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   /*
   * Copyright 2014 The Netty Project
   *
   * The Netty Project 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:
   *
   *   https://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 io.netty.util.internal;
  
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.lang.reflect.Field;
  import java.lang.reflect.Method;
  import java.nio.ByteBuffer;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  
  
  /**
   * Allows to free direct {@link ByteBuffer} by using Cleaner. This is encapsulated in an extra class to be able
   * to use {@link PlatformDependent0} on Android without problems.
   *
   * For more details see <a href="https://github.com/netty/netty/issues/2604">#2604</a>.
   */
  final class CleanerJava6 implements Cleaner {
      private static final long CLEANER_FIELD_OFFSET;
      private static final Method CLEAN_METHOD;
      private static final Field CLEANER_FIELD;
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(CleanerJava6.class);
  
      static {
          long fieldOffset;
          Method clean;
          Field cleanerField;
          Throwable error = null;
          final ByteBuffer direct = ByteBuffer.allocateDirect(1);
          try {
              Object mayBeCleanerField = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                  @Override
                  public Object run() {
                      try {
                          Field cleanerField =  direct.getClass().getDeclaredField("cleaner");
                          if (!PlatformDependent.hasUnsafe()) {
                              // We need to make it accessible if we do not use Unsafe as we will access it via
                              // reflection.
                              cleanerField.setAccessible(true);
                          }
                          return cleanerField;
                      } catch (Throwable cause) {
                          return cause;
                      }
                  }
              });
              if (mayBeCleanerField instanceof Throwable) {
                  throw (Throwable) mayBeCleanerField;
              }
  
              cleanerField = (Field) mayBeCleanerField;
  
              final Object cleaner;
  
              // If we have sun.misc.Unsafe we will use it as its faster then using reflection,
              // otherwise let us try reflection as last resort.
              if (PlatformDependent.hasUnsafe()) {
                  fieldOffset = PlatformDependent0.objectFieldOffset(cleanerField);
                  cleaner = PlatformDependent0.getObject(direct, fieldOffset);
              } else {
                  fieldOffset = -1;
                  cleaner = cleanerField.get(direct);
              }
              clean = cleaner.getClass().getDeclaredMethod("clean");
              clean.invoke(cleaner);
          } catch (Throwable t) {
              // We don't have ByteBuffer.cleaner().
              fieldOffset = -1;
              clean = null;
              error = t;
              cleanerField = null;
          }
  
          if (error == null) {
              logger.debug("java.nio.ByteBuffer.cleaner(): available");
          } else {
              logger.debug("java.nio.ByteBuffer.cleaner(): unavailable", error);
          }
          CLEANER_FIELD = cleanerField;
          CLEANER_FIELD_OFFSET = fieldOffset;
          CLEAN_METHOD = clean;
      }
 
     static boolean isSupported() {
         return CLEANER_FIELD_OFFSET != -1 || CLEANER_FIELD != null;
     }
 
     @Override
     public void freeDirectBuffer(ByteBuffer buffer) {
         if (!buffer.isDirect()) {
             return;
         }
         if (System.getSecurityManager() == null) {
             try {
                 freeDirectBuffer0(buffer);
             } catch (Throwable cause) {
                 PlatformDependent0.throwException(cause);
             }
         } else {
             freeDirectBufferPrivileged(buffer);
         }
     }
 
     private static void freeDirectBufferPrivileged(final ByteBuffer buffer) {
         Throwable cause = AccessController.doPrivileged(new PrivilegedAction<Throwable>() {
             @Override
             public Throwable run() {
                 try {
                     freeDirectBuffer0(buffer);
                     return null;
                 } catch (Throwable cause) {
                     return cause;
                 }
             }
         });
         if (cause != null) {
             PlatformDependent0.throwException(cause);
         }
     }
 
     private static void freeDirectBuffer0(ByteBuffer buffer) throws Exception {
         final Object cleaner;
         // If CLEANER_FIELD_OFFSET == -1 we need to use reflection to access the cleaner, otherwise we can use
         // sun.misc.Unsafe.
         if (CLEANER_FIELD_OFFSET == -1) {
             cleaner = CLEANER_FIELD.get(buffer);
         } else {
             cleaner = PlatformDependent0.getObject(buffer, CLEANER_FIELD_OFFSET);
         }
         if (cleaner != null) {
             CLEAN_METHOD.invoke(cleaner);
         }
     }
 }