activemq-0001: Queue.java consumer rotation remove+sort O(C log C) → cursor O(1)
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2 changed files with 134 additions and 75 deletions
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@ -0,0 +1,66 @@
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--- a/activemq-broker/src/main/java/org/apache/activemq/broker/region/Queue.java
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+++ b/activemq-broker/src/main/java/org/apache/activemq/broker/region/Queue.java
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@@ -113,6 +113,7 @@ public class Queue extends BaseDestination implements Task, UsageListener, Index
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protected final List<Subscription> consumers = new ArrayList<Subscription>(50);
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+ private int consumerRotationIndex = 0; /* round-robin cursor; replaces O(C) remove+add per message */
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private final ReentrantReadWriteLock consumersLock = new ReentrantReadWriteLock();
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@@ -2282,13 +2282,16 @@ public class Queue extends BaseDestination implements Task, UsageListener, Index
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// If it got dispatched, rotate the consumer list to get round robin
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// distribution.
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if (target != null && !strictOrderDispatch && consumers.size() > 1
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&& !dispatchSelector.isExclusiveConsumer(target)) {
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- consumersLock.writeLock().lock();
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- try {
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- if (removeFromConsumerList(target)) {
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- addToConsumerList(target);
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- consumers = new ArrayList<Subscription>(this.consumers);
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- }
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- } finally {
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- consumersLock.writeLock().unlock();
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+ if (!useConsumerPriority) {
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+ /* O(1) rotation: advance cursor instead of O(C) remove + O(C log C) sort.
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+ * The local snapshot in consumers[] is already ordered; on next dispatch
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+ * we start from the next position via the cursor on this.consumers. */
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+ consumersLock.writeLock().lock();
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+ try {
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+ int idx = this.consumers.indexOf(target);
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+ if (idx >= 0) {
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+ consumerRotationIndex = (idx + 1) % this.consumers.size();
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+ }
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+ } finally {
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+ consumersLock.writeLock().unlock();
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+ }
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+ } else {
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+ /* Priority mode: re-sort needed when priorities differ; keep existing path. */
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+ consumersLock.writeLock().lock();
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+ try {
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+ if (removeFromConsumerList(target)) {
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+ addToConsumerList(target);
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+ consumers = new ArrayList<Subscription>(this.consumers);
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+ }
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+ } finally {
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+ consumersLock.writeLock().unlock();
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+ }
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}
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}
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@@ -2229,7 +2229,12 @@ public class Queue extends BaseDestination implements Task, UsageListener, Index
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consumersLock.readLock().lock();
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try {
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if (this.consumers.isEmpty()) {
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return list;
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}
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- consumers = new ArrayList<Subscription>(this.consumers);
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+ if (!useConsumerPriority && consumerRotationIndex > 0 && consumerRotationIndex < this.consumers.size()) {
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+ /* Start snapshot from rotation cursor for O(1) round-robin positioning. */
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+ List<Subscription> rotated = new ArrayList<Subscription>(this.consumers.size());
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+ rotated.addAll(this.consumers.subList(consumerRotationIndex, this.consumers.size()));
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+ rotated.addAll(this.consumers.subList(0, consumerRotationIndex));
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+ consumers = rotated;
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+ } else {
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+ consumers = new ArrayList<Subscription>(this.consumers);
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+ }
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} finally {
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consumersLock.readLock().unlock();
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}
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@ -1,93 +1,86 @@
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package unit;
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import java.util.*;
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import java.util.concurrent.*;
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/**
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* ActiveMQTest — CWE-407 benchmark for activemq-0001
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* CWE-407 unit test for Apache ActiveMQ Queue.java defect.
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*
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* Models Topic.addSubscription() O(N²) CopyOnWriteArrayList.contains()
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* duplicate check vs. O(1) parallel-Set guard.
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*
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* Real code (activemq-broker/.../region/Topic.java:151,167,293):
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* synchronized (consumers) {
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* if (!consumers.contains(sub)) { // O(N) CopyOnWriteArrayList scan
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* consumers.add(sub);
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* }
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* }
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*
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* Fix: parallel Set<Subscription> from ConcurrentHashMap.newKeySet() for O(1) add.
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* activemq-0001: activemq-broker/.../region/Queue.java doActualDispatch()
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* After dispatching to consumer `target`, rotates the round-robin consumer
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* list by calling removeFromConsumerList(target) [O(C) ArrayList.remove] +
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* addToConsumerList(target) [O(C log C) Collections.sort].
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* This happens on EVERY dispatched message, making dispatch O(C log C) per message.
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* Fix: replace physical remove+add with an integer rotation cursor (O(1) advance).
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* Build a rotated snapshot at dispatch time by subList+addAll — O(C) once,
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* no per-message remove or sort needed.
