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From "Sergio Bossa (JIRA)" <>
Subject [jira] [Created] (IO-279) Tailer erroneously consider file as new
Date Sat, 16 Jul 2011 14:37:59 GMT
Tailer erroneously consider file as new

                 Key: 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;; // 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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