locked_hash_set.rs

use std::collections::HashSet;
use std::sync::{Arc, RwLock, RwLockReadGuard};

/// A HashSet that allows controlling when items are actually removed from the list.
/// This can be helpful if you need to keep track of items being added over time
/// and ensuring that they don't get added _and_ removed before you've read them.
struct LockedHashSet {
    values: Arc<RwLock<HashSet<u64>>>,
    values_marked_for_removal: Arc<RwLock<HashSet<u64>>>,
}

impl LockedHashSet {
    fn add(&self, value: u64) {
        self.values.write().unwrap().insert(value);
    }

    fn read(&self) -> RwLockReadGuard<HashSet<u64>> {
        self.values.read().unwrap()
    }

    fn mark_for_removal(&self, value: u64) {
        self.values_marked_for_removal
            .write()
            .unwrap()
            .insert(value);
    }

    fn remove_marked_for_removal(&self) {
        let mut values = self.values.write().unwrap();
        for sequence in self.values_marked_for_removal.write().unwrap().drain() {
            values.remove(&sequence);
        }
    }
}