From 359d0017a920b1e7dab0103aa3479fd6e5a2b5ab Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Thu, 14 Nov 2024 11:49:19 -0500
Subject: ReliableMulticast: retransmit dropped messages

---
 .../derms/net/rmulticast/ReliableMulticast.java    | 42 +++++++++++++++++++---
 1 file changed, 37 insertions(+), 5 deletions(-)

(limited to 'src')

diff --git a/src/main/java/derms/net/rmulticast/ReliableMulticast.java b/src/main/java/derms/net/rmulticast/ReliableMulticast.java
index 464cbb5..f20dd2a 100644
--- a/src/main/java/derms/net/rmulticast/ReliableMulticast.java
+++ b/src/main/java/derms/net/rmulticast/ReliableMulticast.java
@@ -18,7 +18,7 @@ public class ReliableMulticast<T extends Serializable & Hashable> {
     private final Set<MessageID> positiveAcks; // Positively acknowledged messages.
     private final Set<MessageID> negativeAcks; // Negatively acknowledged messages.
     private final Set<Message<T>> received;
-    private final Set<MessageID> retransmissions; // Messages pending retransmission.
+    private final BlockingQueue<Message<T>> retransmissions; // Messages pending retransmission.
     private final AtomicReference<Instant> lastSend;
     private final SocketAddress group;
     private final MulticastSocket inSock, outSock;
@@ -30,7 +30,7 @@ public class ReliableMulticast<T extends Serializable & Hashable> {
         this.positiveAcks = new ConcurrentHashMap<MessageID, Void>().keySet();
         this.negativeAcks = new ConcurrentHashMap<MessageID, Void>().keySet();
         this.received = new ConcurrentHashMap<Message<T>, Void>().keySet();
-        this.retransmissions = new ConcurrentHashMap<MessageID, Void>().keySet();
+        this.retransmissions = new LinkedBlockingQueue<Message<T>>();
         this.lastSend = new AtomicReference<Instant>(Instant.now());
 
         this.group = group;
@@ -44,9 +44,11 @@ public class ReliableMulticast<T extends Serializable & Hashable> {
         this.laddr = laddr;
 
         this.delivered = new LinkedBlockingQueue<Message<T>>();
-        (new Thread(new Receiver())).start();
 
         this.log = Logger.getLogger(this.getClass().getName());
+
+        (new Thread(new Receive())).start();
+        (new Thread(new Retransmit())).start();
     }
 
     public void send(T payload) throws IOException {
@@ -56,19 +58,49 @@ public class ReliableMulticast<T extends Serializable & Hashable> {
                 positiveAcks.toArray(new MessageID[0]),
                 negativeAcks.toArray(new MessageID[0]));
         DatagramPacket pkt = Packet.encode(msg, group);
-        outSock.send(pkt);
+        synchronized (outSock) {
+            outSock.send(pkt);
+        }
         positiveAcks.clear();
         (new Thread(new Timeout(msg.id()))).start();
         lastSend.set(Instant.now());
     }
 
-    private class Receiver implements Runnable {
+    private class Receive implements Runnable {
         @Override
         public void run() {
             // TODO
         }
     }
 
+    /** Retransmit dropped messages. */
+    private class Retransmit implements Runnable {
+        private final Logger log;
+
+        private Retransmit() {
+            this.log = Logger.getLogger(this.getClass().getName());
+        }
+
+        @Override
+        public void run() {
+            try {
+                for (;;) {
+                    Message<T> msg = retransmissions.take();
+                    try {
+                        DatagramPacket pkt = Packet.encode(msg, group);
+                        synchronized (outSock) {
+                            outSock.send(pkt);
+                        }
+                    } catch (Exception e) {
+                        log.warning(e.getMessage());
+                    }
+                }
+            } catch (InterruptedException e) {
+                log.info("Retransmit thread interrupted: "+e.getMessage());
+            }
+        }
+    }
+
     private class Timeout implements Runnable {
         MessageID mid;
 
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