import sync
import time

struct SafeCounter {
mut:
    mt sync.Mutex = sync.new_mutex()
pub mut:
    value map[string]int
}

fn (mut c SafeCounter) inc(key string) {
    c.mt.@lock()
    defer {
        c.mt.unlock()
    }
    c.value[key]++
}

fn (mut c SafeCounter) value(key string) int {
    c.mt.@lock()
    defer {
        c.mt.unlock()
    }
    return c.value[key]
}

fn main() {
    mut counter := &SafeCounter{}

    for i := 0; i < 5; i++ {
        spawn fn [mut counter] () {
            for j := 0; j < 100; j++ {
                counter.inc('key')
            }
        }()
    }

    time.sleep(1 * time.second)
    println(counter.value('key'))
}