extern crate rayon;
use rayon::prelude::*;

#[derive(Clone)]
struct Store(u64);

struct Tx(u64);

impl Tx {
    fn verify_and_store(&self, store: &mut Store) -> u64 {
        store.0 += self.0;
        self.0
    }
}

fn verify_and_store(store: &mut Store, txs: Vec<Tx>) {
    use std::cell::RefCell;
    thread_local!(static STORE: RefCell<Option<Store>> = RefCell::new(None));

    let mut result = Vec::new();

    txs.par_iter().map(|tx| {
        STORE.with(|cell| {
            let mut local_store = cell.borrow_mut();
            if local_store.is_none() {
                *local_store = Some(store.clone());
            }
            tx.verify_and_store(local_store.as_mut().unwrap())
        })
    }).collect_into(&mut result);
}

fn main() {
    let txs = vec![Tx(0), Tx(1)];
    let mut store = Store(0);
    verify_and_store(&mut store, txs);
}