Let's assume I have two assemblies:
MyExecutable.dll version 1.0.0
MyClassLibrary.dll version 1.0.0
Now, MyExecutable.dll currently uses MyClassLibrary.dll's classes and methods (which include some algorithms). Most of those algorithms were made on the run, being that later I'll want to refine them if needed. This means, I won't change the interface of those classes but the code itself will see some changes.
The question at hand is, MyExecutable.dll will be expecting MyClassLibrary.dll 1.0.0 and I'll want it to use version 1.0.1 (or something like that). I don't want to have to recompile MyExecutable.dll(because actually there might be more than just one executable using MyClassLibrary.dll). Is there a solution for this problem? I've heard about the GAC, but if possible I'd like to stay away from it.
Thanks
You are looking for Assembly Binding Redirection - this is a configurable way to tell .NET what version assemblies to use.
The first solution is Assembly Binding redirection, already recommended by Oded.
It is advantageous if you have a smaller .dll and want to make something work with its newer versions.
The second option is creating a separate assembly for the interfaces, and referencing only that from the executable.
This way, you can allow third parties to build stuff against your library without giving them the exact library's assembly. (Eg. they can't decompile it with Reflector, so it is more secure this way.)
As long as the interface assembly doesn't change, you can change other stuff in the library pretty much as you want.
Related
I have a MEF-based application which uses adapters to process files. It uses configuration files to determine which directories to watch and which adapter to use to process each type of file. Plugins take the form of a .dll that implements a common interface.
Each .dll requires its own set of dependent libaries. For instance, plugin1.dll might need to use apilibrary.dll and xmllibrary.dll. It is also possible that at a later date I might want to add plugin2.dll, and plugin2.dll might use xmllibrary.dll as well. These dependent libraries are updated regularly, so I can't count on plugin2.dll using the exact same version of xmllibrary.dll used in plugin1.dll.
I'd like to compile each plugin to one .dll file that invisibly includes within itself all of its dependent libraries, which seems like one way to solve this problem. Alternately, I'd like to figure out how each .dll file can look for its dependent libaries in a subfolder, which I believe would also reduce the possibility of versioning conflicts. Or maybe there's a dead simple solution to this problem that I haven't even considered (which is always very, very likely).
Any thoughts?
You should probably try to get this to work with standard .NET loading rules. However, if you do need to control exactly how assemblies are loaded and which versions are loaded, this blog post shows how: Using Loading contexts effectively
I guess you need to weigh up deployability vs. maintenance. The simple solution is to use a tool called ILMerge. ILMerge takes your project output and can take other assemblies and merge them together. This enables you to wrap up all of the assemblies that your plugin is dependent on, and merge them into a single assembly. Optionally you can do things like re-signing with your public key, etc. Here is a good read: Leveraging ILMerge to simplify deployment and your users experience by Daniel Cazzulino.
But while that is good, what happens if a new version of the referenced assembly is distributed that corrects bugs in that which you have embedded? By the rules of Fusions assembly loader, when it loads the types from your referenced assembly, it will see that they have already been loaded, so there is no reason for it to load the updated version. This would then mean you need to recompile your plugin and merge the newer referenced assembly again.
My question would be, is it really that important to ensure a specific version is used? If a newer version provides an updated implementation (that doesn't break backwards compatibility) then surely this should benefit all plugins that need to reference it?
As for as how assemblies are loaded in reference to each other, have a read of Understanding .Net Assemblies and References, which is an invaluable piece of information.
MEF uses standard .NET assembly loading, and everything's loaded in a single AppDomain. You have very little control over how dependencies are loaded - as they just get loaded automatically by the CLR when the assembly is injected via MEF. Normal CLR assembly loading rules apply when using MEF, so dependencies will be loaded as if they were a dependency of your application - no matter where they're located or referenced.
For the most part, if the plugins and their dependencies are properly written, you most likely will not need to worry about this. As long as the versioning in the dependencies is correct, it will likely just work.
So here's the problem. I'm writing some StyleCop plug-in assemblies for use at the company I work for. As such, these assemblies need to reference Microsoft.StyleCop.CSharp.dll for example, which is strongly named.
The problem comes in that if I build this and pass it along to the developers in my group, they must have the same version of the StyleCop dll (currently 4.3.3.0) or it fails to load.
What is the best way to make my add-on rules DLL more independent? Should I just install my 4.3.3.0 version of those subordinate StyleCop dlls in the GAC? Can an assembly (vs an application) use a policy file?
Oh, and one of the main problems is i would like it to work with ANY version of StyleCop the client has installed (or at least 4.3.3.0 or later) if possible.
Many thanks in advance.
Yes you should just install the same version for the other developers. If you do not, you may have unpredictable runtime failures due to changes within StyleCop. Presumably that is why they bothered to increment the version number.
