11:50 #22615

    • ArneOrtlinghaus
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  • Posts: 332
  • I remember the phrase of some enthusiastic programmer colleagues over 10 years ago on a VO-Conference:
    Dotnet is so great: DLL Hell does not exist anymore. All Dlls load the correct version they need. ... and so on. (Runtime errors should also be nearly excluded)

    But this is a joke.

    Thankfully DLL Hell has diminished very much in the last years, not only because of Dot net, but because of many changes in the operating systems and in the programming methods. One of the worse problems were the dlls that had to be registered for com object usage. Fortunately they diminish. Even Crystal Reports with the Runtime version 13 for Dotnet has succeeded getting rid of these dll class registrations.
    Arne

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