unity8 crashed with SIGABRT in __gnu_cxx::__verbose_terminate_handler(), thrown from mir::shell::Surface::name()

StacktraceTop:
 __gnu_cxx::__verbose_terminate_handler() () at ../../../../src/libstdc++-v3/libsupc++/vterminate.cc:95
 __cxxabiv1::__terminate(void (*)()) () at ../../../../src/libstdc++-v3/libsupc++/eh_terminate.cc:38
 std::terminate() () at ../../../../src/libstdc++-v3/libsupc++/eh_terminate.cc:48
 __cxa_throw () at ../../../../src/libstdc++-v3/libsupc++/eh_throw.cc:84
 void boost::throw_exception<boost::exception_detail::error_info_injector<std::runtime_error> >(boost::exception_detail::error_info_injector<std::runtime_error> const&) () at /usr/include/boost/throw_exception.hpp:67

the cause is believed to be a mir surface race condition (at least there is a theory)
need to make it safe to hold shared_ptr<msh::Surface>
possible solution in this MP
https://code.launchpad.net/~robertcarr/mir/hold-surface-alive/+merge/189156

As described in the duplicate bug #1235209, this happens when an application tries to close itself. The application session is closed, destroying underlying mir surface resources, but then information about the destroyed surface (it's name) is requested leading to a crash. Still trying to get the details about why the name is requested.

The thread that crashed is "Thread 6".

Some more information about this issue that may lead to a more informed decision about how to solve it:

The core of the problem is that unity-mir reacts asynchronously to events from the SessionListener. MirSurfaceManager connects to the SessionListener::sessionCreatedSurface() signal using Qt::ConnectionType type = Qt::AutoConnection (the default value) [1] which means that if the emitter and the receiver are in different threads, the event is dispatched through the main loop at a later time. Changing this to Qt::BlockedQueuedConnection, which forces for the signal emission mechanism to wait until the event is handled, fixes the problem.

A tangential problem is that the Mir code doesn't currently notify listeners about destroyed surfaces when the session is closed, it only notifies about the session closing. Unity-mir depends on getting surface destruction events to release the mir surface resources it holds (shell::Surface). Adding surface destruction events to shell::ApplicationSession::~ApplicationSession() [2] solves the problem, but conflicts with using Qt::BlockedQueuedConnection as noted above, because in that case the emitter and the receiver are the same thread, and Qt::BlockedQueuedConnection deadlocks.

We have (at least) two options:

(a) Share shell::Surface ownership with the shell, as is done in https://code.launchpad.net/~robertcarr/mir/hold-surface-alive/+merge/189400

(b) Change [1] to use Qt::BlockedQueuedConnection, and change unity-mir to automatically release surface resources when receiving the session stopping signal, without needing explicit surface destruction events.

If option (a) doesn't have any unintended side effects, it would be my preference since it's conceptually cleaner/simpler, and has fewer edge cases.

[1] https://bazaar.launchpad.net/~mir-team/unity-mir/trunk/view/99/src/modules/Unity/Application/mirsurfacemanager.cpp#L64

[2] This is the same problem and fix as in https://bazaar.launchpad.net/~robertcarr/mir/hold-surface-alive/revision/1066

> The core of the problem is that unity-mir reacts asynchronously to events from the SessionListener. MirSurfaceManager
> connects to the SessionListener::sessionCreatedSurface() signal using Qt::ConnectionType type = Qt::AutoConnection

That was meant to be SessionListener::sessionDestroyingSurface signal...

Because, the event is handled at a later time in the main Qt loop, the underlying ms::Surface has been already destroyed when the handler is invoked, causing the crash.

This bug was fixed in the package mir - 0.0.14+13.10.20131010-0ubuntu1

---------------
mir (0.0.14+13.10.20131010-0ubuntu1) saucy; urgency=low

  [ Colin Watson ]
  * Don't build-depend on valgrind on arm64 for now, as it is not yet
    ported there.

  [ Ubuntu daily release ]
  * Automatic snapshot from revision 1095
 -- Ubuntu daily release <email address hidden> Thu, 10 Oct 2013 01:17:01 +0000