Created attachment 124934 [details]
gdb on the core file

I had done the steps outlined in comment 3 to bug 99717, except more
of it and with some fat-fingering along the way.  Sometime while I was
typing those STR, the program ended.  

Notably, the terminal output did *not* show the assertion.  The
assertion in GtkYieldMutex::ThreadsLeave() at gtkinst.cxx:312 reads

    assert(yieldCount == 0);

I apologize for the vagueness of this report.

These may be of interest in the attached terminal output ...

    line  gdb command
    ----  -------------------------------
      34  info threads
      43  backtrace
     123  thread apply all backtrace full