Incomming locking loop

src/mail/incoming.rs

@@ -1,8 +1,10 @@
 use std::collections::HashMap;
+use std::pin::Pin;
 use std::sync::{Arc, Weak};
 use std::time::Duration;
 
-use anyhow::Result;
+use anyhow::{anyhow, bail, Result};
+use futures::{future::BoxFuture, Future, FutureExt};
 use k2v_client::{CausalValue, CausalityToken, K2vClient, K2vValue};
 use rusoto_s3::{PutObjectRequest, S3Client, S3};
 use tokio::sync::watch;
@@ -20,6 +22,12 @@ const INCOMING_PK: &str = "incoming";
 const INCOMING_LOCK_SK: &str = "lock";
 const INCOMING_WATCH_SK: &str = "watch";
 
+// When a lock is held, it is held for LOCK_DURATION (here 5 minutes)
+// It is renewed every LOCK_DURATION/3
+// If we are at 2*LOCK_DURATION/3 and haven't renewed, we assume we
+// lost the lock.
+const LOCK_DURATION: Duration = Duration::from_secs(300);
+
 pub async fn incoming_mail_watch_process(
     user: Weak<User>,
     creds: Credentials,
@@ -124,55 +132,158 @@ async fn handle_incoming_mail(user: &Arc<User>, s3: &S3Client, inbox: &Arc<Mailb
 fn k2v_lock_loop(k2v: K2vClient, pk: &'static str, sk: &'static str) -> watch::Receiver<bool> {
     let (held_tx, held_rx) = watch::channel(false);
 
-    tokio::spawn(async move {
-        let _ = k2v_lock_loop_internal(k2v, pk, sk, held_tx).await;
-    });
+    tokio::spawn(k2v_lock_loop_internal(k2v, pk, sk, held_tx));
 
     held_rx
 }
 
+#[derive(Clone, Debug)]
+enum LockState {
+    Unknown,
+    Empty,
+    Held(UniqueIdent, u64, CausalityToken),
+}
+
 async fn k2v_lock_loop_internal(
     k2v: K2vClient,
     pk: &'static str,
     sk: &'static str,
     held_tx: watch::Sender<bool>,
-) -> std::result::Result<(), watch::error::SendError<bool>> {
-    let pid = gen_ident();
+) {
+    let (state_tx, mut state_rx) = watch::channel::<LockState>(LockState::Unknown);
+    let mut state_rx_2 = state_rx.clone();
 
-    let mut state: Option<(UniqueIdent, u64, CausalityToken)> = None;
-    loop {
-        let held_until = match &state {
-            None => None,
-            Some((_holder, expiration_time, _ct)) => Some(expiration_time),
-        };
+    let our_pid = gen_ident();
 
