Crash when pressing "controls" button

[treapster]

Latest commit from main. When pressing controls button, everything freezes and crashes. Build config: cmake -DCMAKE_CXX_FLAGS="-D_GLIBCXX_DEBUG" -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++

clang version 16.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Stack trace:

``` фев 13 07:04:11 sasus plasmashell[207104]: [DEBUG][gkick_synth_process] synth->buffer_callback фев 13 07:04:13 sasus plasmashell[207104]: /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/debug/safe_iterator.h:328: фев 13 07:04:13 sasus plasmashell[207104]: In function: фев 13 07:04:13 sasus plasmashell[207104]: _Safe_iterator<_Iterator, _Sequence, _Category> & фев 13 07:04:13 sasus plasmashell[207104]: gnu_debug::_Safe_iterator *, std:: фев 13 07:04:13 sasus plasmashell[207104]: vector>>, фев 13 07:04:13 sasus plasmashell[207104]: std::vector>, фев 13 07:04:13 sasus plasmashell[207104]: std::forward_iterator_tag>::operator++() [_Iterator = gnu_cxx:: фев 13 07:04:13 sasus plasmashell[207104]: normal_iterator *, std:: фев 13 07:04:13 sasus plasmashell[207104]: vector>>, _Sequence = фев 13 07:04:13 sasus plasmashell[207104]: std::vector>, _Category = фев 13 07:04:13 sasus plasmashell[207104]: std::forward_iterator_tag] фев 13 07:04:13 sasus plasmashell[207104]: Error: attempt to increment a singular iterator. фев 13 07:04:13 sasus plasmashell[207104]: Objects involved in the operation: фев 13 07:04:13 sasus plasmashell[207104]: iterator "this" @ 0x7ffe501bb370 { фев 13 07:04:13 sasus plasmashell[207104]: type = gnu_cxx::normal_iterator > const*, std::vector >, std::allocator > > > > (constant iterator); фев 13 07:04:13 sasus plasmashell[207104]: state = singular; фев 13 07:04:13 sasus plasmashell[207104]: references sequence with type 'std::debug::vector >, std::allocator > > >' @ 0x556ea9cffdf8 фев 13 07:04:13 sasus plasmashell[207104]: } фев 13 07:04:13 sasus systemd[1]: Started Process Core Dump (PID 207284/UID 0). фев 13 07:04:13 sasus pipewire[1187]: spa.alsa: front:0p: follower avail:10 delay:10 target:1024 thr:1024, resync (1 suppressed) фев 13 07:04:19 sasus systemd-coredump[207285]: Process 207104 (ArdourGUI) of user 1000 dumped core. Stack trace of thread 207104: #0 0x00007f5ac786783c n/a (libc.so.6 + 0x8e83c) #1 0x00007f5ac7817668 raise (libc.so.6 + 0x3e668) #2 0x00007f5ac77ff4b8 abort (libc.so.6 + 0x264b8) #3 0x00007f5ac7c67f52 _ZNK11__gnu_debug16_Error_formatter8_M_errorEv (libstdc++.so.6 + 0x9ff52) #4 0x00007f5a48bcf705 _ZN11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPKSt10unique_ptrI10RkObserverSt14default_deleteIS4_EENSt9__cxx19986vectorIS7_SaIS7_EEEEENSt7__debug6vectorIS7_SC_EESt20forward_iterator_tagEppEv (geonkick_lv2.so + 0x46705) #5 0x00007f5a48bf9dd8 _ZN9ViewState15mainViewChangedENS_4ViewE (geonkick_lv2.so + 0x70dd8) #6 0x00007f5a48c7ad06 _ZN12RkEventQueue16RkEventQueueImpl14processActionsEv (geonkick_lv2.so + 0xf1d06) #7 0x00007f5a48c76916 _ZN12RkEventQueue12processQueueEv (geonkick_lv2.so + 0xed916) #8 0x00007f5a48c83192 _ZN6RkMain10RkMainImpl4execEb (geonkick_lv2.so + 0xfa192) #9 0x00007f5a48bb9748 _ZL10gkick_idlePv (geonkick_lv2.so + 0x30748) #10 0x00007f5a9000317f n/a (libsuil_x11_in_gtk2.so + 0x217f) #11 0x00007f5ac90cc3ee n/a (libglib-2.0.so.0 + 0x5b3ee) #12 0x00007f5ac90caf69 n/a (libglib-2.0.so.0 + 0x59f69) #13 0x00007f5ac9129367 n/a (libglib-2.0.so.0 + 0xb8367) #14 0x00007f5ac90cbb97 g_main_loop_run (libglib-2.0.so.0 + 0x5ab97) #15 0x00007f5ac8d2f473 gtk_main (libgtk-x11-2.0.so.0 + 0x138473) #16 0x00007f5ac9400f59 _ZN9Gtkmm2ext2UI3runER8Receiver (libgtkmm2ext.so.0 + 0x5bf59) #17 0x0000556e9879f6c7 main (ardour-8.2.0 + 0x4aa6c7) #18 0x00007f5ac7800cd0 n/a (libc.so.6 + 0x27cd0) #19 0x00007f5ac7800d8a __libc_start_main (libc.so.6 + 0x27d8a) #20 0x0000556e987a4fc5 n/a (ardour-8.2.0 + 0x4affc5) ```

Demangled relevant part of the stacktrace:

