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/*
 * 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.ratis.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.atomic.AtomicReference;

/**
 * Use a {@link Daemon},
 * which repeatedly waits for a signal to run a method.
 * 
 * This class is threadsafe.
 *
 * @see AwaitForSignal
 */
public class AwaitToRun implements AutoCloseable {
  public static final Logger LOG = LoggerFactory.getLogger(AwaitToRun.class);

  private final class RunnableImpl implements Runnable {
    private final Runnable runMethod;

    private RunnableImpl(Runnable runMethod) {
      this.runMethod = runMethod;
    }

    @Override
    public void run() {
      while(!Thread.currentThread().isInterrupted()) {
        try {
          awaitForSignal.await();
        } catch (InterruptedException e) {
          LOG.info("{} is interrupted", awaitForSignal);
          Thread.currentThread().interrupt();
          return;
        }

        try {
          runMethod.run();
        } catch (Throwable t) {
          LOG.error(name + ": runMethod failed", t);
        }
      }
    }
  }

  private final String name;
  private final AwaitForSignal awaitForSignal;
  private final AtomicReference daemon;

  public AwaitToRun(Object namePrefix, Runnable runMethod) {
    this.name = namePrefix + "-" + JavaUtils.getClassSimpleName(getClass());
    this.awaitForSignal = new AwaitForSignal(name);
    this.daemon = new AtomicReference<>(Daemon.newBuilder()
        .setName(name)
        .setRunnable(new RunnableImpl(runMethod))
        .build());
  }

  /** Similar to {@link Thread#start()}. */
  public AwaitToRun start() {
    final Daemon d = daemon.get();
    if (d != null) {
      d.start();
      LOG.info("{} started", d);
    } else {
      LOG.warn("{} is already closed", name);
    }
    return this;
  }

  /** Signal to run. */
  public void signal() {
    awaitForSignal.signal();
  }

  @Override
  public void close() {
    final Daemon d = daemon.getAndSet(null);
    if (d == null) {
      return;
    }

    d.interrupt();
    try {
      d.join();
    } catch (InterruptedException e) {
      LOG.warn(d + ": join is interrupted", e);
      Thread.currentThread().interrupt();
    }
  }

  @Override
  public String toString() {
    return name;
  }
}