Fixed kdeconnectd deadlock on Windows caused by systemvolumeplugin

IAudioEndpointVolumeCallback::Release was called in callback functions of IMMNotificationClient (through the call to SystemvolumePlugin::sendSinkList), however https://docs.microsoft.com/en-us/windows/win32/api/mmdeviceapi/nn-mmdeviceapi-immnotificationclient points out that:
*To avoid dead locks, the client should never call IMMDeviceEnumerator::RegisterEndpointNotificationCallback or IMMDeviceEnumerator::UnregisterEndpointNotificationCallback in its implementation of IMMNotificationClient methods.
*The client should never release the final reference on an MMDevice API object during an event callback.

So I moved that part of code to another thread so it will successfully run after callback functions work out and call only if endpoint needs to be released (device was removed), so it won't spawn new thread for every generated event

plugins/systemvolume/systemvolumeplugin-win.cpp

@@ -23,10 +23,73 @@ K_PLUGIN_CLASS_WITH_JSON(SystemvolumePlugin, "kdeconnect_systemvolume.json")
 
 // Private classes of SystemvolumePlugin
 
+class SystemvolumePlugin::CAudioEndpointVolumeCallback : public IAudioEndpointVolumeCallback
+{
+    LONG _cRef;
+
+public:
+    CAudioEndpointVolumeCallback(SystemvolumePlugin &x, QString sinkName) : enclosing(x), name(std::move(sinkName)), _cRef(1) {}
+    ~CAudioEndpointVolumeCallback(){};
+
+    // IUnknown methods -- AddRef, Release, and QueryInterface
+
+    ULONG STDMETHODCALLTYPE AddRef() override
+    {
+        return InterlockedIncrement(&_cRef);
+    }
+
+    ULONG STDMETHODCALLTYPE Release() override
+    {
+        ULONG ulRef = InterlockedDecrement(&_cRef);
+        if (ulRef == 0)
+        {
+            delete this;
+        }
+        return ulRef;
+    }
+
+    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, VOID **ppvInterface) override
+    {
+        if (IID_IUnknown == riid)
+        {
+            AddRef();
+            *ppvInterface = (IUnknown *)this;
+        }
+        else if (__uuidof(IMMNotificationClient) == riid)
+        {
+            AddRef();
+            *ppvInterface = (IMMNotificationClient *)this;
+        }
+        else
+        {
+            *ppvInterface = NULL;
+            return E_NOINTERFACE;
+        }
+        return S_OK;
+    }
+
+    // Callback method for endpoint-volume-change notifications.
+
+    HRESULT STDMETHODCALLTYPE OnNotify(PAUDIO_VOLUME_NOTIFICATION_DATA pNotify) override
+    {
+        NetworkPacket np(PACKET_TYPE_SYSTEMVOLUME);
+        np.set<int>(QStringLiteral("volume"), (int)(pNotify->fMasterVolume * 100));
+        np.set<bool>(QStringLiteral("muted"), pNotify->bMuted);
+        np.set<QString>(QStringLiteral("name"), name);
+        enclosing.sendPacket(np);
+
+        return S_OK;
+    }
+
+private:
+    SystemvolumePlugin &enclosing;
+    QString name;
+};
+
 class SystemvolumePlugin::CMMNotificationClient : public IMMNotificationClient
 {
 
-  public:
+public:
     CMMNotificationClient(SystemvolumePlugin &x) : enclosing(x), _cRef(1){};
 
     ~CMMNotificationClient(){};
@@ -85,14 +148,59 @@ class SystemvolumePlugin::CMMNotificationClient : public IMMNotificationClient
         return S_OK;
     }
 
+    struct RemovedDeviceThreadData {
+
+        QString qDeviceId;
+        SystemvolumePlugin* plugin;
+
+    };
+
+    static DWORD WINAPI releaseRemovedDevice(_In_ LPVOID lpParameter) {
+
+        auto* data = static_cast<RemovedDeviceThreadData*>(lpParameter);
+
+        if (!data->plugin->sinkList.empty())
+        {
+            auto idToNameIterator = data->plugin->idToNameMap.find(data->qDeviceId);
+            if (idToNameIterator == data->plugin->idToNameMap.end()) return 0;
+
+            QString& sinkName = idToNameIterator.value();
+
+            auto sinkListIterator = data->plugin->sinkList.find(sinkName);
+            if (sinkListIterator == data->plugin->sinkList.end()) return 0;
+
+            auto& sink = sinkListIterator.value();
+
+            sink.first->UnregisterControlChangeNotify(sink.second);
+            sink.first->Release();
+            sink.second->Release();
+
+            data->plugin->idToNameMap.remove(data->qDeviceId);
+            data->plugin->sinkList.remove(sinkName);
+        }
+
+        data->plugin->sendSinkList();
+
+        return 0;
+    }
+
     HRESULT STDMETHODCALLTYPE OnDeviceRemoved(LPCWSTR pwstrDeviceId) override
     {
-        enclosing.sendSinkList();
+        static RemovedDeviceThreadData data {};
+        data.qDeviceId = QString::fromWCharArray(pwstrDeviceId);
+        data.plugin = &enclosing;
+
+        DWORD threadId;
+        HANDLE threadHandle = CreateThread(NULL, 0, releaseRemovedDevice, &data, 0, &threadId);
+        CloseHandle(threadHandle);
+
         return S_OK;
     }
 
