Trouble with nested connections

[stevenlovegrove]

Safe Recursion and Modification While Iterating

Based on your README, I think the code snippet below is meant to work, but I'm encountering some kind of stack corruption or memory invalidation or something when running (it's causing allocation of a really large value (probably from uninitialized memory). I'm seeing similar behaviour in my own program which I've tried to recreate in this minimal test case.

#include <iostream>
#include <signals/signals.hpp>

int main( int /*argc*/, char** /*argv*/ )
{
    fteng::signal<void(void)> test;

    test.connect([&test](){
        std::cout << "A" << std::endl;
        test.connect([&test](){std::cout << "B" << std::endl;});
        test.connect([&test](){std::cout << "C" << std::endl;});
    });

    std::cout << "=============" << std::endl;
    test();
    std::cout << "=============" << std::endl;
    test();

    return 0;
}

Outputs:

=============
A
libc++abi: terminating with uncaught exception of type std::bad_alloc: std::bad_alloc

1  __pthread_kill                                                                                                                                                                                      (x86_64) /usr/lib/system/libsystem_kernel.dylib       0x7fff2049392e 
2  pthread_kill                                                                                                                                                                                        (x86_64) /usr/lib/system/libsystem_pthread.dylib      0x7fff204c25bd 
3  abort                                                                                                                                                                                               (x86_64) /usr/lib/system/libsystem_c.dylib            0x7fff20417411 
4  abort_message                                                                                                                                                                                       (x86_64) /usr/lib/libc++abi.dylib                     0x7fff20485ef2 
5  demangling_terminate_handler()                                                                                                                                                                      (x86_64) /usr/lib/libc++abi.dylib                     0x7fff204775e5 
6  _objc_terminate()                                                                                                                                                                                   (x86_64h) /usr/lib/libobjc.A.dylib                    0x7fff20370595 
7  std::__terminate(void ( *)())                                                                                                                                                                       (x86_64) /usr/lib/libc++abi.dylib                     0x7fff20485307 
8  __cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception *)                                                                                                                                             (x86_64) /usr/lib/libc++abi.dylib                     0x7fff20487beb 
9  __cxa_throw                                                                                                                                                                                         (x86_64) /usr/lib/libc++abi.dylib                     0x7fff20487bb2 
10 operator new(unsigned long)                                                                                                                                                                         (x86_64) /usr/lib/libc++abi.dylib                     0x7fff2048786f 
11 std::__libcpp_allocate(unsigned long, unsigned long)                                                                                                                                                new                                              253  0x1000096cd    
12 std::allocator<fteng::details::sig_base::call>::allocate(unsigned long)                                                                                                                             memory                                           1664 0x100009615    
13 std::allocator_traits<std::allocator<fteng::details::sig_base::call>>::allocate(std::allocator<fteng::details::sig_base::call>&, unsigned long)                                                     memory                                           1400 0x1000094ad    
14 std::__split_buffer<fteng::details::sig_base::call, std::allocator<fteng::details::sig_base::call>&>::__split_buffer(unsigned long, unsigned long, std::allocator<fteng::details::sig_base::call>&) __split_buffer                                   318  0x100009402    
15 std::__split_buffer<fteng::details::sig_base::call, std::allocator<fteng::details::sig_base::call>&>::__split_buffer(unsigned long, unsigned long, std::allocator<fteng::details::sig_base::call>&) __split_buffer                                   317  0x10000900d    
16 void std::vector<fteng::details::sig_base::call>::__emplace_back_slow_path<>()                                                                                                                      vector                                           1668 0x100008d39    
17 fteng::details::sig_base::call& std::vector<fteng::details::sig_base::call>::emplace_back<>()                                                                                                       vector                                           1690 0x100008b2b    
18 fteng::connection_raw fteng::signal<void ()>::connect<main::$_0::operator()() const::'lambda0'()>(main::$_0::operator()() const::'lambda0'()&&) const                                               signals.hpp                                      307  0x100009d57    
19 main::$_0::operator()() const                                                                                                                                                                       main.cpp                                         11   0x100009c0f    
20 fteng::connection_raw fteng::signal<void ()>::connect<main::$_0>(main::$_0&&) const::'lambda'(void *)::operator()(void *) const                                                                     signals.hpp                                      308  0x100009b8c    
21 fteng::connection_raw fteng::signal<void ()>::connect<main::$_0>(main::$_0&&) const::'lambda'(void *)::__invoke(void *)                                                                             signals.hpp                                      308  0x100009b65    
22 void fteng::signal<void ()>::operator()<>() const                                                                                                                                                   signals.hpp                                      229  0x100006c6a    
23 main                                                                                                                                                                                                main.cpp                                         15   0x100006948    
24 start                                                                                                                                                                                               (x86_64) /usr/lib/system/libdyld.dylib                0x7fff204ddf5d 

Originally I thought there was some issue with the scope of the lambda related to #20 but I see the same on the PR that was raised against that issue (https://github.com/mikezackles/signals/tree/issue-20) or when using a simple functor:

void method_B() { std::cout << "B" << std::endl; }
void method_C() { std::cout << "C" << std::endl; }

int main( int /*argc*/, char** /*argv*/ )
{
    fteng::signal<void(void)> test;

    test.connect([&test](){
        std::cout << "A" << std::endl;
        test.connect(method_B);
        test.connect(method_C);
    });

    std::cout << "=============" << std::endl;
    test();
    std::cout << "=============" << std::endl;
    test();

    return 0;
}

If I comment out the last connection (of the C printout) then I see what might be considered expected output:

=============
A
=============
A
B

Though depending on how the iteration is implemented I might have expected the first invocation to print A\nB and the second to print A\nB\nB (especially since the loop looks like for (size_t i = 0, n = calls.size(); i < n; ++i) in operator().

I've not been able to figure out what is going wrong - I can't see any iterators getting invalidated or something with the recursive modification...

Any thoughts appreciated!