in reply to [SOLVED] Strange IO + concurrency issue

I'm not entirely sure what you are trying to achieve, but the issue seems to be that you are only locking the file open not the file writes.

 so :-
fork 1                      fork 2

takes the lock
opens file1
releases the lock
starts writing data
gets pre-empted
                            takes the lock
                            opens file1 (& deletes contents)
                            releases the lock
                            starts writing data 

Etc....

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So potentially many children all writing to the same file at the same time. If you get each fork to write a different character to the file you'll see what's happening.

It's usually better to get each child to write to its own temp file, File::Temp, then rename it.

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Re^2: Strange IO + concurrency issue
by vsespb (Chaplain) on Sep 28, 2013 at 17:16 UTC
    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).
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