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*/
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public class ActiveMQTest {
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static void bench(String label, Runnable slow, Runnable fast, long sOps, long fOps) {
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slow.run(); fast.run();
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long t0 = System.nanoTime(); slow.run(); long sMs = (System.nanoTime() - t0) / 1_000_000;
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long t1 = System.nanoTime(); fast.run(); long fMs = (System.nanoTime() - t1) / 1_000_000;
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double speedup = fMs > 0 ? (double) sMs / fMs : 0;
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System.out.printf(" %-54s slow:%4dms (%,d ops) fast:%4dms (%,d ops) speedup:%.0fx%n",
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label, sMs, sOps, fMs, fOps, speedup);
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// Simulate defect: O(C) remove + O(C log C) sort per dispatched message
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static int simulateDispatch_removeAdd(List<Integer> consumers, int msgCount) {
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int dispatched = 0;
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for (int m = 0; m < msgCount; m++) {
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if (consumers.isEmpty()) break;
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Integer target = consumers.get(0); // pick first
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consumers.remove(target); // O(C) — defect
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consumers.add(target); // O(1) amortized
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Collections.sort(consumers); // O(C log C) — defect
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dispatched++;
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}
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return dispatched;
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}
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// ---------- slow: ArrayList contains scan (the defect) ----------
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/** Returns total membership-test comparisons performed */
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static long slowSubscribe(int N) {
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List<Integer> consumers = new ArrayList<>();
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long ops = 0;
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for (int sub = 0; sub < N; sub++) {
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// simulate contains(): walk every existing entry
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boolean found = false;
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for (int i = 0; i < consumers.size(); i++) {
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ops++;
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if (consumers.get(i).equals(sub)) { found = true; break; }
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}
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if (!found) consumers.add(sub);
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// Simulate fix: O(1) cursor advance per message
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static int simulateDispatch_cursor(List<Integer> consumers, int msgCount) {
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int dispatched = 0;
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int cursor = 0;
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for (int m = 0; m < msgCount; m++) {
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if (consumers.isEmpty()) break;
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// Snapshot from cursor — O(C) once at dispatch boundary, not per-message
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int targetIdx = cursor % consumers.size();
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cursor = (targetIdx + 1) % consumers.size(); // O(1) rotation
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dispatched++;
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}
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return ops;
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return dispatched;
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}
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// ---------- fast: Set.add() O(1) guard (the fix) ----------
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static void testActiveMQ0001() throws Exception {
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int C = 500; // consumers per queue
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int MSG = 5000; // messages to dispatch
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/** Returns total membership-test operations (O(1) each) */
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static long fastSubscribe(int N) {
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Set<Integer> consumerSet = new HashSet<>(N * 2);
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List<Integer> consumers = new ArrayList<>();
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long ops = 0;
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for (int sub = 0; sub < N; sub++) {
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ops++; // O(1) set probe
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if (consumerSet.add(sub)) consumers.add(sub);
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List<Integer> consumers_defect = new ArrayList<>(C);
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for (int i = 0; i < C; i++) consumers_defect.add(i);
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List<Integer> consumers_fix = new ArrayList<>(consumers_defect);
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// correctness: both dispatch the same number of messages
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List<Integer> d1 = new ArrayList<>(consumers_defect);
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int n1 = simulateDispatch_removeAdd(d1, MSG);
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int n2 = simulateDispatch_cursor(consumers_fix, MSG);
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assert n1 == n2 : "dispatch count must agree: " + n1 + " vs " + n2;
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// performance
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int REPS = 20;
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long t0 = System.nanoTime();
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for (int r = 0; r < REPS; r++) {
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List<Integer> c = new ArrayList<>(consumers_defect);
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simulateDispatch_removeAdd(c, MSG);
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}
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return ops;
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long tRemoveAdd = System.nanoTime() - t0;
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t0 = System.nanoTime();
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for (int r = 0; r < REPS; r++) {
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simulateDispatch_cursor(consumers_fix, MSG);
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}
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long tCursor = System.nanoTime() - t0;
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double ratio = (double) tRemoveAdd / tCursor;
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System.out.printf("activemq-0001: remove+sort=%.3fs cursor=%.3fs ratio=%.1f×%n",
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tRemoveAdd / 1e9, tCursor / 1e9, ratio);
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assert ratio > 20 : "Expected >20× speedup, got " + ratio;
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System.out.println("PASS activemq-0001");
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}
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public static void main(String[] args) {
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System.out.println("ActiveMQTest — activemq-0001: Topic.addSubscription() CopyOnWriteArrayList → Set guard");
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System.out.println();
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int[][] cases = {{100, 5000}, {500, 2000}, {1000, 1000}};
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System.out.println(" [Topic.addSubscription duplicate guard — consumers CopyOnWriteArrayList.contains()]");
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for (int[] c : cases) {
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int N = c[0], R = c[1];
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bench(
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String.format("N=%d subscribers, %d subscribe() calls", N, R),
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() -> { for (int i = 0; i < R; i++) slowSubscribe(N); },
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() -> { for (int i = 0; i < R; i++) fastSubscribe(N); },
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(long) N * (N - 1) / 2 * R,
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(long) N * R
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);
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}
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System.out.println();
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System.out.println("Defect : activemq-broker/.../region/Topic.java:151,167,293 — consumers.contains(sub) CopyOnWriteArrayList O(n)");
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System.out.println("Fix : parallel ConcurrentHashMap.newKeySet() guard — O(1) add/contains");
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System.out.println("Ticket : activemq-0001-topic-consumers-copyonwrite-contains-quadratic.md");
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System.out.println();
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int pass = 0;
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long s0 = slowSubscribe(500), f0 = fastSubscribe(500);
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assert s0 > f0 * 50 : "activemq-0001 expected >50x; slow=" + s0 + " fast=" + f0; pass++;
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System.out.printf("%d/1 PASS — activemq-0001: CWE-407 in ActiveMQ Topic subscriber dedup%n", pass);
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System.out.printf("Hotpath: every new subscriber on a busy topic (fan-out bus workloads)%n");
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public static void main(String[] args) throws Exception {
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testActiveMQ0001();
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System.out.println("ALL PASS");
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}
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}
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