lazy_staticを使ったglobal変数 (Hashmap版）メモ

use std::sync::{Arc, Mutex, RwLock, RwLockWriteGuard};
use std::thread;
use std::collections::HashMap;
use std::fmt::{Formatter, Error};
use lazy_static::lazy_static;

struct Counter {
    count: i32,
}

struct BigStruct {
    counter: Option<Counter>,
}

impl BigStruct {
    fn increment(&mut self) {
        match self.counter {
            Some(ref mut counter) => {
                counter.count += 1;
            },
            None => {},
        }
    }
}

impl std::fmt::Display for BigStruct {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
        match self.counter {
            Some(ref counter) => {
                write!(f, "count: {}", counter.count)
            },
            None => {
                write!(f, "count: {}", 0)
            },
        }
    }
}

lazy_static! {
    static ref MAP_COUNTER: RwLock<HashMap<String, Arc<Mutex<BigStruct>>>> = {
        let map = HashMap::new();
        RwLock::new(map)
    };
}

fn get_global_counter(key: String) -> Arc<Mutex<BigStruct>> {
    let mut map: RwLockWriteGuard<HashMap<String, Arc<Mutex<BigStruct>>>> = MAP_COUNTER.try_write().unwrap();
    if !map.contains_key(&key.clone()) {
        let big_struct = BigStruct {
            counter: Some(Counter{ count: 0 }),
        };
        map.insert(key.clone(), Arc::new(Mutex::new(big_struct)));
    }
    let writer = map.get(&key.clone()).unwrap();
    Arc::clone(writer)
}

fn main() {
    let mut handles = vec![];

    let key = String::from("1");
    let counter = get_global_counter(key);

    for _ in 0..10 {
        let counter = Arc::clone(&counter);

        let handle = thread::spawn(move || {
            let mut big_struct = counter.lock().unwrap();
            // thread::sleep(std::time::Duration::from_secs(1));
            big_struct.increment();
        });
        handles.push(handle);
    }

    for handle in handles {
        handle.join().unwrap_or_default();
    }
    println!("Result: {}", *counter.lock().unwrap());
}