Sorry, I had notifications muted for this repository. I don't have time nor motivation for open source these days but I'd be happy to add someone as maintainer

This member could be accessed at the same from different threads leading to random (rare) crashes.

Fixes #1875

Sure. TSAN seems to be happy with the moved lockers. I'll play for a while and send a PR if I don't see any issue with it.

FWIW,I've been playing with this patch since then and it works fine

diff --git a/src/platform/qt/InputController.cpp b/src/platform/qt/InputController.cpp
index f19130dd..681f98d5 100644
--- a/src/platform/qt/InputController.cpp
+++ b/src/platform/qt/InputController.cpp
@@ -650,14 +650,17 @@ void InputController::sendGamepadEvent(QEvent* event) {
 }

 void InputController::postPendingEvent(GBAKey key) {
+       QWriteLocker l(&m_eventsLock);
        m_pendingEvents.insert(key);
 }

 void InputController::clearPendingEvent(GBAKey key) {
+       QWriteLocker l(&m_eventsLock);
        m_pendingEvents.remove(key);
 }

 bool InputController::hasPendingEvent(GBAKey key) const {
+       QReadLocker l(&m_eventsLock);
        return m_pendingEvents.contains(key);
 }

diff --git a/src/platform/qt/InputController.h b/src/platform/qt/InputController.h
index 5c2c8502..72a766c9 100644
--- a/src/platform/qt/InputController.h
+++ b/src/platform/qt/InputController.h
@@ -10,6 +10,7 @@

 #include <QImage>
 #include <QMutex>
+#include <QReadWriteLock>
 #include <QObject>
 #include <QSet>
 #include <QTimer>
@@ -181,6 +182,7 @@ private:
        QTimer m_gamepadTimer{nullptr};

        QSet<GBAKey> m_pendingEvents;
+       mutable QReadWriteLock m_eventsLock;

Hello,

I've been seeing a few crashes related to InputController::m_pendingEvents.

The backtrace looks like this:

Thread 1 (Thread 0x7f35f883f640 (LWP 406716)):
#0  QHashNode<GBAKey, QHashDummyValue>::same_key (key0=<synthetic pointer>: GBA_KEY_A, h0=1385392141, this=0x55b745df3af0) at /usr/include/qt/QtCore/qhash.h:175
#1  QHash<GBAKey, QHashDummyValue>::findNode (h=1385392141, akey=<synthetic pointer>: GBA_KEY_A, this=0x55b21d54e488) at /usr/include/qt/QtCore/qhash.h:931
#2  QHash<GBAKey, QHashDummyValue>::findNode (ahp=0x0, akey=<synthetic pointer>: GBA_KEY_A, this=0x55b21d54e488) at /usr/include/qt/QtCore/qhash.h:950
#3  QHash<GBAKey, QHashDummyValue>::contains (akey=<synthetic pointer>: GBA_KEY_A, this=0x55b21d54e488) at /usr/include/qt/QtCore/qhash.h:920
#4  QSet<GBAKey>::contains (value=<synthetic pointer>: GBA_KEY_A, this=0x55b21d54e488) at /usr/include/qt/QtCore/qset.h:97
#5  QGBA::InputController::hasPendingEvent (this=this@entry=0x55b21d54e258, key=key@entry=GBA_KEY_A) at /home/eijebong/mgba/src/platform/qt/InputController.cpp:661
#6  0x000055b21b78348a in QGBA::InputController::pollEvents (this=0x55b21d54e258) at /home/eijebong/mgba/src/platform/qt/InputController.cpp:392
#7  0x000055b21b755511 in QGBA::CoreController::updateKeys (this=this@entry=0x55b21d61b8c0) at /home/eijebong/mgba/src/platform/qt/CoreController.cpp:904
#8  0x000055b21b757dcd in QGBA::CoreController::finishFrame (this=0x55b21d61b8c0) at /home/eijebong/mgba/src/platform/qt/CoreController.cpp:939
#9  0x00007f36300923ac in GBAFrameEnded (gba=0x7f3624221000) at /home/eijebong/mgba/src/gba/gba.c:848
#10 0x00007f36300b87d2 in _startHdraw (timing=<optimized out>, context=0x7f3624221cd0, cyclesLate=6) at /home/eijebong/mgba/src/gba/video.c:183
#11 0x00007f36300315a2 in mTimingTick (timing=timing@entry=0x7f36242228f0, cycles=<optimized out>) at /home/eijebong/mgba/src/core/timing.c:98
#12 0x00007f3630090f20 in GBAProcessEvents (cpu=0x7f3624597000) at /home/eijebong/mgba/src/gba/gba.c:291
#13 0x00007f363003047a in _mCoreThreadRun (context=0x55b21d61b8d0) at /home/eijebong/mgba/src/core/thread.c:202
#14 0x00007f362d8603e9 in start_thread () from /usr/lib/libpthread.so.0
#15 0x00007f362c2e3293 in clone () from /usr/lib/libc.so.6

