Examples of Toxic Code Snippets

1. The Hadoop's compare method

The first example is outdated and license-violating online code clones in an answer to a Stack Overflow question regarding how to implement RawComparator in Hadoop. The figure below shows, on the left, a code snippet embedded as a part of the accepted answer. The snippet shows how Hadoop implements the compare method in its WritableComparator class. The code snippet on the right shows another version of the same method, but at this time extracted from the latest version (as of October 3, 2017) of Hadoop.

We can see that they both are highly similar except a line containing buffer.reset(null,0,0); which was added on November 21, 2014. The added line is intended for cleaning up the reference in the buffer variable and avoid excess heap usage (issue no. HADOOP-11323).

/* Code in Stack Overflow post ID 22315734 (no license) */
public int compare(byte[] b1,int s1,int l1,byte[] b2,int s2,int l2) {
  try {
    buffer.reset(b1, s1, l1); // parse key1
    key1.readFields(buffer);
    buffer.reset(b2, s2, l2); // parse key2
    key2.readFields(buffer);
  } catch (IOException e) {
    throw new RuntimeException(e);
  }
  return compare(key1, key2); // compare them
}
        

/* WritableComparator.java (2014-11-21) (Apache v.2.0 license) */
public int compare(byte[] b1,int s1,int l1,byte[] b2,int s2,int l2) {
  try {
    buffer.reset(b1, s1, l1);  // parse key1
    key1.readFields(buffer);
    buffer.reset(b2, s2, l2);  // parse key2
    key2.readFields(buffer);
    buffer.reset(null, 0, 0);  // clean up reference
  } catch (IOException e) {
    throw new RuntimeException(e);
  }
  return compare(key1, key2);  // compare them
}
        

While this change has already been introduced into the compare method several years ago, the code example in Stack Overflow post is still unchanged. In addition, the original code snippet of WritableComparator class in Hadoop is distributed with Apache license version 2.0 while its cloned instance on Stack Overflow contains only the compare method and ignores its license statement on top of the file.

There are two potential issues for this. First, the code snippet may appear to be under Stack Overflow's CC BY-SA 3.0 instead of its original Apache license. Second, if the code snippet is copied and incorporated into another software project with a conflicting license, a legal issue may arise.

2. The Hadoop's humanReadableInt method

The second motivating example of a toxic code snippet with more disrupting changes than the first one can be found in an answer to a Stack Overflow question regarding how to format files sizes in a human readable form. The figure below shows, on the left, a code snippet to perform the task from the StringUtils class in Hadoop.

The code snippet on the right shows another version of the same method, but at this time extracted from the latest version of Hadoop. We can see that they are totally different. The humanReadableInt method is rewritten on February 5, 2013 to solve an issue of a race condition (issue no. HADOOP-9252). Similar to the first example, the clone code snippet on Stack Overflow does not include its original Apache v.2.0 license.

/* Code in Stack Overflow post ID 801987 (no license) */
public static String humanReadableInt(long number) {
    long absNumber = Math.abs(number);
    double result = number;
    String suffix = "";
    if (absNumber < 1024) {
      // nothing
    } else if (absNumber < 1024 * 1024) {
      result = number / 1024.0;
      suffix = "k";
    } else if (absNumber < 1024 * 1024 * 1024) {
      result = number / (1024.0 * 1024);
      suffix = "m";
    } else {
      result = number / (1024.0 * 1024 * 1024);
      suffix = "g";
    }
    return oneDecimal.format(result) + suffix;
  }
            

/* StringUtils.java (2013-02-05) (Apache v.2.0 license) */
public static String humanReadableInt(long number) {
  return TraditionalBinaryPrefix.long2String(number,"",1);
}