``` #0 0x00007f5ac786783c n/a (libc.so.6 + 0x8e83c) #1 0x00007f5ac7817668 raise (libc.so.6 + 0x3e668) #2 0x00007f5ac77ff4b8 abort (libc.so.6 + 0x264b8) #3 0x00007f5ac7c67f52 __gnu_debug::_Error_formatter::_M_error() const (libstdc++.so.6 + 0x9ff52) #4 0x00007f5a48bcf705 __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator> const*, std::__cxx1998::vector>, std::allocator>>>>, std::__debug::vector>, std::allocator>>>, std::forward_iterator_tag>::operator++() (geonkick_lv2.so + 0x46705) #5 0x00007f5a48bf9dd8 ViewState::mainViewChanged(ViewState::View) (geonkick_lv2.so + 0x70dd8) #6 0x00007f5a48c7ad06 RkEventQueue::RkEventQueueImpl::processActions() (geonkick_lv2.so + 0xf1d06) #7 0x00007f5a48c76916 RkEventQueue::processQueue() (geonkick_lv2.so + 0xed916) #8 0x00007f5a48c83192 RkMain::RkMainImpl::exec(bool) (geonkick_lv2.so + 0xfa192) #9 0x00007f5a48bb9748 gkick_idle(void*) (geonkick_lv2.so + 0x30748) ```

A quick google search suggests that "singular iterator" in the error message essentially means "uninitialized". But the mainViewChanged is generated from macro and doesn't really do anything fancy with iterators aside from for loop over observers, so it's not clear at all how can we get invalid iterator into RkObjectImpl::observersList unless it itself is in some invalid state. I hope you'll be able to figure it out...

Sidenote: consider building geonkick with D_GLIBCXX_DEBUG and using it for some time, maybe you'll find some more crashes before i do:)

[iurienistor]

Yes, I know this, but this is because of debug build trying to print something that is not accessible. In release this is not a problem.

[iurienistor]

Is this when trying to switch the view from the top bar buttons?

[treapster]

Is this when trying to switch the view from the top bar buttons?

Yes

[treapster]

Yes, I know this, but this is because of debug build trying to print something that is not accessible. In release this is not a problem.

I built with -DCMAKE_BUILD_TYPE=Release and i get the same problem. Although even if i did not, it would be even worse.

[iurienistor]

Actually I cannot reproduce. O thought maybe building with clang, but no. Ubuntu 22.04.3 LTS Clang: 14.0.0

[treapster]

Actually I cannot reproduce.

You built with -DCMAKE_CXX_FLAGS="-D_GLIBCXX_DEBUG" -DCMAKE_BUILD_TYPE=Release and did not get the crash?

