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.cassandra.utils;
  
  import java.lang.reflect.Field;
  import java.lang.reflect.Method;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.function.Predicate;
  
  public class ReflectionUtils
  {
      private ReflectionUtils()
      {
  
      }
  
      public static Field getModifiersField() throws NoSuchFieldException
      {
          return getField(Field.class, "modifiers");
      }
  
      public static Field getField(Class<?> clazz, String fieldName) throws NoSuchFieldException
      {
          // below code works before Java 12
          try
          {
              return clazz.getDeclaredField(fieldName);
          }
          catch (NoSuchFieldException e)
          {
              // this is mitigation for JDK 17 (https://bugs.openjdk.org/browse/JDK-8210522)
              try
              {
                  Method getDeclaredFields0 = Class.class.getDeclaredMethod("getDeclaredFields0", boolean.class);
                  getDeclaredFields0.setAccessible(true);
                  Field[] fields = (Field[]) getDeclaredFields0.invoke(clazz, false);
                  for (Field field : fields)
                  {
                      if (fieldName.equals(field.getName()))
                      {
                          return field;
                      }
                  }
              }
              catch (ReflectiveOperationException ex)
              {
                  e.addSuppressed(ex);
              }
              throw e;
          }
      }
  
      /**
       * Used by the in-jvm dtest framework to remove entries from private map fields that otherwise would prevent
       * collection of classloaders (which causes metaspace OOMs) or otherwise interfere with instance restart.
       * @param clazz The class which has the map field to clear
       * @param instance an instance of the class to clear (pass null for a static member)
       * @param mapName the name of the map field to clear
       * @param shouldRemove a predicate which determines if the entry in question should be removed
       * @param <K> The type of the map key
       * @param <V> The type of the map value
       */
      public static <K, V> void clearMapField(Class<?> clazz, Object instance, String mapName, Predicate<Map.Entry<K, V>> shouldRemove) {
          try
          {
              Field mapField = getField(clazz, mapName);
              mapField.setAccessible(true);
              // noinspection unchecked
              Map<K, V> map = (Map<K, V>) mapField.get(instance);
              // Because multiple instances can be shutting down at once,
              // synchronize on the map to avoid ConcurrentModificationException
              synchronized (map)
              {
                  // This could be done with a simple `map.entrySet.removeIf()` call
                  // but for debugging purposes it is much easier to keep it like this.
                  Iterator<Map.Entry<K,V>> it = map.entrySet().iterator();
                  while (it.hasNext()) {
                      Map.Entry<K,V> entry = it.next();
                      if (shouldRemove.test(entry))
                      {
                          it.remove();
                      }
                  }
              }
          }
          catch (NoSuchFieldException | IllegalAccessException ex)
          {
              throw new RuntimeException(String.format("Could not clear map field %s in class %s", mapName, clazz), ex);
          }
      }
  
      public static <T> void setFieldToNull(T object, Class<T> declaringClass, String fieldName)
      {
          try
          {
              Field field = declaringClass.getDeclaredField(fieldName);
              field.setAccessible(true);
              field.set(object, null);
          }
          catch (NoSuchFieldException e)
          {
              throw new RuntimeException(String.format("Could not find field %s in %s", fieldName, object.getClass()));
          }
          catch (IllegalAccessException e)
          {
              throw new RuntimeException(String.format("Could not set field %s in %s", fieldName, object.getClass()), e);
          }
      }
  }
  