What's the purpose of default pa_mainloop thread in QT?

Question

I write a helloworld of QAudioOutput by QT5.15.2 like this:

`

#include <QCoreApplication>
#include <QAudioOutput>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QAudioOutput *m_pAudioOutput = nullptr;
    QIODevice *m_pAudioDevice = nullptr;

    QAudioDeviceInfo info(QAudioDeviceInfo::defaultOutputDevice());
    if (info.deviceName().isEmpty())
    {
        qInfo() << "No default auido output device available!";
        return 0;
    }

    return a.exec();
}

` Then run it on Debian 10.9 x64, and gdb attach to the process, show threads:

`

(gdb) info threads
  Id   Target Id                                        Frame
* 1    Thread 0x7f62b082d8c0 (LWP 12787) "HelloQtAudio" 0x00007f62b2753589 in __GI___poll (fds=0x5562098188a0, nfds=1,
    timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
  2    Thread 0x7f62b0513700 (LWP 12788) "threaded-ml"  0x00007f62b2753589 in __GI___poll (fds=0x7f62a4007030, nfds=3,
    timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f62b0513700 (LWP 12788))]
#0  0x00007f62b2753589 in __GI___poll (fds=0x7f62a4007030, nfds=3, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
29  in ../sysdeps/unix/sysv/linux/poll.c
(gdb) bt
#0  0x00007f62b2753589 in __GI___poll (fds=0x7f62a4007030, nfds=3, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007f62b263f131 in ?? () from /lib/x86_64-linux-gnu/libpulse.so.0
#2  0x00007f62b26309a0 in pa_mainloop_poll () from /lib/x86_64-linux-gnu/libpulse.so.0
#3  0x00007f62b2630fee in pa_mainloop_iterate () from /lib/x86_64-linux-gnu/libpulse.so.0
#4  0x00007f62b26310a0 in pa_mainloop_run () from /lib/x86_64-linux-gnu/libpulse.so.0
#5  0x00007f62b263f079 in ?? () from /lib/x86_64-linux-gnu/libpulse.so.0
#6  0x00007f62b22d3468 in ?? () from /usr/lib/x86_64-linux-gnu/pulseaudio/libpulsecommon-12.2.so
#7  0x00007f62b2b4ffa3 in start_thread (arg=<optimized out>) at pthread_create.c:486
#8  0x00007f62b275deff in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb)

`

I do nothing in my main, why does QT starts a pa_mainloop_run thread? Is it usable? Then if call m_pAudioOutput->start(), it start another same thread, does it means a thread pool increasing workers?

I'm trying to resolve an alsa underrun bug in audio playback.

What's the purpose of default pa_mainloop thread in QT?

0 Answers0