How do I define a DynamicMethod for a delegate that has an out-parameter, like this?
public delegate void TestDelegate(out Action a);
Let's say I simply want a method that sets the a argument to null when I call the method.
Note that I know that a probably better way to handle this would be to make the method return the Action delegate, but this is just a simplified part of a larger project, and the method in question already returns a value, I need to handle the out parameter in addition to it, hence the question.
I tried this:
using System;
using System.Text;
using System.Reflection.Emit;
namespace ConsoleApplication8
{
public class Program
{
public delegate void TestDelegate(out Action a);
static void Main(String[] args)
{
var method = new DynamicMethod("TestMethod", typeof(void),
new Type[] { typeof(Action).MakeByRefType() });
var il = method.GetILGenerator();
// a = null;
il.Emit(OpCodes.Ldnull);
il.Emit(OpCodes.Starg, 0);
// return
il.Emit(OpCodes.Ret);
var del = (TestDelegate)method.CreateDelegate(typeof(TestDelegate));
Action a;
del(out a);
}
}
}
However, I get this:
VerificationException was unhandled:
Operation could destabilize the runtime.
on the del(out a); line.
Note that if I comment out the two lines that load a null on the stack and attempts to store it into the argument, the method runs without exceptions.
Edit: Is this the best approach?
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldnull);
il.Emit(OpCodes.Stind_Ref);
An out argument is just a ref argument with the OutAttribute applied to the parameter.
To store to the by-ref argument, you need to use the stind opcode, because the argument itself is a managed pointer to the object's actual location.
ldarg.0
ldnull
stind.ref
Related
I am trying to dynamically build a type with a method that calls into an external delegate by using System.Reflection.Emit. However when I try to call this method, my program crashes with the exception in the title at the method call. Here's my code so far:
private static void TestMethodReal() => Console.Out.WriteLine("Inside TestMethod");
// In Main()
var method = typeof(Program).GetMethod(nameof(TestMethodReal), BindingFlags.Static | BindingFlags.NonPublic)!;
var builder = MyTypeBuilder.GetTypeBuilder("TestType");
var testMethod = builder.DefineMethod("TestMethod", MethodAttributes.Public, typeof(void), Type.EmptyTypes);
var generator = testMethod.GetILGenerator();
generator.EmitCall(OpCodes.Callvirt, method, null);
generator.Emit(OpCodes.Ret);
dynamic inst = Activator.CreateInstance(builder.CreateType()!)!;
inst.TestMethod(); // <--- Exception is thrown here
The MyTypeBuilder class and GetTypeBuilder method is from this answer, slightly modified to accept a parameter for the type's name.
This program is supposed to create a new dynamic class with a method called TestMethod that calls the actual TestMethodReal method, instantiate the class, and call the method.
What am I missing?
You're using the wrong dispatch mechanism!
OpCodes.Callvirt is for virtual method calls, eg. overridable instance methods, the resolution of which needs to be deferred until runtime.
For static method invocation you'll want a plain old OpCodes.Call instruction instead:
generator.EmitCall(OpCodes.Call, method, Types.EmptyTypes);
This question already has answers here:
C# GetDelegateForFunctionPointer with generic delegate
(6 answers)
Closed 2 years ago.
Precondition
The .net method that I will get its pointer is:
public static method
have no overloads
arguments and return value just ValueType (unsafe pointer, primitive type, unmanaged struct)
Reason
Get the method pointer so I can call in C++ program.
This works for me but I need to declare delegate for every method.
I want to get rid of doing things over and over again.
In .net side:
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate void UpdateDelegate(float delta);
public static void* GetUpdatePointer()
{
var delegateInstance = = new UpdateDelegate(Update);
var pfnUpdate = Marshal.GetFunctionPointerForDelegate(delegateInstance);
return (void*)pfnUpdate;
}
public static Update(float delta)=>{...}
In C++ side:
typedef void (_stdcall * FuncPtr)(float);
void foo()
{
//just pseudo-code showing where is the pfnUpdate from.
FuncPtr pfnUpdate = (FuncPtr)GetUpdatePointer();
pfnUpdate(0.01f);
}
what I want
In c#, I export GetMethodPointer for my native code. It will return a function pointer to specified method, and this pointer can be invoked by native program via stdcall calling convention.
