C++ Boost Asio Pool threading with lambda functions and pass by reference variables

Question

I have a lambda function I would like to post to a boost pool. The lambda function makes use of a large object which is passed by reference. However, I can't seem to make this code run properly.

#include <boost/asio.hpp>
#include <iostream>

int main() {
    int large_object = 10;
    auto f1 = [&large_object](int x) {
        std::cout << "this is a very large object that needs passed by ref " << large_object << std::endl;
        std::cout << x << std::endl;
        std::this_thread::sleep_for(std::chrono::seconds {3});
        std::cout << "DONE SLEEPING!" << std::endl;
    };

    int processor_count = 2;  // consider that this CPU has two processors

    // Launch the pool with n threads.
    boost::asio::thread_pool pool(processor_count);

    int x = 2;
    // Submit a function to the pool.
    boost::asio::post(pool, [x]{f1(x);});

    pool.join();

    return 0;
}

Is it possible to post this lambda function to a boost pool?

Thank you for your time.

Answer 1

You need to capture f1 too, just like other variables. Lambda is a variable:

 [x, f1]{f1(x);});

(Or by reference)

By the way, if you want simple thread pool execution, consider also std::async .