com.amazonaws.services.kinesis.multilang.DrainChildSTDOUTTask Maven / Gradle / Ivy

/*
 * Copyright 2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Amazon Software License (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 * http://aws.amazon.com/asl/
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.services.kinesis.multilang;

import java.io.BufferedReader;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * This class is used to drain the STDOUT of the child process. After the child process has been given a shutdown
 * message and responded indicating that it is shutdown, we attempt to close the input and outputs of that process so
 * that the process can exit.
 * 
 * To understand why this is necessary, consider the following scenario:
 * 
 * 
 * Child process responds that it is done with shutdown.
 * Child process prints debugging text to STDOUT that fills the pipe buffer so child becomes blocked.
 * Parent process doesn't drain child process's STDOUT.
 * Child process remains blocked.
 * 
 * 
 * To prevent the child process from becoming blocked in this way, it is the responsibility of the parent process to
 * drain the child process's STDOUT. We reprint each drained line to our log to permit debugging.
 */
class DrainChildSTDOUTTask extends LineReaderTask {

    private static final Log LOG = LogFactory.getLog(DrainChildSTDOUTTask.class);

    DrainChildSTDOUTTask() {
    }

    @Override
    protected HandleLineResult handleLine(String line) {
        LOG.info("Drained line for shard " + getShardId() + ": " + line);
        return new HandleLineResult();
    }

    @Override
    protected Boolean returnAfterException(Exception e) {
        LOG.info("Encountered exception while draining STDOUT of child process for shard " + getShardId(), e);
        return false;
    }

    @Override
    protected Boolean returnAfterEndOfInput() {
        return true;
    }

    public LineReaderTask initialize(BufferedReader reader, String shardId) {
        return initialize(reader, shardId, "Draining STDOUT for " + shardId);
    }
}