File locking?

[dbohdan]

Is there a way to lock a file on Linux and *BSD from Joker? I could not find one. My goal is to ensure only one instance of a script at a time can modify a file. Is there a way to use Bolt as a locking mechanism? I see the option of shelling out to flock(1) or wrapping my Joker script in a shell script that runs it with flock, but a native solution would be more convenient and elegant.

P.S.: Thanks for making Joker! I run it on NetBSD on SDF. It builds and runs on NetBSD without issue.

[candid82]

Currently there is no way to do it. Looks like Go provides syscall.Flock function that could be wrapped and exposed in Joker, but syscall package is OS-specific and I'd like to avoid OS-specific APIs.
I think you can use Bolt for locking if you don't mind creating a temporary file. E.g.

(def db (joker.bolt/open "temp.db" 0600)) ;; First process will acquire a lock, subsequent processes will block until the lock is release with (joker.bolt/close db) call

;; Do stuff

(joker.bolt/close db) ;; This releases the lock.

[candid82]

I run it on NetBSD on SDF

Just read about SDF. This is really cool!

[dbohdan]

Avoiding non-portable APIs makes sense. I'll try Bolt; it likely fits my use case. It looks like Bolt implements its own cross-platform abstraction over flock (Windows implementation). There are Go libraries that provide a similar abstraction, but one would have to research their quality and pick one (e.g., gofrs/flock#41 may be a problem with the library and not the OS API).

I'll leave the issue open: other users could be interested, and I might do the research and PR the feature for you to review at some point.