On a Linux terminal, there is a recursive lock issue when using both video playback and recording functions simultaneously

[a_Wu]

I encountered a recursive lock issue in the QT program on a Linux terminal while using both recording and video playback functions. After investigation, it was found to be a lock re-entry issue with the Pulsaiudio plugin on QT.
I use QAudioInput to obtain data for sound input (i.e. recording) and QAudioOutput to obtain data for sound output (i.e. video playback)

GDB infos:
(gdb) bt
#0 0x0000007fa5227978 in __pthread_mutex_lock_full () from /lib/aarch64-linux-gnu/libpthread.so.0
#1 0x0000007fa0d0e61c in pa_mutex_lock () from /usr/lib/aarch64-linux-gnu/pulseaudio/libpulsecommon-12.2.so
#2 0x0000007f9c43924c in ?? () from /usr/local/bin/audio/libqtmedia_pulse.so
#3 0x0000007f9c43985c in ?? () from /usr/local/bin/audio/libqtmedia_pulse.so
#4 0x0000007fa48b5eec in ?? () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#5 0x0000007fa48ba718 in QTimer::timeout(QTimer::QPrivateSignal) () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#6 0x0000007fa48ade04 in QObject::event(QEvent*) () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#7 0x0000007fa56d4d8c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/aarch64-linux-gnu/libQt5Widgets.so.5
#8 0x0000007fa56db72c in QApplication::notify(QObject*, QEvent*) () from /usr/lib/aarch64-linux-gnu/libQt5Widgets.so.5
#9 0x0000007fa48807c8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#10 0x0000007fa48d8350 in QTimerInfoList::activateTimers() () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#11 0x0000007fa48d8b98 in ?? () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#12 0x0000007fa7ebe674 in g_main_context_dispatch () from /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#13 0x0000007fa7ebe8e8 in ?? () from /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#14 0x0000007fa7ebe984 in g_main_context_iteration () from /usr/lib/aarch64-linux-gnu/libglib-2.0.so.0
#15 0x0000007fa48d8eac in QEventDispatcherGlib::processEvents(QFlagsQEventLoop::ProcessEventsFlag) () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#16 0x0000007fa487f0f8 in QEventLoop::exec(QFlagsQEventLoop::ProcessEventsFlag) () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#17 0x0000007fa4887968 in QCoreApplication::exec() () from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#18 0x0000000000484f9c in main ()

(gdb) p (pthread_mutex_t)$x0
$2 = pthread_mutex_t = {Type = Recursive, Status = Acquired, possibly with waiters, Owner ID = 24138, Robust = No, Shared = No, Protocol = Priority inherit, Times acquired by the owner = 13662}

The following is the QT source code that may be related to the issue:

class QPulseAudioEngine : public QObject
{
    Q_OBJECT

public:
    QPulseAudioEngine(QObject *parent = 0);
    ~QPulseAudioEngine();

    static QPulseAudioEngine *instance();
    pa_threaded_mainloop *mainloop() { return m_mainLoop; }
    pa_context *context() { return m_context; }

    inline void lock()
    {
        if (m_mainLoop)
            pa_threaded_mainloop_lock(m_mainLoop);
    }

    inline void unlock()
    {
        if (m_mainLoop)
            pa_threaded_mainloop_unlock(m_mainLoop);
    }

    inline void wait(pa_operation *op)
    {
        while (m_mainLoop && pa_operation_get_state(op) == PA_OPERATION_RUNNING)
            pa_threaded_mainloop_wait(m_mainLoop);
    }

Has anyone encountered a similar situation before?

[SGaist]

Hi and welcome to devnet,

Which version of Qt 5 is it ?
Please note that Qt 5 has reached end of life a long time ago. You should consider moving to Qt 6.

[JoeCFD]

@a_Wu use raw gstreamer pipeline code and drop Qt multimedia module.

[a_Wu]

Hello! Version is 5.15.2
I found that there is another dependency library that may be using the same plugin Pulselink as QT's QAudioInput/QAudioOutput
I have considered using QT 6, but I would rather determine what caused it
Thank you.

[SGaist]

One thing you can test is the latest version of the Qt 5.15 series to see if it behaves in the same manner.

[a_Wu]

Alright, thank you for your suggestion. I'll give it a try