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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Work logged] (IO-279) Tailer erroneously considers file as new
Date Thu, 11 Apr 2019 12:15:01 GMT


ASF GitHub Bot logged work on IO-279:

                Author: ASF GitHub Bot
            Created on: 11/Apr/19 12:14
            Start Date: 11/Apr/19 12:14
    Worklog Time Spent: 10m 
      Work Description: garydgregory commented on issue #40: IO-279: Added ignoreNew parameter
on instantiating Tailer.
   Hi @Misiu,
   Thanks for the ping.
   I am -1 to this PR because:
   - It breaks binary compatibility. You can tell since this build is broken. See the red
"All checks have failed" note on this page and the associated Travis builds.
   - It does not contain a unit test to test the new feature.
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Issue Time Tracking

    Worklog Id:     (was: 226080)
    Time Spent: 20m  (was: 10m)

> Tailer erroneously considers file as new
> ----------------------------------------
>                 Key: IO-279
>                 URL:
>             Project: Commons IO
>          Issue Type: Bug
>    Affects Versions: 2.0.1, 2.4
>            Reporter: Sergio Bossa
>            Priority: Major
>         Attachments: IO-279.patch, disable_resetting.patch, fix-tailer.patch, modify-test-fixed.patch,
>          Time Spent: 20m
>  Remaining Estimate: 0h
> 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;
>; // 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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