win-wasapi: Handle changes to the default monitoring device

Splits the WASAPINotify class out of win-wasapi.cpp and makes it a
shared object in the plugin, then also creates a callback to reset
audio monitoring if the default output device changes.

plugins/win-wasapi/wasapi-notify.cpp

@@ -0,0 +1,121 @@
+#include "wasapi-notify.hpp"
+
+#include <windows.h>
+#include <assert.h>
+
+#include <util/threading.h>
+
+class NotificationClient : public IMMNotificationClient {
+	volatile long refs = 1;
+	WASAPINotifyDefaultDeviceChangedCallback cb;
+
+public:
+	NotificationClient(WASAPINotifyDefaultDeviceChangedCallback cb) : cb(cb)
+	{
+		assert(cb);
+	}
+
+	STDMETHODIMP_(ULONG) AddRef()
+	{
+		return (ULONG)os_atomic_inc_long(&refs);
+	}
+
+	STDMETHODIMP_(ULONG) STDMETHODCALLTYPE Release()
+	{
+		long val = os_atomic_dec_long(&refs);
+		if (val == 0)
+			delete this;
+		return (ULONG)val;
+	}
+
+	STDMETHODIMP QueryInterface(REFIID riid, void **ptr)
+	{
+		if (riid == IID_IUnknown) {
+			*ptr = (IUnknown *)this;
+		} else if (riid == __uuidof(IMMNotificationClient)) {
+			*ptr = (IMMNotificationClient *)this;
+		} else {
+			*ptr = nullptr;
+			return E_NOINTERFACE;
+		}
+
+		InterlockedIncrement(&refs);
+		return S_OK;
+	}
+
+	STDMETHODIMP OnDeviceAdded(LPCWSTR) { return S_OK; }
+
+	STDMETHODIMP OnDeviceRemoved(LPCWSTR) { return S_OK; }
+
+	STDMETHODIMP OnDeviceStateChanged(LPCWSTR, DWORD) { return S_OK; }
+
+	STDMETHODIMP OnPropertyValueChanged(LPCWSTR, const PROPERTYKEY)
+	{
+		return S_OK;
+	}
+
+	STDMETHODIMP OnDefaultDeviceChanged(EDataFlow flow, ERole role,
+					    LPCWSTR id)
+	{
+		if (cb && id)
+			cb(flow, role, id);
+
+		return S_OK;
+	}
+};
+
+WASAPINotify::WASAPINotify()
+{
+	HRESULT res = CoCreateInstance(__uuidof(MMDeviceEnumerator), nullptr,
+				       CLSCTX_ALL,
+				       __uuidof(IMMDeviceEnumerator),
+				       (LPVOID *)enumerator.Assign());
+	if (SUCCEEDED(res)) {
+		notificationClient = new NotificationClient(
+			std::bind(&WASAPINotify::OnDefaultDeviceChanged, this,
+				  std::placeholders::_1, std::placeholders::_2,
+				  std::placeholders::_3));
+		enumerator->RegisterEndpointNotificationCallback(
+			notificationClient);
+	} else {
+		enumerator.Clear();
+	}
+}
+
+WASAPINotify::~WASAPINotify()
+{
+	if (enumerator) {
+		enumerator->UnregisterEndpointNotificationCallback(
+			notificationClient);
+		enumerator.Clear();
+	}
+
+	notificationClient.Clear();
+}
+
+void WASAPINotify::AddDefaultDeviceChangedCallback(
+	void *handle, WASAPINotifyDefaultDeviceChangedCallback cb)
+{
+	if (!handle)
+		return;
+
+	std::lock_guard<std::mutex> l(mutex);
+	defaultDeviceChangedCallbacks[handle] = cb;
+}
+
+void WASAPINotify::RemoveDefaultDeviceChangedCallback(void *handle)
+{
+	if (!handle)
+		return;
+
+	std::lock_guard<std::mutex> l(mutex);
+	defaultDeviceChangedCallbacks.erase(handle);
+}
+
+void WASAPINotify::OnDefaultDeviceChanged(EDataFlow flow, ERole role,
+					  LPCWSTR id)
+{
+	std::lock_guard<std::mutex> l(mutex);
+	for (const auto &cb : defaultDeviceChangedCallbacks)
+		cb.second(flow, role, id);
+}