Fix QAudioSink::stateChanged signal emitting

1. Ensure sending the signal from QAudioSink's thread.
2. QAudioSink backends emit signals from different threads what may
   cause a case when queued events are outdated and should be filtered.

The patch has been decoupled from the big change
codereview.qt-project.org/c/qt/qtmultimedia/+/474485

Task-number: QTBUG-113194
Pick-to: 6.5
Change-Id: I68002c243dea814c4309b14b1fbd7b618392ab11
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/multimedia/audio/qaudiosink.cpp b/src/multimedia/audio/qaudiosink.cpp
index 4bcf85f9c..e63fa5fc2 100644
--- a/src/multimedia/audio/qaudiosink.cpp
+++ b/src/multimedia/audio/qaudiosink.cpp
@@ -89,7 +89,12 @@ QAudioSink::QAudioSink(const QAudioDevice &audioDevice, const QAudioFormat &form
 {
     d = QPlatformMediaDevices::instance()->audioOutputDevice(format, audioDevice, parent);
     if (d)
-        connect(d, SIGNAL(stateChanged(QAudio::State)), SIGNAL(stateChanged(QAudio::State)));
+        connect(d, &QPlatformAudioSink::stateChanged, this, [this](QAudio::State state) {
+            // if the signal has been emitted from another thread,
+            // the state may be already changed by main one
+            if (state == d->state())
+                emit stateChanged(state);
+        });
     else
         qWarning() << ("No audio device detected");
 }