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....

[download]

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.

In reply to Re: Strange IO + concurrency issue by RichardK
in thread [SOLVED] Strange IO + concurrency issue by vsespb

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