我会坚持类型安全原则:我知道已经有Marshal.GetFunctionPointerForDelegate
但这需要在 C++/CLI 中进行函数指针类型转换,并隐藏编组非托管->托管的工作方式(调试要困难得多,我不喜欢不理解场景中发生的情况)。刚刚注意到该方法类似于this https://stackoverflow.com/questions/4982404/c-cli-class-wrapper-for-c-library-callbacks但不需要托管本机类(开销更少)。请告诉我您是否知道如何进一步简化它(维护类型安全和编组控制)并减少开销。
以下是C++/CLIWrapper.h
header:
#include <gcroot.h>
using namespace System;
using namespace System::Runtime::InteropServices;
namespace LibraryWrapper
{
// Declare the cdecl function that will be used
void cdecl_allocate_buffer(void *opaque, void **buffer);
public ref class Library
{
public:
// The BufferAllocator delegate declaration, available to any clr language
// [In, Out] attributes needed (?) to pass the pointer as reference
delegate void BufferAllocator([In, Out] IntPtr% buffer);
internal:
// The stored delegate ref to be used later
BufferAllocator ^_allocate_buffer;
private:
// Native handle of the ref Library class, castable to void *
gcroot<Library^> *_native_handle;
// C library context
lib_context_base *_lib_context_base;
public:
Library();
~Library();
// The clr callback setter equivalent to the C counterpart, don't need
// the context because in CLR we have closures
void SetBufferAllocateCallback(BufferAllocator ^allocateBuffer);
};
}
遵循 C++/CLiWrapper.cpp
定义:
#include "wrapper.h"
namespace LibraryWrapper
{
Library::Library()
{
// Construct the native handle
_native_handle = new gcroot<Library^>();
// Initialize the library base context
_lib_context_base = new_lib_context_base();
// Null the _allocate_buffer delegate instance
_allocate_buffer = nullptr;
}
Library::~Library()
{
free_lib_context_base(_lib_context_base);
delete _native_handle;
}
void Library::SetBufferAllocateCallback(BufferAllocator ^allocateBuffer)
{
_allocate_buffer = allocateBuffer;
// Call the C lib callback setter. Use _native_handle pointer as the opaque data
set_allocate_buffer_callback(_lib_context_base, cdecl_allocate_buffer,
_native_handle);
}
void cdecl_allocate_buffer(void *opaque, void **buffer)
{
// Cast the opaque pointer to the hnative_handle ref (for readability)
gcroot<Library^> & native_handle = *((gcroot<Library^>*)opaque);
// Prepare a IntPtr wrapper to the buffer pointer
IntPtr buffer_cli(*buffer);
// Call the _allocate_buffer delegate in the library wrapper ref
native_handle->_allocate_buffer(buffer_cli);
// Set the buffer pointer to the value obtained calling the delegate
*buffer = buffer_cli.ToPointer();
}
}
可以这样使用(C#):
// Allocate a ~10mb buffer in unmanaged memory. Will be deallocated
// automatically when buffer go out of scope
IntPtr _buffer = Marshal.AllocHGlobal(10000000);
// Init the library wrapper
Library library = new Library();
// Set the callback wrapper with an anonymous method
library.SetBufferAllocateCallback(delegate(ref IntPtr buffer)
{
// Because we have closure, I can use the _buffer variable in the outer scope
buffer = _buffer;
});