Classes Can A Single Net Dll Contain
Because of ABI incompatibilities between compilers and even different versions of the same compiler, exporting C++ classes from DLLs is a tricky business. Luckily, with some care it is possible to do this safely, by employing abstract interfaces.
classes can a single net dll contain
There are other methods of exporting C++ classes from DLLs (here's one good discussion of the subject). The one presented here is the cleanest - the least amount of information is shared between the DLL and the application using it - just the generic interface header defining IKlass and an implicit agreement about the signature of the factory function.
For messier ecosystems that cannot guarantee a more recent vintage of the .Net framework, multi-targeting can help to widen the reach of shared libraries. This allows you to compile a single project natively for both .Net Standard and your preferred version of the .Net Framework, though it does come at a cost of having to manage multiple sets of compiled output.
Version 2.0 of .Net Standard finally provided a single set of APIs that could be applied across .Net Core 2.0, .Net Framework 4.6.1 and Xamarin. It also provided a compatibility shim that allows .Net Framework assemblies to be used directly by .Net Standard libraries.
This tutorial shows, how to build a simple Class Library .DLL in the C# Programming Language. The Class Library .DLL contains program code, data, and resources that can be can used by other programs and are easily implemented into other Visual Studio projects.
The following code example is a C# version of the Class Library. The Class Library .DLL contains program code, data, and resources. The Class Library in this example will feature a custom Math API that has a set of functions to Substract, Devide and Multiply numbers
Our Console App project is relatively small and will consist of 2 files. The Program.cs which is the entry point of our application, and the MathLibrary.dll file which contains our API containing the methods to devide, multiply, substract numbers.
The Program.cs file is a C# class that contains the Main method, which serves as the entry point of our Console Application. Usually In computer programming, an entry point is where the first instructions of a program are executed. Here we will manage the Console UI, use functions from the MathLibrary.dll and display it's results on screen.
There are really two ways to take advantage of all these extra resources: write tests which themselves use parallelization (so that when the system is only running a single test, it still takes advantage of all the resources); or, let the unit test framework run many tests at the same time, to help take advantage of the available resource.
The typical structure of a unit test is to test a single thing in relative isolation. This doesn't give much opportunity for the test itself to become parallelized, unless the code under test is itself parallelized. Therefore, the best way to ensure that unit tests can run at the full speed of the host computer is to run many of them at the same time.
The first is the runner, which is the program (or third party plugin to a program) that is responsible for looking for one or more test assemblies, and then activating the test frameworks that it finds therein. It generally contains very little knowledge about how the test frameworks work, and instead relies on xunit.runner.utility to do most of the heavy lifting. Through the runner utility library, it can discover test cases and then ask for them to be run. It does not itself understand how this discovery or execution works, but instead relies on the runner utility library to understand those details.
When we say "Parallelism in Test Frameworks", what we mean specifically is how a test framework may choose to support running tests within a single assembly in parallel with one another. The next section, "Parallelism in Runners", we mean how a test runner may choose to support running test assemblies in parallel against each other.
By default, each test class is a unique test collection. Tests within the same test class will not run in parallel against each other. Let's examine a very simple test assembly, one with a single test class:
If we need to indicate that multiple test classes should not be run in parallel against one another, then we place them into the same test collection. This is simply a matter of decorating each test class with an attribute that places them into the same uniquely named test collection:
This instructs xUnit.net not run these two classes against each other in parallel. Our total run time now goes back to approximately 8 seconds, which indicates that the tests did indeed run one after another.
You can only have one of these attributes per assembly; if you want to combine multiple behaviors, do it with a single attribute. Also be aware that these values affect only this assembly; if multiple assemblies are running in parallel against one another, they have their own independent values.
This feature proved to be very useful during our large-scale migration. It made easy to list up-front non .NET Standard compliant code of core assemblies we had to migrate. Also for each non-compliant class and method matched, the list of non-supported classes, methods and fields consumed is provided.
For a more intuitive assessment we used the NDepend metric view, that highlighted the classes and methods matched by the non-compliant code query edited above. With this information it has been much easier to anticipate hot-spots. When more than 500 classes are involved in a migration, begin able to anticipate and plan upfront is not a luxury but a necessity.
Concerning the High Test Coverage Ratio discipline we abided by for a long time there is not much to say. We have 14K unit tests and a ratio of 86% coverage on a 4.500 classes application. We have a lot of confidence in our test suites to catch early accidental regressions. As a matter of fact it saved us dozens of time during this migration. It is not just about the manual testing time saved, the friction saved by releasing product with few bugs, it is also about the satisfaction of working with thousands of gentle gardians that watch daily over our code.
Concerning the Layered Architecture it really helped because the large set of classes and methods using a UI framework to refactor or move out from .NET Standard assemblies was de-facto layered. We listed those classes and methods with a code query and exported this set to the dependency graph. The query can be easily tweaked to list from high-level to low-level. But the graphical representation of dependencies was convenient to help understanding at each step what was going on and what should be done.
I recently came across the ScreenToGif OSS project. I enjoy using this popular tool when I need it and I was curious to have a look at its source code. Its 700+ classes are all entangled: from any two namespaces A and B there is a path from A to B and a path from B to A. I had a chance to discuss this with Nicke Manarin the developer of ScreenToGif that wrote:
@Andrew O Dennison there is no dogma. Many classes and methods can be large but linear (with no switch/if/else scope) think of InitializeComponent() methods. Some short classes (or even a grape of classes) can be entirely tested with a single test. What really matters (to us at least) is the percentage of the code covered by tests and indeed tested. This is why we stuff our code with assertions. Assertion are not just for tests but also for tested code. This way there is no need to externalize a state to have an assertion that checks its validity!
The configuration I ran into probably isn't that common, but I have seen it used in a few places. Essentially, you have a console application that contains xUnit (or some other testing framework like MSTest) tests. You can then easily run certain tests from the command line, without having to use the specific xUnit or MSTest test runner/harness.
The error message gives you a hint as to how to fix it, Compile with /main, but the compiler is assuming you actually want both Program classes. In reality, we don't need the auto generated one at all, as we have our own.
In computing, DLL Hell is a term for the complications that arise when one works with dynamic-link libraries (DLLs) used with Microsoft Windows operating systems, particularly legacy 16-bit editions, which all run in a single memory space.
A key reason for the version incompatibility is the structure of the DLL file. The file contains a directory of the individual methods (procedures, routines, etc.) contained within the DLL and the types of data they take and return. Even minor changes to the DLL code can cause this directory to be re-arranged, in which case an application that calls a particular method believing it to be the 4th item in the directory might end up calling an entirely different and incompatible routine, which would normally cause the application to crash.
A particular version of a library can be compatible with some programs that use it and incompatible with others. Windows has been particularly vulnerable to this because of its emphasis on dynamic linking of C++ libraries and Object Linking and Embedding (OLE) objects. C++ classes export many methods, and a single change to the class, such as a new virtual method, can make it incompatible with programs that were built against an earlier version. Object Linking and Embedding has very strict rules to prevent this: interfaces are required to be stable, and memory managers are not shared. This is insufficient, however, because the semantics of a class can change. A bug fix for one application may result in the removal of a feature from another. Before Windows 2000, Windows was vulnerable to this because the COM class table was shared across all users and processes. Only one COM object in one DLL/EXE could be declared as having a specific global COM Class ID on a system. If any program needed to create an instance of that class, it got whatever was the current centrally registered implementation. As a result, an installation of a program that installed a new version of a common object might inadvertently break other programs that were previously installed. 350c69d7ab