There is always a second thread that looks like this:

Thread 4 (Thread 0x7f3625bb4bc0 (LWP 406689)):
#0  0x00007f36301a434a in ?? () from /usr/lib/libSDL2-2.0.so.0
#1  0x000055b21b82f7fd in mSDLUpdateJoysticks (events=events@entry=0x55b21b9b4b40 <QGBA::InputController::s_sdlEvents>, config=0x7ffc26c28f90) at /home/eijebong/mgba/src/platform/sdl/sdl-events.c:351
#2  0x000055b21b7849e9 in QGBA::InputController::updateJoysticks (this=0x55b21d54e258) at /home/eijebong/mgba/src/platform/qt/ConfigController.h:88
#3  0x00007f362c88ba06 in ?? () from /usr/lib/libQt5Core.so.5
#4  0x00007f362c88fa7b in QTimer::timeout(QTimer::QPrivateSignal) () from /usr/lib/libQt5Core.so.5
#5  0x00007f362c8810ef in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#6  0x00007f362d31e702 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#7  0x00007f362c85479a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#8  0x00007f362c8ac695 in QTimerInfoList::activateTimers() () from /usr/lib/libQt5Core.so.5
#9  0x00007f362c8acf42 in ?? () from /usr/lib/libQt5Core.so.5
#10 0x00007f362806c43c in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#11 0x00007f36280ba1d9 in ?? () from /usr/lib/libglib-2.0.so.0
#12 0x00007f362806b221 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#13 0x00007f362c8ad311 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#14 0x00007f362c85311c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#15 0x00007f362c85b5a4 in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#16 0x000055b21b72034d in main (argc=<optimized out>, argv=0x7ffc26c28eb0) at /home/eijebong/mgba/src/platform/qt/main.cpp:116

In frame 0, the hash_node it's trying to compare to is not valid anymore which lead me to think it was a race condition on m_pendingEvents, thread 0 reading it while thread 4 is writing it.

After recompiling with thread-sanitizer, I got this:

