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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
#nullable enable
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Linq.Expressions;
using System.Reflection;
namespace Microsoft.Extensions.Internal;
[RequiresUnreferencedCode("ObjectMethodExecutor performs reflection on arbitrary types.")]
[RequiresDynamicCode("ObjectMethodExecutor performs reflection on arbitrary types.")]
internal sealed class ObjectMethodExecutor
{
private readonly object?[]? _parameterDefaultValues;
private readonly MethodExecutorAsync? _executorAsync;
private readonly MethodExecutor? _executor;
private static readonly ConstructorInfo _objectMethodExecutorAwaitableConstructor =
typeof(ObjectMethodExecutorAwaitable).GetConstructor(new[] {
typeof(object), // customAwaitable
typeof(Func<object, object>), // getAwaiterMethod
typeof(Func<object, bool>), // isCompletedMethod
typeof(Func<object, object>), // getResultMethod
typeof(Action<object, Action>), // onCompletedMethod
typeof(Action<object, Action>) // unsafeOnCompletedMethod
})!;
private ObjectMethodExecutor(MethodInfo methodInfo, TypeInfo targetTypeInfo, object?[]? parameterDefaultValues)
{
ArgumentNullException.ThrowIfNull(methodInfo);
MethodInfo = methodInfo;
MethodParameters = methodInfo.GetParameters();
TargetTypeInfo = targetTypeInfo;
MethodReturnType = methodInfo.ReturnType;
var isAwaitable = CoercedAwaitableInfo.IsTypeAwaitable(MethodReturnType, out var coercedAwaitableInfo);
IsMethodAsync = isAwaitable;
AsyncResultType = isAwaitable ? coercedAwaitableInfo.AwaitableInfo.ResultType : null;
// Upstream code may prefer to use the sync-executor even for async methods, because if it knows
// that the result is a specific Task<T> where T is known, then it can directly cast to that type
// and await it without the extra heap allocations involved in the _executorAsync code path.
_executor = GetExecutor(methodInfo, targetTypeInfo);
if (IsMethodAsync)
{
_executorAsync = GetExecutorAsync(methodInfo, targetTypeInfo, coercedAwaitableInfo);
}
_parameterDefaultValues = parameterDefaultValues;
}
private delegate ObjectMethodExecutorAwaitable MethodExecutorAsync(object target, object?[]? parameters);
private delegate object? MethodExecutor(object target, object?[]? parameters);
private delegate void VoidMethodExecutor(object target, object?[]? parameters);
public MethodInfo MethodInfo { get; }
public ParameterInfo[] MethodParameters { get; }
public TypeInfo TargetTypeInfo { get; }
public Type? AsyncResultType { get; }
// This field is made internal set because it is set in unit tests.
public Type MethodReturnType { get; internal set; }
public bool IsMethodAsync { get; }
public static ObjectMethodExecutor Create(MethodInfo methodInfo, TypeInfo targetTypeInfo)
{
return new ObjectMethodExecutor(methodInfo, targetTypeInfo, null);
}
public static ObjectMethodExecutor Create(MethodInfo methodInfo, TypeInfo targetTypeInfo, object?[] parameterDefaultValues)
{
ArgumentNullException.ThrowIfNull(parameterDefaultValues);
return new ObjectMethodExecutor(methodInfo, targetTypeInfo, parameterDefaultValues);
}
/// <summary>
/// Executes the configured method on <paramref name="target"/>. This can be used whether or not
/// the configured method is asynchronous.
/// </summary>
/// <remarks>
/// Even if the target method is asynchronous, it's desirable to invoke it using Execute rather than
/// ExecuteAsync if you know at compile time what the return type is, because then you can directly
/// "await" that value (via a cast), and then the generated code will be able to reference the
/// resulting awaitable as a value-typed variable. If you use ExecuteAsync instead, the generated
/// code will have to treat the resulting awaitable as a boxed object, because it doesn't know at
/// compile time what type it would be.
/// </remarks>
/// <param name="target">The object whose method is to be executed.</param>
/// <param name="parameters">Parameters to pass to the method.</param>
/// <returns>The method return value.</returns>
public object? Execute(object target, object?[]? parameters)
{
Debug.Assert(_executor != null, "Sync execution is not supported.");
return _executor(target, parameters);
}
/// <summary>
/// Executes the configured method on <paramref name="target"/>. This can only be used if the configured
/// method is asynchronous.
/// </summary>
/// <remarks>
/// If you don't know at compile time the type of the method's returned awaitable, you can use ExecuteAsync,
/// which supplies an awaitable-of-object. This always works, but can incur several extra heap allocations
/// as compared with using Execute and then using "await" on the result value typecasted to the known
/// awaitable type. The possible extra heap allocations are for:
///
/// 1. The custom awaitable (though usually there's a heap allocation for this anyway, since normally
/// it's a reference type, and you normally create a new instance per call).