//avoid gc collect this object
static List<Delegate> KeepReference = new List<Delegate>();
public unsafe static void* GetMethodPointer(string name)
{
System.Reflection.MethodInfo methodInfo = typeof(PhysicsMain).GetMethod(name);
// also mark this delegate with [UnmanagedFunctionPointer(CallingConvention.StdCall)] attribute
Type delegateType = ConstructDelegateTypeWithMethodInfo(methodInfo);
var delegateInstance = Delegate.CreateDelegate(delegateType, methodInfo);
KeepReference.Add(delegateInstance);
return (void*)Marshal.GetFunctionPointerForDelegate(delegateInstance);
}
I need ConstructDelegateTypeWithMethodInfo to create a delegate with the same signature as the specified method. And mark [UnmanagedFunctionPointer(CallingConvention.StdCall)] attribute for it so that can be marshaled as a function pointer.
I think it may using IL, Reflection, even Asm to do this. Or using IL to write the whole GetMethodPointer method.
Finally, I got a solution these days. Firstly, I came across Expression.GetDelegateType given by this post. But it did't work for me, because Marshal.GetFunctionPointerForDelegate doesn't support generic delegate type generate by Expression.GetDelegateType. I thought there might be a clue in implementation of Expression.GetDelegateType. So, I browsed referencesource and got a internal method called MakeNewCustomDelegate. This link gives code about how to call the internal method. Things are readily solved!
Edit: I forgot to say, the default unmanaged calling convension of a delegate is stdcall, so we don't need to mark the delegate with [UnmanagedFunctionPointer(CallingConvention.StdCall)] explicitly.
In your example you assume that the class of the method is know function (PhysicsMain).
If UpdateDelegate is also known you can use it easily:
Type delegateType = typeof(UpdateDelegate);
var delegateInstance = Delegate.CreateDelegate(delegateType, methodInfo);
But you can also get this type by name only:
Type delegateType = Type.GetType("Namespace.ClassName+UpdateDelegate");
var delegateInstance = Delegate.CreateDelegate(delegateType, methodInfo);
You can look at delegateType.CustomAttributes and verify that the type has UnmanagedFunctionPointer attribute.
I'm generating a random number from 1-1000. I have 200 functions named function1, function4, function 10, function 11, etc. What I would like to do is execute a specific function depending on if the number generated requires a function, and ignore it if not.
My first thought was to create an int[] containing all of the values that would trigger a function, and if the int[] contains the random number to use if statements to figure out what the number is. I'm concerned that it must be a really crude solution to an easy problem though.
I know the "best way" to do something is subjective, but is there a better way to accomplish this?
UPDATE: As per comments, I should probably have started out by pointing out that doing this for 200 functions is probably a good sign that there is some serious issue in your design. This is probably an XY question where you are trying to solve a problem in some crazy way and asking about your intended solution instead of asking about the problem itself.
That said I'll leave the original answer because it's still good advice when mapping a reasonable amount of function calls that can/will change during the life cylce of your app or dynamically as the code runs.
I won't get into why you are doing this, but I'll try to at least point you in the right direction so this doesn't become a complete nightmare when you need to modify/expand behavior:
You can map numbers to function calls using delegates and a dictionary. Assuming your functions take no arguments and return void you'd do:
var functionsMap = new Dictionary<int, Action>();
//map functions
var r = getSomeRandomNumber();
if (functions.TryGetValue(r), out var a)
a(); //invoke function
Mapping functions is simply adding keys and values:
functionsMap.Add(1, () => function1());
functionsMap.Add(3, () => function3());
//etc.
If your functions take arguments or return values, you'd use the adequate delegate: Action<T>, Func<T1, T2> etc.
You can use reflection to invoke appropriate method:
Type exampleType = exampleObject.GetType();
MethodInfo exampleMethod = exampleType.GetMethod(methodName);
exampleMethod.Invoke(this, null);
Where methodName can be created using your random number.
Without commenting on the wisdom of having 200 functions named the way yours are, you can use reflection to determine whether a given functionX() exists, like so:
public void ExecuteDynamicMethod(int number)
{
// Modify these two lines with your app's dll/exe and class type:
Assembly assembly = Assembly.LoadFile("...Assembly1.dll");
Type type = assembly.GetType("YourClassType");
if (type != null)
{
MethodInfo methodInfo = type.GetMethod("function" + number);
if (methodInfo != null)
{
object classInstance = Activator.CreateInstance(type, null);
methodInfo.Invoke(classInstance, null); // null = "no function arguments"
}
}
}
This can then be called for a given value like
ExecuteDynamicMethod(14);
See this SO answer for the inspiration behind this.
Reflection can be used for this purpose. I want to give and keep below example for not only the objective of the question but also for future reference. Also, of course that many function is not good but below code shows the approach that can work with many functions if they have similar name (like starting with "function" keyword).
