boost::detail::nullary_function causes stack overflow when copied

[yhirsch@…]

Hi,

It seems as though boost::detail::nullary_function implement a perfect forwarding constructor incorrectly, which causes a stack overflow:

Here is a simple example:

#include <boost/thread/detail/nullary_function.hpp>
#include <boost/system/detail/error_code.ipp>

int main(int argc, char* argv[])
{
    boost::detail::nullary_function<void ()> f1;
    auto f2 = f1;
}

This ends up invoking nullary_function.hpp:81 which keeps invoking iself recursively, resulting in a stack overflow.

[jeff]

From the history, it seems the bug in nullary_function has been there for a couple of years. A simple way to fix is to add another overload

      nullary_function(nullary_function& other) BOOST_NOEXCEPT :
      impl(other.impl)
      {
      }

Or to add enable_if to

      template<typename F, typename = typename boost::enable_if<!boost::is_same<typename decay<F>::type, this_type>::value>::type>
      nullary_function(BOOST_THREAD_RV_REF(F) f):
      impl(new impl_type<typename decay<F>::type>(thread_detail::decay_copy(boost::forward<F>(f))))
      {}

[jeff]

Fix a typo in the second code block: it should be enable_if_c instead of enable_if. also this_type is nullary_function<void()> or nullary_function<R()> (depending on the specialization).

      using this_type = nullary_function<void()>; 
      template<typename F, typename = typename boost::enable_if_c<!boost::is_same<typename decay<F>::type, this_type>::value>::type>
      nullary_function(BOOST_THREAD_RV_REF(F) f):
      impl(new impl_type<typename decay<F>::type>(thread_detail::decay_copy(boost::forward<F>(f))))
      {}

[viboes]

Thanks for the report. I'll try to fix it soon but a PR on github would help as well.

[viboes]

I've some trouble identifying where there is recursion

      template<typename F>
      nullary_function(BOOST_THREAD_RV_REF(F) f):
      impl(new impl_type<typename decay<F>::type>(thread_detail::decay_copy(boost::forward<F>(f))))
      {}

impl_type is not nullary_function, isn't it? Could you clarify?

[viboes]

Oh, I believe I see it now.

The problem is on the open overloads

#ifdef BOOST_NO_CXX11_RVALUE_REFERENCES
      template<typename F>
      explicit nullary_function(F& f);
#endif
      template<typename F>
      nullary_function(BOOST_THREAD_RV_REF(F) f);

[viboes]

​https://github.com/boostorg/thread/commit/d8d549cf3e01fe74779cd421d88d7079c3a25b49

[viboes]

Please reopen if you believe the fix is not good enough.