I am writing an application that allows the user to create custom algorithms for computing values over a collection of objects. Simply put, i will be having a string with the source code of class with one method.
The solution I have implemented is to compile the string source code in a separate dll for each such custom algorithm and then load them using Assembly.Load and instantiate the class saved in the dll. From a maintainability point of views, this means that i have to store the source code in the db (for example) and also manage the existence of the compiled dlls (recreate by compiling again the source code if it is missing)
Is there a better way to do this, considering the new features of .Net 4.0?
EDIT:
The input source code is C# and i am using CSharpCodeProvider to compile the code. The custom classes are all derived from a base class and they override the method that actually holds the computation logic. What i would really like to do is to get rid of the dll management and not lose (too much) performance in compiling all the classes every time my application starts up
I would look at scripting languages; IronPython is easy to embed, or there are JavaScript engines for .NET. Simple, and usually fast enough.
If (comments) you need to use c#, I would:
build all the current methods at the same time into one assembly; solves a lot of problems
if the data changes during execution, make use of AppDomains so that I can unload them
I've done something similar where the model/rules were XML, running it through a transform to get c#, and compiling with CSharpCodeProvider (or whatever); and simply polling every minute or so to see if a new build is required
The CSharpCodeProvider has been around for a while and should fit the ticket. It can be used to generate the separate libraries like you have been doing (perhaps you are using the CSharpCodeProvider), but it can also be used to generate dynamic class objects. If they all implement an interface you can cast the objects as an interface or you can use reflection to invoke your logic. Here is a codeproject article to achieve something similar:
http://www.codeproject.com/KB/dotnet/dynacodgen.aspx
Related
I see more and more open source libraries using .NET 5's Source Generators which improves their performance.
As much as I can understand from the docs, they are meant to replace System.Reflection becomes it comes at the expense of performance. Is that true? What I personally know about source generators is that when they introduced them in .NET 5, they were meant to generate C# code based on the .proto data contract files.
There is a clone library of MediatR which uses Source Generators instead of System.Reflection.
Could you simplify the source generators benefits and usage in that MediatR library and overall?
Source generators are really nothing magic - it's just some custom piece of code that generates text into files, which then get inserted into the compilation process and becomes part of the binary output (e.g. DLL or EXE) as if it was manually typed in by hand in some source file before you hit compile.
The only "magic" here is the formalized concept of analyzers-as-generators, which enables Visual Studio to automatically pass in the original source code into your custom generator routine and include the output whenever you build your project.
One application of source generators is to create specialized, type-specific code for some operation that otherwise would require run-time reflection. Run-time reflection is typically rather slow and CPU intensive, yet often needed in order to centralize logic for common operations on unknown objects. A common example is the serialization and deserialization of objects. This could be done either through reflection (lookup properties at run-time, invoke the getters and setters, etc) or through faster, type specific code that directly references properties and reads/writes to and from data streams. However, creating such specialized code for every type is a lot of boring, repetitive work and so - enter source generators. They can do the "reflection" during build time and output slim, fast code into temporary .cs files, which get compiled with the product.
In Java we have used the javaagent argument and ASM (http://asm.ow2.org/) utilities to modify the byte code at run/load time in memory by the classloader . (aka Add a method call to a method in a class dynamically).
Once example of this is where you remove all calls to Log4j to speed up an application (http://surguy.net/articles/removing-log-messages.xml).
I’m trying to figure out how to do this same process on runtime with C# / .Net. I have seen that you can manipulate the CIL for .Net, but I haven’t found an example of this at runtime.
System.Reflection.Emit seems to be the closest .Net equitant where you can dynamically create classes, but is there a way to add to or override existing classes using this?
I have never used Mono.Cecil for generating dynamic code (it does make your life much easy if you want to instrument assemblies though).
In .Net if you want to generate code you can use System.CodeDom and System.Reflection.Emit. One particular useful class that enables you to inject methods dynamically is DynamicMethod.
Check out the newer features in .net 4, I think most of what your looking for is in the System.Dynamic namespace.
Check out this post on DuckTyping
It's been a while since I looked at it (I'm pretty much a Java bunny) but I think the Mono project had something called Cecil which did at least some of this.
I am developing a .NET 4.0 client that will utilize a C Library for data processing. The user will be able to specify the DLL file they wish to load for processing.
I am doing late binding / assembly loading as described here. http://blogs.msdn.com/b/jonathanswift/archive/2006/10/03/dynamically-calling-an-unmanaged-dll-from-.net-_2800_c_23002900_.aspx
For each DLL, the same method call sequences will be the same in my client, but the method signatures will change or the data structs passed in will change. The data populated with the structures will be different depending on the version of the DLL and other factors. Example, the definition of MyStruct will change depending on the version of the DLL.
public delegate int INTF_my_method(ref MyStruct pDataStruct);
What design patterns or design decision are recommended for this approach? I need to load the appropriate C method delegates and data definitions based on the version of the DLL that the user has specified, and populate the structures appropriately. Has anyone done something like this before?
There is no clean approach to this, neither in managed code nor native code. The best you could possibly do is to declare an interface type that tries to cover all possible versions and then write concrete wrapper classes for each individual version of the API. If there's at least some common functionality then you can shovel that in a base class.
Notable too is that you cannot just let the user pick a DLL, you have to pair the DLL with the concrete wrapper class instance.
Building this kind of flexibility in your program is obviously very expensive.
