在IMMDeviceEnumerator上调用SAFE_RELEASE时崩溃

Question

I am using a service to detect the connection of head set. When the microphone is connected and disconnected, I am getting notification. The thing is, when I end the service manually, I am facing a crash in the service while doing SAFE_RELEASE. Here is the code...

NotifyHandsetConnectionStatus::NotifyHandsetConnectionStatus() : _cRef(1), _pEnumerator(NULL){}

NotifyHandsetConnectionStatus::~NotifyHandsetConnectionStatus()
{
 //   SAFE_RELEASE(_pEnumerator)
    if (_pEnumerator)
    { 
        _pEnumerator->Release(); // CRASH
        _pEnumerator = NULL;
    }
}

void NotifyHandsetConnectionStatus::Init(DWORD threadID)
{
    PTTThreadID = threadID;
    HRESULT hr = S_OK;

    CoInitialize(NULL);

    if (_pEnumerator == NULL)
    {
        // Get enumerator for audio endpoint devices.
        hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER,
            __uuidof(IMMDeviceEnumerator), (void**)&_pEnumerator);
    }

    if (hr == S_OK)
    {
        _pEnumerator->RegisterEndpointNotificationCallback(this);
    }
}

and here is the class declaration...

class NotifyHandsetConnectionStatus : public IMMNotificationClient
{
    LONG _cRef;
    IMMDeviceEnumerator *_pEnumerator;
    DWORD PTTThreadID;
public:
    NotifyHandsetConnectionStatus();
    ~NotifyHandsetConnectionStatus();

    void Init(DWORD threadID);
    ULONG STDMETHODCALLTYPE AddRef() override;
    virtual ULONG STDMETHODCALLTYPE Release() override;
    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, VOID **ppvInterface) override;
    HRESULT STDMETHODCALLTYPE OnDeviceStateChanged(LPCWSTR pwstrDeviceId, DWORD dwNewState) override;
    HRESULT STDMETHODCALLTYPE OnDeviceAdded(LPCWSTR pwstrDeviceId) override
    {
        return S_OK;
    }
    HRESULT STDMETHODCALLTYPE OnDeviceRemoved(LPCWSTR pwstrDeviceId) override
    {
        return S_OK;
    }
    HRESULT STDMETHODCALLTYPE OnPropertyValueChanged(LPCWSTR pwstrDeviceId, const PROPERTYKEY key) override
    {
        return S_OK;
    }
    HRESULT STDMETHODCALLTYPE OnDefaultDeviceChanged( EDataFlow flow, ERole role, LPCWSTR pwstrDeviceId) override
    {
        return S_OK;
    }
};

Answer 1

Your code as posted does not crash, not even without unregistering the callback. Checked by copy-pasting what you have and adding what you didn't. The IUnknown methods are missing, but pretty unlikely to have anything to do with it. Just make sure that your Release() function doesn't get called too often, delete this only works once.

There are plenty of reasons for code like this to crash, heap corruption is every C++ programmer's nasty loud neighbor and he is forever most likely to show up at the most inopportune moment. With program exit being a very likely time to get that neighbor to turn the dial to eleven, that's when you touch heap sections you haven't needed for a while. Very hard to debug, the corruption happened much earlier.

Isolate the problem, start by turning the service into a console mode app that goes through all the same motions so it is easier to debug. And you can use heap diagnostic tools like UMHD.exe. Write unit tests for individual chunks of code.

Answer 2

似乎需要Unregister the IMMDeviceEnumerator before calling Release() 。

_pEnumerator->UnregisterEndpointNotificationCallback(this);