O thought maybe building with clang, but no. Ubuntu 22.04.3 LTS Clang: 14.0.0

Out of curiosity i tried building with gcc before and i get the same issue there

[iurienistor]

On what controls are you pressing and this is happening?

[treapster]

On what controls are you pressing and this is happening?

I just open geonkick and press "controls" in the top bar and it crashes right away, before it even renders contols themselves. Probably you have to select a kit first, in my case the selected kit is Unfa-Tutorial.

[treapster]

Important clarification: it only happens in ardour and not in standalone mode, and it does not even reproduce in another session in ardour! Seems like it happens only with specific "spoiled" session...

[iurienistor]

@treapster I even tried with Windows/Ardour... it is ok.

[iurienistor]

@treapster Debian/Adour is ok too.. debug build

[treapster]

I wonder if you'll be able to repro it with the session. The existing geonkick instance in this session is broken, but the new ones seem to work... session.zip

[treapster]

Okay, i figured how to reliably reproduce: build in release mode with -D_GLIBCXX_ASSERTIONS or without any flags, create an empty session, add geonkick instance with some drumkit. Save, close, rebuild with -D_GLIBCXX_DEBUG, open session, try to open Controls view and it breaks. It's difficult to say whether it indicates an actual issue or it's a side effect of GLIBCXX_DEBUG, because here is what gcc doc says:

Note that this flag changes the sizes and behavior of standard class templates such as std::vector, and therefore you can only link code compiled with debug mode and code compiled without debug mode if no instantiation of a container is passed between the two translation units.

If some std struct(not necessarily a vector) gets serialized in raw form during session saving, then it is may be just incompatibility of GLIBCXX_DEBUG with regular build. Or it may be passed around to non-CXX_DEBUG code, though it is unlikely because it works either way with new sessions. Maybe i really shouldn't use GLIBCXX_DEBUG, or maybe there is in fact some invalid state only detected in debug mode, i dont know:)

[iurienistor]

@treapster The Geonkick saves the UI view state into the plugin state as json format. When it loads back... it it might load incorrectly. Try to comment this

                //if (m.name == "UiSettings" && m.value.IsObject())
                //        uiSettings->fromJsonObject(m.val

in the function

GeonkickApi::setState(const std::string &data)
{
        rapidjson::Document document;
        document.Parse(data.c_str());
        if (!document.IsObject())
                return;

        for (const auto &m: document.GetObject()) {
                //if (m.name == "UiSettings" && m.value.IsObject())
                //        uiSettings->fromJsonObject(m.value);
                if (m.name == "KitState" && m.value.IsObject()) {
                        auto kitState = std::make_unique<KitState>();
                        kitState->fromJsonObject(m.value);
                        setKitState(std::move(kitState));
                }
        }
}

[iurienistor]

Okay, i figured how to reliably reproduce: build in release mode with -D_GLIBCXX_ASSERTIONS or without any flags, create an empty session, add geonkick instance with some drumkit. Save, close, rebuild with -D_GLIBCXX_DEBUG, open session, try to open Controls view and it breaks. It's difficult to say whether it indicates an actual issue or it's a side effect of GLIBCXX_DEBUG, because here is what gcc doc says

I tried this, I cannot reproduce on my end. Also your session is ok too on my end. :)... could you attach the Geonkick plugin binaries?

[treapster]

I tried this, I cannot reproduce on my end. Also your session is ok too on my end. :)... could you attach the Geonkick plugin binaries?

Wow, what a flaky bug is that! Here are the binaries, built on manjaro with clang 16.0.6/libc 2.38/libstdc++ 13.2.1 geonkick.zip

[treapster]

I missed your comment about setState function, but I can say that it is not about GLIBCXX_DEBUG incompatibility: i built the plugin with

 cmake -DCMAKE_CXX_FLAGS="-D_GLIBCXX_ASSERTIONS -stdlib=libc++" -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++

And now it just segfaults when choosing e.g AVL drumkit from presets, just after launch in standalone mode. The RkObject::RkObjectImpl::inf_ptr->o_ptr is null if i check in gdb.

