Re^2: Strange IO + concurrency issue

[vsespb]

So potentially many children all writing to the same file at the same time.

See above Re^2: Strange IO + concurrency issue - write-to file is actually protected (although it's extremely unclear in code). What was not protected is file copy (where destination file is unique)

It's usually better to get each child to write to its own temp file

Same, in this case there are no concurrent writes to same file (even copy writes to unique file).