org.rocksdb.AbstractNativeReference Maven / Gradle / Ivy

// Copyright (c) 2016, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

package org.rocksdb;

/**
 * AbstractNativeReference is the base-class of all RocksDB classes that have
 * a pointer to a native C++ {@code rocksdb} object.
 * 
 * AbstractNativeReference has the {@link AbstractNativeReference#dispose()}
 * method, which frees its associated C++ object.
 * 
 * This function should be called manually, however, if required it will be
 * called automatically during the regular Java GC process via
 * {@link AbstractNativeReference#finalize()}.
 * 
 * Note - Java can only see the long member variable (which is the C++ pointer
 * value to the native object), as such it does not know the real size of the
 * object and therefore may assign a low GC priority for it; So it is strongly
 * suggested that you manually dispose of objects when you are finished with
 * them.
 */
public abstract class AbstractNativeReference implements AutoCloseable {

  /**
   * Returns true if we are responsible for freeing the underlying C++ object
   *
   * @return true if we are responsible to free the C++ object
   * @see #dispose()
   */
  protected abstract boolean isOwningHandle();

  /**
   * Frees the underlying C++ object
   * 
   * It is strong recommended that the developer calls this after they
   * have finished using the object.
   * 
   * Note, that once an instance of {@link AbstractNativeReference} has been
   * disposed, calling any of its functions will lead to undefined
   * behavior.
   */
  @Override
  public abstract void close();

  /**
   * @deprecated Instead use {@link AbstractNativeReference#close()}
   */
  @Deprecated
  public final void dispose() {
    close();
  }

  /**
   * Simply calls {@link AbstractNativeReference#dispose()} to free
   * any underlying C++ object reference which has not yet been manually
   * released.
   *
   * @deprecated You should not rely on GC of Rocks objects, and instead should
   * either call {@link AbstractNativeReference#close()} manually or make
   * use of some sort of ARM (Automatic Resource Management) such as
   * Java 7's try-with-resources
   * statement
   */
  @Override
  @Deprecated
  protected void finalize() throws Throwable {
    if(isOwningHandle()) {
      //TODO(AR) log a warning message... developer should have called close()
    }
    dispose();
    super.finalize();
  }
}