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From "Herman Meerlo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IO-279) Tailer erroneously considers file as new
Date Fri, 26 Apr 2013 07:22:17 GMT

    [ https://issues.apache.org/jira/browse/IO-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13642647#comment-13642647
] 

Herman Meerlo commented on IO-279:
----------------------------------

Yes I replaced all 3 instances of System.currentTimeMillis()

The test will indeed still fail, it doesn't solve the specific case of differentiating between
the touch of a file and overwriting the contents of the file with the exact same amount of
bytes. It solves this specific bug as the title says 'Tailer erroneously considers file as
new'. So I guess it is better to create a new ticket and attach the testcase to that ticket,
because that is a different bug (which is very hard to solve as has already been said by most
of us).
                
> 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, 2.4
>            Reporter: Sergio Bossa
>             Fix For: 2.4
>
>         Attachments: fix-tailer.patch, IO-279.patch, modify-test-fixed.patch, modify-test.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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