C++ Implementing threadpool in a mathematical application

I was looking at this question and I was wondering how I can convert this program into a thread pool.

Here, I like to call twine_range at each thread. However, it requires arguments. In addition, this function affects the global variable twine_primes which is at the risk of multiple access.

I also don't care about the order of the results.

Any <thread> or <boost/thread.hpp> based solution is welcome.

#include <string>
#include <iostream>
#include <vector>

std::vector<long> twine_primes;

bool is_prime(long a)
{
    if(a<2l)
        return false;
    if(a==2l)
        return true;
    for(long i=2;i*i<=a;i++)
        if(a%i==0)
            return false;
    return true;
}

void twine_range(long l1,long l2)
{
    for(long l=l1;l<=l2;l++)
        if(is_prime(l) && is_prime(l+2))
            twine_primes.push_back(l);
}

int main()
{

    twine_range(10000000l,20000000l);

    for(long l:twine_primes)
    {
        std::cout
            <<l<<" and "<<(l+2)
            <<" are twine prime numbers."
            << std::endl;
    }

    return 0;
}