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[Michi Henning <michi.henning@xxxxxxxxxxxxx>]

In an attempt to diagnose this more, I ran the vs-thumb sub-processes
with strace and still managed to reproduce the problem.

Here is the code snippet that runs when we don't hear back from a sub-
process within ten seconds. (Please forgive the filthy code; this is the
result of endless hacking around trying to narrow down the problem.)

    qDebug() << "timeout, state =" << process_.state();
    if (process_.state() != QProcess::NotRunning)
    {
        qDebug() << "killing process" << process_.pid();
        int rc = kill(process_.processId(), SIGKILL);
        assert(rc == 0);
        //process_.kill();
    }
    int status;
    qDebug() << "calling waitpid for process" << process_.pid();
    int rc = waitpid(process_.pid(), &status, 0);
    qDebug() << "waitpid for process" << process_.pid() << "returned";
    qDebug() << "waitpid() returned" << rc;
    error_ = exe_path_.toStdString() + " (pid " + to_string(process_.pid()) + ") did not return after " +
             to_string(timeout_ms_) + " milliseconds";

So, we call kill(), immediately followed by waitpid(). Here is the trace
I see when the problem happens:

thumbnailer-service: [02:28:39.385] timeout, state = 2
thumbnailer-service: [02:28:39.385] killing process 16965
thumbnailer-service: [02:28:39.386] calling waitpid for process 16965
Changing to state PAUSED
Changing to state PAUSED
thumbnailer-service: [02:29:09.395] waitpid for process 16965 returned
thumbnailer-service: [02:29:09.396] waitpid() returned 16965

(Ignore the two "Changing state" messages; these are from other vs-thumb
processes that are still running.)

Note the time stamps: we sent the kill at 28:39, but waitpid doesn't
return until 30 seconds later.

While things are hanging like this, the process sits as a zombie in the
process table.

I've attached the strace log. The last line shows that the process was
killed (also 30 seconds late), at the time waitpid() returned.

** Attachment added: "vs-thumb.strace.16965"
   https://bugs.launchpad.net/ubuntu/+source/gstreamer1.0/+bug/1466273/+attachment/4420215/+files/vs-thumb.strace.16965

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https://bugs.launchpad.net/bugs/1466273

Title:
  gstreamer fails intermittently

Status in Thumbnail generator for all kinds of files:
  New
Status in gstreamer package in Ubuntu:
  New
Status in gstreamer1.0 package in Ubuntu:
  New

Bug description:
  gstreamer occasionally fails to extract a thumbnail from a video file.
  It's clearly a race condition because, almost all of the time, it
  succeeds. To reproduce:

  Check out the thumbnailer/devel branch at r217 and build it. Then:

  cd build/src/vs-thumb

  ./vs-thumb fd://0 ./x.jpg <../../../tests/media/testvideo.ogg

  Point a browser at the generated x.jpg file and check that the image
  was extracted correctly.

  Now run

  while ./vs-thumb fd://0 ./x.jpg <../../../tests/media/testvideo.ogg ;
  do :; done

  Within maybe a hundred iterations or so, I get:

  Error creating thumbnail: ThumbnailExtractor: change_state(): reading
  async messages: GStreamer error: negotiation problem.

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