我使用C/C++LI包装C库. C库旨在从非托管C类中使用.这意味着库函数接受C对象指针,然后在回调中提供该指针.这使得回调代码能够将请求重定向到调用C对象中的适当事件函数.
实际的功能非常复杂,所以我将问题空间简化为几个基本项：
// C library function signature
void CLibFunc(CLIBCALLBACK *callback,void *caller);
// C callback signature
// Second parameter is meant to point to the calling C++ object
typedef int (__stdcall CLIBCALLBACK) (int param1,void *caller);
// C callback implementation
int CallBackImpl(int param1,void* caller)
{
// Need to call the ManagedCaller's EventFunction from here
// ???
}
// C++/CLI caller class
public ref class ManagedCaller
{
public:
void CallerFunction(void)
{
// Call the C library function
// Need to pass some kind of this class pointer that refers to this object
CLibFunc(CallBackImpl,????);
}
void EventFunction(param1)
{
}
}
现在需要从托管C类调用C库函数.在C/C++LI下,垃圾收集器在内存中移动对象,因此将一个简单的固定指针传递给该类不再起作用.我可以通过固定对象来解决问题,但不建议这样做,因为它会导致内存碎片.似乎另一种选择是使用auto_gcroot指针,但我对托管C相当新,我不知道如何使这项工作.
解决方法
这恰好与我正在进行的工作类似.
这是一篇关于使用C类提供本机回调的博客文章：http://blogs.microsoft.co.il/blogs/alon/archive/2007/05/29/Native-Callback.aspx
我不熟悉从C调用C成员函数,但我已经为另一个C类做了一个接口(抽象基类)来进行回调(类似于文章).以下是我为以下内容提供桥梁的基本示例：
// Interface (abstract base) class providing the callback
class IProvider {
public:
virtual ~IProvider() {}
virtual void Callback() = 0;
};
// User class of the callback
class CUser {
IProvider * m_pProvider;
public:
CUser(IProvider * pProvider) {
m_pProvider = pProvider;
}
void DoSomething() {
m_pProvider->Callback();
}
};
// Implementation of the interface class
class CHelloWorldProvider : public IProvider {
void Callback() {
printf("Hello World!");
}
};
// Usage of the callback provider in a pure native setting
void PureNativeUsage() {
CHelloWorldProvider oProvider;
CUser oUser(&oProvider);
oUser.DoSomething();
}
现在,为了使其可用于提供者的托管实现,我们必须创建一系列提供桥接的类.
// Where gcroot is defined
#include <vcclr.h>
// Managed provider interface class
public interface class IManagedProvider {
void Callback();
};
// Native bridge class that can be passed to the user
class CProviderBridge : public IProvider {
// Give the managed class full access
friend ref class ManagedProviderBase;
// Store a reference to the managed object for callback redirects
gcroot<IManagedProvider ^> m_rManaged;
public:
void Callback(){
m_rManaged->Callback();
}
};
// Managed provider base class,this provides a managed base class for extending
public ref class ManagedProviderBase abstract : public IManagedProvider {
// Pointer to the native bridge object
CProviderBridge * m_pNative;
protected:
ManagedProviderBase() {
// Create the native bridge object and set the managed reference
m_pNative = new CProviderBridge();
m_pNative->m_rManaged = this;
}
public:
~ManagedProviderBase() {
delete m_pNative;
}
// Returns a pointer to the native provider object
IProvider * GetProvider() {
return m_pNative;
}
// Makes the deriving class implement the function
virtual void Callback() = 0;
};
// Pure managed provider implementation (this could also be declared in another library and/or in C#/VB.net)
public ref class ManagedHelloWorldProvider : public ManagedProviderBase {
public:
virtual void Callback() override {
Console::Write("Hello World");
}
};
// Usage of the managed provider from the native user
void MixedUsage() {
ManagedHelloWorldProvider ^ rManagedProvider = gcnew ManagedHelloWorldProvider;
CUser oUser(rManagedProvider->GetProvider());
oUser.DoSomething();
}
这是我的示例的修改版本,可以在上面的CLibFunc中使用.这假设C函数执行回调的方式是准确的.
此外,根据您的回调类的参与程度以及您需要多少扩展自由,这可能会稍微减少一些.
// Where gcroot is defined
#include <vcclr.h>
// C callback signature
// Second parameter is meant to point to the calling C++ object
typedef int (__stdcall CLIBCALLBACK) (int param1,void *caller);
// C library function
void CLibFunc(CLIBCALLBACK *callback,void *caller) {
// Do some work
(*callback)(1234,caller);
// Do more work
}
// Managed caller interface class
public interface class IManagedCaller {
void EventFunction(int param1);
};
// C++ native bridge struct
struct CCallerBridge {
// Give the managed class full access
friend ref class ManagedCaller;
// Store a reference to the managed object for callback redirects
gcroot<IManagedCaller ^> m_rManaged;
public:
// Cast the caller to the native bridge and call managed event function
// Note: This must be __stdcall to prevent function call stack corruption
static int __stdcall CallBackImpl(int param1,void * caller) {
CCallerBridge * pCaller = (CCallerBridge *) caller;
pCaller->m_rManaged->EventFunction(param1);
return 0;
}
};
// C++/CLI caller class
public ref class ManagedCaller : public IManagedCaller {
// Pointer to the native bridge object
CCallerBridge * m_pNative;
public:
ManagedCaller() {
// Create the native bridge object and set the managed reference
m_pNative = new CCallerBridge();
m_pNative->m_rManaged = this;
}
~ManagedCaller() {
delete m_pNative;
}
// Calls the C library function
void CallerFunction() {
CLibFunc(CCallerBridge::CallBackImpl,m_pNative);
}
// Managed callback function
virtual void EventFunction(int param1) {
Console::WriteLine(param1);
}
};
// Usage
int main(array<System::String ^> ^args) {
ManagedCaller ^ oCaller = gcnew ManagedCaller();
oCaller->CallerFunction();
return 0;
}
