File system locking - is there a way to create file system based locks without using a NIF in Erlang?

lpil · November 23, 2022, 6:00pm

Hello gang!

Is there a way to create file system based locks without using a NIF in Erlang?

Cheers,
Louis

starbelly · November 23, 2022, 6:21pm

I’m afraid not. All the modes are documented in file, but to be sure I looked at erts/emulator/nifs/common/prim_file_nif.c, modes that are not documented are dropped on the floor. Likewise, flock and friends are not exposed anywhere.

There’s probably a good reason for this not being supported, interested in an answer to that.

lpil · November 23, 2022, 6:54pm

Alas! Thank you for investigating for me

garazdawi · November 23, 2022, 7:10pm

github.com/erlang/otp

Introduce file:flock/2

erlang:master ← lukaszsamson:ls-add-flock

opened 04:19PM - 27 Aug 22 UTC

lukaszsamson

+388 -7

This PR extends `file` module with new function `flock/2`. It allows locking fil…es for shared or exclusive access on Unix and Windows. Rationale: Currently the OTP lacks suitable APIs allowing fine grained control over access to filesystem. Those can be especially useful for applications like language tools, compilers (e.g. elixir compiler), IDEs (like language servers) that share access to the same filesystem directories. Please note that this is a first draft that received only a little testing on macOS platform. I would like to get some guidance if the direction I took is acceptable and if the OTP Team would be interested in merging this. The documentation will also need further improvements. Related manpages and documentation: 1. https://linux.die.net/man/2/flock 2. https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/flock.2.html 3. http://www.polarhome.com/service/man/?qf=flock&tf=2&of=Solaris&sf=3UCB 4. https://www.freebsd.org/cgi/man.cgi?query=flock&sektion=2 5. https://man.openbsd.org/flock.2 6. https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-lockfileex 7. https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-unlockfileex 8. https://docs.microsoft.com/en-us/windows/win32/fileio/locking-and-unlocking-byte-ranges-in-files CC @josevalim

lpil · November 23, 2022, 7:52pm

Ah wonderful, I will subscribe to that PR and look forward to it’s being merged.