#include<stdio.h>
#include<thread>
#include<vector>
#include<mutex>
#include<unistd.h>
using namespace std;

vector<uint64_t> already_done;
mutex already_done_mutex;
uint64_t fib(int x){
	if(already_done.size() > x)
		return already_done[x];
	if (x < 2) {
		return 1;
	}
	// lock here
	already_done_mutex.lock();
	if(already_done.size() > x){
		// unlock
		already_done_mutex.unlock();
		return already_done[x];
	}
	uint64_t result = fib(x-1) + fib(x-2);
	already_done.push_back(result);
	// unlock here
	already_done_mutex.unlock();
	return result;
	
}

void calc_and_print(int n){
	printf("%d: %lu\n", n, fib(n));
}

int main(){
	vector<thread> threads;
	already_done.push_back(1);
	already_done.push_back(1);
	already_done.push_back(2);

	for(int i = 1; i < 100; i++){
		threads.push_back(    thread(calc_and_print, i)   );
	}
	/* alternative:
	for(int i = 0; i < threads.size(); i++)
		threads[i].join();
	 */
	for(auto &t : threads){
		t.join();
		printf("Just joined another thread!  Another one bites the dust!\n");
	}
	return 0;
}