Sometimes you need to synchronize your block of code, but Mutex is too coarse-grained, because it always locks, no matter what objects your code accesses. The Futex (from "file mutex") is more fine-grained and uses a file as an entrance lock to your code.

First, install it:

$ gem install futex

Then, use it like this:

require 'futex'
Futex.new('/tmp/my-file.txt').open do |f|
  IO.write(f, 'Hello, world!')
end

The file /tmp/my-file.txt.lock will be created and used as an entrance lock. It will won't be deleted afterwards.

If you are not planning to write to the file, it is recommended to get a non-exclusive/shared access to it, by providing false to the method open():

require 'futex'
Futex.new('/tmp/my-file.txt').open(false) do |f|
  IO.read(f)
end

For better traceability you can provide a few arguments to the constructor of the Futex class, including:

• log: an object that implements debug() method, which will receive supplementary messages from the locking mechanism;

• logging: set it to true if you want to see logs;

• timeout: the number of seconds to wait for the lock availability (Futex::CantLock exception is raised when the wait is expired);

• sleep: the number of seconds to wait between attempts to acquire the lock file (the smaller the number, the more responsive is the software, but the higher the load for the file system and the CPU);

• lock: the absolute path of the lock file;

That's it.

How to contribute

Read these guidelines. Make sure you build is green before you contribute your pull request. You will need to have Ruby 2.3+ and Bundler installed. Then:

$ bundle update
$ bundle exec rake

If it's clean and you don't see any error messages, submit your pull request.