     HRESULT STDMETHODCALLTYPE OnDeviceStateChanged(LPCWSTR pwstrDeviceId, DWORD dwNewState) override
     {
+        if (dwNewState == DEVICE_STATE_UNPLUGGED) return OnDeviceRemoved(pwstrDeviceId);
+
         enclosing.sendSinkList();
         return S_OK;
     }
@@ -103,74 +211,11 @@ class SystemvolumePlugin::CMMNotificationClient : public IMMNotificationClient
         return S_OK;
     }
 
-  private:
+private:
     LONG _cRef;
     SystemvolumePlugin &enclosing;
 };
 
-class SystemvolumePlugin::CAudioEndpointVolumeCallback : public IAudioEndpointVolumeCallback
-{
-    LONG _cRef;
-
-  public:
-    CAudioEndpointVolumeCallback(SystemvolumePlugin &x, QString sinkName) : enclosing(x), name(sinkName), _cRef(1) {}
-    ~CAudioEndpointVolumeCallback(){};
-
-    // IUnknown methods -- AddRef, Release, and QueryInterface
-
-    ULONG STDMETHODCALLTYPE AddRef() override
-    {
-        return InterlockedIncrement(&_cRef);
-    }
-
-    ULONG STDMETHODCALLTYPE Release() override
-    {
-        ULONG ulRef = InterlockedDecrement(&_cRef);
-        if (ulRef == 0)
-        {
-            delete this;
-        }
-        return ulRef;
-    }
-
-    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, VOID **ppvInterface) override
-    {
-        if (IID_IUnknown == riid)
-        {
-            AddRef();
-            *ppvInterface = (IUnknown *)this;
-        }
-        else if (__uuidof(IMMNotificationClient) == riid)
-        {
-            AddRef();
-            *ppvInterface = (IMMNotificationClient *)this;
-        }
-        else
-        {
-            *ppvInterface = NULL;
-            return E_NOINTERFACE;
-        }
-        return S_OK;
-    }
-
-    // Callback method for endpoint-volume-change notifications.
-
-    HRESULT STDMETHODCALLTYPE OnNotify(PAUDIO_VOLUME_NOTIFICATION_DATA pNotify) override
-    {
-        NetworkPacket np(PACKET_TYPE_SYSTEMVOLUME);
-        np.set<int>(QStringLiteral("volume"), (int)(pNotify->fMasterVolume * 100));
-        np.set<bool>(QStringLiteral("muted"), pNotify->bMuted);
-        np.set<QString>(QStringLiteral("name"), name);
-        enclosing.sendPacket(np);
-
-        return S_OK;
-    }
-
-  private:
-    SystemvolumePlugin &enclosing;
-    QString name;
-};
-
 SystemvolumePlugin::SystemvolumePlugin(QObject *parent, const QVariantList &args)
     : KdeConnectPlugin(parent, args),
       sinkList()
@@ -204,19 +249,8 @@ bool SystemvolumePlugin::sendSinkList()
     QJsonDocument document;
     QJsonArray array;
 
-    HRESULT hr;
-    if (!sinkList.empty())
-    {
-        for (auto const &sink : sinkList)
-        {
-            sink.first->UnregisterControlChangeNotify(sink.second);
-            sink.first->Release();
-            sink.second->Release();
-        }
-        sinkList.clear();
-    }
     IMMDeviceCollection *devices = nullptr;
-    hr = deviceEnumerator->EnumAudioEndpoints(eRender, DEVICE_STATE_ACTIVE, &devices);
+    HRESULT hr = deviceEnumerator->EnumAudioEndpoints(eRender, DEVICE_STATE_ACTIVE, &devices);
 
     if (hr != S_OK)
     {
@@ -234,6 +268,7 @@ bool SystemvolumePlugin::sendSinkList()
         PROPVARIANT deviceProperty;
         QString name;
         QString desc;
+        LPWSTR deviceId;
         float volume;
         BOOL muted;
 
@@ -267,6 +302,8 @@ bool SystemvolumePlugin::sendSinkList()
             device->Release();
             continue;
         }
+
+        device->GetId(&deviceId);
         endpoint->GetMasterVolumeLevelScalar(&volume);
         endpoint->GetMute(&muted);
 
@@ -275,9 +312,14 @@ bool SystemvolumePlugin::sendSinkList()
         sinkObject.insert(QStringLiteral("maxVolume"), (qint64)100);
 
         // Register Callback
-        callback = new CAudioEndpointVolumeCallback(*this, name);
+        QString qDeviceId = QString::fromWCharArray(deviceId);
-        sinkList[name] = qMakePair(endpoint, callback);
+        if (!sinkList.contains(qDeviceId)) {
-        endpoint->RegisterControlChangeNotify(callback);
+            callback = new CAudioEndpointVolumeCallback(*this, name);
+            endpoint->RegisterControlChangeNotify(callback);
+            sinkList[name] = qMakePair(endpoint, callback);
+        }
+
+        idToNameMap[qDeviceId] = name;
 
         device->Release();
         array.append(sinkObject);

plugins/systemvolume/systemvolumeplugin-win.h

@@ -41,6 +41,7 @@ class Q_DECL_EXPORT SystemvolumePlugin : public KdeConnectPlugin
     IMMDeviceEnumerator* deviceEnumerator;
     CMMNotificationClient* deviceCallback;
     QMap<QString, QPair<IAudioEndpointVolume *, CAudioEndpointVolumeCallback *>> sinkList;
+    QMap<QString, QString> idToNameMap;
 
     bool sendSinkList();
 };