audio: retain WASAPI clients only after initialization (#807)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #782 

## Description of change

This addresses an issue only seen on Linux + WINE.

Defer retaining WASAPI clients until `Initialize` succeeds.

Before this PR, temporary clients created during DirectShow device
capability probing were retained as active audio clients, causing
Wine/Linux crashes in DDR and popn.

Also covers IAudioClient3, dummy, ASIO, WaveOut, and null-device
initialization paths, for consistency.

## Testing
WIP

src/spice2x/hooks/audio/audio.cpp

@@ -53,9 +53,39 @@ namespace hooks::audio {
     std::string ASIO_DRIVER_NAME = "";
     bool ASIO_FORCE_UNLOAD_ON_STOP = false;
 
-    // private globals
-    IAudioClient *CLIENT = nullptr;
     std::mutex INITIALIZE_LOCK; // for asio
+
+    IAudioClient *CLIENT = nullptr;
+    static std::mutex CLIENT_LOCK;
+    static bool CLIENT_STOPPING = false;
+
+    void set_active_client(IAudioClient *client, const char *source) {
+        IAudioClient *previous_client = nullptr;
+        {
+            std::lock_guard lock(CLIENT_LOCK);
+
+            if (CLIENT_STOPPING || CLIENT == client) {
+                return;
+            }
+            if (client) {
+                client->AddRef();
+            }
+
+            previous_client = CLIENT;
+            CLIENT = client;
+        }
+
+        if (previous_client) {
+            previous_client->Release();
+        }
+
+        if (client) {
+            log_info(
+                "audio",
+                "active client selected by {} after successful initialization",
+                source);
+        }
+    }
 }
 
 static HRESULT STDAPICALLTYPE CoCreateInstance_hook(
@@ -133,11 +163,17 @@ namespace hooks::audio {
 
     void stop() {
         log_info("audio", "stopping");
-        if (CLIENT) {
+        IAudioClient *client = nullptr;
-            CLIENT->Stop();
+        {
-            CLIENT->Release();
+            std::lock_guard lock(CLIENT_LOCK);
+            CLIENT_STOPPING = true;
+            client = CLIENT;
             CLIENT = nullptr;
         }
+        if (client) {
+            client->Stop();
+            client->Release();
+        }
         stop_low_latency();
 
         // release the ASIO drivers we kept pinned for the process lifetime now that we are

src/spice2x/hooks/audio/audio_private.h

@@ -14,4 +14,6 @@ namespace hooks::audio {
     extern std::mutex INITIALIZE_LOCK;
     extern bool VOLUME_HOOK_ENABLED;
     extern LowLatencyAudioClient *LOW_LATENCY_CLIENT;
+
+    void set_active_client(IAudioClient *client, const char *source);
 }

src/spice2x/hooks/audio/backends/mmdevice/device.cpp

@@ -95,11 +95,6 @@ HRESULT STDMETHODCALLTYPE WrappedIMMDevice::Activate(
         }
         std::lock_guard initialize_guard(hooks::audio::INITIALIZE_LOCK, std::adopt_lock);
 
-        // release old audio client if initialized
-        if (hooks::audio::CLIENT) {
-            hooks::audio::CLIENT->Release();
-        }
-
         IAudioClient *client = nullptr;
         if (iid == IID_IAudioClient) {
             client = wrap_audio_client(reinterpret_cast<IAudioClient *>(*ppInterface));
@@ -107,9 +102,6 @@ HRESULT STDMETHODCALLTYPE WrappedIMMDevice::Activate(
             client = wrap_audio_client3(reinterpret_cast<IAudioClient3 *>(*ppInterface));
         }
         *ppInterface = client;
-        // persist the audio client
-        hooks::audio::CLIENT = client;
-        hooks::audio::CLIENT->AddRef();
 
     } else if (iid == __uuidof(IAudioEndpointVolume) && hooks::audio::VOLUME_HOOK_ENABLED) {
         *ppInterface = new WrappedIAudioEndpointVolume(reinterpret_cast<IAudioEndpointVolume *>(*ppInterface));

src/spice2x/hooks/audio/backends/mmdevice/null_device.cpp

@@ -153,19 +153,9 @@ HRESULT STDMETHODCALLTYPE NullMMDevice::Activate(
     log_info("audio::null", "NullMMDevice::Activate {}", guid2s(iid));
 
     if (iid == IID_IAudioClient) {
-
-        // release any previously persisted client
-        if (hooks::audio::CLIENT != nullptr) {
-            hooks::audio::CLIENT->Release();
-        }
-
         auto *client = static_cast<IAudioClient *>(new DummyIAudioClient(new NullDiscardBackend()));
         *ppInterface = client;
 
-        // persist the audio client
-        hooks::audio::CLIENT = client;
-        hooks::audio::CLIENT->AddRef();
-
         return S_OK;
     }
 

src/spice2x/hooks/audio/backends/wasapi/audio_client.cpp

@@ -302,6 +302,7 @@ HRESULT STDMETHODCALLTYPE WrappedIAudioClient::Initialize(
                 device_format->nChannels * (device_format->wBitsPerSample / 8));
     }
 
+    hooks::audio::set_active_client(this, "WrappedIAudioClient::Initialize");
     return ret;
 }
 HRESULT STDMETHODCALLTYPE WrappedIAudioClient::GetBufferSize(UINT32 *pNumBufferFrames) {
@@ -651,5 +652,6 @@ HRESULT STDMETHODCALLTYPE WrappedIAudioClient::InitializeSharedAudioStream(
     log_info("audio::wasapi", "IAudioClient3::InitializeSharedAudioStream success, hr={}", FMT_HRESULT(ret));
     copy_wave_format(&hooks::audio::FORMAT, pFormat);
     copy_wave_format(&this->device_format, pFormat);
+    hooks::audio::set_active_client(this, "WrappedIAudioClient::InitializeSharedAudioStream");
     return ret;
 }

src/spice2x/hooks/audio/backends/wasapi/dummy_audio_client.cpp

@@ -75,13 +75,17 @@ HRESULT STDMETHODCALLTYPE DummyIAudioClient::Initialize(
     log_info("audio::wasapi", "IAudioClient::Initialize hook hit");
     print_format(ShareMode, StreamFlags, hnsBufferDuration, hnsPeriodicity, pFormat);
 
-    CHECK_RESULT(this->backend->on_initialize(
+    HRESULT ret = this->backend->on_initialize(
         &ShareMode,
         &StreamFlags,
         &hnsBufferDuration,
         &hnsPeriodicity,
         pFormat,
-        AudioSessionGuid));
+        AudioSessionGuid);
+    if (SUCCEEDED(ret)) {
+        hooks::audio::set_active_client(this, "DummyIAudioClient::Initialize");
+    }
+    CHECK_RESULT(ret);
 }
 HRESULT STDMETHODCALLTYPE DummyIAudioClient::GetBufferSize(UINT32 *pNumBufferFrames) {
     static std::once_flag printed;