[英]Unexpected poor performance of delegates in C#
我之前發布過這個關於在C#中動態編譯代碼的問題 ,答案又引出了另一個問題。
一個建議是我使用代理,我嘗試過並且它們運行良好。 然而,它們比直接呼叫慢大約8.4 X,這沒有任何意義。
這段代碼有什么問題?
我的結果,.Net 4.0,64位,直接運行exe:62,514,530
public static int Execute(int i) { return i * 2; }
private void button30_Click(object sender, EventArgs e)
{
CSharpCodeProvider foo = new CSharpCodeProvider();
var res = foo.CompileAssemblyFromSource(
new System.CodeDom.Compiler.CompilerParameters()
{
GenerateInMemory = true,
CompilerOptions = @"/optimize",
},
@"public class FooClass { public static int Execute(int i) { return i * 2; }}"
);
var type = res.CompiledAssembly.GetType("FooClass");
var obj = Activator.CreateInstance(type);
var method = type.GetMethod("Execute");
int i = 0, t1 = Environment.TickCount, t2;
//var input = new object[] { 2 };
//for (int j = 0; j < 10000000; j++)
//{
// input[0] = j;
// var output = method.Invoke(obj, input);
// i = (int)output;
//}
//t2 = Environment.TickCount;
//MessageBox.Show((t2 - t1).ToString() + Environment.NewLine + i.ToString());
t1 = Environment.TickCount;
for (int j = 0; j < 100000000; j++)
{
i = Execute(j);
}
t2 = Environment.TickCount;
MessageBox.Show("Native: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString());
var func = (Func<int, int>) Delegate.CreateDelegate(typeof (Func<int, int>), method);
t1 = Environment.TickCount;
for (int j = 0; j < 100000000; j++)
{
i = func(j);
}
t2 = Environment.TickCount;
MessageBox.Show("Dynamic delegate: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString());
Func<int, int> funcL = Execute;
t1 = Environment.TickCount;
for (int j = 0; j < 100000000; j++)
{
i = funcL(j);
}
t2 = Environment.TickCount;
MessageBox.Show("Delegate: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString());
}
正如漢斯在關於你的問題的評論中提到的那樣, Execute
方法非常簡單,幾乎肯定會被你的“原生”測試中的抖動所強調。
所以你所看到的不是標准方法調用和委托調用之間的比較,而是內聯i * 2
操作和委托調用之間的比較。 (並且i * 2
操作可能歸結為只有一個機器指令,大約可以達到最快速度。)
使您的Execute
方法更復雜,以防止內聯(和/或使用MethodImplOptions.NoInlining
編譯器提示); 那么你將在標准方法調用和委托調用之間進行更現實的比較。 在大多數情況下,差異可以忽略不計:
[MethodImpl(MethodImplOptions.NoInlining)]
static int Execute(int i) { return ((i / 63.53) == 34.23) ? -1 : (i * 2); }
public static volatile int Result;
private static void Main(string[] args)
{
const int iterations = 100000000;
{
Result = Execute(42); // pre-jit
var s = Stopwatch.StartNew();
for (int i = 0; i < iterations; i++)
{
Result = Execute(i);
}
s.Stop();
Console.WriteLine("Native: " + s.ElapsedMilliseconds);
}
{
Func<int, int> func;
using (var cscp = new CSharpCodeProvider())
{
var cp = new CompilerParameters { GenerateInMemory = true, CompilerOptions = @"/optimize" };
string src = @"public static class Foo { public static int Execute(int i) { return ((i / 63.53) == 34.23) ? -1 : (i * 2); } }";
var cr = cscp.CompileAssemblyFromSource(cp, src);
var mi = cr.CompiledAssembly.GetType("Foo").GetMethod("Execute");
func = (Func<int, int>)Delegate.CreateDelegate(typeof(Func<int, int>), mi);
}
Result = func(42); // pre-jit
var s = Stopwatch.StartNew();
for (int i = 0; i < iterations; i++)
{
Result = func(i);
}
s.Stop();
Console.WriteLine("Dynamic delegate: " + s.ElapsedMilliseconds);
}
{
Func<int, int> func = Execute;
Result = func(42); // pre-jit
var s = Stopwatch.StartNew();
for (int i = 0; i < iterations; i++)
{
Result = func(i);
}
s.Stop();
Console.WriteLine("Delegate: " + s.ElapsedMilliseconds);
}
}
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