"QThread: Destroyed while thread is still running" printed on shutdown

[Gerry Boland]

Sending SIGTERM to unity8 causes this slightly concerning error message to be printed:

QThread: Destroyed while thread is still running

Going a quick dig, I see it came from DashCommunicator:

(gdb) break src/corelib/thread/qthread.cpp:417
Breakpoint 1 at 0x7fafce6bd935: file thread/qthread.cpp, line 417.
(gdb) cont
Continuing.
^C
Program received signal SIGINT, Interrupt.
0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
81 in ../sysdeps/unix/syscall-template.S
(gdb) signal SIGTERM
Continuing with signal SIGTERM.

Breakpoint 1, QThread::~QThread (this=0x203d1f0, __in_chrg=<optimized out>) at thread/qthread.cpp:417
417 thread/qthread.cpp: No such file or directory.
(gdb) t
[Current thread is 1 (Thread 0x7fafcfcaf800 (LWP 19100))]
(gdb) info threads
  Id Target Id Frame
  23 Thread 0x7fafc178b700 (LWP 19101) "unity8" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  22 Thread 0x7fafc0f8a700 (LWP 19102) "unity8" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  21 Thread 0x7fafbbfff700 (LWP 19103) "MirServerThread" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  20 Thread 0x7fafbb7fe700 (LWP 19104) "RPC Thread" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  19 Thread 0x7fafb951d700 (LWP 19105) "MirServerThread" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  18 Thread 0x7fafb8ac0700 (LWP 19106) "Input dispatch" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  17 Thread 0x7fafaa0db700 (LWP 19107) "Mir/Snapshot" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  16 Thread 0x7fafa98da700 (LWP 19108) "Mir/IPC" 0x00007fafcddc54f3 in epoll_wait () at ../sysdeps/unix/syscall-template.S:81
  15 Thread 0x7fafa90d9700 (LWP 19109) "Mir/IPC" 0x00007fafcddc54f3 in epoll_wait () at ../sysdeps/unix/syscall-template.S:81
  14 Thread 0x7faf9db6d700 (LWP 19110) "QQmlThread" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  13 Thread 0x7faf8de65700 (LWP 19111) "gmain" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  12 Thread 0x7faf85664700 (LWP 19112) "gdbus" 0x00007fafcbceea91 in g_variant_type_info_check (
    info=info@entry=0x7fafcbd504b0 <g_variant_type_info_basic_table+368>, container_class=container_class@entry=0 '\000')
    at /build/glib2.0-ajuDY6/glib2.0-2.46.1/./glib/gvarianttypeinfo.c:158
  11 Thread 0x7faf8d3ff700 (LWP 19113) "dconf worker" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  10 Thread 0x7faf7eba6700 (LWP 19114) "dashCommunicato" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  9 Thread 0x7faf73fff700 (LWP 19115) "unity8" 0x00007fafcddc54f3 in epoll_wait () at ../sysdeps/unix/syscall-template.S:81
  8 Thread 0x7faf735f9700 (LWP 19118) "unity8" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  7 Thread 0x7faf71dd9700 (LWP 19119) "Qt bearer threa" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  6 Thread 0x7faf63fff700 (LWP 19121) "QQuickPixmapRea" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  5 Thread 0x7faf615ad700 (LWP 19123) "Thread (pooled)" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  4 Thread 0x7faf5ffa0700 (LWP 19124) "QThread" 0x00007fafcddb98dd in poll () at ../sysdeps/unix/syscall-template.S:81
  3 Thread 0x7faf5f79f700 (LWP 19125) "QProcessManager" 0x00007fafcddbb743 in select () at ../sysdeps/unix/syscall-template.S:81
  2 Thread 0x7faf5ef5e700 (LWP 19135) "QSGRenderThread" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fafcfcaf800 (LWP 19100) "unity8" QThread::~QThread (this=0x203d1f0, __in_chrg=<optimized out>)
    at thread/qthread.cpp:417

