[gstreamer-bugs] [Bug 614545] New: gstalsasrc mixer task spins 100% CPU when USB sound card is removed

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=614545
  GStreamer | gst-plugins-base | 0.10.28

           Summary: gstalsasrc mixer task spins 100% CPU when USB sound
                    card is removed
    Classification: Desktop
           Product: GStreamer
           Version: 0.10.28
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: sam.revitch at gmail.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


I'm trying to use GStreamer 0.10.28 to play audio from a USB FM radio to the
desktop sound card.  The FM radio provides a USB audio class interface
supported by the ALSA snd-usb-audio driver.  I can use the following command to
set up a pipeline to listen to the radio:

gst-launch-0.10 alsasrc device="plughw:1" \! audioconvert \! alsasink

Unfortunately, if the sound card is unplugged while such a pipeline is running,
attempts to stop the pipeline will generate the following type of console
message:

** (gst-launch-0.10:15447): CRITICAL **: Resources for ring buffer 0x16ec1b0
still acquired

If this is done from an application which remains running after the pipeline is
stopped, it will be left with a thread spinning at 100% CPU.

It would appear that the ring buffer is not being released because the alsasrc
plugin's gst_alsasrc_unprepare() function is returning failure.  This is
apparently caused by ENODEV errors from snd_pcm_drop() and snd_pcm_hw_free(),
which it may benefit from ignoring.

Secondarily, the task_monitor_alsa() task function is calling poll() on a file
descriptor that has become bad, and poll() isn't waiting.  The task is not
being shut down because the ring buffer release failed, and the task function
contains no logic to throttle itself or shut itself down in this case, so it
spins at 100% CPU.

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