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From arina-ielchiieva <...@git.apache.org>
Subject [GitHub] drill pull request #660: DRILL-5052: Option to debug generated Java code usi...
Date Thu, 08 Dec 2016 15:26:54 GMT
Github user arina-ielchiieva commented on a diff in the pull request:

    https://github.com/apache/drill/pull/660#discussion_r91276697
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/compile/CachedClassLoader.java
---
    @@ -0,0 +1,70 @@
    +/**
    + * 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.drill.exec.compile;
    +
    +import java.net.URL;
    +import java.net.URLClassLoader;
    +import java.util.Map;
    +import java.util.concurrent.ConcurrentMap;
    +
    +import com.google.common.collect.MapMaker;
    +
    +/**
    + * Class loader for "plain-old Java" generated classes.
    + * Very basic implementation: allows defining a class from
    + * byte codes and finding the loaded classes. Delegates
    + * all other class requests to the thread context class
    + * loader. This structure ensures that a generated class can
    + * find both its own inner classes as well as all the standard
    + * Drill implementation classes.
    + */
    +
    +public class CachedClassLoader extends URLClassLoader {
    +
    +  /**
    +   * Cache of generated classes. Semantics: a single thread defines
    +   * the classes, many threads may access the classes.
    +   */
    +
    +  private ConcurrentMap<String, Class<?>> cache = new MapMaker().concurrencyLevel(4).makeMap();
    +
    +  public CachedClassLoader( ) {
    +    super(new URL[0], Thread.currentThread().getContextClassLoader());
    +  }
    +
    +  public void addClass( String fqcn, byte[] byteCodes ) {
    +
    +    assert ! cache.containsKey( fqcn );
    +    Class<?> newClass = defineClass(fqcn, byteCodes, 0, byteCodes.length);
    +    cache.put( fqcn, newClass );
    +  }
    +
    +  @Override
    +  public Class<?> findClass(String className) throws ClassNotFoundException {
    +    Class<?> theClass = cache.get( className );
    +    if ( theClass != null ) {
    +      return theClass; }
    +    return super.findClass(className);
    +  }
    +
    +  public void addClasses(Map<String, byte[]> results) {
    +    for ( String key : results.keySet() ) {
    +      addClass( key, results.get( key ) );
    +    }
    --- End diff --
    
    Using iteration over map via entry set is more efficient than via key set:
        for (Map.Entry<String, byte[]> result : results.entrySet()) {
          addClass(result.getKey(), result.getValue());
        }


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