passing functor to std::thread with ctor parameters. is it possible?

Question

class worker { std::atomic_bool done; std::string segment_name; bi::named_mutex mutex; std::string file_name; data_segment_state state; unsigned long data_size; std::unique_ptr<unsigned char> data; protected: void operator()() { while(!done) { } } public: worker(const std::string& _segment_name, bi::managed_shared_memory& segment) : done{false}, segment_name{_segment_name}, mutex{bi::open_or_create, segment_name.c_str() }, file_name {}, state {data_segment_state::not_received }, data_size{0}, data {segment.construct<unsigned char>(segment_name.c_str())[chunk_size](0) } } worker(worker&& rhs) : done {rhs.done.load()} , mutex(bi::open_or_create, rhs.segment_name.c_str()), segment_name{rhs.segment_name}, file_name {rhs.file_name}, state {rhs.state }, data_size{rhs.data_size}, data {std::move(rhs.data)} { } };

...

 std::string worker_name; std::thread t{worker{worker_name, segment}}; In instantiation of 'struct std::_Bind_simple<worker()>': thread:137:47: required from 'std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = worker; _Args = {}]' error: no type named 'type' in 'class std::result_of<worker()>' typedef typename result_of<_Callable(_Args...)>::type result_type;

what is a valid thread initialization with functional object? full text of error: error: no type named 'type' in 'class
std::result_of' typedef typename result_of<_Callable(_Args...)>::type result_type; ^

"does also produces the same error with a using default ctor" No it doesn't. I guess you are not showing us the code that you are compiling, and you're actually getting some other error that we can't possibly guess. — Jonathan Wakely
– Jonathan Wakely, Commented Oct 1, 2015 at 12:30
let me update the question with a code as full as I can, and output of GCC from console — amigo421
– amigo421, Commented Oct 1, 2015 at 12:36
You should really have done that before asking a question. See stackoverflow.com/help/mcve — Jonathan Wakely
– Jonathan Wakely, Commented Oct 1, 2015 at 12:37

amigo421 · Accepted Answer · 2015-10-02 13:35:51Z

4

The issue was in the my inattention: operator() was in protected section . moving to public solves the problem

answered Oct 2, 2015 at 13:35

amigo421

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sh03 · Accepted Answer · 2015-10-01 12:28:17Z

Just pass the constructed functor:

std::thread t(worker{str, 10});

Live demo

The constructor of std::thread you are referring to takes a constructed function object and arguments that will be passed when calling that function object. So in your case the arguments would be passed to operator().

Using std::ref is pointless there, str will bind directly to the constructor parameter, you don't need to protect it from decaying.

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