/*
 * 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.hadoop.hbase.conf;

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.testclassification.ClientTests;
import org.apache.hadoop.hbase.testclassification.SmallTests;
import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Tag(SmallTests.TAG)
@Tag(ClientTests.TAG)
public class TestConfigurationManager {

  private static final Logger LOG = LoggerFactory.getLogger(TestConfigurationManager.class);

  static class DummyConfigurationObserver implements ConfigurationObserver {
    private boolean notifiedOnChange = false;
    private final ConfigurationManager cm;

    public DummyConfigurationObserver(ConfigurationManager cm) {
      this.cm = cm;
      register();
    }

    @Override
    public void onConfigurationChange(Configuration conf) {
      notifiedOnChange = true;
    }

    // Was the observer notified on Configuration change?
    public boolean wasNotifiedOnChange() {
      return notifiedOnChange;
    }

    public void resetNotifiedOnChange() {
      notifiedOnChange = false;
    }

    public void register() {
      cm.registerObserver(this);
    }

    public void deregister() {
      cm.deregisterObserver(this);
    }
  }

  /**
   * Test if observers get notified by the <code>ConfigurationManager</code> when the Configuration
   * is reloaded.
   */
  @Test
  public void testCheckIfObserversNotified() {
    Configuration conf = new Configuration();
    ConfigurationManager cm = new ConfigurationManager();
    DummyConfigurationObserver d1 = new DummyConfigurationObserver(cm);

    // Check if we get notified.
    cm.notifyAllObservers(conf);
    assertTrue(d1.wasNotifiedOnChange());
    d1.resetNotifiedOnChange();

    // Now check if we get notified on change with more than one observers.
    DummyConfigurationObserver d2 = new DummyConfigurationObserver(cm);
    cm.notifyAllObservers(conf);
    assertTrue(d1.wasNotifiedOnChange());
    d1.resetNotifiedOnChange();
    assertTrue(d2.wasNotifiedOnChange());
    d2.resetNotifiedOnChange();

    // Now try deregistering an observer and verify that it was not notified
    d2.deregister();
    cm.notifyAllObservers(conf);
    assertTrue(d1.wasNotifiedOnChange());
    d1.resetNotifiedOnChange();
    assertFalse(d2.wasNotifiedOnChange());
  }

  // Register an observer that will go out of scope immediately, allowing
  // us to test that out of scope observers are deregistered.
  private void registerLocalObserver(ConfigurationManager cm) {
    new DummyConfigurationObserver(cm);
  }

  /**
   * Test if out-of-scope observers are deregistered on GC.
   */
  @Test
  public void testDeregisterOnOutOfScope() {
    Configuration conf = new Configuration();
    ConfigurationManager cm = new ConfigurationManager();

    boolean outOfScopeObserversDeregistered = false;

    // On my machine, I was able to cause a GC after around 5 iterations.
    // If we do not cause a GC in 100k iterations, which is very unlikely,
    // there might be something wrong with the GC.
    for (int i = 0; i < 100000; i++) {
      registerLocalObserver(cm);
      cm.notifyAllObservers(conf);

      // 'Suggest' the system to do a GC. We should be able to cause GC
      // atleast once in the 2000 iterations.
      System.gc();

      // If GC indeed happened, all the observers (which are all out of scope),
      // should have been deregistered.
      if (cm.getNumObservers() <= i) {
        outOfScopeObserversDeregistered = true;
        break;
      }
    }
    if (!outOfScopeObserversDeregistered) {
      LOG.warn("Observers were not GC-ed! Something seems to be wrong.");
    }
    assertTrue(outOfScopeObserversDeregistered);
  }
}
