remove redundant File.length() check to fix race condition

[gregallen]

See #47

[belingueres]

IMHO this patch does not FIX the race condition, rather just ignore it. I think the check provides a valuable fail-fast mechanism to detect possible problems (as you just did) but removing it won't solve the race condition. The concurrency issue is at a higher level and it is there where it should be fixed.

[gregallen]

the issue should be safe to ignore since multiple writers to the same file will each succeed in writing their own full copy of the file (on unix) whereas on windows they will either block or fail early.

If you don't wish to merge please can you suggest a way forward?

• maven dependencies plugin needs to be marked not thread safe
• how can the maven plugin goal lock across multi module parallel builds?
• suggest a test case that triggers the file length test to fail AND the files are not in a good state after all copy goals have completed - I'm not convinced this is possible
• can the check be changed to instead test the number of bytes written?

[belingueres]

I suggest to translate this discussion to the maven developer mailing list to get more answers.

[gregallen]

actually, here's another point on why I think the post-copy length check is flawed - it can never be thread safe / concurrency friendly, since there's no telling how much time may pass between completion of the file copy and the length check.

Imagine a couple of not too fanciful scenarios:

1. There is a directory listener that promptly appends a checksum to files when they appear in the destination directory.
2. Or, the destination file is over-written several times with different contents - e.g. by an optimizer, or an incrementally newer version.

On these grounds, I think the only sane strategy for checking in plexus-util has to be no stronger that a check on number of bytes written

[slachiewicz]

@slawekjaranowski wdyt?