/// 2. The custom awaiter (whether or not it's a value type, since if it's not, you need a new instance
/// of it, and if it is, it will have to be boxed so the calling code can reference it as an object).
/// 3. The async result value, if it's a value type (it has to be boxed as an object, since the calling
/// code doesn't know what type it's going to be).
/// </remarks>
/// <param name="target">The object whose method is to be executed.</param>
/// <param name="parameters">Parameters to pass to the method.</param>
/// <returns>An object that you can "await" to get the method return value.</returns>
public ObjectMethodExecutorAwaitable ExecuteAsync(object target, object?[]? parameters)
{
Debug.Assert(_executorAsync != null, "Async execution is not supported.");
return _executorAsync(target, parameters);
}
public object? GetDefaultValueForParameter(int index)
{
if (_parameterDefaultValues == null)
{
throw new InvalidOperationException($"Cannot call {nameof(GetDefaultValueForParameter)}, because no parameter default values were supplied.");
}
if (index < 0 || index > MethodParameters.Length - 1)
{
throw new ArgumentOutOfRangeException(nameof(index));
}
return _parameterDefaultValues[index];
}
private static MethodExecutor GetExecutor(MethodInfo methodInfo, TypeInfo targetTypeInfo)
{
// Parameters to executor
var targetParameter = Expression.Parameter(typeof(object), "target");
var parametersParameter = Expression.Parameter(typeof(object?[]), "parameters");
// Build parameter list
var paramInfos = methodInfo.GetParameters();
var parameters = new List<Expression>(paramInfos.Length);
for (int i = 0; i < paramInfos.Length; i++)
{
var paramInfo = paramInfos[i];
var valueObj = Expression.ArrayIndex(parametersParameter, Expression.Constant(i));
var valueCast = Expression.Convert(valueObj, paramInfo.ParameterType);
// valueCast is "(Ti) parameters[i]"
parameters.Add(valueCast);
}
// Call method
var instanceCast = Expression.Convert(targetParameter, targetTypeInfo.AsType());
var methodCall = Expression.Call(instanceCast, methodInfo, parameters);
// methodCall is "((Ttarget) target) method((T0) parameters[0], (T1) parameters[1], ...)"
// Create function
if (methodCall.Type == typeof(void))
{
var lambda = Expression.Lambda<VoidMethodExecutor>(methodCall, targetParameter, parametersParameter);
var voidExecutor = lambda.Compile();
return WrapVoidMethod(voidExecutor);
}
else
{
// must coerce methodCall to match ActionExecutor signature
var castMethodCall = Expression.Convert(methodCall, typeof(object));
var lambda = Expression.Lambda<MethodExecutor>(castMethodCall, targetParameter, parametersParameter);
return lambda.Compile();
}
}
private static MethodExecutor WrapVoidMethod(VoidMethodExecutor executor)
{
return delegate (object target, object?[]? parameters)
{
executor(target, parameters);
return null;
};
}
private static MethodExecutorAsync GetExecutorAsync(
MethodInfo methodInfo,
TypeInfo targetTypeInfo,
CoercedAwaitableInfo coercedAwaitableInfo)
{
// Parameters to executor
var targetParameter = Expression.Parameter(typeof(object), "target");
var parametersParameter = Expression.Parameter(typeof(object[]), "parameters");
// Build parameter list
var paramInfos = methodInfo.GetParameters();
var parameters = new List<Expression>(paramInfos.Length);
for (int i = 0; i < paramInfos.Length; i++)
{
var paramInfo = paramInfos[i];
var valueObj = Expression.ArrayIndex(parametersParameter, Expression.Constant(i));
var valueCast = Expression.Convert(valueObj, paramInfo.ParameterType);
// valueCast is "(Ti) parameters[i]"
parameters.Add(valueCast);
}
// Call method
var instanceCast = Expression.Convert(targetParameter, targetTypeInfo.AsType());
var methodCall = Expression.Call(instanceCast, methodInfo, parameters);
// Using the method return value, construct an ObjectMethodExecutorAwaitable based on
// the info we have about its implementation of the awaitable pattern. Note that all
// the funcs/actions we construct here are precompiled, so that only one instance of
// each is preserved throughout the lifetime of the ObjectMethodExecutor.