Gdb trace:

``` #0 RkObject::RkObjectImpl::parent (this=0x0) at /home/denis/randomshit/geonkick/src/redkite/src/RkObjectImpl.cpp:69 #1 0x0000555555601e37 in RkObject::RkObjectImpl::~RkObjectImpl (this=0x5555558983f0) at /home/denis/randomshit/geonkick/src/redkite/src/RkObjectImpl.cpp:55 #2 0x0000555555601f89 in RkObject::RkObjectImpl::~RkObjectImpl (this=0x0) at /home/denis/randomshit/geonkick/src/redkite/src/RkObjectImpl.cpp:40 #3 0x00005555555bfe79 in PercussionModel::~PercussionModel (this=0x0) at /home/denis/randomshit/geonkick/src/percussion_model.h:38 #4 0x00005555555c0a67 in KitModel::loadModelData (this=0x5555558983a0) at /home/denis/randomshit/geonkick/src/kit_model.cpp:196 #5 0x0000555555588552 in std::__1::__function::__value_func::operator()[abi:v160006]() const (this=) at /usr/bin/../include/c++/v1/__functional/function.h:510 #6 std::__1::function::operator()() const (this=) at /usr/bin/../include/c++/v1/__functional/function.h:1156 #7 GeonkickApi::kitUpdated (this=) at /home/denis/randomshit/geonkick/src/geonkick_api.h:309 #8 GeonkickApi::notifyKitUpdated()::$_0::operator()() const (this=) at /home/denis/randomshit/geonkick/src/geonkick_api.cpp:1693 #9 std::__1::__invoke[abi:v160006](GeonkickApi::notifyKitUpdated()::$_0&) (__f=...) at /usr/bin/../include/c++/v1/__functional/invoke.h:394 #10 std::__1::__invoke_void_return_wrapper::__call(GeonkickApi::notifyKitUpdated()::$_0&) (__args=...) at /usr/bin/../include/c++/v1/__functional/invoke.h:487 #11 std::__1::__function::__alloc_func, void ()>::operator()[abi:v160006]() (this=) at /usr/bin/../include/c++/v1/__functional/function.h:185 #12 std::__1::__function::__func, void ()>::operator()() ( this=) at /usr/bin/../include/c++/v1/__functional/function.h:356 #13 0x00005555556083ce in std::__1::__function::__value_func::operator()[abi:v160006]() const (this=) at /usr/bin/../include/c++/v1/__functional/function.h:510 ```

[treapster]

Here is what happens:

• the destructor of RkObject runs and RkObject is destroyed
• Then a single member of RkObject o_ptr is destroyed, it is of type unique_ptr<RkObjectImpl>
• the destructor of o_ptr sets it's own value to zero(while copying it to temporary value), and calls the destructor of RkObjectImpl on the value
• The destructor of RkObjectImpl references the parent RkObject, which is already destroyed, and tries to access it's o_ptr to get the parent, but it is alreay set to zero and segfaults. I also don't understand why it tries to get parent through double dereference instead of using it's own parentObject member, but in any case the parent is already destroyed at that point so it is illegal.

[treapster]

I tried removing the lines:

--- a/src/redkite/src/RkObjectImpl.cpp
+++ b/src/redkite/src/RkObjectImpl.cpp
@@ -51,9 +51,6 @@ RkObject::RkObjectImpl::~RkObjectImpl()
         }
         observersList.clear();

-        // Remove myself from the paren object.
-        if (inf_ptr->parent())
-                inf_ptr->parent()->removeChild(inf_ptr);
 }

But it does not help much: it apparently fixes standalone mode(edit: not quite, now segfault happens when you close the window, also because of destructors doing something naughty), but in ardour it causes a different crash(also on window close) so weird that i don't even get a stacktrace:

фев 14 04:06:51 sasus kernel: ArdourGUI[5771]: segfault at 111 ip 0000000000000111 sp 00007ffd2f533da8 error 14 in ardour-8.2.0[55fb67a79000+369000]
фев 14 04:06:51 sasus kernel: Code: Unable to access opcode bytes at RIP 0xe7.
фев 14 04:06:51 sasus systemd[1]: Created slice Slice /system/systemd-coredump.
фев 14 04:06:51 sasus systemd[1]: Started Process Core Dump (PID 5963/UID 0).
фев 14 04:06:54 sasus systemd-coredump[5964]: [🡕] Process 5771 (ArdourGUI) of user 1000 dumped core.

                                                 Stack trace of thread 5771:
                                                 #0  0x0000000000000111 n/a (n/a + 0x0)
                                                 ELF object binary architecture: AMD x86-64

So, there are probably multiple use-after-free/double-delete bugs on Redkite side which don't show up with default gcc+libstdc++ build purely by coincedence, but make demons come out of your nose if you change stdlib or add more runtime validation via LIBCXX_DEBUG.

[iurienistor]