If you don't want to do this, you can configure a different assembly binding in the app.config file. In the config the actual version number which you intend to use at runtime is needed. And yes, this can even be done via policy. But again, I think you are better served by including the correct DLL in the first place.
In your project, go to the properties on the StyleCop reference. Try setting the "Specific Version" property to false.
I'm building a tool in managed code (mostly C++/CLI) in two versions, a 'normal user' version and a 'pro' version.
The fact that the core code is identical between the two versions has caused me a little trouble as I want to package the resulting tool as a single assembly (DLL) and I don't want to have to include the .cpp files for the common code in the projects of the two versions of the tools. I'd rather have a project for the common code and a project for each version of the tool and have each version of the tools project depend on the common code and link it in as desired.
In unmanaged C++ I'd do this by placing the common code in a static library and linking both versions of the tool to it. I don't seem to be able to get this to work in C++/CLI. It seems that I'm forced to build the common code into a DLL assembly and that results in more DLL's than I'd like.
So, in summary, I can't work out how to build the common code in one project and link it with each of the final product projects to produce two single DLL assemblies that both include the common code.
I'm probably doing something wrong but I tried to work out how to do this using netmodules and whatever and I just couldn't get it to work. In the end the only way I got it working was to tell the linker to link the build products of the common code assembly rather than the results which works but is a bit of a hack IMHO.
Anyway, does anyone have any suggestions for how I SHOULD be solving this problem?
Edited: I guess I should have mentioned the fact that the assemblies generated are not 100% managed code, they contain a mix of managed and unmanaged code as is, probably, quite common with assemblies produced with C++/CLI...
If you are annoyed at all the DLLs, download ILMerge. I use this to bundle together multiple DLL's into an easy-to-use .EXE for my clients.
If I'm understanding this correctly, you have a solution which contains two projects. One project for the "normal" user and one project for the "pro" user. Visual Studio allows you to add a "link" to another file source from another project. If your "pro" version has the real core code file, and in your "normal" version you add existing -> find the file in the "pro" project, and click the down arrow by the Add button and select "Add as Link". Now you have single file that is literally the same between two projects.
As said, ILmerge is one way. Personally, if you're bundling some exe with a lot of DLLs, I favor Netz.
You could use modules. You can link them into an assembly using the assembly linker, al.exe.
That's the downside of the .Net compilation process, you can't have things like static libraries and the header files that hold them together, everything is held in one big dll file and the only way to share information is to either build a common dll and reference it from other assemblies or to duplicate the code in each dll (possibly by copying/linking .cs files between projects).
Note that the 2nd way will declare different types, even though they have the same name. This will bite you on the ass with stuff like remoting (or anything that requires casting to specific shared interfaces between processes).
Remotesoft Salamander will hook you up. It's basically a native compiler and linker.
When using mono (or cygwin is an option) mkbundle may also be a valid choice.
To preface, I've been working with C# for a few months, but I'm completely unfamiliar with concepts like deployment and assemblies, etc. My questions are many and varied, although I'm furiously Googling and reading about them to no avail (I currently have Pro C# 2008 and the .NET 3.5 Platform in front of me).
We have this process and it's composed of three components: an engine, a filter, and logic for the process. We love this process so much we want it reused in other projects. So now I'm starting to explore the space beyond one solution, one project.
Does this sound correct? One huge Solution:
Process A, exe
Process B, exe
Process C, exe
Filter, dll
Engine, dll
The engine is shared code for all of the processes, so I'm assuming that can be a shared assembly? If a shared assembly is in the same solution as a project that consumes it, how does it get consumed if it's supposed to be in the GAC? I've read something about a post build event. Does that mean the engine.dll has to be reployed on every build?
Also, the principle reason we separated the filter from the process (only one process uses it) is so that we can deploy the filter independently from the process so that the process executable doesn't need to be updated. Regardless of if that's best practice, let's just roll with it. Is this possible? I've read that assemblies link to specific versions of other assemblies, so if I update the DLL only, it's actually considered tampering. How can I update the DLL without changing the EXE? Is that what a publisher policy is for?
By the way, is any of this stuff Google-able or Amazon-able? What should I look for? I see lots of books about C# and .NET, but none about deployment or building or testing or things not related to the language itself.
I agree with Aequitarum's analysis. Just a couple additional points:
The engine is shared code for all of the processes, so I'm assuming that can be a shared assembly?
That seems reasonable.
If a shared assembly is in the same solution as a project that consumes it, how does it get consumed if it's supposed to be in the GAC?
Magic.
