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https://issues.apache.org/jira/browse/IO-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13637320#comment-13637320
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Sebb commented on IO-279:
-------------------------
The test seems wrong to me.
Only one line is written to the file, yet the check says:
{code}
assertEquals("1 line count", 2, lines.size());
{code}
Also, I'm not sure that changing the file modification date should be ignored.
How can one tell the difference between a file that has been touched from one
that has been re-written to the same length?
Potentially it may even be the same data - that would be an unusual use-case,
but not impossible.
For example, a rotating logger that records events but does not include a
timestamp. The same event sequence could recur.
A further problem with the test case in the patch is that it does not check the
data, only the line count.
> 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: IO-279.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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