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.

Code:

#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:

Code:

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