Create thread inside class with function from same class

c++, c++11, multithreading

Solution

`foo_func` is a (non-`static`) member function, and it needs an instance of `foo` on which to operate. This instance must be provided to the thread constructor. If you refer to the std::thread::thread reference page it explains what code is executed in the new thread. The relevant point is that which refers to `f` being a pointer to member function:

- If `f` is pointer to a member function of class `T`, then it is called. The return value is ignored. Effectively, the following code is executed:

- `(t1.*f)(t2, ..., tN)` if the type of `t1` is either `T`, reference to `T` or reference to type derived from `T`.

- `((*t1).*f)(t2, ..., tN)` otherwise.

so it is clear that the instance is required.

Change to:

for(...) some_threads.push_back(std::thread(&foo::foo_func, this));

Simple example:

#include <iostream>
#include <thread>
#include <vector>

class foo
{
public:
    void make_foo_func_threads()
    {
        for (int i = 0; i < 5; ++i)
            some_threads.push_back(std::thread(&foo::foo_func, this));
        for (auto& t: some_threads) t.join();
    }

private:
    void foo_func() { std::cout << "Hello\n"; }
    std::vector<std::thread> some_threads;
};

int main()
{
    foo f;
    f.make_foo_func_threads();
}

Problem

I want to be able to define a class with some data members, and a function which has access to those data members, which are to be private. I then want a public function, which creates some threads, which operate on the data members of the class. I am having some trouble getting my code to compile. Don't worry about mutex or data protection, this isn't going to be a problem, since this is just some example code for testing. ``` class foo { public: void make_foo_func_threads(); private: void foo_func(); char private_data; std::vector<std::thread> some_threads; } void foo::foo_func() { while(1) { private_data = 'A'; } } void foo::make_foo_func_thread() { for(...) some_threads.push_back(std::thread(foo_func)); for(...) some_threads.join(); } ``` The compiler is giving me the error: 'no matching call to std::thread::thread()' Apparently there is 'no known conversion for argument 1 from `<unresolved overloaded function type>` to `void (foo::*&&)'`. Erm, yeah, I have no idea what that means apart from the compiler is having trouble understanding how to resolve foo_func - I think. How can I help the compiler understand what I am trying to do, so it won't bother me with any more errors. No doubt the code I have written is not legal, and if that is the case could someone explain why that is the case to me. Thanks!

Original source