OK, its not magic. Let's suppose that in your solution your process project has a reference to the engine project. When you build the solution, you'll produce a project assembly that has a reference to the engine assembly. Visual Studio then copies the various files to the right directories. When you execute the process assembly, the runtime loader knows to look in the current directory for the engine assembly. If it cannot find it there, it looks in the global assembly cache. (This is a highly simplified view of loading policy; the real policy is considerably more complex than that.)
Stuff in the GAC should be truly global code; code that you reasonably expect large numbers of disparate projects to use.
Does that mean the engine.dll has to be reployed on every build?
I'm not sure what you mean by "redeployed". Like I said, if you have a project-to-project reference, the build system will automatically copy the files around to the right places.
the principle reason we separated the filter from the process (only one process uses it) is so that we can deploy the filter independently from the process so that the process executable doesn't need to be updated
I question whether that's actually valuable. Scenario one: no filter assembly, all filter code is in project.exe. You wish to update the filter code; you update project.exe. Scenario two: filter.dll, project.exe. You wish to update the filter code; you update filter.dll. How is scenario two cheaper or easier than scenario one? In both scenarios you're updating a file; why does it matter what the name of the file is?
However, perhaps it really is cheaper and easier for your particular scenario. The key thing to understand about assemblies is assemblies are the smallest unit of independently versionable and redistributable code. If you have two things and it makes sense to version and ship them independently of each other, then they should be in different assemblies; if it does not make sense to do that, then they should be in the same assembly.
I've read that assemblies link to specific versions of other assemblies, so if I update the DLL only, it's actually considered tampering. How can I update the DLL without changing the EXE? Is that what a publisher policy is for?
An assembly may be given a "strong name". When you name your assembly Foo.DLL, and you write Bar.EXE to say "Bar.EXE depends on Foo.DLL", then the runtime will load anything that happens to be named Foo.DLL; file names are not strong. If an evil hacker gets their own version of Foo.DLL onto the client machine, the loader will load it. A strong name lets Bar.EXE say "Bar.exe version 1.2 written by Bar Corporation depends on Foo.DLL version 1.4 written by Foo Corporation", and all the verifications are done against the cryptographically strong keys associated with Foo Corp and Bar Corp.
So yes, an assembly may be configured to bind only against a specific version from a specific company, to prevent tampering. What you can do to update an assembly to use a newer version is create a little XML file that tells the loader "you know how I said I wanted Foo.DLL v1.4? Well, actually if 1.5 is available, its OK to use that too."
What should I look for? I see lots of books about C# and .NET, but none about deployment or building or testing or things not related to the language itself.
Deployment is frequently neglected in books, I agree.
I would start by searching for "ClickOnce" if you're interested in deployment of managed Windows applications.
Projects can reference assemblies or projects.
When you reference another assembly/project, you are allowed to use all the public classes/enums/structs etc in the referenced assembly.
You do not need to have all of them in one solution. You can have three solutions, one for each Process, and all three solutions can load Engine and Filter.
Also, you could have Process B and Process C reference the compiled assemblies (the .dll's) of the Engine and Filter and have similar effect.
As long as you don't set the property in the reference to an assembly to require a specific version, you can freely update DLLs without much concern, providing the only code changes were to the DLL.
Also, the principle reason we
separated the filter from the process
(only one process uses it) is so that
we can deploy the filter independently
from the process so that the process
executable doesn't need to be updated.
Regardless of if that's best practice,
let's just roll with it. Is this
possible?
I actually prefer this method of updating. Less overhead to update only files that changed rather than everything everytime.
As for using the GAC, whole other level of complexity I won't get into.
Tamper proofing your assemblies can be done by signing them, which is required to use the GAC in the first place, but you should still be fine so long as a specific version is not required.
My recommendation is to read a book about the .NET framework. This will really help you understand the CLR and what you're doing.
Applied Microsoft .NET Framework Programming was a book I really enjoyed reading.
You mention the engine is shared code, which is why you put it in a separate project under your solution. There's nothing wrong with doing it this way, and it's not necessary to add this DLL to the GAC. During your development phase, you can just add a reference to your engine project, and you'll be able to call the code from that assembly. When you want to deploy this application, you can either deploy the engine DLL with it, or you can add the engine DLL to the GAC (which is another ball of wax in and of itself). I tend to lean against GAC deployments unless it's truly necessary. One of the best features of .NET is the ability to deploy everything you need to run your application in one folder without having to copy stuff to system folders (i.e. the GAC).
If you want to achieve something like dynamically loading DLL's and calling member methods from your processor without caring about specific version, you can go a couple of routes. The easiest route is to just set the Specific Version property to False when you add the reference. This will give you the liberty of changing the DLL later, and as long as you don't mess with method signatures, it shouldn't be a problem. The second option is the MEF (which uses Reflection and will be part of the framework in .NET 4.0). The idea with the MEF is that you can scan a "plugins" style folder for DLL's that implement specific functionality and then call them dynamically. This gives you some additional flexibility in that you can add new assemblies later without the need to modify your references.
