std::thread leads to Abort

[User Name:]

I'm trying to code a program for dealing with prime numbers. The idea is to have the prime list readable by all threads, but writeable by 1.

#include "gmpxx.h"

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

// primes must be initialised with at least the first two prime numbers.
static std::vector<mpz_class> primes = {2, 3};

// integer sqrt
static mpz_class sqrt(mpz_class n)
{
    mpf_class x, y = n;
    
    do{
        x = y;
        y = (x + n / x) / 2;
    }while(abs(y - x) >= 1);
    
    return y;
}

// extends primes to the lowest prime greater than or equal to n
static void extend_primes(mpz_class n)
{
    // Unfortunately, the primes can't efficiently, if at all, be extended concurrently...
    static std::mutex m;
    std::lock_guard<std::mutex> lock(m);
    
    for(mpz_class i = primes.back() + 2;i <= n;i += 2)
    {
        bool prime = true; // Assume i is prime.
        
        for(auto j = primes.begin();prime && *j <= sqrt(i);j++)
            if(i % *j == 0)
                prime = false;
        
        if(prime)
            primes.push_back(i);
    }
}

int main()
{
    extend_primes(7);
    std::thread t(extend_primes, 19); // This (or a resulting call) must be the cause. When commented out, everything works fine.
    
    for(auto i = primes.begin();i < primes.end();i++)
        std::cout << i->get_str() << " ";
    
    std::cout << std::endl;
    return 0;
}

The error:

$ gcc -ggdb -std=c++0x -lstdc++ -lgmp -o prime prime.cpp
$ ./prime 
terminate called after throwing an instance of 'std::system_error'
  what():  
Aborted