create threaded class functions with arguments inside class

Question

I have an object of class AI, which has a private non static void function which has a lot of arguments: minmax(double& val,double alpha, double beta, unsigned short depth, board* thisTurn); because this is a very time intensive function I want to use a number of threads to run it concurrently, therefor I must create a thread with this function inside another function inside the AI class;

According toThis question to make threads inside member functions containing non static member functions wiht no arguments of said class, one must call:

std::thread t(&myclass::myfunc,this);

And according to this tutorial threads of fucntions with multiple arguments can be created as such:

std::thread t(foo,4,5)

where the function 'foo' has 2 integer arguments

However I desire to mix these to things, to call a function which has arguments, which is also a non static member function, from inside the class that it is a member of, and i am not sure how to mix these to things.

I have off course tried (remember that it is inside a function inside the AI class):

std::thread t(&AI::minmax,val,alpha,beta,depth,thisTurn,this);

and

std::thread t(&AI::minmax,this,val,alpha,beta,depth,thisTurn);

But both cases fails with a compile error like this:

error: no matching constructor for initialization of 'std::thread'
candidate constructor template not viable: requires single argument '__f', but
  7 arguments were provided

My question is therefor, if or if not, it is even possiple to -- from inside a member function of a class -- call a non static member function which has several arguments as a thread, and if this is the case, how it is done.

This question is however not wether or not it is a good idea to use multithreading in my specific case.

Edit

After doing some testing i realized that i can not call functions with arguments as threads at all, not even non-member functions with only one argument called directly from main, this was however solved by asking this other question where i realized that i simply need to add the flag -std=c++11 (because apparantly macs don't always use all c++11 features as standard) after doing so the answer works fine.

try std::thread t(&AI::minmax,this,std::ref(val),alpha,beta,depth,thisTurn,this); — Piotr Skotnicki
– Piotr Skotnicki, Commented Feb 14, 2017 at 8:25
@PiotrSkotnicki doing so gives the same error as before, and this new error no matching function for call to '__invoke' — Nikolaj
– Nikolaj, Commented Feb 14, 2017 at 9:57
@PiotrSkotnicki You have one "this" too much. It should read std::thread t(&AI::minmax, this, std::ref(val), alpha, beta, depth, thisTurn);. — pschill
– pschill, Commented Feb 14, 2017 at 10:40
@pschill a copy-paste of OP's code but probably you're right — Piotr Skotnicki
– Piotr Skotnicki, Commented Feb 14, 2017 at 10:46

pschill · Accepted Answer · 2017-02-14 10:44:00Z

0

You need to wrap references using std::ref. The following example compiles fine:

#include <iostream>
#include <thread>

class board;

class AI
{
public:

    void minmax(double& val, double alpha, double beta, unsigned short depth, board* thisTurn)
    {
        std::cout << "minmax" << std::endl;
    }

    void spawnThread()
    {
        double val;
        double alpha;
        double beta;
        unsigned short depth;
        board* thisTurn;

        std::thread t(&AI::minmax, this, std::ref(val), alpha, beta, depth, thisTurn);

        t.join();
    }

};

int main()
{
    AI ai;
    ai.spawnThread();
}

answered Feb 14, 2017 at 10:44

pschill

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2 Comments

Nikolaj Over a year ago

that example code still produces two error: firstly: std::ref cause compiler error: error: no matching function for call to '__invoke'followed by several lines of: ...in file included from... but in the end indicating that the problem is std::ref(val). Secondly it cause the old

no matching constructor for initialization of 'std::thread' candidate constructor template not viable: requires single argument '__f', but       7 arguments were provided

pschill Over a year ago

@Nikolaj The code I posted compiles well in Visual Studio 2015 (see rextester.com/ALGB12143). I do not have VS2013 here to test the code, and earlier versions will not work because #include <thread> is missing there. What compiler do you use?

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