Assume below is Methods.cs
using System;
using System.Reflection;
namespace YourMethodNamespace
{
public class YourMethodClass
{
public void function1()
{
Console.WriteLine("Function-1");
}
public void function2()
{
Console.WriteLine("Function-2");
}
...
public void function200()
{
Console.WriteLine("Function-200");
}
public static void invokeMethodsDynamically(int randomNumber){
Type yourClassType = typeof(YourMethodClass);
ConstructorInfo yourClassConstructorInfo = yourClassType.GetConstructor(Type.EmptyTypes);
object yourClassObject = yourClassConstructorInfo.Invoke(new object[]{});
//If the constructor has parameters, then we can pass them by this way. Like below;
/*ConstructorInfo yourClassConstructorInfo = yourClassType.GetConstructor(new[]{typeof(int)});
object yourClassObject = yourClassConstructorInfo.Invoke(new object[]{3});
*/
MethodInfo[] methodInfoArr = yourClassType.GetMethods();
foreach(MethodInfo methodInfo in methodInfoArr){
if(methodInfo.Name == "function" + randomNumber){
methodInfo.Invoke(yourClassObject, null);
}
}
}
}
}
Let's say below is Program.cs
using System;
using YourMethodNamespace;
namespace YourProgramNamespace
{
public class YourProgramClass
{
public static void Main()
{
Random random = new Random();
int randomNumber = random.Next(1, 201);
//If Methods.cs is in another Assembly
/*string pathToDllAssembly = #"Domain.dll";
Assembly dllAssembly = Assembly.LoadFrom(pathToDllAssembly);
Type methodsClassType = dllAssembly.GetType("YourMethodNamespace.YourMethodClass");
ConstructorInfo methodClassConstructorInfo = methodsClassType.GetConstructor(Type.EmptyTypes);
object methodsClassObject = methodClassConstructorInfo.Invoke(new object[]{});
MethodInfo methodInfo = methodsClassType.GetMethod("invokeMethodsDynamically");
methodInfo.Invoke(methodsClassObject, new object[]{randomNumber});
*/
YourMethodClass.invokeMethodsDynamically(randomNumber, null);
}
}
}
Also for testing and observing, below link can be used.
https://repl.it/#erdsavasci/ReflectionTest
Based on the following question, I found some odd behaviour of the c# compiler.
The following is valid C#:
static void K() {}
static void Main()
{
var k = new Action(new Action(new Action(K))));
}
What I do find strange is the compiler 'deconstructing' the passed delegate.
The ILSpy output is as follows:
new Action(new Action(new Action(null, ldftn(K)), ldftn(Invoke)).Invoke);
As one can see, it automatically decides to use the Invoke method of the delegate. But why?
As it is, the code is unclear. Do we have a triply-wrapped delegate (actual) or is the inner delegate just 'copied' to the outer ones (my initial thought).
Surely if the intent was like the compiler emitted the code, one should have written:
var k = new Action(new Action(new Action(K).Invoke).Invoke);
Similar to the decompiled code.
Can anyone justify the reason for this 'surprising' transformation?
Update:
I can only think of one possible use-case for this; delegate type conversion. Eg:
delegate void Baz();
delegate void Bar();
...
var k = new Baz(new Bar( new Action (K)));
Perhaps the compiler should emit a warning if the same delegate types are used.
The spec (section 7.6.10.5) says:
The new delegate instance is initialized with the same invocation list as the delegate instance given by E.
Now suppose the compiler translated it to something similar to your suggestion of:
new Action( a.Target, a.Method)
That would only ever create a delegate with an invocation list of a single method call. For a multi-cast delegate, it would violate the spec.
Sample code:
using System;
class Program
{
static void Main(string[] args)
{
Action first = () => Console.WriteLine("First");
Action second = () => Console.WriteLine("Second");
Action both = first + second;
Action wrapped1 =
(Action) Delegate.CreateDelegate(typeof(Action),
both.Target, both.Method);
Action wrapped2 = new Action(both);
Console.WriteLine("Calling wrapped1:");
wrapped1();
Console.WriteLine("Calling wrapped2:");
wrapped2();
}
}
Output:
Calling wrapped1:
Second
Calling wrapped2:
First
Second
As you can see, the real behaviour of the compiler matches the spec - your suggested behaviour doesn't.
This is partly due to the somewhat odd "sometimes single-cast, sometimes multi-cast" nature of Delegate, of course...
When you try to treat a delegate as a method, the compiler actually uses the delegate's Invoke() method. So, for example, the two lines below compile to the exact same IL (both call Invoke()):
k();
k.Invoke();
I assume the oddity you're seeing is a consequence of this. The delegate constructor expects a method (or rather, a method group), but it gets a delegate instead. So it treats it as a method and uses the Invoke() method.
