[ILUG] Slightly Off Topic : Concurrent Access to a Text File in a bash script - can I enforce thread safety

[Oisin Kim]

Hi All,

not a linux question, but I know there are some bash experts out there, so
hope this can be answered by someone.

Basically I have a very simple script, it will generate checksums for some
files and write the details to a log file, since the number of files is
small, and the server has a will have a large number of CPUs I'd like to run
the checksums in parallel.

What concerns me is how I can be sure that writes to the log file are
"thread safe", so that different processes don't corrupt the entries.

I've not been able to get any process writing to the file to overlap, but
that was on a limited test of 1000 files, and on my laptop.

Something as simple as this:

for i in *.* do
    cksum $i >> log.file &
done

So far I can't get two cksum processes to overlap each other in the log.file,
but I understand this might be hardware/file numbers.

I googled around and couldn't find something that answered this, so sorry if
I am asking a dumb question!

Thanks in advance,
Oisin