A quick google search suggests that "singular iterator" in the error message essentially means "uninitialized". But the mainViewChanged is generated from macro and doesn't really do anything fancy with iterators aside from for loop over observers, so it's not clear at all how can we get invalid iterator into RkObjectImpl::observersList unless it itself is in some invalid state. I hope you'll be able to figure it out...

I think I understand what is the problem. The observers list is updated during the loop iteration over in one of the the observer callback (usually Redkite was not yet designed with this... but in Geonkick there is a such code introduced by ViewState... which maybe is not so useful) ... and we get a problem with the iteration... there is a need to update the code in order to take in consideration these updates... i'll come later with a fix.

 void prot \
        { \
                for (const auto& ob: rk__observers()) { \
                        RK_LOG_DEBUG("observerCallback[get]: " << RkObject::name()); \
                        RK_LOG_DEBUG("observerCallback[get]: " << ob.get()); \
                        RK_LOG_DEBUG("observerCallback[get]: " << ob.get()->object()->name()); \
                        auto observer = dynamic_cast<rk__observer_ ##ObseverName *>(ob.get()); \
                        RK_LOG_DEBUG("object[call_0]...");                \
                        if (observer) { \
                                RK_LOG_DEBUG("object[call]..."); \
                                RK_LOG_DEBUG("object[call] : " << ob->object()->name()); \
                                observer->observerCallback(val); \
                                RK_LOG_DEBUG("object[end] : " << ob->object()->name()); \
                        } \
                } \

this one can introduce new observers in the list observer->observerCallback(val);

[iurienistor]

@treapster Hi, I pushed the commit into the main branch https://github.com/Geonkick-Synthesizer/geonkick/commit/e76fb2d8527e430fa082fabf5e51e6c1295ba162 this should fix the problem.

[treapster]

@treapster Hi, I pushed the commit into the main branch e76fb2d this should fix the problem.

Thanks, it fixed the original problem for build with gcc, but as i said above there are also bugs with RkObject destruction which make the plugin unusable if compiled with clang and -stdlib=libc++. I'd appreciate if you look into that too:).

[iurienistor]

Here is what happens:

* the destructor of `RkObject` runs and RkObject is destroyed

RkObject [1] is the interface, and has the member unique_ptr... cannot be destroyed before unique_ptr. RkObject is not parent of RkObjectImpl.

* Then a single member of RkObject `o_ptr` is destroyed, it is of type `unique_ptr<RkObjectImpl>`

* the destructor of o_ptr sets it's own value to zero(while copying it to temporary value), and calls the destructor of RkObjectImpl on the value

I don't think I understand what you mean.

* The destructor of RkObjectImpl references the parent RkObject, which is already destroyed,

No, the parent is not destroyed because it contains the children the one of which is being destroyed... the we are talking RkObject [1].

and tries to access it's o_ptr to get the parent, but it is alreay set to zero and segfaults.

The ~RkObjectImpl() accesses the interface though inf_ptr... inf_ptr->parent() { o_ptr->parent(); }... and if you mean that at this moment the unique o_ptr is reset to to zero? and is not accessible o_ptr->parent(); ?... Hm,... it would crash every time. I don't think. But I'll try to reproduce and see what is happening. Thanks for investigations.

[treapster]

The ~RkObjectImpl() accesses the interface though inf_ptr... inf_ptr->parent() { o_ptr->parent(); }... and if you mean that at this moment the unique o_ptr is reset to to zero?

Yes, i think where i said "parent" i meant interface, and the implementation object references inteface object which already was destroyed, and tries to find a pointer to itself which is already set to zero. I have no idea why it works with gcc standard lib, but with clang+libc++ it crashes every time as you said.

[treapster]

Here is what happens:

* the destructor of `RkObject` runs and RkObject is destroyed

RkObject [1] is the interface, and has the member unique_ptr... cannot be destroyed before unique_ptr.

