Copilot commented on code in PR #17:
URL: 
https://github.com/apache/sling-org-apache-sling-rewriter/pull/17#discussion_r4413814554


##########
src/main/java/org/apache/sling/rewriter/impl/FactoryMap.java:
##########
@@ -0,0 +1,62 @@
+/*
+ * 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.sling.rewriter.impl;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.osgi.framework.ServiceReference;
+
+/**
+ * Stores the highest-ranked factory for each pipeline type.
+ */
+class FactoryMap<T> {
+
+    protected final Map<ServiceReference<T>, T> services = new HashMap<>();
+
+    private volatile Map<String, T> factories = Collections.emptyMap();
+
+    public T getFactory(final String type) {
+        return this.factories.get(type);
+    }
+
+    public synchronized void bind(final ServiceReference<T> reference, final T 
factory) {
+        this.services.put(reference, factory);
+        this.updateFactories();
+    }
+
+    public synchronized void unbind(final ServiceReference<T> reference) {
+        this.services.remove(reference);
+        this.updateFactories();
+    }
+
+    private void updateFactories() {
+        final List<ServiceReference<T>> references = new 
ArrayList<>(this.services.keySet());
+        references.sort(Collections.reverseOrder());
+        final Map<String, T> updated = new HashMap<>();
+        for (final ServiceReference<T> reference : references) {
+            final String type = (String) 
reference.getProperty(FactoryCache.PROPERTY_TYPE);
+            if (type != null) {
+                updated.putIfAbsent(type, this.services.get(reference));
+            }
+        }
+        this.factories = updated;
+    }

Review Comment:
   `updateFactories()` rebuilds the full type->factory map and sorts *all* 
tracked references on every bind/unbind/update. If many factories exist or 
service properties churn, this can become a hotspot. Consider maintaining 
per-type ranked sets (or per-type best reference) so updates are O(log n) per 
affected type rather than O(n log n) over all services each time.



##########
src/main/java/org/apache/sling/rewriter/impl/TransformerFactoryCache.java:
##########
@@ -0,0 +1,98 @@
+/*
+ * 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.sling.rewriter.impl;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.apache.sling.rewriter.ProcessingContext;
+import org.apache.sling.rewriter.TransformerFactory;
+import org.apache.sling.rewriter.impl.FactoryCache.TransformerFactoryEntry;
+import org.osgi.framework.ServiceReference;
+
+final class TransformerFactoryCache extends FactoryMap<TransformerFactory> {
+
+    static final TransformerFactoryEntry[] EMPTY_ENTRY_ARRAY = new 
TransformerFactoryEntry[0];
+    static final TransformerFactoryEntry[][] EMPTY_DOUBLE_ENTRY_ARRAY = 
{EMPTY_ENTRY_ARRAY, EMPTY_ENTRY_ARRAY};
+    static final TransformerFactory[] EMPTY_FACTORY_ARRAY = new 
TransformerFactory[0];
+    static final TransformerFactory[][] EMPTY_DOUBLE_FACTORY_ARRAY = 
{EMPTY_FACTORY_ARRAY, EMPTY_FACTORY_ARRAY};
+
+    private TransformerFactoryEntry[][] cached;
+
+    @Override
+    public synchronized void bind(final ServiceReference<TransformerFactory> 
reference, final TransformerFactory factory) {
+        super.bind(reference, factory);
+        this.cached = null;
+    }
+
+    @Override
+    public synchronized void unbind(final ServiceReference<TransformerFactory> 
reference) {
+        super.unbind(reference);
+        this.cached = null;
+    }
+
+    /**
+     * Get global factories in ascending service ranking order, split into pre 
and post transformers.
+     */
+    public synchronized TransformerFactoryEntry[][] 
getGlobalTransformerFactoryEntries() {
+        if (this.cached == null) {
+            final List<ServiceReference<TransformerFactory>> references = new 
ArrayList<>(this.services.keySet());
+            Collections.sort(references);
+            final List<TransformerFactoryEntry> pre = new ArrayList<>();
+            final List<TransformerFactoryEntry> post = new ArrayList<>();
+            for (final ServiceReference<TransformerFactory> reference : 
references) {
+                if (FactoryCache.MODE_GLOBAL.equalsIgnoreCase((String) 
reference.getProperty(FactoryCache.PROPERTY_MODE))) {
+                    final TransformerFactoryEntry entry = new 
TransformerFactoryEntry(this.services.get(reference), reference);
+                    if (entry.order < 0) {
+                        pre.add(entry);
+                    } else {
+                        post.add(entry);
+                    }
+                }
+            }
+            if (pre.isEmpty() && post.isEmpty()) {
+                this.cached = EMPTY_DOUBLE_ENTRY_ARRAY;
+            } else {
+                this.cached = new TransformerFactoryEntry[][] {
+                    pre.toArray(EMPTY_ENTRY_ARRAY), 
post.toArray(EMPTY_ENTRY_ARRAY)
+                };
+            }
+        }
+        return this.cached;
+    }

Review Comment:
   The previous implementation explicitly sorted the resulting 
`TransformerFactoryEntry[]` arrays; this version relies solely on 
`ServiceReference` ordering and insertion order in `pre`/`post`. If 
`TransformerFactoryEntry` ordering differs from `ServiceReference` ordering (or 
changes in the future), this can alter global transformer execution order. To 
preserve prior behavior deterministically, sort `pre` and `post` (or the 
resulting arrays) using `TransformerFactoryEntry`’s natural ordering before 
caching.



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