Show HN: Linux CLI tool to provide mutex locks for long running bash ops

34 pointsbigattichouse1 year ago20 comments

Been exploring claude and spec-based coding, I think it turned out fairly successful. It's just a simple unix-style tool that gives you a single command to use in bash scripts to simplify mutex or semaphore locking of execution.

sluongng 1y

Why not https://man7.org/linux/man-pages/man2/flock.2.html?

yjftsjthsd-h 1y

Nit: Probably https://man7.org/linux/man-pages/man1/flock.1.html (shell command, not the underlying libc function)

anitil 1y

This was my first thought and I suppose flock(1) could be used to recreate a lot of this. But it does come with some other quality-of-life improvements like being able to list all currently-used locks, having a lock holdable by N processes etc.

Zacru 1y

Because that's a syscall ;) https://man7.org/linux/man-pages/man1/flock.1.html is the command line manual.

I would say one good reason is that

  waitlock myapp &
  JOB_PID=$!
  # ... do exclusive work ...
  kill $JOB_PID

is a lot easier to use and remember than

  (; flock -n 9 || exit 1; # ... commands executed under lock ...; ) 9>/var/lock/mylockfile

yjftsjthsd-h 1y

Why

  (; flock -n 9

and not

  ( flock -n 9

?

apopapo 1y

It's a "for" loop.

marklgr 1y

Could you elaborate?

apopapo 1y

A for loop in a shell script may sometimes look like this:

`for ((i = 0 ; i < max ; i++ )); do echo "$i"; done`

Here this is essentially a "while" loop, meaning it will keep executing the commands as long as we don't reach `exit 1`.

(; flock -n 9 || exit 1; # ... commands executed under lock ...; )

yjftsjthsd-h 1y

It doesn't seem to work?

  [~] 0 $ ( flock -n 9 || exit 1; echo in loop ; sleep 3 ; echo done working ; ) 9>~/tmp/mylock
  in loop
  done working
  [~] 0 $ (; flock -n 9 || exit 1; echo in loop ; sleep 3 ; echo done working ; ) 9>~/tmp/mylock
  -bash: syntax error near unexpected token `;'
  [~] 2 $

(This is bash)

permalac 1y

Flock can be used in a single line for example for cronjobs.

Flock -s file && script.

Pretty simple. (I forgot the argument, I think is -s..

bigattichouseOP1y

just pushed a change so now it's:

waitlock myapp & #... do stuff waitlock --done myapp

ethan_smith 1y

flock is indeed built-in: `flock -xn /tmp/mylock.lock -c "echo running locked command"` does mutex locking in bash. Your tool might offer better ergonomics or features beyond flock's capabilities?

teddyh 1y

We already have lockfile: <https://manpages.debian.org/stable/procmail/lockfile.1.en.ht...>.

forrestthewoods 1y

I don’t know the exact threshold at which you should use a real programming language instead of a bash script. But this type of work definitely exceeds it.

anitil 1y

While in general I'd agree, this isn't necessarily just for bash scripts. It could just wrap the execution of another program allowing higher-level logic to handle concurrency and the low-level program to do it's one-at-a-time job

bigattichouseOP1y

Sometimes you have a cron job that takes longer than it should (but inconsistently so), and another cron job that clobbers what that cron job is doing.

asddfgg55 1y

Useful project, I love all things terminal, so I also enjoyed your project.

eddythompson80 1y

You enjoyed the project because you love the terminal?

bigattichouseOP1y

Good enough for me. I created the project because I love terminal, and wanted to make something using Claude (to learn how this tool works, strictly for personal enrichment) that solves a small problem I had with some overlapping cron job management.

eddythompson80 1y

I was saying that in a questioning tone implying that I think the account is a bot.

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