// var getAwaiterFunc = (object awaitable) =>
// (object)((CustomAwaitableType)awaitable).GetAwaiter();
var customAwaitableParam = Expression.Parameter(typeof(object), "awaitable");
var awaitableInfo = coercedAwaitableInfo.AwaitableInfo;
var postCoercionMethodReturnType = coercedAwaitableInfo.CoercerResultType ?? methodInfo.ReturnType;
var getAwaiterFunc = Expression.Lambda<Func<object, object>>(
Expression.Convert(
Expression.Call(
Expression.Convert(customAwaitableParam, postCoercionMethodReturnType),
awaitableInfo.GetAwaiterMethod),
typeof(object)),
customAwaitableParam).Compile();
// var isCompletedFunc = (object awaiter) =>
// ((CustomAwaiterType)awaiter).IsCompleted;
var isCompletedParam = Expression.Parameter(typeof(object), "awaiter");
var isCompletedFunc = Expression.Lambda<Func<object, bool>>(
Expression.MakeMemberAccess(
Expression.Convert(isCompletedParam, awaitableInfo.AwaiterType),
awaitableInfo.AwaiterIsCompletedProperty),
isCompletedParam).Compile();
var getResultParam = Expression.Parameter(typeof(object), "awaiter");
Func<object, object> getResultFunc;
if (awaitableInfo.ResultType == typeof(void))
{
// var getResultFunc = (object awaiter) =>
// {
// ((CustomAwaiterType)awaiter).GetResult(); // We need to invoke this to surface any exceptions
// return (object)null;
// };
getResultFunc = Expression.Lambda<Func<object, object>>(
Expression.Block(
Expression.Call(
Expression.Convert(getResultParam, awaitableInfo.AwaiterType),
awaitableInfo.AwaiterGetResultMethod),
Expression.Constant(null)
),
getResultParam).Compile();
}
else
{
// var getResultFunc = (object awaiter) =>
// (object)((CustomAwaiterType)awaiter).GetResult();
getResultFunc = Expression.Lambda<Func<object, object>>(
Expression.Convert(
Expression.Call(
Expression.Convert(getResultParam, awaitableInfo.AwaiterType),
awaitableInfo.AwaiterGetResultMethod),
typeof(object)),
getResultParam).Compile();
}
// var onCompletedFunc = (object awaiter, Action continuation) => {
// ((CustomAwaiterType)awaiter).OnCompleted(continuation);
// };
var onCompletedParam1 = Expression.Parameter(typeof(object), "awaiter");
var onCompletedParam2 = Expression.Parameter(typeof(Action), "continuation");
var onCompletedFunc = Expression.Lambda<Action<object, Action>>(
Expression.Call(
Expression.Convert(onCompletedParam1, awaitableInfo.AwaiterType),
awaitableInfo.AwaiterOnCompletedMethod,
onCompletedParam2),
onCompletedParam1,
onCompletedParam2).Compile();
Action<object, Action>? unsafeOnCompletedFunc = null;
if (awaitableInfo.AwaiterUnsafeOnCompletedMethod != null)
{
// var unsafeOnCompletedFunc = (object awaiter, Action continuation) => {
// ((CustomAwaiterType)awaiter).UnsafeOnCompleted(continuation);
// };
var unsafeOnCompletedParam1 = Expression.Parameter(typeof(object), "awaiter");
var unsafeOnCompletedParam2 = Expression.Parameter(typeof(Action), "continuation");
unsafeOnCompletedFunc = Expression.Lambda<Action<object, Action>>(
Expression.Call(
Expression.Convert(unsafeOnCompletedParam1, awaitableInfo.AwaiterType),
awaitableInfo.AwaiterUnsafeOnCompletedMethod,
unsafeOnCompletedParam2),
unsafeOnCompletedParam1,
unsafeOnCompletedParam2).Compile();
}
// If we need to pass the method call result through a coercer function to get an
// awaitable, then do so.
var coercedMethodCall = coercedAwaitableInfo.RequiresCoercion
? Expression.Invoke(coercedAwaitableInfo.CoercerExpression, methodCall)
: (Expression)methodCall;
// return new ObjectMethodExecutorAwaitable(
// (object)coercedMethodCall,
// getAwaiterFunc,
// isCompletedFunc,
// getResultFunc,
// onCompletedFunc,
// unsafeOnCompletedFunc);
var returnValueExpression = Expression.New(
_objectMethodExecutorAwaitableConstructor,
Expression.Convert(coercedMethodCall, typeof(object)),
Expression.Constant(getAwaiterFunc),
Expression.Constant(isCompletedFunc),
Expression.Constant(getResultFunc),
Expression.Constant(onCompletedFunc),
Expression.Constant(unsafeOnCompletedFunc, typeof(Action<object, Action>)));
var lambda = Expression.Lambda<MethodExecutorAsync>(returnValueExpression, targetParameter, parametersParameter);
return lambda.Compile();
}
}
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