Crash when callback is disconnected in a dll

[01Pollux]

When using signals2 across multiple DDLs, everything works fine until the dlls gets unloaded, which results in crash the next time we dispatch the signal.
I found this stackoverflow post which describes the same issue i'm having.

The test sample:

Shared.cpp:

#include <boost/dll.hpp>
#include <boost/signals2.hpp>
#include <iostream>

struct SomeInterface
{
    boost::signals2::signal<void()> signal;
};

boost::signals2::connection con;

void init(SomeInterface* iface)
{
    con = iface->signal.connect([] { std::cout << "Hello, Shared!" << std::endl; });
}

void shutdown()
{
    con.disconnect();
}

BOOST_DLL_AUTO_ALIAS(init);
BOOST_DLL_AUTO_ALIAS(shutdown);

Host.cpp:

#include <boost/dll.hpp>
#include <boost/signals2.hpp>
#include <iostream>

struct SomeInterface
{
    boost::signals2::signal<void()> signal;
};

int main()
{
    SomeInterface* iface = new SomeInterface;

    {
        boost::dll::shared_library dll("Shared", boost::dll::load_mode::append_decorations);

        auto init     = dll.get<void (*)(SomeInterface*)>("init");
        auto shutdown = dll.get<void (*)()>("shutdown");

        init(iface);
        iface->signal();
        shutdown();
    }

    iface->signal();

    return 0;
}

[fmhess]

I noticed you're not disconnecting the slot properly. There is a disconnect method on the connection object.

…

On Fri, Sep 6, 2024, 7:03 PM Yassine Sen ***@***.***> wrote: When using signals2 across multiple DDLs, everything works fine until the dlls gets unloaded, which results in crash the next time we dispatch the signal. I found this stackoverflow post <https://stackoverflow.com/questions/28703432/access-violation-when-using-boostsignals2-and-unloading-dlls> which describes the same issue i'm having. The test sample: Shared.cpp: #include <boost/dll.hpp> #include <boost/signals2.hpp> #include <iostream> struct SomeInterface { boost::signals2::signal<void()> signal; }; boost::signals2::connection con; void init(SomeInterface* iface) { con = iface->signal.connect([] { std::cout << "Hello, Shared!" << std::endl; }); } void shutdown(SomeInterface* iface) { iface->signal.disconnect(con); } BOOST_DLL_AUTO_ALIAS(init);BOOST_DLL_AUTO_ALIAS(shutdown); Host.cpp: #include <boost/dll.hpp> #include <boost/signals2.hpp> #include <iostream> struct SomeInterface { boost::signals2::signal<void()> signal; }; int main() { SomeInterface* iface = new SomeInterface; iface->signal.connect([] { std::cout << "Hello, Host!" << std::endl; }); { boost::dll::shared_library dll("Shared", boost::dll::load_mode::append_decorations); auto init = dll.get<void (*)(SomeInterface*)>("init"); auto shutdown = dll.get<void (*)(SomeInterface*)>("shutdown"); init(iface); iface->signal(); shutdown(iface); } iface->signal(); return 0; } — Reply to this email directly, view it on GitHub <#78>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AARKTX5FGNHJXW5HSF7FQGDZVIYFHAVCNFSM6AAAAABNZNN6Q2VHI2DSMVQWIX3LMV43ASLTON2WKOZSGUYTCMRZHA2TSNQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[01Pollux]

Updated the sample, thanks for pointing it out, however that was not the issue
Anyway, i'll provide the stack trace.

