content: /*
   * 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.calcite.rel.metadata;
  
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.rel.RelNode;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Multimap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.InvocationHandler;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import static org.apache.calcite.linq4j.Nullness.castNonNull;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Implementation of the {@link RelMetadataProvider}
   * interface that caches results from an underlying provider.
   */
  @Deprecated // to be removed before 2.0
  public class CachingRelMetadataProvider implements RelMetadataProvider {
    //~ Instance fields --------------------------------------------------------
  
    private final Map<List, CacheEntry> cache = new HashMap<>();
  
    private final RelMetadataProvider underlyingProvider;
  
    private final RelOptPlanner planner;
  
    //~ Constructors -----------------------------------------------------------
  
    public CachingRelMetadataProvider(
        RelMetadataProvider underlyingProvider,
        RelOptPlanner planner) {
      this.underlyingProvider = underlyingProvider;
      this.planner = planner;
    }
  
    //~ Methods ----------------------------------------------------------------
    @Deprecated // to be removed before 2.0
    @Override public <@Nullable M extends @Nullable Metadata> @Nullable UnboundMetadata<M> apply(
        Class<? extends RelNode> relClass,
        final Class<? extends M> metadataClass) {
      final UnboundMetadata<M> function =
          underlyingProvider.apply(relClass, metadataClass);
      if (function == null) {
        return null;
      }
  
      // TODO jvs 30-Mar-2006: Use meta-metadata to decide which metadata
      // query results can stay fresh until the next Ice Age.
      return (rel, mq) -> {
        final Metadata metadata =
            requireNonNull(function.bind(rel, mq),
                () -> "metadata must not be null, relClass=" + relClass
                    + ", metadataClass=" + metadataClass);
        return metadataClass.cast(
            Proxy.newProxyInstance(metadataClass.getClassLoader(),
                new Class[]{metadataClass},
                new CachingInvocationHandler(metadata)));
      };
    }
  
    @Deprecated // to be removed before 2.0
    @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
        MetadataDef<M> def) {
      return underlyingProvider.handlers(def);
    }
  
    @Override public List<MetadataHandler<?>> handlers(
        Class<? extends MetadataHandler<?>> handlerClass) {
      return underlyingProvider.handlers(handlerClass);
    }
  
    //~ Inner Classes ----------------------------------------------------------
  
    /** An entry in the cache. Consists of the cached object and the timestamp
     * when the entry is valid. If read at a later timestamp, the entry will be
     * invalid and will be re-computed as if it did not exist. The net effect is a
     * lazy-flushing cache. */
    private static class CacheEntry {
      long timestamp;
  
      @Nullable Object result;
    }
  
    /** Implementation of {@link InvocationHandler} for calls to a
     * {@link CachingRelMetadataProvider}. Each request first looks in the cache;
     * if the cache entry is present and not expired, returns the cache entry,
     * otherwise computes the value and stores in the cache. */
    private class CachingInvocationHandler implements InvocationHandler {
      private final Metadata metadata;
  
      CachingInvocationHandler(Metadata metadata) {
        this.metadata = requireNonNull(metadata, "metadata");
      }
  
      @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args)
          throws Throwable {
        // Compute hash key.
        final ImmutableList.Builder<Object> builder = ImmutableList.builder();
        builder.add(method);
        builder.add(metadata.rel());
        if (args != null) {
          for (Object arg : args) {
            // Replace null values because ImmutableList does not allow them.
            builder.add(NullSentinel.mask(arg));
          }
        }
        List<Object> key = builder.build();
  
        long timestamp = planner.getRelMetadataTimestamp(metadata.rel());
  
        // Perform cache lookup.
        CacheEntry entry = cache.get(key);
        if (entry != null) {
          if (timestamp == entry.timestamp) {
            return entry.result;
          }
        }
  
        // Cache miss or stale.
        try {
          Object result = method.invoke(metadata, args);
          if (result != null) {
            entry = new CacheEntry();
            entry.timestamp = timestamp;
            entry.result = result;
            cache.put(key, entry);
          }
          return result;
        } catch (InvocationTargetException e) {
          throw castNonNull(e.getCause());
        }
      }
    }
  }
  