snix/tvix/store/src/pathinfoservice/lru.rs

use async_stream::try_stream;
use futures::stream::BoxStream;
use lru::LruCache;
use nix_compat::nixbase32;
use std::num::NonZeroUsize;
use std::sync::Arc;
use tokio::sync::RwLock;
use tonic::async_trait;
use tracing::instrument;

use tvix_castore::composition::{CompositionContext, ServiceBuilder};
use tvix_castore::Error;

use super::{PathInfo, PathInfoService};

pub struct LruPathInfoService {
    lru: Arc<RwLock<LruCache<[u8; 20], PathInfo>>>,
}

impl LruPathInfoService {
    pub fn with_capacity(capacity: NonZeroUsize) -> Self {
        Self {
            lru: Arc::new(RwLock::new(LruCache::new(capacity))),
        }
    }
}

#[async_trait]
impl PathInfoService for LruPathInfoService {
    #[instrument(level = "trace", skip_all, fields(path_info.digest = nixbase32::encode(&digest)))]
    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
        Ok(self.lru.write().await.get(&digest).cloned())
    }

    #[instrument(level = "trace", skip_all, fields(path_info.root_node = ?path_info.node))]
    async fn put(&self, path_info: PathInfo) -> Result<PathInfo, Error> {
        self.lru
            .write()
            .await
            .put(*path_info.store_path.digest(), path_info.clone());

        Ok(path_info)
    }

    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
        let lru = self.lru.clone();
        Box::pin(try_stream! {
            let lru = lru.read().await;
            let it = lru.iter();

            for (_k,v) in it {
                yield v.clone()
            }
        })
    }
}

#[derive(serde::Deserialize, Debug)]
#[serde(deny_unknown_fields)]
pub struct LruPathInfoServiceConfig {
    capacity: NonZeroUsize,
}

impl TryFrom<url::Url> for LruPathInfoServiceConfig {
    type Error = Box<dyn std::error::Error + Send + Sync>;
    fn try_from(_url: url::Url) -> Result<Self, Self::Error> {
        Err(Error::StorageError(
            "Instantiating a LruPathInfoService from a url is not supported".into(),
        )
        .into())
    }
}

#[async_trait]
impl ServiceBuilder for LruPathInfoServiceConfig {
    type Output = dyn PathInfoService;
    async fn build<'a>(
        &'a self,
        _instance_name: &str,
        _context: &CompositionContext,
    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
        Ok(Arc::new(LruPathInfoService::with_capacity(self.capacity)))
    }
}

#[cfg(test)]
mod test {
    use nix_compat::store_path::StorePath;
    use std::{num::NonZeroUsize, sync::LazyLock};

    use crate::{
        pathinfoservice::{LruPathInfoService, PathInfo, PathInfoService},
        tests::fixtures::PATH_INFO,
    };
    static PATHINFO_2: LazyLock<PathInfo> = LazyLock::new(|| {
        let mut p = PATH_INFO.clone();
        p.store_path = StorePath::from_name_and_digest_fixed("dummy", [1; 20]).unwrap();
        p
    });

    static PATHINFO_2_DIGEST: LazyLock<[u8; 20]> =
        LazyLock::new(|| *PATHINFO_2.store_path.digest());

    #[tokio::test]
    async fn evict() {
        let svc = LruPathInfoService::with_capacity(NonZeroUsize::new(1).unwrap());

        // pathinfo_1 should not be there
        assert!(svc
            .get(*PATH_INFO.store_path.digest())
            .await
            .expect("no error")
            .is_none());

        // insert it
        svc.put(PATH_INFO.clone()).await.expect("no error");

        // now it should be there.
        assert_eq!(
            Some(PATH_INFO.clone()),
            svc.get(*PATH_INFO.store_path.digest())
                .await
                .expect("no error")
        );

        // insert pathinfo_2. This will evict pathinfo 1
        svc.put(PATHINFO_2.clone()).await.expect("no error");

        // now pathinfo 2 should be there.
        assert_eq!(
            Some(PATHINFO_2.clone()),
            svc.get(*PATHINFO_2_DIGEST).await.expect("no error")
        );

        // … but pathinfo 1 not anymore.
        assert!(svc
            .get(*PATH_INFO.store_path.digest())
            .await
            .expect("no error")
            .is_none());
    }
}