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Date: Sat, 16 Jul 2011 14:37:59 +0000 (UTC)
From: "Sergio Bossa (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
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 <904552808.19976.1310827079899.JavaMail.tomcat@hel.zones.apache.org>
Subject: [jira] [Created] (IO-279) Tailer erroneously consider file as new
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Tailer erroneously consider file as new
---------------------------------------

                 Key: IO-279
                 URL: https://issues.apache.org/jira/browse/IO-279
             Project: Commons IO
          Issue Type: Bug
    Affects Versions: 2.0.1
            Reporter: Sergio Bossa


Tailer sometimes erroneously consider the tailed file as new, forcing a repositioning at the start of the file: I'm still unable to reproduce this in a test case, because it only happens to me with huge log files during Apache Tomcat startup.

This is the piece of code causing the problem:

// See if the file needs to be read again
if (length > position) {

    // The file has more content than it did last time
    last = System.currentTimeMillis();
    position = readLines(reader);

} else if (FileUtils.isFileNewer(file, last)) {

    /* This can happen if the file is truncated or overwritten
        * with the exact same length of information. In cases like
        * this, the file position needs to be reset
        */
    position = 0;
    reader.seek(position); // cannot be null here

    // Now we can read new lines
    last = System.currentTimeMillis();
    position = readLines(reader);
}

What probably happens is that the new file content is about to be written on disk, the date is already updated but content is still not flushed, so actual length is untouched and there you go.

In other words, I think there should be some better method to verify the condition above, rather than relying only on dates: keeping and comparing the hash code of the latest line may be a solution, but may hurt performances ... other ideas?

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