Question
我正在将一个C应用程序移植到C#.C应用程序从第三方DLL调用了很多函数，所以我在C#中为这些函数编写了P/Invoke包装器.其中一些C函数分配我必须在C#app中使用的数据，因此我使用IntPtr、Marshal.PtrToStructure和Marshal.Copy将本机数据(数组和 struct )复制到托管变量中.
不幸的是，事实证明C#app比C版本慢得多.快速性能分析表明，上述基于封送的数据复制是瓶颈.I'm considering to speed up the C# code by rewriting it to use pointers instead.由于我没有在C#中使用不安全代码和指针的经验，我需要以下questions方面的专家意见:
- 使用
unsafe个代码和指针而不使用IntPtr和Marshaling有什么缺点？例如，它在任何方面都更不安全(双关语)吗？人们似乎更喜欢编组，但我不知道为什么. - 使用指针进行P/调用真的比使用封送处理快吗？大约可以预期多大的加速比？我找不到任何这方面的基准测试.
Example code
为了让情况更清楚，我拼凑了一个小示例代码(真正的代码要复杂得多).我希望这个例子能说明我所说的"不安全代码和指针"与"IntPtr和Marshal"之间的区别.
C库(DLL)
MyLib.H
#ifndef _MY_LIB_H_
#define _MY_LIB_H_
struct MyData
{
int length;
unsigned char* bytes;
};
__declspec(dllexport) void CreateMyData(struct MyData** myData, int length);
__declspec(dllexport) void DestroyMyData(struct MyData* myData);
#endif // _MY_LIB_H_
MyLib.C
#include <stdlib.h>
#include "MyLib.H"
void CreateMyData(struct MyData** myData, int length)
{
int i;
*myData = (struct MyData*)malloc(sizeof(struct MyData));
if (*myData != NULL)
{
(*myData)->length = length;
(*myData)->bytes = (unsigned char*)malloc(length * sizeof(char));
if ((*myData)->bytes != NULL)
for (i = 0; i < length; ++i)
(*myData)->bytes[i] = (unsigned char)(i % 256);
}
}
void DestroyMyData(struct MyData* myData)
{
if (myData != NULL)
{
if (myData->bytes != NULL)
free(myData->bytes);
free(myData);
}
}
C应用程序
主要的C
#include <stdio.h>
#include "MyLib.H"
void main()
{
struct MyData* myData = NULL;
int length = 100 * 1024 * 1024;
printf("=== C++ test ===\n");
CreateMyData(&myData, length);
if (myData != NULL)
{
printf("Length: %d\n", myData->length);
if (myData->bytes != NULL)
printf("First: %d, last: %d\n", myData->bytes[0], myData->bytes[myData->length - 1]);
else
printf("myData->bytes is NULL");
}
else
printf("myData is NULL\n");
DestroyMyData(myData);
getchar();
}
C# application, which uses IntPtr and Marshal
程序反恐精英
using System;
using System.Runtime.InteropServices;
public static class Program
{
[StructLayout(LayoutKind.Sequential)]
private struct MyData
{
public int Length;
public IntPtr Bytes;
}
[DllImport("MyLib.dll")]
private static extern void CreateMyData(out IntPtr myData, int length);
[DllImport("MyLib.dll")]
private static extern void DestroyMyData(IntPtr myData);
public static void Main()
{
Console.WriteLine("=== C# test, using IntPtr and Marshal ===");
int length = 100 * 1024 * 1024;
IntPtr myData1;
CreateMyData(out myData1, length);
if (myData1 != IntPtr.Zero)
{
MyData myData2 = (MyData)Marshal.PtrToStructure(myData1, typeof(MyData));
Console.WriteLine("Length: {0}", myData2.Length);
if (myData2.Bytes != IntPtr.Zero)
{
byte[] bytes = new byte[myData2.Length];
Marshal.Copy(myData2.Bytes, bytes, 0, myData2.Length);
Console.WriteLine("First: {0}, last: {1}", bytes[0], bytes[myData2.Length - 1]);
}
else
Console.WriteLine("myData.Bytes is IntPtr.Zero");
}
else
Console.WriteLine("myData is IntPtr.Zero");
DestroyMyData(myData1);
Console.ReadKey(true);
}
}
C# application, which uses unsafe code and pointers
程序反恐精英
using System;
using System.Runtime.InteropServices;
public static class Program
{
[StructLayout(LayoutKind.Sequential)]
private unsafe struct MyData
{
public int Length;
public byte* Bytes;
}
[DllImport("MyLib.dll")]
private unsafe static extern void CreateMyData(out MyData* myData, int length);
[DllImport("MyLib.dll")]
private unsafe static extern void DestroyMyData(MyData* myData);
public unsafe static void Main()
{
Console.WriteLine("=== C# test, using unsafe code ===");
int length = 100 * 1024 * 1024;
MyData* myData;
CreateMyData(out myData, length);
if (myData != null)
{
Console.WriteLine("Length: {0}", myData->Length);
if (myData->Bytes != null)
Console.WriteLine("First: {0}, last: {1}", myData->Bytes[0], myData->Bytes[myData->Length - 1]);
else
Console.WriteLine("myData.Bytes is null");
}
else
Console.WriteLine("myData is null");
DestroyMyData(myData);
Console.ReadKey(true);
}
}