From e0196b370e8da38d366d327da57186dd3a44c2b2 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 16 Nov 2024 10:39:06 -0500
Subject: reliable multicast: periodically send acks

---
 src/main/java/derms/net/rmulticast/Heartbeat.java | 63 +++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 src/main/java/derms/net/rmulticast/Heartbeat.java

(limited to 'src/main/java/derms/net/rmulticast/Heartbeat.java')

diff --git a/src/main/java/derms/net/rmulticast/Heartbeat.java b/src/main/java/derms/net/rmulticast/Heartbeat.java
new file mode 100644
index 0000000..43eaaf5
--- /dev/null
+++ b/src/main/java/derms/net/rmulticast/Heartbeat.java
@@ -0,0 +1,63 @@
+package derms.net.rmulticast;
+
+import derms.net.ConcurrentMulticastSocket;
+import derms.net.Packet;
+import derms.util.Wait;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.time.Duration;
+import java.util.Set;
+import java.util.logging.Logger;
+
+/**
+ * Periodically send acknowledgements to the group. Allows acks to propagate even when some
+ * processes wouldn't normally send messages. Also allows processes to populate their set of
+ * group members.
+ */
+class Heartbeat implements Runnable {
+    private static final Duration period = Duration.ofSeconds(30);
+
+    private final InetSocketAddress group;
+    private final InetAddress laddr;
+    private final Set<MessageID> acks, nacks;
+    private final ConcurrentMulticastSocket outSock;
+    private final Logger log;
+
+    Heartbeat(InetSocketAddress group, InetAddress laddr, Set<MessageID> acks, Set<MessageID> nacks, ConcurrentMulticastSocket outSock) throws IOException {
+        this.group = group;
+        this.laddr = laddr;
+        this.acks = acks;
+        this.nacks = nacks;
+        this.outSock = outSock;
+        this.log = Logger.getLogger(this.getClass().getName());
+    }
+
+    @Override
+    public void run() {
+        try {
+            for (;;) {
+                try {
+                    Wait.forDuration(period);
+                    send();
+                } catch (IOException e) {
+                    log.warning(e.getMessage());
+                }
+            }
+        } catch (InterruptedException e) {
+            log.info("Heartbeat thread interrupted: " + e.getMessage());
+        }
+    }
+
+    private void send() throws IOException {
+        HeartbeatMessage msg = new HeartbeatMessage(
+                laddr,
+                acks.toArray(new MessageID[0]),
+                nacks.toArray(new MessageID[0]));
+        DatagramPacket pkt = Packet.encode(msg, group);
+        outSock.send(pkt);
+        acks.clear();
+    }
+}
-- 
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