The destructor of RkObject(and any object)can and will be called before destructors of it's members. So, the RkObject is destroyed(its destructor is run), and then the destructor of unique_ptr runs(which calls the destrucor of contained object)

* Then a single member of RkObject `o_ptr` is destroyed, it is of type `unique_ptr<RkObjectImpl>`

* the destructor of o_ptr sets it's own value to zero(while copying it to temporary value), and calls the destructor of RkObjectImpl on the value

I don't think I understand what you mean.

When o_ptr is destroyed, it first sets itself to nullptr, and only then calls the destructor of contained RkObjectImpl. Or, to be more precise, it is what happens when you build with libc++. Here is implementation of relevant unique_ptr methods in libstdc++:

      ~unique_ptr() noexcept
      {
    static_assert(__is_invocable<deleter_type&, pointer>::value,
              "unique_ptr's deleter must be invocable with a pointer");
    auto& __ptr = _M_t._M_ptr();
    if (__ptr != nullptr)
      get_deleter()(std::move(__ptr));
    __ptr = pointer(); // pointer set to zero after destruction
      }

And here it is from libc++:

  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23 ~unique_ptr() { reset(); }
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23 void reset(pointer __p = pointer()) _NOEXCEPT {
    pointer __tmp = __ptr_.first();
    __ptr_.first() = __p; // first set to zero
    if (__tmp)
      __ptr_.second()(__tmp); // then call deleter
  }

So, unlike libstdc++, libc++ protects you from accesing the object via unique_ptr when it is in the process of destruction, and that is why it crashes every time with libc++ but works with libstdc++

[iurienistor]

@treapster These guys from KDE had the same problem - https://blogs.kde.org/comment/10377#comment-10377

I am quoting:

'That event filter will be triggered during destruction of child widgets (at least for the QEvent::Destroy event, I've also seen it with QEvent::Leave events for instance). And, depending on how the event filter is written, it might use the d pointer of the widget, possibly before checking the event type. That's where it gets interesting: the libc++ implementation of unique_ptr sets it to null before calling the destructor (because it's implemented in terms of reset(nullptr);. In libstdc++ however, unique_ptr's destructor just calls the destructor, its value remains valid during destruction.

So, ok, I need to find a workaround ... I'll think what to do in the case of pImpl pattern. Thanks for the clarification and finding this issue! But, sincerely, I don't like the implementation of the libc++ in this case... because the pointer needs to behave like a raw pointer when working with it... smart pointer to remain transparent.

[treapster]

I suspect that the following fix should be enough:

index c5b926c..ddcd264 100644
--- a/src/redkite/src/RkObjectImpl.cpp
+++ b/src/redkite/src/RkObjectImpl.cpp
@@ -52,8 +52,8 @@ RkObject::RkObjectImpl::~RkObjectImpl()
         observersList.clear();

         // Remove myself from the paren object.
-        if (inf_ptr->parent())
-                inf_ptr->parent()->removeChild(inf_ptr);
+        if (parentObject)
+                parentObject->removeChild(inf_ptr);
 }

 void RkObject::RkObjectImpl::removeChildrens()

But, sincerely, I don't like the implementation of the libc++ in this case... because the pointer needs to behave like a raw pointer when working with it... smart pointer to remain transparent.

I think libc++ is doing the right thing, because in the thread you linked they say that access to library objects during destruction is UB according to standard library, and in general it is grey zone whether doing something with partly-destroyed object is legal. In our case we had an actual UB, because the code in ~RkObjectImpl tried calling parent() method on inf_ptr of already destroyed interface(not mid-destruction!) , and libc++ caught this case indirectly through setting o_ptr to 0. We prevented UB, so it's a win for libc++:)

[iurienistor]

parentObject->removeChild(inf_ptr); yes, as exception for the destructor, but this puts limitations because I might need other logic from the interface not only the parent in the destructor... but ok... for now this is the only modification... the derived impl classes seems not to have additional logic in the destructors.

[treapster]

