From 6258f4c51b1f5632f092db93bbce1ef3eb10bd18 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Mon, 18 Nov 2024 10:57:34 -0500
Subject: rmulticast.ReceivedSet: optimize insertion and search

---
 .../java/derms/net/rmulticast/ReceivedSet.java     | 74 ++++++++++++++--------
 1 file changed, 46 insertions(+), 28 deletions(-)

diff --git a/src/main/java/derms/net/rmulticast/ReceivedSet.java b/src/main/java/derms/net/rmulticast/ReceivedSet.java
index 5fd8ce5..c71a968 100644
--- a/src/main/java/derms/net/rmulticast/ReceivedSet.java
+++ b/src/main/java/derms/net/rmulticast/ReceivedSet.java
@@ -1,17 +1,15 @@
 package derms.net.rmulticast;
 
 import java.net.InetAddress;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.NoSuchElementException;
-import java.util.Queue;
-import java.util.concurrent.ConcurrentLinkedQueue;
+import java.time.Instant;
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
 
 class ReceivedSet<T extends MessagePayload> {
-    private final Queue<Message<T>> received;
+    private final Map<MessageID, Entry<T>> received;
 
     ReceivedSet() {
-        this.received = new ConcurrentLinkedQueue<Message<T>>();
+        this.received = new ConcurrentHashMap<MessageID, Entry<T>>();
     }
 
     /**
@@ -20,20 +18,15 @@ class ReceivedSet<T extends MessagePayload> {
      * @param msg The message to add to the set.
      * @return True if the set did not already contain the specified message.
      */
-    // TODO: faster insertion.
     boolean add(Message<T> msg) {
-        if (contains(msg))
-            return false;
-        received.add(msg);
-        return true;
+        return received.put(msg.id(), new Entry<T>(msg)) == null;
     }
 
-    // TODO: faster search.
     Message<T> getByID(MessageID mid) throws NoSuchElementException {
-        for (Message<T> msg : received)
-            if (msg.id().equals(mid))
-                return msg;
-        throw new NoSuchElementException("message " + mid + " not in received list.");
+        Entry<T> e = received.get(mid);
+        if (e == null)
+            throw new NoSuchElementException("message " + mid + " not in received list.");
+        return e.msg;
     }
 
     boolean contains(MessageID mid) {
@@ -51,31 +44,56 @@ class ReceivedSet<T extends MessagePayload> {
 
     /** Remove the specified message from the set, if it is present. */
     void remove(Message<T> msg) {
-        received.remove(msg);
+        received.remove(msg.id());
     }
 
     /** Retrieves, but does not remove, the oldest message, or returns null if the set is empty. */
     Message<T> peekOldest() {
-        return received.peek();
+        Entry<T> oldest = null;
+        for (Entry<T> e : received.values())
+            if (oldest == null || e.timestamp.isBefore(oldest.timestamp))
+                oldest = e;
+        if (oldest == null)
+            return null;
+        return oldest.msg;
     }
 
     Message<T> mostRecentSentBy(InetAddress member) throws NoSuchElementException {
-        Message<T> recent = null;
-        for (Message<T> msg : received) {
-            if (msg.sender.equals(member))
-                recent = msg;
-        }
+        Entry<T> recent = null;
+        for (Entry<T> e : received.values())
+            if (e.msg.sender.equals(member) && (recent == null || e.timestamp.isAfter(recent.timestamp)))
+                recent = e;
         if (recent == null)
             throw new NoSuchElementException("no message from " + member + " in received list.");
-        return recent;
+        return recent.msg;
     }
 
     List<Message<T>> allSentBy(InetAddress sender) {
         List<Message<T>> sent = new ArrayList<Message<T>>();
-       for (Message<T> msg : received) {
-           if (msg.sender.equals(sender))
-               sent.add(msg);
+       for (Entry<T> e : received.values()) {
+           if (e.msg.sender.equals(sender))
+               sent.add(e.msg);
        }
        return sent;
     }
+
+    private static class Entry<T extends MessagePayload> {
+        private final Message<T> msg;
+        private final Instant timestamp; // The time at which the entry was added to the set.
+
+        private Entry(Message<T> msg) {
+            this.msg = msg;
+            this.timestamp = Instant.now();
+        }
+
+        @Override
+        public int hashCode() {
+            return msg.hashCode();
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return msg.equals(obj);
+        }
+    }
 }
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