This article considers that the readers are aware of .NET assemblies and the CLR internals. If you have any questions on this, you can consider reading following articles by Microsoft:
In this article we are going to straight away discuss the creation and sharing by a simple example.
Create solution file using visual studio 2008 and add a class library project.
I named my project as “TestGACRegistration” and the class as “TestDLL”.
public class TestDLL
public string mymethod()
Now build the class library project.
Add a new console project to the same solution and add the project reference to the “TestGACRegistration” project and you should find the dll available in the references section of the console application project.
static void Main(string args)
TestGACRegistration.TestDLL testdll=new TestGACRegistration.TestDLL();
Now run the console application to see the output:
You see the output returned was M1 and that is correct.
Normally there are many ways of how developers maintains the references to the DLLs in the development environment.
1. Building the DLLs to a specific path and share all the DLLs from the path instead of referring to the class library projects.
2. Adding references directly to the DLLs generated in the bin/release folders of each application.
First option should be used when the DLL is being referenced by multiple projects and we do not want to duplicate the DLLs to be deployed for each project as private. Second one is good when we are having all the DLLs built for one project.
Another way to look at is imagine we have another console application in the solution which points to another all the DLLs in the project. Let us call the console application as “MyConsoleApp2” and the other class library as “AnotherLibrary”. Now, the second console project is referring both the DLLs in the solution and they have been referenced using the second option.
While I was working in the project, I have configured the solution file configuration section to build all the class library projects both in debug and release mode. I have compiled the application both in debug and release mode and the DLLs are built for both the modes in the respective bin/release folders of each application library and the same have been copied in the console application bin/release folders as they referring to these projects.
Now one of the developer thinks that every time he changes the console application 1, it is building the DLL for the second class library too which is not required for the console application 1 and so he goes into the configuration settings of the solution file and he unchecks the build option for the class library 2 for both debug and release modes. While building set up projects for deployment, I simply select the output folders of the projects and I rebuild the solution in release mode without knowing that someone has changed the configuration properties of the solution.
After deploying to another environment, you may find that new changes are not elevated as the new DLLs are not built in the release mode. Unless, if you select output window while building and checking if all the projects are getting compiled.
So, in order to avoid this we will not allow each project to reference the class library project for the DLL but refer to the location where DLLs are copied. This ensures that always the project is referring to the correct DLL compiled.
When we have more references to the same DLL by multiple projects or applications, the DLLs should be in shared mode rather than getting copied to each application’s folder as private assembly. The reason being if we compile the DLL with a small change, we need to deploy all the applications referring to it. Microsoft concept of deployment of shared assemblies in .NET helps in resolving this issue by first registering the DLL in the GAC and all the applications should be referring to the DLL available in the GAC. Also we do not want these DLLs to be copied into the application bin/release folder. To do this, we need to set one property “Copy Local” of the DLL after referencing it.
This ensures that the DLL is not copied to local path of the application whenever you build the project.
If there is only one application that is referencing a DLL and only one or two developers are working in a project and they communicate the changes to each other, then the second option works fine.
You can test the same first without setting the property “Copy Local” to false and then setting it to false.
With setting “True”:
With setting as false:
Again the practices differ from team to team and project to project and so there are no defined practices to be followed. It should always to be considered based on what is best for the team.
To deploy the shared DLLs into the GAC, we need to generate a strong name first using sn.exe. More information on this can be found from Microsoft MSDN:
Now we need to generate the strong name in our example for the class library “TestGACRegistration” in order to deploy it to GAC.
Go to Microsoft Visual studio command prompt and run the strong name key utility as below:
The key should be specified in the AssemblyInfo.cs of the class library. It will be available in the properties folder of the Class library project. Normally, the key would be copied into the organization’s secured folder path and will be referenced.
Add the key attribute as below:
[assembly: AssemblyCopyright("Copyright © Microsoft 2012")]
If you forget to add the key file attribute you would get an error during deployment.
Now, after the coding is completed how can I deploy the shared DLLs in the GAC of the production server? The answer is we can do in two ways:
- Using tool for registering the DLL in the GAC i.e., GACUTIL.exe
- Using a Microsoft setup project
We use the set up project option since we can add all the required DLLs at one shot and we can build and run the MSI file. MSI file takes care of deploying the DLLs into GAC without GACUTIL.exe as it is intelligent to sense based on where the files are to be copied.
Add a new set up project to the solution and name it as “SetupDLLs”.
After project is created then right click on the project and click ViewàFile System and you see 3 project folders already present and so add another folder by right clicking on the “File System On Target Machine” and select “Add Special Folder” and select “Global Assembly Cache” folder. By default, any files that are copied to the “Global Assembly Cache Folder” will be deployed automatically by the set up project.
Now add the DLLs to be deployed to this special folder. In our case we add only one.
Now build the set up project. Let us see what happens if the strong name key was not added to the assembly. Just for testing purpose, I remove the key attribute in the “AssemblyInfo.cs” file and try to build the set up project again.
You would see an error if a shared assembly do not have a strong name specified. Now, revert back the change and run the setup project again.
You would see the following content in the output window now:
------ Pre-build validation for project 'SetupDLLs' completed ------
------ Build started: Project: SetupDLLs, Configuration: Debug ------
Building file 'C:\TestGACRegistration\SetupDLLs\Debug\SetupDLLs.msi'...
Packaging file 'TestGACRegistration.dll'...
========== Build: 1 succeeded or up-to-date, 0 failed, 0 skipped ==========
Now you would see two files got copied into bin/release folder based on the mode you have built the setup project.
Now run the setup.exe and deploy the DLLs. You can manually run the exe file or run from command prompt. We do it manually, but in case if you would like to know the silence installation, refer to the following URL:
After the installation is successful, you can go and check if the DLLs are successfully deployed in the GAC. Location of GAC is normally C:\Winnt\assembly or c:\Windows\assembly.
You see now the DLL is successfully registered in GAC.
Now we can test if this works. One question to ask is: If I change the class library code locally in my solution and build the DLL, do my console application refers to the new DLL?
The answer is No. If you have a DLL registered in GAC with the same version as you have in your local application, always the one in the GAC is referenced. If you want to test the new code, you have to change the version of the DLL in your local application by changing the version in “AssemblyInfo.cs” class located in the property folder of the class library. I have compiled the assembly with version as 126.96.36.199 and deployed in GAC for our example.
If you would like to test it, let us go and change the code in the method as below:
public class TestDLL
public string mymethod()
Now my method should return “M2” instead of “M1” if the console application is referencing the local DLL. Now build the class library and run the console application to see the result.
Still you the see the output as “M1” only. If you want to test it more thoroughly you can delete the class library reference and add it to the console application project to test it and you see it always returns “M1” only.
Now I will change the version and test it again.
// [assembly: AssemblyVersion("1.0.*")]
Now build the class library and add the reference to the new DLL/project for clean testing. You would now see the value displayed as “M2”.
One drawback observed while using the setup project is you cannot uninstall the assembly from the GAC directly unless you uninstall the setup project instance in the computer. This helps in uninstalling the previous version and install new one. If we make new changes to the DLL and these code changes are made for only one of the application purpose, then we would like the other applications with our new version deployment. If we want to do that, we need to change the upgrade code of the set up project and can install another version of the same DLL. We all know GAC supports side-by-side execution of multiple DLLs having same name and different versions.
In a real time, you might find more flexibility in deploying the shared DLLs using the set up project.