WARNING: ThreadSanitizer: data race (pid=413887)
  Read of size 8 at 0x7b24000084f0 by thread T22:
    #0 QHash<GBAKey, QHashDummyValue>::findNode(GBAKey const&, unsigned int) const /usr/include/qt/QtCore/qhash.h:931 (mgba-qt+0x13361d)
    #1 QHash<GBAKey, QHashDummyValue>::findNode(GBAKey const&, unsigned int*) const /usr/include/qt/QtCore/qhash.h:950 (mgba-qt+0x13361d)
    #2 QHash<GBAKey, QHashDummyValue>::contains(GBAKey const&) const /usr/include/qt/QtCore/qhash.h:920 (mgba-qt+0x13361d)
    #3 QSet<GBAKey>::contains(GBAKey const&) const /usr/include/qt/QtCore/qset.h:97 (mgba-qt+0x13361d)
    #4 QGBA::InputController::hasPendingEvent(GBAKey) const /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:661 (mgba-qt+0x13361d)
    #5 QGBA::InputController::pollEvents() /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:392 (mgba-qt+0x133748)
    #6 QGBA::CoreController::updateKeys() /home/eijebong/mgba_asan/src/platform/qt/CoreController.cpp:904 (mgba-qt+0xe4b24)
    #7 QGBA::CoreController::finishFrame() /home/eijebong/mgba_asan/src/platform/qt/CoreController.cpp:939 (mgba-qt+0xe8aa7)
    #8 operator() /home/eijebong/mgba_asan/src/platform/qt/CoreController.cpp:101 (mgba-qt+0xe8c61)
    #9 _FUN /home/eijebong/mgba_asan/src/platform/qt/CoreController.cpp:102 (mgba-qt+0xe8c61)
    #10 _frameEnded /home/eijebong/mgba_asan/src/core/thread.c:120 (libmgba.so.0.9+0x83359)
    #11 GBAFrameEnded /home/eijebong/mgba_asan/src/gba/gba.c:848 (libmgba.so.0.9+0x14e1d5)
    #12 _startHdraw /home/eijebong/mgba_asan/src/gba/video.c:183 (libmgba.so.0.9+0x188a98)
    #13 mTimingTick /home/eijebong/mgba_asan/src/core/timing.c:98 (libmgba.so.0.9+0x872c4)
    #14 GBAProcessEvents /home/eijebong/mgba_asan/src/gba/gba.c:291 (libmgba.so.0.9+0x14bd2c)
    #15 ARMRunLoop /home/eijebong/mgba_asan/src/arm/arm.c:275 (libmgba.so.0.9+0xc8ad1)
    #16 _GBACoreRunLoop /home/eijebong/mgba_asan/src/gba/core.c:662 (libmgba.so.0.9+0x144e2d)
    #17 _mCoreThreadRun /home/eijebong/mgba_asan/src/core/thread.c:202 (libmgba.so.0.9+0x85249)

  Previous write of size 8 at 0x7b24000084f0 by main thread:
    #0 operator new[](unsigned long) /build/gcc/src/gcc/libsanitizer/tsan/tsan_new_delete.cpp:70 (libtsan.so.0+0x8d314)
    #1 QHashData::rehash(int) <null> (libQt5Core.so.5+0x107f04)
    #2 QGBA::InputController::testGamepad(int) /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:587 (mgba-qt+0x1372d5)
    #3 operator() /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:52 (mgba-qt+0x139e75)
    #4 call /usr/include/qt/QtCore/qobjectdefs_impl.h:146 (mgba-qt+0x139e75)
    #5 call<QtPrivate::List<>, void> /usr/include/qt/QtCore/qobjectdefs_impl.h:256 (mgba-qt+0x139e75)
    #6 impl /usr/include/qt/QtCore/qobjectdefs_impl.h:443 (mgba-qt+0x139e75)
    #7 <null> <null> (libQt5Core.so.5+0x2e8a05)
    #8 __libc_start_main <null> (libc.so.6+0x28151)

  Location is heap block of size 136 at 0x7b24000084c0 allocated by main thread:
    #0 operator new[](unsigned long) /build/gcc/src/gcc/libsanitizer/tsan/tsan_new_delete.cpp:70 (libtsan.so.0+0x8d314)
    #1 QHashData::rehash(int) <null> (libQt5Core.so.5+0x107f04)
    #2 QGBA::InputController::testGamepad(int) /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:587 (mgba-qt+0x1372d5)
    #3 operator() /home/eijebong/mgba_asan/src/platform/qt/InputController.cpp:52 (mgba-qt+0x139e75)
    #4 call /usr/include/qt/QtCore/qobjectdefs_impl.h:146 (mgba-qt+0x139e75)
    #5 call<QtPrivate::List<>, void> /usr/include/qt/QtCore/qobjectdefs_impl.h:256 (mgba-qt+0x139e75)
    #6 impl /usr/include/qt/QtCore/qobjectdefs_impl.h:443 (mgba-qt+0x139e75)
    #7 <null> <null> (libQt5Core.so.5+0x2e8a05)
    #8 __libc_start_main <null> (libc.so.6+0x28151)

