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Apache Hadoop Common
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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.hadoop.util;

import org.apache.hadoop.classification.InterfaceStability;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.io.InputStream;

@InterfaceStability.Evolving
public class ThreadUtil {
  
  private static final Logger LOG = LoggerFactory.getLogger(ThreadUtil.class);

  /**
   * Cause the current thread to sleep as close as possible to the provided
   * number of milliseconds. This method will log and ignore any
   * {@link InterruptedException} encountered.
   * 
   * @param millis the number of milliseconds for the current thread to sleep
   */
  public static void sleepAtLeastIgnoreInterrupts(long millis) {
    long start = Time.now();
    while (Time.now() - start < millis) {
      long timeToSleep = millis -
          (Time.now() - start);
      try {
        Thread.sleep(timeToSleep);
      } catch (InterruptedException ie) {
        LOG.warn("interrupted while sleeping", ie);
      }
    }
  }

  /**
   * Convenience method that returns a resource as inputstream from the
   * classpath.
   * 
   * Uses the Thread's context classloader to load resource.
   *
   * @param resourceName resource to retrieve.
   *
   * @throws IOException thrown if resource cannot be loaded
   * @return inputstream with the resource.
   */
  public static InputStream getResourceAsStream(String resourceName)
      throws IOException {
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    if (cl == null) {
      throw new IOException("Can not read resource file '" + resourceName +
          "' because class loader of the current thread is null");
    }
    return getResourceAsStream(cl, resourceName);
  }

  /**
   * Convenience method that returns a resource as inputstream from the
   * classpath using given classloader.
   * 
   *
   * @param cl ClassLoader to be used to retrieve resource.
   * @param resourceName resource to retrieve.
   *
   * @throws IOException thrown if resource cannot be loaded
   * @return inputstream with the resource.
   */
  public static InputStream getResourceAsStream(ClassLoader cl,
        String resourceName)
        throws IOException {
    if (cl == null) {
      throw new IOException("Can not read resource file '" + resourceName +
          "' because given class loader is null");
    }
    InputStream is = cl.getResourceAsStream(resourceName);
    if (is == null) {
      throw new IOException("Can not read resource file '" +
          resourceName + "'");
    }
    return is;
  }


}