QT6 multimedia module crashes on iOS

After several hours of playing sounds my iOS app crashes and the QT Creator displays the following stack trace:

1 caulk::thread::join() (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/caulk.framework/caulk 0x7fff49a06293
2 std::__shared_ptr_emplace<AURemoteIO::IOThread, std::allocator<AURemoteIO::IOThread>>::__on_zero_shared() (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438a7469
3 AURemoteIO::Stop() (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438a58d3
4 ausdk::AUMethodStop(void *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438f3529
5 QDarwinAudioSink::audioDeviceStop() qdarwinaudiosink.mm 619 0x10ffa7afd
6 QDarwinAudioSink::audioDeviceIdle() qdarwinaudiosink.mm 629 0x10ffa7b68
7 QDarwinAudioSink::renderCallback(void *, unsigned int *, AudioTimeStamp const *, unsigned int, unsigned int, AudioBufferList *) qdarwinaudiosink.mm 446 0x10ffa7ab7
8 ausdk::AUInputElement::PullInput(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438f12d2
9 AUInputFormatConverter2::InputProc(OpaqueAudioConverter *, unsigned int *, AudioBufferList *, AudioStreamPacketDescription * *, void *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff4382cf27
10 acv1::AudioConverterChain::CallInputProc(unsigned int) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff30323840
11 acv1::AudioConverterChain::FillBufferFromInputProc(unsigned int *, CADeprecated::CABufferList *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff3032467f
12 acv1::BufferedAudioConverter::GetInputBytes(unsigned int, unsigned int&, CADeprecated::CABufferList const *&) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff3045c7bd
13 acv1::CBRConverter::RenderOutput(CADeprecated::CABufferList *, unsigned int, unsigned int&, AudioStreamPacketDescription *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff303091bc
14 acv1::BufferedAudioConverter::FillBuffer(unsigned int&, AudioBufferList&, AudioStreamPacketDescription *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff3045c589
15 acv1::AudioConverterChain::RenderOutput(CADeprecated::CABufferList *, unsigned int, unsigned int&, AudioStreamPacketDescription *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff303235bb
16 acv1::BufferedAudioConverter::FillBuffer(unsigned int&, AudioBufferList&, AudioStreamPacketDescription *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff3045c589
17 acv1::_AudioConverterFillComplexBuffer(OpaqueAudioConverter *, int ( *)(OpaqueAudioConverter *, unsigned int *, AudioBufferList *, AudioStreamPacketDescription * *, void *), void *, unsigned int *, AudioBufferList *, AudioStreamPacketDescription *, AudioStreamPacketDependencyInfo *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff30491df6
18 AudioConverterFillComplexBuffer (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AudioToolboxCore.framework/AudioToolboxCore 0x7fff303a3680
19 AUConverterBase::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff4382b617
20 AURemoteIO::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438a4317
21 ausdk::AUBase::DoRender(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int, AudioBufferList&) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438f06a9
22 AURemoteIO::PerformIO(unsigned int, unsigned int, unsigned int, AudioTimeStamp const&, AudioTimeStamp const&, AudioBufferList const *, AudioBufferList *, unsigned int&) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438af7df
23 _XPerformIO (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438e9817
24 mshMIGPerform (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libAudioToolboxUtility.dylib 0x7fff2e30936a
25 MSHMIGDispatchMessage (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libAudioToolboxUtility.dylib 0x7fff2e309759
26 void * caulk::thread_proxy<std::tuple<caulk::thread::attributes, AURemoteIO::IOThread::IOThread(AURemoteIO&, caulk::thread::attributes const&, caulk::mach::os_workgroup const&)::'lambda'(), std::tuple<>>>(void *) (x86_64) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/AudioToolbox.framework/libEmbeddedSystemAUs.dylib 0x7fff438a7200
27 _pthread_start (x86_64) /usr/lib/system/libsystem_pthread.dylib 0x7fff6da2b8fc
28 thread_start (x86_64) /usr/lib/system/libsystem_pthread.dylib 0x7fff6da27443

QT Creator screenshot:

unfortunately, QT Creator does not display the values of the variables.

My application output:

Starting a sound. . Main thread: true
Starting a sound. . Main thread: true
Starting a sound. . Main thread: true
Starting a sound. . Main thread: true
Stopping a loop. Main thread: true
Stopping a loop. Main thread: true
Starting a sound. . Main thread: true
Stopping a sound. Main thread: true
Starting a sound. . Main thread: true
Starting a sound. . Main thread: true
Stopping a loop. Main thread: true
Stopping a loop. Main thread: true
Starting a loop . Main thread: true

it means that QAudioSink::stateChanged callback was called 2 times with QAudio::IdleState:

void QtSoundDevice::onStateChanged(QAudio::State state)
{
    std::lock_guard lock(playMutex);

    switch (state)
    {
    case QAudio::ActiveState:
        //qDebug() << "QAudio::ActiveState";
        break;

    case QAudio::SuspendedState:
        //qDebug() << "QAudio::ActiveState";
        break;

    case QAudio::StoppedState:
        //qDebug() << "QAudio::StoppedState";
        break;

    case QAudio::IdleState:

        //qDebug() << "QAudio::IdleState, loopWithStateChanged = " << loopWithStateChanged;

        if (loopWithStateChanged)
        {
            qDebug() << "Continuing a loop." << " Main thread: " << qtil::OnMainThread();

            //looks like we need to call start() at this point, because others do not take an effect
            //audioOutput.suspend();
            //audioOutput.reset();
            //audioOutput.resume();

            SeekToStart();

            //Workaround of QTBUG-99893 QAudioSink::start does not play sound if called from its stateChanged signal handler on MacOS and iOS
#ifdef __APPLE__
            audioOutput.reset();
#endif

            audioOutput.start(pDevice);
        }
        else
        {
            //On MacOS QtSoundDevice::onStateChanged handler is called multiple times with QAudio::IdleState parameter
            //when the sound finishes to play.
            if (IsStarted())
            {
                qDebug() << "Stopping a loop." << " Main thread: " << qtil::OnMainThread();

                pDevice = nullptr;

                ClearFlags();

                emit done();
            }
            else
            {
#ifndef __APPLE__
                assert(false);
#endif
            }
        }

        break;
    }
}

and then I called QAudioSink::start:

void QtSoundDevice::CommonStart(QIODevice * p_device, float, bool loop)
{
    qDebug() << (loop ? "Starting a loop" : "Starting a sound.") << ". Main thread: " << qtil::OnMainThread();

    std::lock_guard lock(playMutex);

    //sound restarts without stop() call
    //audioOutput.stop();

    audioOutput.reset();

    pDevice = p_device;

    SeekToStart();

    ClearFlags();

    loopWithStateChanged = loop;

    audioOutput.start(pDevice);
}

as you may have guessed, audioOutput is a variable of type QAudioSink declared here:

class QtSoundDevice : public QObject, public awl::quick_link
{
    Q_OBJECT

public:

    //skipped some code here ...

    bool IsStarted() const
    {
        return pDevice != nullptr;
    }

signals:

    void done();

private slots:

    void onStateChanged(QAudio::State);

private:

    void SeekToStart()
    {
        pDevice->seek(44); // skip wav header
    }

    void ClearFlags()
    {
        loopWithStateChanged = false;
    }

    QIODevice* pDevice = nullptr;

    QAudioSink audioOutput;

    bool loopWithStateChanged;
};

The conclusion is that using QT multimedia can cause a severe depression of the central nervous system.

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