Another thing to note is that there are Setup and Deployment project templates built into Visual Studio that you can use to generate MSI packages for deploying your projects. MSDN has lots of documentation related to this subject that you can check out, here:
http://msdn.microsoft.com/en-us/library/ybshs20f%28VS.80%29.aspx
Do not use the GAC on your build machine, it is a deployment detail. Visual Studio automatically copies the DLL into build directory of your application when you reference the DLL. That ensures that you'll run and debug with the expected version of the DLL.
When you deploy, you've got a choice. You can ship the DLL along with the application that uses it, stored in the EXE installation folder. Nothing special is needed, the CLR can always find the DLL and you don't have to worry about strong names or versions. A bug fix update is deployed simply by copying the new DLL into the EXE folder.
When you have several installed apps with a dependency on the DLL then deploying bug fix updates can start to get awkward. Since you have to copy to the DLL repeatedly, once for each app. And you can get into trouble when you update some apps but not others. Especially so when there's a breaking change in the DLL interface that requires the app to be recompiled. That's DLL Hell knocking, the GAC can solve that.
We found some guidance on this issue at MSDN. We started with two separate solution with no shared code, and then abstracted the commonalities to a shared assemblies. We struggled with ways to isolate changes in the shared code to impact only the projects that were ready for it. We were terrible at Open/Close.
We tried
branching the shared code for each project that used it and including it in the solution
copying the shared assembly from the shared solution when we made changes
coding pre-build events to build the shared code solution and copy the assembly
Everything was a real pain. We ended up using one large solution with all the projects in it. We branch each project as we want to stage features closer to production. This branches the shared code as well. It's simplified things a lot and we get a better idea of what tests fail across all projects, as the common code changes.
As far as deployment, our build scripts are setup to build the code and copy only the files that have changed, including the assemblies, to our environments.
By default, you have a hardcoded version number in your project (1.0.0.0). As long as you don't change it, you can use all Filter builds with the Process assembly (it only knows it should use the 1.0.0.0 version). This is not the best solution, however, because how do you distinguish between various builds yourself?
Another option is use different versions of the Filter by the same Process. You should add an app.config file to the Process project, and include a bindingRedirect element (see the docs). Whenever the Runtime looks for a particular version of the Filter, it's "redirected" to a version indicated in the config. Unfortunately, this means that although you don't have to update the Process assembly, you'll have to update the config file with the new version.
Whenever you encounter versioning problems, you can use Fuslogvw.exe (fusion log viewer) to troubleshoot these.
Have fun!
ulu
Our media center add-in is shipped as a single DLL which lives in the GAC (mediabrowser.dll), we allow users to write extensions for our add-in by referencing our DLL and accessing the pre-defined extensibility points.
On load we search through a plug-in directory, load all the assemblies in the directory, search the assemblies for a type implementing IPlugin and execute initialiaztion routine on an instance of the plugin. I am aware that this is not the most robust design (for example: we may want to look at appdomain isolation for plugin later on) but it works alright now.
As it stands, this seems to be working fine, except for one big caveat.
When plugin writers compile their plugins the plugin references mediabrowser.dll with a specific version. Later on when we revise our dll (to fix bugs or add features) all addins that were written against earlier versions of mediabrowser.dll break.
I have thought of a few solutions to this problem (note the assembly is in the GAC):
Ship a publisher policy with with mediabrowser.dll that will redirect all earlier compatible versions of mediabrowser.dll to the current version (this must also live in the GAC).
Ship a separate assembly which contains all the fixed extension points and contracts, be extra prudent about changing this assembly, have plugin writers link against this assembly. (but still look at using publisher policies for non-breaking changes to the interfaces)
Let a third party worry about this stuff and leverage MEF or some other framework that takes care of this kind of stuff.
Hookup AppDomain.CurrentDomain.AssemblyResolve and resolve the earlier versions of the assembly to the current version. This will only work if the assembly of that specific version is not in the GAC.
Are there any other solutions to this problem that I am missing?
Update I ended up going with option 4.
I see you have picked an answer but if you are still open to ideas there is another option to consider (the very one used by the .NET framework): do not increment your assembly version between builds (but do increment your assembly build number).
This will allow your assembly to retain it's same strong name, not breaking plugin compat, and still allow you to distinguish builds from each other (using the assembly build number).
You can see this in action in .NET 2.0 through 3.5. Those releases all use the assembly version 2.0.50727 but have distinct build versions.
As long as you do not break your interface contracts (which you should never do anyway) this approach is quite reasonable.