You can load different versions of your DLLs, but only from separate AppDomains. That is, for each DLL you want to load, you will have to create a new AppDomain.
I am looking for a way to transform some classes from Java to .Net in a code gen way.
Not at run time, but re-generate a handful of business objects as needed (not often).
the catch is, i want to have full control of how they end up. So while java classes have get and set methods, i will create a property out of them.
the only way i can think of for now, is to read the file using c#, get the necessary members, and maybe feed them to a code gen template. at the very lease, i could throw them into a database, and something like code smith could generate .net classes based on a template and the updated database table.
any other ideas/utilities?
my solution was to use reflection to write out java class members as xml, and than plugging that into codesmith template to create .net classes. the neat part is that it can be automated as a step on build server
Have a look at IKVM.
I've been searching for this for quite a while with no luck so far. Is there an equivalent to Java's ClassFileTransformer in .NET? Basically, I want to create a class CustomClassFileTransformer (which in Java would implement the interface ClassFileTransformer) that gets called whenever a class is loaded, and is allowed to tweak it and replace it with the tweaked version.
I know there are frameworks that do similar things, but I was looking for something more straightforward, like implementing my own ClassFileTransformer. Is it possible?
EDIT #1. More details about why I need this:
Basically, I have a C# application and I need to monitor the instructions it wants to run in order to detect read or write operations to fields (operations Ldfld and Stfld) and insert some instructions before the read/write takes place.
I know how to do this (except for the part where I need to be invoked to replace the class): for every method whose code I want to monitor, I must:
Get the method's MethodBody using MethodBase.GetMethodBody()
Transform it to byte array with MethodBody.GetILAsByteArray(). The byte[] it returns contains the bytecode.
Analyse the bytecode as explained here, possibly inserting new instructions or deleting/modifying existing ones by changing the contents of the array.
Create a new method and use the new bytecode to create its body, with MethodBuilder.CreateMethodBody(byte[] il, int count), where il is the array with the bytecode.
I put all these tweaked methods in a new class and use the new class to replace the one that was originally going to be loaded.
An alternative to replacing classes would be somehow getting notified whenever a method is invoked. Then I'd replace the call to that method with a call to my own tweaked method, which I would tweak only the first time is invoked and then I'd put it in a dictionary for future uses, to reduce overhead (for future calls I'll just look up the method and invoke it; I won't need to analyse the bytecode again). I'm currently investigating ways to do this and LinFu looks pretty interesting, but if there was something like a ClassFileTransformer it would be much simpler: I just rewrite the class, replace it, and let the code run without monitoring anything.
An additional note: the classes may be sealed. I want to be able to replace any kind of class, I cannot impose restrictions on their attributes.
EDIT #2. Why I need to do this at runtime.
I need to monitor everything that is going on so that I can detect every access to data. This applies to the code of library classes as well. However, I cannot know in advance which classes are going to be used, and even if I knew every possible class that may get loaded it would be a huge performance hit to tweak all of them instead of waiting to see whether they actually get invoked or not.
POSSIBLE (BUT PRETTY HARDCORE) SOLUTION. In case anyone is interested (and I see the question has been faved, so I guess someone is), this is what I'm looking at right now. Basically I'd have to implement the profiling API and I'll register for the events that I'm interested in, in my case whenever a JIT compilation starts. An extract of the blogpost:
In your ICorProfilerCallback2::ModuleLoadFinished callback, you call ICorProfilerInfo2::GetModuleMetadata to get a pointer to a metadata interface on that module.
QI for the metadata interface you want. Search MSDN for "IMetaDataImport", and grope through the table of contents to find topics on the metadata interfaces.
Once you're in metadata-land, you have access to all the types in the module, including their fields and function prototypes. You may need to parse metadata signatures and this signature parser may be of use to you.
In your ICorProfilerCallback2::JITCompilationStarted callback, you may use ICorProfilerInfo2::GetILFunctionBody to inspect the original IL, and ICorProfilerInfo2::GetILFunctionBodyAllocator and then ICorProfilerInfo2::SetILFunctionBody to replace that IL with your own.
The great news: I get notified when a JIT compilation starts and I can replace the bytecode right there, without having to worry about replacing the class, etc. The not-so-great news: you cannot invoke managed code from the API's callback methods, which makes sense but means I'm on my own parsing the IL code, etc, as opposed to be able to use Cecil, which would've been a breeze.
I don't think there's a simpler way to do this without using AOP frameworks (such as PostSharp). If anyone has any other idea please let me know. I'm not marking the question as answered yet.
I don't know of a direct equivalent in .NET for this.
However, there are some ways to implement similar functionality, such as using Reflection.Emit to generate assemblies and types on demand, uing RealProxy to create proxy objects for interfaces and MarshalByRefObject objects. However, to advise what to use, it would be important to know more about the actual use case.
After quite some research I'm answering my own question: there isn't an equivalent to the ClassFileTransformer in .NET, or any straightforward way to replace classes.
It's possible to gain control over the class-loading process by hosting the CLR, but this is pretty low-level, you have to be careful with it, and it's not possible in every scenario. For example if you're running on a server you may not have the rights to host the CLR. Also if you're running an ASP.NET application you cannot do this because ASP.NET already provides a CLR host.
It's a pity .NET doesn't support this; it would be so easy for them to do this, they just have to notify you before a class is loaded and give you the chance to modify the class before passing it on the CLR to load it.