parentObject->removeChild(inf_ptr); yes, as exception for the destructor, but this puts limitations because I might need other logic from the interface not only the parent in the destructor... but ok... for now this is the only modification... the derived impl classes seems not to have additional logic in the destructors.

Since the interface is already destroyed at that point, we can't get anything from it in the destructor of impl. But as you said, we don't need it either, so it should be fine. I also wonder why redkite was designed that way - if we had an actual interface/abstract class and an implementation derived from it, the derived class could be sure that it's base is alive at all times, since the base is destroyed last. Current implementation kinda looks like it was rewritten from c.

[iurienistor]

@treapster "I also wonder why redkite was designed that way"... the story is long... the version 1.0 of Geonkick was developed in Qt, and it was only the standalone version.... than people asked for the plugin, and when the plugin was done than Qt for embedded UI is a problem. I needed for a small gui toolkit that met the requirements for the embedded GUI. There were some but... I was too lazy, and didn't want to change the code of Geonkick, and developed an interface almost compatible with Qt... with the same behavior. Thus, abstract interfaces would require to changed many things in Geonkick.

But yes, pimpl not actually needed even in this case... but I was thinking maybe Redkite would be used as shared library too and there is a need export the symbols (and keep the binary compatibility). But actually for the plugins is required only linked statically... and better maybe all in the header... no libredkite.a would be needed too... but I don't want to change now this library because it worked well until now.

What I am doing now here (https://github.com/Geonkick-Synthesizer/redkite) is an upgrade of Redkite, and instead of Widgets (that are system windows) to be only graphics widgets, and only one system window. This will not load the hosts with many new system windows when the plugin is embedded, but only one window... and the rest of the widgets are graphics, the interface will remain the same, and all stuff also related to pimpl. Probably this version of Redkite I hope to start use in Geonkick in the next releases... but there is some work to be done.

[treapster]

@iurienistor thanks for a detailed response, i didn't know about pimpl and how it allows to preserve ABI compatibility. And the qt reimplementation part is very interesting! BTW, did you know about JUCE when starting with geonkick, and if yes, why did you stick with qt?

but I don't want to change now this library because it worked well until now.

Now that we caught the bug, i hope it will continue working just as well. I erroneously said above that there may be multiple memory ussues, but it was just my incorrect fix which introduced use-after-free:). With the latest patch using parentObject, all segfaults are gone.

What I am doing now here (https://github.com/Geonkick-Synthesizer/redkite) is an upgrade of Redkite, and instead of Widgets (that are system windows) to be only graphics widgets, and only one system window. This will not load the hosts with many new system windows when the plugin is embedded, but only one window... and the rest of the widgets are graphics, the interface will remain the same, and all stuff also related to pimpl. Probably this version of Redkite I hope to start use in Geonkick in the next releases... but there is some work to be done.

Thank you for working on that and improving Redkite further!

[iurienistor]

And the qt reimplementation part is very interesting! BTW, did you know about JUCE when starting with geonkick, and if yes, why did you stick with qt?

Qt implementation of pimpl idiom has something that also prevents creating additional memory when there are inheritance, the same added in Redkite. Geonkick first was developed as standalone, never thought to make as plugin.... even more to know issues related to plugins that are GUI embedded and need to be self-sufficient... and Qt is not sutiable for this.

[iurienistor]

@treapster

With the latest patch using parentObject, all segfaults are gone.

I pushed a commit to the main branch - https://github.com/Geonkick-Synthesizer/geonkick/commit/1d20f0069c4bbd7213609a355a727af3172d9b20

Thanks for helping to find and fix this bug!