(gdb) bt
#0 0x00007fafce6bd935 in QThread::~QThread() (this=0x203d1f0, __in_chrg=<optimized out>) at thread/qthread.cpp:417
#1 0x00007faf845e5ef2 in () at /usr/lib/x86_64-linux-gnu/unity8/qml/Unity/DashCommunicator/libDashCommunicator-qml.so
#2 0x00007fafce8d1d2b in QObjectPrivate::deleteChildren() (this=this@entry=0x2033f40) at kernel/qobject.cpp:1950
#3 0x00007fafce8db620 in QObject::~QObject() (this=<optimized out>, __in_chrg=<optimized out>) at kernel/qobject.cpp:1030
#4 0x00007fafcf5b52bd in QQuickItem::~QQuickItem() (this=0x2033f10, __in_chrg=<optimized out>) at items/qquickitem.cpp:2223
#5 0x00007fafcf5cf7c6 in QQmlPrivate::QQmlElement<QQuickItem>::~QQmlElement() (this=0x2033f10, __in_chrg=<optimized out>)
    at ../../include/QtQml/../../src/qml/qml/qqmlprivate.h:98
#6 0x00007fafcf5cf7c6 in QQmlPrivate::QQmlElement<QQuickItem>::~QQmlElement() (this=0x2033f10, __in_chrg=<optimized out>)
    at ../../include/QtQml/../../src/qml/qml/qqmlprivate.h:98
#7 0x00007fafce8d1d2b in QObjectPrivate::deleteChildren() (this=this@entry=0x2017c10) at kernel/qobject.cpp:1950
#8 0x00007fafce8db620 in QObject::~QObject() (this=<optimized out>, __in_chrg=<optimized out>) at kernel/qobject.cpp:1030
#9 0x00007fafcf5b52bd in QQuickItem::~QQuickItem() (this=0x2015e10, __in_chrg=<optimized out>) at items/qquickitem.cpp:2223
#10 0x00007fafcf5cf86e in QQmlPrivate::QQmlElement<QQuickRectangle>::~QQmlElement() (this=0x2015e10, __in_chrg=<optimized out>)
    at items/qquickrectangle_p.h:128
#11 0x00007fafcf5cf86e in QQmlPrivate::QQmlElement<QQuickRectangle>::~QQmlElement() (this=0x2015e10, __in_chrg=<optimized out>)
    at ../../include/QtQml/../../src/qml/qml/qqmlprivate.h:98
#12 0x00007fafcf5cf86e in QQmlPrivate::QQmlElement<QQuickRectangle>::~QQmlElement() (this=0x2015e10, __in_chrg=<optimized out>)
    at ../../include/QtQml/../../src/qml/qml/qqmlprivate.h:98
#13 0x00007fafcf66b1aa in QQuickView::~QQuickView() (this=0x1f8ff70, __in_chrg=<optimized out>) at items/qquickview.cpp:225
#14 0x000000000040fade in ()
#15 0x000000000040a123 in ()
#16 0x0000000000406374 in ()
#17 0x00007fafcdcdea40 in __libc_start_main (main=
    0x4062f0, argc=1, argv=0x7ffe2523b688, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffe2523b678) at libc-start.c:289
#18 0x0000000000406419 in _start ()

[Gerry Boland (gerboland)]

DashCommunicator inherits QThread. From the QThread docs:

"Note that deleting a QThread object will not stop the execution of the thread it manages. Deleting a running QThread (i.e. isFinished() returns false) will probably result in a program crash. Wait for the finished() signal before deleting the QThread."

So to fix this, need to refactor DashCommunicator a bit to only delete the QThread after the thread's finished() signal has fired.

[Launchpad Janitor (janitor)]

This bug was fixed in the package unity8 - 8.11+16.04.20160111.1-0ubuntu1

---------------
unity8 (8.11+16.04.20160111.1-0ubuntu1) xenial; urgency=medium

  [ Albert Astals Cid ]
  * Clear fake item icon name as soon as it goes invisible (LP:
    #1531172)
  * Fix LVWPH test failing on Xenial (Qt 5.5)
  * Fix dragging so that test passes on Xenial
  * Fix focus on the dash page header text field with new SDK (LP:
    #1528178)
  * Make the card creator test pass again
  * Quit the dash communicator thread before destroying it (LP:
    #1508485)
  * Remove duplicated override_dh_auto_clean
  * SDK changed the name they give to the buttons, follow

  [ Andrea Cimitan ]
  * Fix a broken binding

  [ CI Train Bot ]
  * Resync trunk.
  * Update translation template

  [ Daniel d'Andrada ]
  * Have "make tryFoo" work with Qt 5.5
  * Make DragHandle tests run again.

  [ Lukáš Tinkl ]
  * Fix dismissing the launcher when clicking/tapping outside (LP:
    #1531339, #1530940)
  * Fix panel drop shadow and click-to-focus of maximized apps (LP:
    #1531854)
  * Fix wifi access point indicator items signal strength icon on
    desktop

  [ Michael Terry ]
  * Guard against a couple odd timing scenarios for the too-many-failed-
    login-attempts lockout screen.
  * Skip the wizard's password screens if there is already a password
    set by other means. (LP: #1531268)
  * Stop the emergency dialer from accidentally exposing the mtp
    service. (LP: #1525981)

  [ Michael Zanetti ]
  * Make sure the triangle of the quicklist is in bounds (LP: #1531340)

  [ Pawel Stolowski ]
  * Changes 'shareData' and 'contentType' attributes to 'share-data' and
    'content-type', to match existing naming schema.

 -- Michał Sawicz <email address hidden> Mon, 11 Jan 2016 17:38:49 +0000