Casper: Segmentation fault

[sgpearse]

To reproduce:

1. On Casper, build a debug version of Vapor on main
2. Run vapor, and close it

Most of the time the application will seg fault. Sometimes it gets lucky. I haven't seen this after loading data.

[shaomeng]

Might be a usage of QT windows/widgets that went wrong, but cannot identify what:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x2aaadb6c4700 (LWP 203138)]
0x00002aaab0856ce8 in QAbstractEventDispatcherPrivate::allocateTimerId() () from /lib64/libQt5Core.so.5
(gdb) bt
#0  0x00002aaab0856ce8 in QAbstractEventDispatcherPrivate::allocateTimerId() () at /lib64/libQt5Core.so.5
#1  0x00002aaab0857179 in QAbstractEventDispatcher::registerTimer(int, Qt::TimerType, QObject*) ()
    at /lib64/libQt5Core.so.5
#2  0x00002aaab0883e9e in QObject::startTimer(int, Qt::TimerType) () at /lib64/libQt5Core.so.5
#3  0x00002aaaaababec4 in qDBusAddTimeout () at /lib64/libQt5DBus.so.5
#4  0x00002aaab2e65ddb in _dbus_timeout_list_add_timeout () at /lib64/libdbus-1.so.3
#5  0x00002aaab2e508ba in dbus_connection_send_with_reply () at /lib64/libdbus-1.so.3
#6  0x00002aaaaabaf6d3 in QDBusConnectionPrivate::sendInternal(QDBusPendingCallPrivate*, void*, int) ()
    at /lib64/libQt5DBus.so.5
#7  0x00002aaab08831de in QObject::event(QEvent*) () at /lib64/libQt5Core.so.5
#8  0x00002aaab0859b05 in doNotify(QObject*, QEvent*) () at /lib64/libQt5Core.so.5
#9  0x00002aaab0859c1b in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /lib64/libQt5Core.so.5
#10 0x00002aaab085c503 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
    at /lib64/libQt5Core.so.5
#11 0x00002aaab08a8ab3 in postEventSourceDispatch(_GSource*, int (*)(void*), void*) () at /lib64/libQt5Core.so.5
#12 0x00002aaab7470099 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#13 0x00002aaab74703f8 in g_main_context_iterate.isra.19 () at /lib64/libglib-2.0.so.0
#14 0x00002aaab74704ac in g_main_context_iteration () at /lib64/libglib-2.0.so.0
#15 0x00002aaab08a845c in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
    at /lib64/libQt5Core.so.5
#16 0x00002aaab08586db in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib64/libQt5Core.so.5
#17 0x00002aaab06ab7f8 in QThread::exec() () at /lib64/libQt5Core.so.5
#18 0x00002aaaaaba03b5 in QDBusConnectionManager::run() () at /lib64/libQt5DBus.so.5
#19 0x00002aaab06afe71 in QThreadPrivate::start(void*) () at /lib64/libQt5Core.so.5
#20 0x00002aaaae293ea5 in start_thread () at /lib64/libpthread.so.0
#21 0x00002aaab144c8dd in clone () at /lib64/libc.so.6

[clyne]

@shaomeng have you tried valgrind?

[shaomeng]

@shaomeng have you tried valgrind?

Valgrind finds hundreds of problematic blocks during a simple open vapor close vapor operation. (almost half a million if you look at the still reachable block count, though I don't know what that means.) Don't know how helpful it is to this particular issue. (But definitely tells something about vapor and qt and other dependencies as a whole.)

==1320406== HEAP SUMMARY:
==1320406==     in use at exit: 41,442,031 bytes in 481,113 blocks
==1320406==   total heap usage: 2,894,124 allocs, 2,413,011 frees, 5,798,714,793 bytes allocated
==1320406== 
==1320406== LEAK SUMMARY:
==1320406==    definitely lost: 13,752 bytes in 180 blocks
==1320406==    indirectly lost: 60,136 bytes in 597 blocks
==1320406==      possibly lost: 4,320 bytes in 34 blocks
==1320406==    still reachable: 41,281,191 bytes in 479,628 blocks
==1320406==                       of which reachable via heuristic:
==1320406==                         stdstring          : 33 bytes in 1 blocks
==1320406==                         length64           : 4,960 bytes in 82 blocks
==1320406==                         newarray           : 2,096 bytes in 51 blocks
==1320406==                         multipleinheritance: 53,744 bytes in 38 blocks
==1320406==         suppressed: 0 bytes in 0 blocks
==1320406== Rerun with --leak-check=full to see details of leaked memory

Resources:
This discussion concludes that "still reachable" blocks don't pose threats most of the times.

[shaomeng]

Regarding reproducing on other linux platforms:
I cannot reproduce it on cisl-vapor after 2 dozens of tries.

[clyne]

At one time @StasJ had a filter set up that would remove the Qt and OpenGL errors and leave you with useful information.

[sgpearse]

Need to test on test platforms with installer build.

[sgpearse]

@shaomeng Will test this with an installer on Casper.

[clyne]

@shaomeng just a reminder that we still need to test after casper comes back up

cc: @sgpearse