Im trying to create a simple wrapper to be used by my application when creating threads in lew of std::thread. The only purpose of using this app thread wrapper is to ensure some code gets invoked on every spawned thread consistently. I thought this would be trivial, but the std::thread constructor and argument passing is rather complex and Im getting very cryptic build errors here.
This is a simple example of what I'm trying to do:
#include <thread>
class AppThread : public std::thread
{
template< class Function, class... Args >
static void wrap( Function&& f, Args&&... args )
{
//Some code
f( std::forward<Args>( args )... );
}
public:
template< class Function, class... Args >
explicit AppThread( Function&& f, Args&&... args ) : std::thread( AppThread::wrap<Function,Args...>,
std::forward<Function>( f ), std::forward<Args>( args )... )
{}
};
void runA() {}
void runB( int x ) {}
main()
{
AppThread thread1 = AppThread( runA );
//AppThread thread2 = AppThread( runB, 5 );
}
I'd like to be able to drop in AppThread wherever std:thread is being used, so extending and overriding the constructor seems like the best approach. But passing those arguments through to my wrapped method causes this cascade of errors ( gcc 7.2 )
In file included from thread_wrap.cpp:1:0:
gcc-7.2.0/include/c++/7.2.0/thread: In instantiation of ‘struct std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >’:
gcc-7.2.0/include/c++/7.2.0/thread:127:22: required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(void (&)()); _Args = {void (&)()}]’
thread_wrap.cpp:15:130: required from ‘AppThread::AppThread(Function&&, Args&& ...) [with Function = void (&)(); Args = {}]’
thread_wrap.cpp:24:41: required from here
gcc-7.2.0/include/c++/7.2.0/thread:240:2: error: no matching function for call to ‘std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >::_M_invoke(std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >::_Indices)’
operator()()
^~~~~~~~
gcc-7.2.0/include/c++/7.2.0/thread:231:4: note: candidate: template<long unsigned int ..._Ind> decltype (std::__invoke((_S_declval<_Ind>)()...)) std::thread::_Invoker<_Tuple>::_M_invoke(std::_Index_tuple<_Ind ...>) [with long unsigned int ..._Ind = {_Ind ...}; _Tuple = std::tuple<void (*)(void (&)()), void (*)()>]
_M_invoke(_Index_tuple<_Ind...>)
^~~~~~~~~
gcc-7.2.0/include/c++/7.2.0/thread:231:4: note: template argument deduction/substitution failed:
gcc-7.2.0/include/c++/7.2.0/thread: In substitution of ‘template<long unsigned int ..._Ind> decltype (std::__invoke(_S_declval<_Ind>()...)) std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >::_M_invoke<_Ind ...>(std::_Index_tuple<_Ind1 ...>) [with long unsigned int ..._Ind = {0, 1}]’:
gcc-7.2.0/include/c++/7.2.0/thread:240:2: required from ‘struct std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >’
gcc-7.2.0/include/c++/7.2.0/thread:127:22: required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(void (&)()); _Args = {void (&)()}]’
thread_wrap.cpp:15:130: required from ‘AppThread::AppThread(Function&&, Args&& ...) [with Function = void (&)(); Args = {}]’
thread_wrap.cpp:24:41: required from here
gcc-7.2.0/include/c++/7.2.0/thread:233:29: error: no matching function for call to ‘__invoke(std::__tuple_element_t<0, std::tuple<void (*)(void (&)()), void (*)()> >, std::__tuple_element_t<1, std::tuple<void (*)(void (&)()), void (*)()> >)’
-> decltype(std::__invoke(_S_declval<_Ind>()...))
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
In file included from gcc-7.2.0/include/c++/7.2.0/tuple:41:0,
from gcc-7.2.0/include/c++/7.2.0/bits/unique_ptr.h:37,
from gcc-7.2.0/include/c++/7.2.0/memory:80,
from gcc-7.2.0/include/c++/7.2.0/thread:39,
from thread_wrap.cpp:1:
gcc-7.2.0/include/c++/7.2.0/bits/invoke.h:89:5: note: candidate: template<class _Callable, class ... _Args> constexpr typename std::__invoke_result<_Functor, _ArgTypes>::type std::__invoke(_Callable&&, _Args&& ...)
__invoke(_Callable&& __fn, _Args&&... __args)
^~~~~~~~
gcc-7.2.0/include/c++/7.2.0/bits/invoke.h:89:5: note: template argument deduction/substitution failed:
gcc-7.2.0/include/c++/7.2.0/bits/invoke.h: In substitution of ‘template<class _Callable, class ... _Args> constexpr typename std::__invoke_result<_Functor, _ArgTypes>::type std::__invoke(_Callable&&, _Args&& ...) [with _Callable = void (*)(void (&)()); _Args = {void (*)()}]’:
gcc-7.2.0/include/c++/7.2.0/thread:233:29: required by substitution of ‘template<long unsigned int ..._Ind> decltype (std::__invoke(_S_declval<_Ind>()...)) std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >::_M_invoke<_Ind ...>(std::_Index_tuple<_Ind1 ...>) [with long unsigned int ..._Ind = {0, 1}]’
gcc-7.2.0/include/c++/7.2.0/thread:240:2: required from ‘struct std::thread::_Invoker<std::tuple<void (*)(void (&)()), void (*)()> >’
gcc-7.2.0/include/c++/7.2.0/thread:127:22: required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(void (&)()); _Args = {void (&)()}]’
thread_wrap.cpp:15:130: required from ‘AppThread::AppThread(Function&&, Args&& ...) [with Function = void (&)(); Args = {}]’
thread_wrap.cpp:24:41: required from here
gcc-7.2.0/include/c++/7.2.0/bits/invoke.h:89:5: error: no type named ‘type’ in ‘struct std::__invoke_result<void (*)(void (&)()), void (*)()>’
Could definitely use some insight here! Thanks
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