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From "Niall Pemberton (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (IO-279) Tailer erroneously considers file as new
Date Fri, 08 Jun 2012 02:06:24 GMT

     [ https://issues.apache.org/jira/browse/IO-279?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Niall Pemberton updated IO-279:
-------------------------------

    Attachment: IO-279.patch

Firstly I don't know why System.currentTimeMillis() is used. What matters is if the files
lastModified time compared to its previous lastModified value.

I agree with Chris that the lastModified time should be stored after the file is read.
                
> Tailer erroneously considers 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
>             Fix For: 2.4
>
>         Attachments: IO-279.patch
>
>
> Tailer sometimes erroneously considers 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:
> {code}
> // 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);
> }
> {code}
> 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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