[#2187] Add lock-free ConcurrentMessageAudit

Fully lock-free message audit using ConcurrentHashMap for producer
lookup using computeIfAbsent and AtomicBitArrayBin for CAS-based
per-producer bit operations. No synchronized blocks for audit hot
path.

Author: mattrpav

activemq-client/src/main/java/org/apache/activemq/ConcurrentMessageAudit.java

@@ -0,0 +1,200 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.activemq;
+
+import java.util.Iterator;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.activemq.command.MessageId;
+import org.apache.activemq.command.ProducerId;
+import org.apache.activemq.util.AtomicBitArrayBin;
+import org.apache.activemq.util.IdGenerator;
+
+/**
+ * A lock-free message audit backed by {@link ConcurrentHashMap} and
+ * {@link AtomicBitArrayBin}.
+ *
+ * <p>The upstream {@code ActiveMQMessageAudit} wraps every operation in a
+ * single {@code synchronized(this)} block, serializing all threads regardless
+ * of which producer they are working with. This class eliminates all
+ * synchronization on the hot path:
+ * <ul>
+ *   <li>{@link ConcurrentHashMap#computeIfAbsent} for lock-free producer
+ *       lookup and atomic insertion</li>
+ *   <li>{@link AtomicBitArrayBin} for CAS-based bit-level mutations &mdash;
+ *       no {@code synchronized} blocks anywhere in the hot path</li>
+ * </ul>
+ *
+ * <p>Producer count is bounded by {@link #getMaximumNumberOfProducersToTrack()}.
+ * When the limit is exceeded, entries are evicted in iteration order (approximate
+ * FIFO). The per-producer audit window is controlled by {@link #getAuditDepth()}.
+ */
+public class ConcurrentMessageAudit {
+
+    public static final int DEFAULT_WINDOW_SIZE = 2048;
+    public static final int MAXIMUM_PRODUCER_COUNT = 64;
+
+    private volatile int auditDepth;
+    private volatile int maximumNumberOfProducersToTrack;
+    private final ConcurrentHashMap<String, AtomicBitArrayBin> map;
+
+    public ConcurrentMessageAudit() {
+        this(DEFAULT_WINDOW_SIZE, MAXIMUM_PRODUCER_COUNT);
+    }
+
+    public ConcurrentMessageAudit(int auditDepth, int maximumNumberOfProducersToTrack) {
+        this.auditDepth = auditDepth;
+        this.maximumNumberOfProducersToTrack = maximumNumberOfProducersToTrack;
+        this.map = new ConcurrentHashMap<>(maximumNumberOfProducersToTrack);
+    }
+
+    public int getAuditDepth() {
+        return auditDepth;
+    }
+
+    public void setAuditDepth(int auditDepth) {
+        this.auditDepth = auditDepth;
+    }
+
+    public int getMaximumNumberOfProducersToTrack() {
+        return maximumNumberOfProducersToTrack;
+    }
+
+    public void setMaximumNumberOfProducersToTrack(int maximumNumberOfProducersToTrack) {
+        this.maximumNumberOfProducersToTrack = maximumNumberOfProducersToTrack;
+        evictExcess();
+    }
+
+    public boolean isDuplicate(String id) {
+        var seed = IdGenerator.getSeedFromId(id);
+        if (seed == null) {
+            return false;
+        }
+        var bab = getOrCreate(seed);
+        var index = IdGenerator.getSequenceFromId(id);
+        if (index >= 0) {
+            return bab.setBit(index, true);
+        }
+        return false;
+    }
+
+    public boolean isDuplicate(final MessageId id) {
+        if (id == null) {
+            return false;
+        }
+        var pid = id.getProducerId();
+        if (pid == null) {
+            return false;
+        }
+        var bab = getOrCreate(pid.toString());
+        return bab.setBit(id.getProducerSequenceId(), true);
+    }
+
+    public void rollback(final MessageId id) {
+        if (id == null) {
+            return;
+        }
+        var pid = id.getProducerId();
+        if (pid == null) {
+            return;
+        }
+        var bab = map.get(pid.toString());
+        if (bab != null) {
+            bab.setBit(id.getProducerSequenceId(), false);
+        }
+    }
+
+    public void rollback(final String id) {
+        var seed = IdGenerator.getSeedFromId(id);
+        if (seed == null) {
+            return;
+        }
+        var bab = map.get(seed);
+        if (bab != null) {
+            long index = IdGenerator.getSequenceFromId(id);
+            bab.setBit(index, false);
+        }
+    }
+
+    public boolean isInOrder(final String id) {
+        if (id == null) {
+            return true;
+        }
+        var seed = IdGenerator.getSeedFromId(id);
+        if (seed == null) {
+            return true;
+        }
+        var bab = map.get(seed);
+        if (bab != null) {
+            var index = IdGenerator.getSequenceFromId(id);
+            return bab.isInOrder(index);
+        }
+        return true;
+    }
+
+    public boolean isInOrder(final MessageId id) {
+        if (id == null) {
+            return false;
+        }
+        var pid = id.getProducerId();
+        if (pid == null) {
+            return false;
+        }
+        var bab = getOrCreate(pid.toString());
+        return bab.isInOrder(id.getProducerSequenceId());
+    }
+
+    public long getLastSeqId(ProducerId id) {
+        var bab = map.get(id.toString());
+        if (bab != null) {
+            return bab.getLastSetIndex();
+        }
+        return -1;
+    }
+
+    public void clear() {
+        map.clear();
+    }
+
+    public int getProducerCount() {
+        return map.size();
+    }
+
+    private AtomicBitArrayBin getOrCreate(String key) {
+        var bab = map.get(key);
+        if (bab != null) {
+            return bab;
+        }
+        bab = map.computeIfAbsent(key, k -> new AtomicBitArrayBin(auditDepth));
+        evictExcess();
+        return bab;
+    }
+
+    private void evictExcess() {
+        var max = maximumNumberOfProducersToTrack;
+        while (map.size() > max) {
+            var it = map.keySet().iterator();
+            if (it.hasNext()) {
+                it.next();
+                it.remove();
+            } else {
+                break;
+            }
+        }
+    }
+}