spark-gpu-master/launcher/src/main/java/org/apache/spark/launcher/OutputRedirector.java
/*
 * 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.spark.launcher;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.concurrent.ThreadFactory;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Redirects lines read from a given input stream to a j.u.l.Logger (at INFO level).
 */
class OutputRedirector {

  private final BufferedReader reader;
  private final Logger sink;
  private final Thread thread;

  private volatile boolean active;

  OutputRedirector(InputStream in, ThreadFactory tf) {
    this(in, OutputRedirector.class.getName(), tf);
  }

  OutputRedirector(InputStream in, String loggerName, ThreadFactory tf) {
    this.active = true;
    this.reader = new BufferedReader(new InputStreamReader(in));
    this.thread = tf.newThread(new Runnable() {
      @Override
      public void run() {
        redirect();
      }
    });
    this.sink = Logger.getLogger(loggerName);
    thread.start();
  }

  private void redirect() {
    try {
      String line;
      while ((line = reader.readLine()) != null) {
        if (active) {
          sink.info(line.replaceFirst("\\s*$", ""));
        }
      }
    } catch (IOException e) {
      sink.log(Level.FINE, "Error reading child process output.", e);
    }
  }

  /**
   * This method just stops the output of the process from showing up in the local logs.
   * The child's output will still be read (and, thus, the redirect thread will still be
   * alive) to avoid the child process hanging because of lack of output buffer.
   */
  void stop() {
    active = false;
  }

}
