我使用的是 c++ dll来进行一些背景计算，我试图让它向我的调用 C# 代码。
为了做到这一点，我注册了一个回调方法，接受一个 StringBuilder 作为参数(在网上发现这是一个正确的方法)。
这是我的'c++´代码。
// --------------------------------------------
// ----------------- C++ CODE -----------------
// --------------------------------------------
// ----------------- dll api methods
// a custom class to contain some progress report stuff... basically, most important is
// that it contains the callback as ProgressCallback _callback;
CustomEventHandler* _eventHandler = NULL;
// definition of the callback type
typedef void(__stdcall* ProgressCallback)(char* log);
// method to register the callback method
int __stdcall SetCallbackFunction(ProgressCallback callback) {
// from https://stackoverflow.com/a/41910450/2490877
#pragma EXPORT_FUNCTION
// I encapsulated the callback into a custom class
_eventHandler = new CustomEventHandler();
_eventHandler->setEventHandler(callback);
// test all is ok => no problem at this stage, all works great, the
// passed-in callback is called with correct message.
logToCallback("All is ok while testing the method. So far so good!!");
return 0;
}
// the long and slow method (note that I might call it several times from c# during the
// one run
int __stdcall DoLooongStuff() {
// from https://stackoverflow.com/a/41910450/2490877
#pragma EXPORT_FUNCTION
// ------ this is a LOOOONG method that regualrly logs stuff via the callback,
// here an example....
char buf[1000];
sprintf_s(buf, "This is a sample progress log with some formats :%i %i %g", 1, 2, 3.1415);
logToCallback(buf);
// --- the above works a few times without any problem
return 0;
}
//--- this is a static method I use to send progress messages back
static void logToCallback(char* message) {
if (_eventHandler) {
_eventHandler->logToCallback(message);
}
}
// --------------- CustomEventHandlerClass
// ------- class declaration ------
class CustomEventHandler {
public:
void setEventHandler(ProgressCallback callback);
void logToCallback(char* message);
protected:
ProgressCallback _callback;
}
// ----- class implementation
// set the callback method
void CustomEventHandler::setEventHandler(ProgressCallback callback) {
_callback = callback;
}
void CustomEventHandler::logToCallback(char* message) {
if (_callback) {
_callback(message); // <========= this is where the debugger stops:
// no more info than the annoying System.ExecutionEngineException...
// I've tried to pass a constant message like "1234" but got the same issue...
//_callback("1234");
// if however I remove the call to the callback, I don't get errors
// (I know this doesn't mean I don't have any...)
}
}
现在调用c#的代码，我用的是下面的代码。
// --------------------------------------------
// ----------------- C# CODE ------------------
// --------------------------------------------
// ----- the delegate type to be passed to the dll
public delegate bool CallbackFunction([MarshalAs(UnmanagedType.LPStr)] StringBuilder log);
// ----- prepare to load the dll's methods (I only show the SetCallback code here, other api methods
// are declared and loaded the same way)
private delegate int _SetCallbackFunction_(CallbackFunction func);
private _SetCallbackFunction_ SetCallbackFunction_Dll;
public int SetCallbackFunction(CallbackFunction func) {
return SetCallbackFunction_Dll(func);
}
// loading methods
private T GetDelegate<T>(string procName) where T : class {
IntPtr fp = GetProcAddress(_dllHandle, procName);
return fp != IntPtr.Zero ? Marshal.GetDelegateForFunctionPointer(fp, typeof(T)) as T : null;
}
async Task loadDllMethods() {
// load the delegates => great, it works!
SetCallbackFunction_Dll = GetDelegate<_SetCallbackFunction_>("SetCallbackFunction");
// set callback in DLL, calls the delegate once successfully...
SetCallbackFunction(cSharpCallback);
await doTask();
}
async Task doTask() {
// start the long dll method, that fires the callback to monitor progress
while (someConditionIsMet) {
DoLooongStuff(); // => calls the dll with registered callback!
}
}
// the actual callback
bool cSharpCallback(StringBuilder strBuilder) {
// this is called a few times successfully with the expected message!
Console.WriteLine(strBuilder.ToString());
return true;
}
我在不同的线程中寻找错误的原因。我曾因 "buf´"太小而出错，所以我只是确保它足够大。我还发现"&_callback "总是指向同一个地方（确实如此！）。
我已经没有搜索选项了，任何帮助都将是非常感激的。请注意，我注意到一个专家在dll集成，Marshalling等，我把参考资料，我发现的提示!
我找到了我的问题的答案，感谢 此职位:
为了保持未管理的函数指针的活力（防止GC），你需要在一个变量中持有一个委托的实例。
所以，修改后的代码只在C#中使用
// -------------- PREVIOUS CODE
async Task loadDllMethods() {
// load the delegates => great, it works!
SetCallbackFunction_Dll = GetDelegate<_SetCallbackFunction_>("SetCallbackFunction");
// set callback in DLL, calls the delegate once successfully...
SetCallbackFunction(cSharpCallback);
await doTask();
}
// -------------- WORKING CODE!!!!
// add static reference....
static CallbackFunction _callbackInstance = new CallbackFunction(cSharpCallback); // <==== Added reference to prevent GC!!!
async Task loadDllMethods() {
// load the delegates => great, it works!
SetCallbackFunction_Dll = GetDelegate<_SetCallbackFunction_>("SetCallbackFunction");
// create callback!!!
SetCallbackFunction(_callbackInstance); // <====== pass the instance here, not the method itself!!!
await doTask();
}
注：我还改变了 StringBuilder 到 string !