semalock

semalock is a Rust library for controlling concurrent access to files on POSIX operating systems in an efficient manner.

It uses a combination of POSIX named semaphores and exclusive file locks to safely and efficiently acquire exclusive access to a file. This has been observed to be particularly efficient on Linux, with under 5% of CPU time spent on lock overhead with 8192 processes.

Usage

The following shows usage of semalock. This program opens /some/file and appends some text to it. Try it with GNU parallel to measure performance amongst multiple competing processes.

// Acquire and open a file and semaphore
let mut lock = Semalock::new(Path::new("/some/file"));

// Do some stuff to the file
lock.with(|lock| {
    lock.file
        .seek(SeekFrom::End())
        .and_then(|_| lock.file.write(b"hello world\n"))
});

Supported Operating Systems

The following operating systems have been tested:

• GNU/Linux 4.16

The following operating systems have not been tested but should work:

• FreeBSD
• GNU/Linux 2.6+
• macOS 10.4+
• NetBSD
• OpenBSD

Supported operating systems must support provide the following:

• flock
• sem_get_value
• sem_open
• sem_post
• sem_timedwait
• sem_unlink

The following will not work:

• Windows NT

Release Notes

0.3.1 - 2020-02-25

• Fix a compilation error on x86 - thanks to @unpluggedcoder

0.3.0 - 2019-09-13

• Semalock::with now takes an FnOnce instead of an Fn.
• Various project hygiene changes

0.2.0 - 2018-05-14

• Initial release.

Developer Notes

To run the tests, execute the following:

cargo test

To release the create, perform the following:

1. Edit Cargo.toml, bumping the version as appropriate.
2. Edit README.md, adding an entry to the Release Notes.
3. Commit these changes and push them to master.
4. Create and push a tag that starts with "v" -- e.g. "v0.4.0"

Author

Jason Longshore hello@jasonlongshore.com