From 4b2778f02dbc932c90a673fcf95f98c2df923b54 Mon Sep 17 00:00:00 2001
From: Ken Cooke <ken@highfidelity.io>
Date: Sat, 20 Aug 2016 12:22:47 -0700
Subject: [PATCH] Re-implement the continuous detection of device changes for
 all platforms, using a background thread. This prevents the glitches caused
 by calling checkDevices() on the audio processing thread.

---
 libraries/audio-client/src/AudioClient.cpp | 41 +++++++++++++++++-----
 libraries/audio-client/src/AudioClient.h   |  3 +-
 2 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/libraries/audio-client/src/AudioClient.cpp b/libraries/audio-client/src/AudioClient.cpp
index cf43730258..8f8d17d4ad 100644
--- a/libraries/audio-client/src/AudioClient.cpp
+++ b/libraries/audio-client/src/AudioClient.cpp
@@ -67,6 +67,33 @@ Setting::Handle<int> windowSecondsForDesiredReduction("windowSecondsForDesiredRe
                                                       DEFAULT_WINDOW_SECONDS_FOR_DESIRED_REDUCTION);
 Setting::Handle<bool> repetitionWithFade("repetitionWithFade", DEFAULT_REPETITION_WITH_FADE);
 
+// background thread that continuously polls for device changes
+class CheckDevicesThread : public QThread {
+public:
+    const unsigned long DEVICE_CHECK_INTERVAL_MSECS = 2 * 1000;
+
+    CheckDevicesThread(AudioClient* audioClient)
+        : _audioClient(audioClient) {
+
+        connect(qApp, &QCoreApplication::aboutToQuit, [this] {
+            _quit = true;
+        });
+    }
+
+    void run() override {
+        while (!_quit) {
+
+            //qDebug() << "Checking for audio device changes...";
+            _audioClient->checkDevices();
+
+            QThread::msleep(DEVICE_CHECK_INTERVAL_MSECS);
+        }
+    }
+
+    AudioClient* _audioClient { nullptr };
+    bool _quit { false };
+};
+
 AudioClient::AudioClient() :
     AbstractAudioInterface(),
     _audioInput(NULL),
@@ -121,14 +148,14 @@ AudioClient::AudioClient() :
 
     connect(&_receivedAudioStream, &InboundAudioStream::mismatchedAudioCodec, this, &AudioClient::handleMismatchAudioFormat);
 
-
     _inputDevices = getDeviceNames(QAudio::AudioInput);
     _outputDevices = getDeviceNames(QAudio::AudioOutput);
 
-    const qint64 DEVICE_CHECK_INTERVAL_MSECS = 2 * 1000;
-    QTimer* updateTimer = new QTimer(this);
-    connect(updateTimer, &QTimer::timeout, this, &AudioClient::checkDevices);
-    updateTimer->start(DEVICE_CHECK_INTERVAL_MSECS);
+    // start a thread to detect any device changes
+    QThread* checkDevicesThread = new CheckDevicesThread(this);
+    checkDevicesThread->setObjectName("CheckDevices Thread");
+    checkDevicesThread->setPriority(QThread::LowPriority);
+    checkDevicesThread->start();
 
     configureReverb();
 
@@ -1349,9 +1376,6 @@ qint64 AudioClient::AudioOutputIODevice::readData(char * data, qint64 maxSize) {
 }
 
 void AudioClient::checkDevices() {
-#   if defined(Q_OS_LINUX) || defined (Q_OS_WIN)
-    // on Windows and Linux, this causes dropouts in the audio stream
-#   else
     QVector<QString> inputDevices = getDeviceNames(QAudio::AudioInput);
     QVector<QString> outputDevices = getDeviceNames(QAudio::AudioOutput);
 
@@ -1361,7 +1385,6 @@ void AudioClient::checkDevices() {
 
         emit deviceChanged();
     }
-#   endif
 }
 
 void AudioClient::loadSettings() {
diff --git a/libraries/audio-client/src/AudioClient.h b/libraries/audio-client/src/AudioClient.h
index 9db2cc0489..1ee4b92a0c 100644
--- a/libraries/audio-client/src/AudioClient.h
+++ b/libraries/audio-client/src/AudioClient.h
@@ -139,6 +139,8 @@ public:
     
     QVector<AudioInjector*>& getActiveLocalAudioInjectors() { return _activeLocalAudioInjectors; }
 
+    void checkDevices();
+
     static const float CALLBACK_ACCELERATOR_RATIO;
 
 #ifdef Q_OS_WIN
@@ -312,7 +314,6 @@ private:
 
     QVector<QString> _inputDevices;
     QVector<QString> _outputDevices;
-    void checkDevices();
 
     bool _hasReceivedFirstPacket = false;