Host.exe!boost::detail::sp_counted_base::release() Line 119	C++
Host.exe!boost::detail::shared_count::~shared_count() Line 432	C++
Host.exe!boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>::~shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>()	C++
Host.exe!boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>::`scalar deleting destructor'(unsigned int)	C++
Host.exe!std::destroy_at<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>(boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>> * const _Location) Line 306	C++
Host.exe!std::_Default_allocator_traits<std::allocator<std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *>>>::destroy<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>(std::allocator<std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *>> & __formal, boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>> * const _Ptr) Line 707	C++
Host.exe!std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *>::_Freenode<std::allocator<std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *>>>(std::allocator<std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *>> & _Al, std::_List_node<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,void *> * _Ptr) Line 317	C++
Host.exe!std::list<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>,std::allocator<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>>::erase(const std::_List_const_iterator<std::_List_val<std::_List_simple_types<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>>> _Where) Line 1417	C++
Host.exe!boost::signals2::detail::grouped_list<int,std::less<int>,boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>::erase(const std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>> & key, const std::_List_iterator<std::_List_val<std::_List_simple_types<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>>> & it) Line 165	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::nolock_cleanup_connections_from(boost::signals2::detail::garbage_collecting_lock<boost::signals2::mutex> & lock, bool grab_tracked, const std::_List_iterator<std::_List_val<std::_List_simple_types<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<enum boost::signals2::detail::slot_meta_group,boost::optional<int>>,boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>>,boost::signals2::mutex>>>>> & begin, unsigned int count) Line 453	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::nolock_cleanup_connections(boost::signals2::detail::garbage_collecting_lock<boost::signals2::mutex> & lock, bool grab_tracked, unsigned int count) Line 474	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::nolock_force_unique_connection_list(boost::signals2::detail::garbage_collecting_lock<boost::signals2::mutex> & lock) Line 489	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::create_new_connection(boost::signals2::detail::garbage_collecting_lock<boost::signals2::mutex> & lock, const boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>> & slot) Line 516	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::nolock_connect(boost::signals2::detail::garbage_collecting_lock<boost::signals2::mutex> & lock, const boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>> & slot, boost::signals2::connect_position position) Line 560	C++
Host.exe!boost::signals2::detail::signal_impl<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::connect(const boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>> & slot, boost::signals2::connect_position position) Line 168	C++
Host.exe!boost::signals2::signal<void __cdecl(void),boost::signals2::optional_last_value<void>,int,std::less<int>,boost::function<void __cdecl(void)>,boost::function<void __cdecl(boost::signals2::connection const &)>,boost::signals2::mutex>::connect(const boost::signals2::slot<void __cdecl(void),boost::function<void __cdecl(void)>> & slot, boost::signals2::connect_position position) Line 699	C++
Host.exe!main() Line 25	C++

[01Pollux]

As stated on the stackoverflow post, one could wrap the signal around an interface to delegate the connect() method to the owner of the signal, however a fix to this issue would be nicer than the extra indirection for a workaround.

    using Connection       = boost::signals2::connection;
    using ScopedConnection = boost::signals2::scoped_connection;

    template<typename... SigTy> class Signal
    {
    public:
        using base_type = boost::signals2::signal<SigTy...>;
        using slot_type = typename base_type::slot_type;
        using slot_ex   = typename base_type::extended_slot_type;

    private:
        struct ISignal
        {
            virtual ~ISignal()                                = default;
            virtual Connection Connect(const slot_type& slot) = 0;
            virtual Connection ConnectEx(const slot_ex& slot) = 0;
        };

        struct SignalImpl : ISignal
        {
            [[nodiscard]] Connection Connect(const slot_type& slot) override
            {
                return m_Signal.connect(slot);
            }
            [[nodiscard]] Connection ConnectEx(const slot_ex& slot) override
            {
                return m_Signal.connect_extended(slot);
            }
            base_type m_Signal;
        };

    public:
        Connection Connect(const slot_type& slot)
        {
            return m_Signal->Connect(slot);
        }

        Connection ConnectEx(const slot_ex& slot)
        {
            return m_Signal->ConnectEx(slot);
        }

        template<typename... Args> auto Invoke(Args&&... args)
        {
            auto impl = static_cast<SignalImpl*>(m_Signal.get());
            return impl->m_Signal(std::forward<Args>(args)...);
        }

    private:
        std::unique_ptr<ISignal> m_Signal = std::make_unique<SignalImpl>();
    };