As for the meaning, it is delegate that calls delegate that calls the actual method. You can verify this yourself by accessing the delegate's Method and Target properties. In the case of the outer-most delegate, Method is Action.Invoke and Target the inner delegate.
delegate is a class
Action delegate has a constructor like so
public extern Action(object #object, IntPtr method);
Since K is a static method there is no need to pass object to inner most action instance as first argument and hence it passes null
Since second argument is pointer to function therefore it passes pointer of K method using ldftn function
for the remaining Action instances the object is passed is inner Action and the second parameter is the Invoke method since when you call a delegate you're actually calling the Invoke method
Summary
var action = new Action(K) => Action action = new Action(null, ldftn(K))
new Action(action) => new Action(action, ldftn(Action.Invoke))
I hope this explains what is happening?
When i call CreateDelegate(delegateType) i get a System.ArgumentException, which according to MSDN is because the delegateType has the wrong number of parameters or the wrong parameter types.
The strange part is the code I'm using is almost all copied from MSDN. My function as whole:
public static void AssertRaisesEvent(Action action, object obj, string eventName, NumberOfTimes numberOfTimesRaised)
{
eventCounter = 0;
EventInfo eventInfo = obj.GetType().GetEvent(eventName);
Type tDelegate = eventInfo.EventHandlerType;
Type returnType = GetDelegateReturnType(tDelegate);
if (returnType != typeof(void))
throw new ApplicationException("Delegate has a return type.");
var handler =
new DynamicMethod("CompletedHandler",
typeof(int),
GetDelegateParameterTypes(tDelegate),
obj.GetType());
// Generate a method body. This method loads a string, calls
// the Show method overload that takes a string, pops the
// return value off the stack (because the handler has no
// return type), and returns.
//
ILGenerator ilgen = handler.GetILGenerator();
FieldInfo counterFieldInfo = typeof (AssertionHelpers).GetField("eventCounter",
BindingFlags.NonPublic | BindingFlags.Static);
ilgen.Emit(OpCodes.Ldfld, counterFieldInfo);
ilgen.Emit(OpCodes.Ldc_I4, 1);
ilgen.Emit(OpCodes.Add);
ilgen.Emit(OpCodes.Pop);
ilgen.Emit(OpCodes.Ret);
// Complete the dynamic method by calling its CreateDelegate
// method. Use the "add" accessor to add the delegate to
// the invocation list for the event.
//
var delParams = GetDelegateParameterTypes(tDelegate);
var handlerParams = handler.GetParameters();
Delegate dEmitted = handler.CreateDelegate(tDelegate);
eventInfo.GetAddMethod().Invoke(obj, new Object[] { dEmitted });
...
As you can see the comments are even there. As you also can see i have delParams and handlerParams variables which have the same number of parameters of the same type.
What is going on here?
MSDN: http://msdn.microsoft.com/en-us/library/ms228976.aspx
EDIT:
The event im trying to bind to:
private NullTransaction transaction;
public delegate void CompletedEventHandler(object testParam);
internal class NullTransaction : ITransaction
{
public event CompletedEventHandler Completed;
public void Dispose()
{
// no implementation
}
public void Complete()
{
// no implementation
if(Completed != null)
Completed.Invoke(this);
}
}
Most events don't return anything - in fact you assert that it has no return-type. You then declare your custom method (handler) as returning int, and try to bind it to a delegate that doesn't return an int. This won't work.
Also; your stack isn't valid for returning an int, since you "pop" the result.
i.e. I created a test with
public event EventHandler SomeEvent;
and bound to it; so then here:
Delegate dEmitted = handler.CreateDelegate(tDelegate);
you'll find that tDelegate is EventHandler. That doesn't match handler, which returns int.
Re the stack (comments); consider:
ilgen.Emit(OpCodes.Ldfld, counterFieldInfo); <=== should be ldsfld, by the way
ilgen.Emit(OpCodes.Ldc_I4, 1); // stack is now [counter] [1]
ilgen.Emit(OpCodes.Add); // stack is now [counter + 1]
ilgen.Emit(OpCodes.Pop); // stack is now empty
ilgen.Emit(OpCodes.Ret); // return
You've loaded two values, added them up, thrown the result away, and then returned. But you haven't returned the int that you claim to - this will fail IL inspection.
If you change:
var handler =
new DynamicMethod("CompletedHandler",
null,
GetDelegateParameterTypes(tDelegate),
obj.GetType());
and:
ilgen.Emit(OpCodes.Ldsfld, counterFieldInfo);
ilgen.Emit(OpCodes.Ldc_I4_1);
ilgen.Emit(OpCodes.Add);
ilgen.Emit(OpCodes.Stsfld, counterFieldInfo);
ilgen.Emit(OpCodes.Ret);
then it might work as you intend.
Also; this is simpler:
Delegate dEmitted = handler.CreateDelegate(tDelegate);
eventInfo.AddEventHandler(obj, dEmitted);