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I have two shell scripts that may be run in parallel but may also be run one at a time. Both scripts rely on an initial setup step that takes a while and can't be run by both at the same time.

To allow for parallel execution for the remainder, I've wrapped the setup step in control flow using flock based on this recommendation.

This seems to work fine, but I'm not sure if the if-else construct is fully safe. Are there any hidden issues here that I'm missing?

set -euxo pipefail
(
    # Only run setup if we're the first to acquire the lock
    if flock -x -n 200 ; then
        # Time-consuming setup that can't be run in parallel
    else
        # Wait for the lock to be released and then continue, timeout on 600s
        flock -x -w 600 200;
    fi
) 200>/tmp/setup.lock

# Rest of the script that relies on setup being done
Etheryte
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  • What shell is this using? Probably `bash`, right? "Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally." – Kusalananda May 17 '21 at 12:23
  • If `flock` invocation did what you mention in comment that should be OK, however, what is `200>` use for ? is it a bad copy/paste ? – Archemar May 17 '21 at 12:23
  • @Archemar No, it's redirecting file descriptor 200, set up by `flock`. – Kusalananda May 17 '21 at 12:25
  • @Kusalananda This is bash, yes, forgot to note that, sorry. As for the 200, the example shown in the command's manpage uses that descriptor but I have no strong inclination for it, thanks for pointing that out. There's a question on the specific number [over here](https://stackoverflow.com/a/13551882/1470607), for anyone else interested. – Etheryte May 17 '21 at 13:22

0 Answers0