From dba41282cac86a740c007498709e996b9fa3e59b Mon Sep 17 00:00:00 2001
From: Aria <me@aria.rip>
Date: Thu, 19 Oct 2023 21:00:26 +0100
Subject: wip: broadcast message batching

---
 broadcast/src/handler.rs | 119 ++++++++++++++++++++++++++++-------------------
 1 file changed, 72 insertions(+), 47 deletions(-)

(limited to 'broadcast/src/handler.rs')

diff --git a/broadcast/src/handler.rs b/broadcast/src/handler.rs
index b38e2b7..4ee2664 100644
--- a/broadcast/src/handler.rs
+++ b/broadcast/src/handler.rs
@@ -10,35 +10,42 @@ use std::{
     time::Duration,
 };
 
-use crate::{msg::*, topology::Topology};
+use crate::{batch::MessageBatch, msg::*, topology::Topology};
 
 use common::{
     msg::{MessageHeader, Output},
     msg_id::{gen_msg_id, MessageID},
     Handler,
 };
-
-const RETRY_TIMEOUT_SECS: u64 = 1;
+const MAX_STABLE_DELAY_MS: Duration = Duration::from_millis(700);
 
 pub struct BroadcastHandler {
     node_id: String,
     seen: RwLock<HashSet<BroadcastTarget>>,
     topology: Topology,
-    output: Output<BroadcastBody>,
+    batch: Mutex<MessageBatch>,
+    pub(crate) output: Output<BroadcastBody>,
     attempted_broadcasts: Mutex<HashMap<MessageID, Task<()>>>,
 }
 
 impl Handler for BroadcastHandler {
     type Body = BroadcastBody;
 
-    fn init(node_id: String, node_ids: Vec<String>, output: Output<Self::Body>) -> Self {
-        BroadcastHandler {
+    fn init(node_id: String, node_ids: Vec<String>, output: Output<Self::Body>) -> Arc<Self> {
+        let max_message_delay = MAX_STABLE_DELAY_MS / (node_ids.len() / node_ids.len()) as u32;
+
+        let this = Arc::new(Self {
             node_id,
             topology: Topology::dense(node_ids.clone()),
             seen: RwLock::new(HashSet::new()),
             output,
             attempted_broadcasts: Mutex::default(),
-        }
+            batch: Mutex::new(MessageBatch::new(max_message_delay, 1000)),
+        });
+
+        smol::spawn(this.clone().poll_batch()).detach();
+
+        this
     }
 
     fn handle<'a>(
@@ -51,20 +58,37 @@ impl Handler for BroadcastHandler {
                 BroadcastBody::Broadcast {
                     msg_id: Some(msg_id),
                     message,
-                    path,
                 } => {
                     future::zip(
-                        self.receive_broadcast(&header.src, path, message),
+                        self.receive_broadcast(message),
                         self.send_broadcast_ok(&header.src, msg_id),
                     )
                     .await;
                 }
+
+                BroadcastBody::BroadcastBatch {
+                    msg_id: Some(msg_id),
+                    messages,
+                } => {
+                    future::zip(
+                        self.receive_broadcast_batch(messages),
+                        self.send_broadcast_ok(&header.src, msg_id),
+                    )
+                    .await;
+                }
+
                 BroadcastBody::Broadcast {
                     msg_id: None,
                     message,
-                    path,
                 } => {
-                    self.receive_broadcast(&header.src, path, message).await;
+                    self.receive_broadcast(message).await;
+                }
+
+                BroadcastBody::BroadcastBatch {
+                    msg_id: None,
+                    messages,
+                } => {
+                    self.receive_broadcast_batch(messages).await;
                 }
 
                 BroadcastBody::Topology { msg_id, topology } => {
@@ -127,48 +151,49 @@ impl BroadcastHandler {
     }
 
     /// Receive a given message, and broadcast it onwards if it is new
-    async fn receive_broadcast(
-        self: &Arc<Self>,
-        src: &str,
-        previous_path: Option<Vec<String>>,
-        message: BroadcastTarget,
-    ) {
+    async fn receive_broadcast(self: &Arc<Self>, message: BroadcastTarget) {
         let new = self.seen.write().await.insert(message);
         if !new {
             return;
         }
 
-        // Race all send futures
-        let mut previous_path = previous_path.unwrap_or_else(|| vec![]);
-        previous_path.push(src.to_string());
-        let mut tasks = self.attempted_broadcasts.lock().await;
-        for target in self
-            .topology
-            .targets(&self.node_id, previous_path.iter().map(String::as_str))
-            .await
-        {
-            let msg_id = gen_msg_id();
-            let this = self.clone();
-            let path = previous_path.clone();
-            tasks.insert(
-                msg_id,
-                smol::spawn(async move {
-                    loop {
-                        this.output
-                            .send(
-                                &target,
-                                &BroadcastBody::Broadcast {
-                                    msg_id: Some(msg_id),
-                                    message,
-                                    path: Some(path.clone()),
-                                },
-                            )
-                            .await;
+        let mut batch = self.batch.lock().await;
+        batch.add(message);
+    }
 
-                        Timer::after(Duration::from_secs(RETRY_TIMEOUT_SECS)).await;
-                    }
-                }),
-            );
+    async fn receive_broadcast_batch(self: &Arc<Self>, message: Vec<BroadcastTarget>) {
+        let mut batch = self.batch.lock().await;
+        let mut seen = self.seen.write().await;
+        let mut new = false;
+
+        for message in message.into_iter() {
+            new |= seen.insert(message);
+            batch.add(message);
+        }
+
+        if !new {
+            return;
+        }
+    }
+
+    async fn poll_batch(self: Arc<Self>) {
+        loop {
+            let mut batch = self.batch.lock().await;
+            if batch.should_broadcast() {
+                let mut tasks = self.attempted_broadcasts.lock().await;
+                for target in self.topology.all_targets(&self.node_id).await {
+                    let msg_id = gen_msg_id();
+                    let this = self.clone();
+                    tasks.insert(msg_id, smol::spawn(batch.broadcast(this, target, msg_id)));
+                }
+
+                batch.clear();
+            }
+
+            let time = batch.sleep_time();
+            drop(batch);
+
+            Timer::after(time).await;
         }
     }
 }
-- 
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