[GitHub] [cassandra] Mmuzaf commented on a diff in pull request #2133: CASSANDRA-15254 Support update statements over the SettingsTable virtual table

["Mmuzaf (via GitHub)" <gi...@apache.org>]

Mmuzaf commented on code in PR #2133:
URL: https://github.com/apache/cassandra/pull/2133#discussion_r1148114197


##########
src/java/org/apache/cassandra/config/registry/ConfigurationRegistry.java:
##########
@@ -0,0 +1,401 @@
+/*
+ * 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.cassandra.config.registry;
+
+import java.util.AbstractMap;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+
+import com.google.common.collect.ImmutableMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.cassandra.config.Config;
+import org.apache.cassandra.config.Mutable;
+import org.apache.cassandra.config.StringConverters;
+import org.apache.cassandra.exceptions.ConfigurationException;
+import org.yaml.snakeyaml.introspector.Property;
+
+import static org.apache.cassandra.config.Properties.defaultLoader;
+import static org.apache.cassandra.config.registry.PrimitiveUnaryConverter.convertSafe;
+import static org.apache.commons.lang3.ClassUtils.primitiveToWrapper;
+
+
+/**
+ * This is a simple configuration property registry that stores all the {@link Config} settings, it doesn't
+ * take into account any configuration changes that might happen during properties replacement between releases.
+ */
+public class ConfigurationRegistry implements Registry
+{
+    private static final Logger logger = LoggerFactory.getLogger(ConfigurationRegistry.class);
+    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
+    private final Supplier<Config> configProvider;
+    private final Map<ConfigurationListener.ChangeType, ConfigurationListenerList> propertyChangeListeners = new EnumMap<>(ConfigurationListener.ChangeType.class);
+    private final Map<String, List<TypedConstraintAdapter<?>>> constraints = new HashMap<>();
+    private volatile boolean initialized;
+    private Map<String, PropertyAdapter> properties = Collections.emptyMap();
+
+    public ConfigurationRegistry(Supplier<Config> configProvider)
+    {
+        this.configProvider = configProvider;
+        // Initialize the property change listeners.
+        for (ConfigurationListener.ChangeType type : ConfigurationListener.ChangeType.values())
+            propertyChangeListeners.put(type, new ConfigurationListenerList());
+    }
+
+    private void lazyInit()
+    {
+        if (initialized)
+            return;
+
+        rwLock.writeLock().lock();
+        try
+        {
+            if (initialized)
+                return;
+            properties = ImmutableMap.copyOf(defaultLoader()
+                                             .flatten(Config.class)
+                                             .entrySet()
+                                             .stream()
+                                             .map(e -> new AbstractMap.SimpleEntry<>(e.getKey(), new PropertyAdapter(configProvider, e.getValue())))
+                                             .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)));
+            Set<String> leftConstraints = new HashSet<>(constraints.keySet());
+            leftConstraints.removeAll(properties.keySet());
+            if (!leftConstraints.isEmpty())
+                throw new ConfigurationException("Constraints are defined for non-existing properties:" + leftConstraints);
+            Set<String> leftListeners = propertyChangeListeners.values().stream()
+                                                               .map(l -> l.wrappers.keySet())
+                                                               .flatMap(Collection::stream)
+                                                               .collect(Collectors.toSet());
+            leftListeners.removeAll(properties.keySet());
+            if (!leftListeners.isEmpty())
+                throw new ConfigurationException("Listeners are defined for non-existing properties:" + leftListeners);
+            initialized = true;
+        }
+        finally
+        {
+            rwLock.writeLock().unlock();
+        }
+    }
+
+    @Override public void set(String name, @Nullable Object value)
+    {
+        lazyInit();
+        PropertyAdapter property = properties.get(name);

Review Comment:
   It might be true, but according to my understanding the publication of configuration variables is safe for the following reasons:
   - we read the volatile `initialized` variable each time the `lazyInit();` accessed;
   - we do a safe publication for the `properties` variable as the ImmutableMap and double-check locking are used for; 
   
   We have `happens-before` here and will see the non-null `PropertyAdapter property` (if it exists).



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