-        let now = now_msec();
-        let wait_half_held_time = async {
-            match held_until {
-                None => futures::future::pending().await,
-                Some(t) => tokio::time::sleep(Duration::from_millis((now_msec() - t) / 2)).await,
-            }
-        };
-
-        unimplemented!();
-
-        /*
-        tokio::select! {
-            ret = k2v_wait_value_changed(&k2v, pk, sk, &state.as_ref().map(|(_, _, ct)| ct.clone())) => {
-                match ret {
-                    Err(e) => {
-                        held_tx.send(false)?;
-                        tokio::time::sleep(Duration::from_secs(30)).await;
-                        continue;
-                    }
-                    Ok(cv) => {
-                        unimplemented!();
+    // Loop 1: watch state of lock in K2V, save that in corresponding watch channel
+    let watch_lock_loop: BoxFuture<Result<()>> = async {
+        let mut ct = None;
+        loop {
+            match k2v_wait_value_changed(&k2v, pk, sk, &ct).await {
+                Err(e) => {
+                    error!(
+                        "Error in k2v wait value changed: {} ; assuming we no longer hold lock.",
+                        e
+                    );
+                    state_tx.send(LockState::Unknown)?;
+                    tokio::time::sleep(Duration::from_secs(30)).await;
+                }
+                Ok(cv) => {
+                    let mut lock_state = None;
+                    for v in cv.value.iter() {
+                        if let K2vValue::Value(vbytes) = v {
+                            if vbytes.len() == 32 {
+                                let ts = u64::from_be_bytes(vbytes[..8].try_into().unwrap());
+                                let pid = UniqueIdent(vbytes[8..].try_into().unwrap());
+                                if lock_state
+                                    .map(|(pid2, ts2)| ts > ts2 || (ts == ts2 && pid > pid2))
+                                    .unwrap_or(true)
+                                {
+                                    lock_state = Some((pid, ts));
+                                }
+                            }
+                        }
                     }
+                    state_tx.send(
+                        lock_state
+                            .map(|(pid, ts)| LockState::Held(pid, ts, cv.causality.clone()))
+                            .unwrap_or(LockState::Empty),
+                    )?;
+                    ct = Some(cv.causality);
                 }
             }
+            info!("Stopping lock state watch");
         }
-        */
     }
+    .boxed();
+
+    // Loop 2: notify user whether we are holding the lock or not
+    let lock_notify_loop: BoxFuture<Result<()>> = async {
+        loop {
+            let now = now_msec();
+            let held_with_expiration_time = match &*state_rx.borrow_and_update() {
+                LockState::Held(pid, ts, _ct) if *pid == our_pid => {
+                    let expiration_time = *ts - (LOCK_DURATION / 3).as_millis() as u64;
+                    if now < expiration_time {
+                        Some(expiration_time)
+                    } else {
+                        None
+                    }
+                }
+                _ => None,
+            };
+            held_tx.send(held_with_expiration_time.is_some())?;
+
+            let await_expired = async {
+                match held_with_expiration_time {
+                    None => futures::future::pending().await,
+                    Some(expiration_time) => {
+                        tokio::time::sleep(Duration::from_millis(expiration_time - now)).await
+                    }
+                };
+            };
+
+            tokio::select!(
+                r = state_rx.changed() => {
+                    r?;
+                }
+                _ = held_tx.closed() => bail!("held_tx closed, don't need to hold lock anymore"),
+                _ = await_expired => continue,
+            );
+        }
+    }
+    .boxed();
+
+    // Loop 3: acquire lock when relevant
+    let take_lock_loop: BoxFuture<Result<()>> = async {
+        loop {
+            let now = now_msec();
+            let state: LockState = state_rx_2.borrow_and_update().clone();
+            let (acquire_at, ct) = match state {
+                LockState::Unknown => {
+                    // If state of the lock is unknown, don't try to acquire
+                    state_rx_2.changed().await?;
+                    continue;
+                }
+                LockState::Empty => (now, None),
+                LockState::Held(pid, ts, ct) => {
+                    if pid == our_pid {
+                        (ts - (2 * LOCK_DURATION / 3).as_millis() as u64, Some(ct))
+                    } else {
+                        (ts, Some(ct))
+                    }
+                }
+            };
+
+            // Wait until it is time to acquire lock
+            if acquire_at > now {
+                tokio::select!(
+                    r = state_rx_2.changed() => {
+                        // If lock state changed in the meantime, don't acquire and loop around
+                        r?;
+                        continue;
+                    }
+                    _ = tokio::time::sleep(Duration::from_millis(acquire_at - now)) => ()
+                );
+            }
+
+            // Acquire lock
+            let mut lock = vec![0u8; 32];
+            lock[..8].copy_from_slice(&u64::to_be_bytes(now_msec()));
+            lock[8..].copy_from_slice(&our_pid.0);
+            if let Err(e) = k2v.insert_item(pk, sk, lock, ct).await {
+                error!("Could not take lock: {}", e);
+                tokio::time::sleep(Duration::from_secs(30)).await;
+            }
+
+            // Wait for new information to loop back
+            state_rx_2.changed().await?;
+        }
+    }
+    .boxed();
+
+    let res = futures::try_join!(watch_lock_loop, lock_notify_loop, take_lock_loop);
+    info!("lock loop exited: {:?}", res);
 }
 
 async fn k2v_wait_value_changed<'a>(