Begin add watch mechanism to Bayou

1 files changed, 110 insertions, 9 deletions

diff --git a/src/bayou.rs b/src/bayou.rs
index 7a76222..f6e0fb7 100644
--- a/src/bayou.rs
+++ b/src/bayou.rs
@@ -1,18 +1,21 @@
 use std::str::FromStr;
+use std::sync::{Arc, Weak};
 use std::time::{Duration, Instant};
 
 use anyhow::{anyhow, bail, Result};
-use log::debug;
+use log::{debug, error, info};
 use rand::prelude::*;
 use serde::{Deserialize, Serialize};
 use tokio::io::AsyncReadExt;
+use tokio::sync::{watch, Notify};
 
-use k2v_client::{BatchDeleteOp, BatchReadOp, Filter, K2vClient, K2vValue};
+use k2v_client::{BatchDeleteOp, BatchReadOp, CausalityToken, Filter, K2vClient, K2vValue};
 use rusoto_s3::{
     DeleteObjectRequest, GetObjectRequest, ListObjectsV2Request, PutObjectRequest, S3Client, S3,
 };
 
 use crate::cryptoblob::*;
+use crate::k2v_util::k2v_wait_value_changed;
 use crate::login::Credentials;
 use crate::time::now_msec;
 
@@ -34,6 +37,8 @@ const CHECKPOINT_MIN_OPS: usize = 16;
 // between processes doing .checkpoint() and those doing .sync()
 const CHECKPOINTS_TO_KEEP: usize = 3;
 
+const WATCH_SK: &str = "watch";
+
 pub trait BayouState:
     Default + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync + 'static
 {
@@ -52,8 +57,12 @@ pub struct Bayou<S: BayouState> {
 
     checkpoint: (Timestamp, S),
     history: Vec<(Timestamp, S::Op, Option<S>)>,
+
     last_sync: Option<Instant>,
     last_try_checkpoint: Option<Instant>,
+
+    watch: Arc<K2vWatch>,
+    last_sync_watch_ct: Option<CausalityToken>,
 }
 
 impl<S: BayouState> Bayou<S> {
@@ -61,6 +70,8 @@ impl<S: BayouState> Bayou<S> {
         let k2v_client = creds.k2v_client()?;
         let s3_client = creds.s3_client()?;
 
+        let watch = K2vWatch::new(creds, path.clone(), WATCH_SK.to_string())?;
+
         Ok(Self {
             bucket: creds.bucket().to_string(),
             path,
@@ -71,6 +82,8 @@ impl<S: BayouState> Bayou<S> {
             history: vec![],
             last_sync: None,
             last_try_checkpoint: None,
+            watch,
+            last_sync_watch_ct: None,
         })
     }
 
@@ -106,7 +119,7 @@ impl<S: BayouState> Bayou<S> {
         };
 
         if self.checkpoint.0 > checkpoint.0 {
-            bail!("Existing checkpoint is more recent than stored one");
+            bail!("Loaded checkpoint is more recent than stored one");
         }
 
         if let Some(ck) = checkpoint.1 {
@@ -132,7 +145,7 @@ impl<S: BayouState> Bayou<S> {
                 partition_key: &self.path,
                 filter: Filter {
                     start: Some(&ts_ser),
-                    end: None,
+                    end: Some(WATCH_SK),
                     prefix: None,
                     limit: None,
                     reverse: false,
@@ -186,12 +199,9 @@ impl<S: BayouState> Bayou<S> {
         let i0 = self
             .history
             .iter()
-            .enumerate()
             .zip(ops.iter())
-            .skip_while(|((_, (ts1, _, _)), (ts2, _))| ts1 == ts2)
-            .map(|((i, _), _)| i)
-            .next()
-            .unwrap_or(self.history.len());
+            .take_while(|((ts1, _, _), (ts2, _))| ts1 == ts2)
+            .count();
 
         if ops.len() > i0 {
             // Remove operations from first position where histories differ
@@ -259,6 +269,8 @@ impl<S: BayouState> Bayou<S> {
             )
             .await?;
 
+        self.watch.notify.notify_one();
+
         let new_state = self.state().apply(&op);
         self.history.push((ts, op, Some(new_state)));
 
@@ -427,6 +439,95 @@ impl<S: BayouState> Bayou<S> {
     }
 }
 
+// ---- Bayou watch in K2V ----
+
+struct K2vWatch {
+    pk: String,
+    sk: String,
+    rx: watch::Receiver<Option<CausalityToken>>,
+    notify: Notify,
+}
+
+impl K2vWatch {
+    /// Creates a new watch and launches subordinate threads.
+    /// These threads hold Weak pointers to the struct;
+    /// the exit when the Arc is dropped.
+    fn new(creds: &Credentials, pk: String, sk: String) -> Result<Arc<Self>> {
+        let (tx, rx) = watch::channel::<Option<CausalityToken>>(None);
+        let notify = Notify::new();
+
+        let watch = Arc::new(K2vWatch { pk, sk, rx, notify });
+
+        tokio::spawn(Self::watcher_task(
+            Arc::downgrade(&watch),
+            creds.k2v_client()?,
+            tx,
+        ));
+        tokio::spawn(Self::updater_task(
+            Arc::downgrade(&watch),
+            creds.k2v_client()?,
+        ));
+
+        Ok(watch)
+    }
+
+    async fn watcher_task(
+        self_weak: Weak<Self>,
+        k2v: K2vClient,
+        tx: watch::Sender<Option<CausalityToken>>,
+    ) {
+        let mut ct = None;
+        while let Some(this) = Weak::upgrade(&self_weak) {
+            info!("bayou k2v watch loop iter: ct = {:?}", ct);
+            let update = tokio::select!(
+                _ = tokio::time::sleep(Duration::from_secs(60)) => continue,
+                r = k2v_wait_value_changed(&k2v, &this.pk, &this.sk, &ct) => r,
+            );
+            match update {
+                Err(e) => {
+                    error!("Error in bayou k2v wait value changed: {}", e);
+                    tokio::time::sleep(Duration::from_secs(30)).await;
+                }
+                Ok(cv) => {
+                    if tx.send(Some(cv.causality.clone())).is_err() {
+                        break;
+                    }
+                    ct = Some(cv.causality);
+                }
+            }
+        }
+        info!("bayou k2v watch loop exiting");
+    }
+
+    async fn updater_task(self_weak: Weak<Self>, k2v: K2vClient) {
+        while let Some(this) = Weak::upgrade(&self_weak) {
+            let ct: Option<CausalityToken> = this.rx.borrow().clone();
+            let rand = u128::to_be_bytes(thread_rng().gen()).to_vec();
+
+            tokio::select!(
+                _ = tokio::time::sleep(Duration::from_secs(60)) => (),
+                _ = this.notify.notified() => {
+                    if let Err(e) = k2v
+                        .insert_item(
+                            &this.pk,
+                            &this.sk,
+                            rand,
+                            ct,
+                        )
+                        .await
+                    {
+                        error!("Error in bayou k2v watch updater loop: {}", e);
+                        tokio::time::sleep(Duration::from_secs(30)).await;
+                    }
+                }
+            )
+        }
+        info!("bayou k2v watch updater loop exiting");
+    }
+}
+
+// ---- TIMESTAMP CLASS ----
+
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
 pub struct Timestamp {
     pub msec: u64,