  Thread T22 'CPU Thread' (tid=413913, running) created by main thread at:
    #0 pthread_create /build/gcc/src/gcc/libsanitizer/tsan/tsan_interceptors_posix.cpp:962 (libtsan.so.0+0x5efab)
    #1 ThreadCreate /home/eijebong/mgba_asan/include/mgba-util/platform/posix/threading.h:81 (libmgba.so.0.9+0x83914)
    #2 mCoreThreadStart /home/eijebong/mgba_asan/src/core/thread.c:332 (libmgba.so.0.9+0x83914)
    #3 QGBA::CoreController::start() /home/eijebong/mgba_asan/src/platform/qt/CoreController.cpp:369 (mgba-qt+0xe43de)
    #4 QGBA::Window::setController(QGBA::CoreController*, QString const&) /home/eijebong/mgba_asan/src/platform/qt/Window.cpp:1915 (mgba-qt+0x1f1bad)
    #5 QGBA::Window::selectROM() /home/eijebong/mgba_asan/src/platform/qt/Window.cpp:337 (mgba-qt+0x1f2b1b)
    #6 void std::__invoke_impl<void, void (QGBA::Window::*&)(), QGBA::Window*&>(std::__invoke_memfun_deref, void (QGBA::Window::*&)(), QGBA::Window*&) /usr/include/c++/10.2.0/bits/invoke.h:73 (mgba-qt+0x203b47)
    #7 std::__invoke_result<void (QGBA::Window::*&)(), QGBA::Window*&>::type std::__invoke<void (QGBA::Window::*&)(), QGBA::Window*&>(void (QGBA::Window::*&)(), QGBA::Window*&) /usr/include/c++/10.2.0/bits/invoke.h:95 (mgba-qt+0x203b47)
    #8 void std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>::__call<void, , 0ul>(std::tuple<>&&, std::_Index_tuple<0ul>) /usr/include/c++/10.2.0/functional:416 (mgba-qt+0x203b47)
    #9 void std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>::operator()<, void>() /usr/include/c++/10.2.0/functional:499 (mgba-qt+0x203b47)
    #10 void std::__invoke_impl<void, std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>&>(std::__invoke_other, std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>&) /usr/include/c++/10.2.0/bits/invoke.h:60 (mgba-qt+0x203b47)
    #11 std::enable_if<std::__and_<std::is_void<void>, std::__is_invocable<std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>&> >::value, void>::type std::__invoke_r<void, std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>&>(std::_Bind<void (QGBA::Window::*(QGBA::Window*))()>&) /usr/include/c++/10.2.0/bits/invoke.h:153 (mgba-qt+0x203b47)
    #12 std::_Function_handler<void (), std::_Bind<void (QGBA::Window::*(QGBA::Window*))()> >::_M_invoke(std::_Any_data const&) /usr/include/c++/10.2.0/bits/std_function.h:291 (mgba-qt+0x203b47)
    #13 std::function<void ()>::operator()() const /usr/include/c++/10.2.0/bits/std_function.h:622 (mgba-qt+0xb57e7)
    #14 QGBA::Action::trigger(bool) /home/eijebong/mgba_asan/src/platform/qt/Action.cpp:75 (mgba-qt+0xb57e7)
    #15 operator() /home/eijebong/mgba_asan/src/platform/qt/ActionMapper.cpp:86 (mgba-qt+0xb5d51)
    #16 call /usr/include/qt/QtCore/qobjectdefs_impl.h:146 (mgba-qt+0xb5d51)
    #17 call<QtPrivate::List<bool>, void> /usr/include/qt/QtCore/qobjectdefs_impl.h:256 (mgba-qt+0xb5d51)
    #18 impl /usr/include/qt/QtCore/qobjectdefs_impl.h:443 (mgba-qt+0xb5d51)
    #19 <null> <null> (libQt5Core.so.5+0x2e8a05)
    #20 __libc_start_main <null> (libc.so.6+0x28151)

SUMMARY: ThreadSanitizer: data race /usr/include/qt/QtCore/qhash.h:931 in QHash<GBAKey, QHashDummyValue>::findNode(GBAKey const&, unsigned int) const

which confirms said theory. Here thread 22 is reading while thread 0 is writing.

This is related to the code here: https://github.com/mgba-emu/mgba/blob/756c6e18abfb2691a1ceac371624a5956823d303/src/platform/qt/InputController.cpp#L652-L662 which could use a QReadWriteLock I guess. Since I don't know the code base there might be a better solution though.

Oh sorry, I didn't check currently open PRs