Heavily tested, but simple filelocking solution using flock command. It guarantees unlocking of files.

It works for sure on MRI 1.8, 1.9, 2.0, JRuby in both 1.8 and 1.9 mode, and Rubinius.

This gem doesn't support NFS. You can use it with GlusterFS, though.

Filelock '/tmp/path/to/lock' do
  # do blocking operation
end

You can also pass the timeout for blocking operation (default is 60 seconds):

Filelock '/tmp/path/to/lock', :timeout => 10 do
  # do blocking operation
end

You can detect timeout by catching Filelock::ExecTimeout.

You can also pass a non-zero wait timeout for grabbing the lock (default is 1 day):

Filelock '/tmp/path/to/lock', :wait => 3600 do
  # do blocking operation
end

You can detect this kind of timeout by catching Filelock::WaitTimeout. Note that a wait timeout of 0 will block until the lock can be acquired instead of raising Filelock::WaitTimeout.

Note that lock file directory must already exist, and lock file is not removed after unlock.

Filelock '/tmp/path/to/lock' do |file|
  file.truncate
  file.write Process.pid
end

Does it support NFS?

No. You can use more complex lockfile gem if you want to support NFS.

The code is so short. Why shouln't I just copy-paste it?

Because even such short code can have issues in future. File locking is very fragile operation. You may expect new releases of this gem fixing discovered bogus behavior (or introducing awesome features).

You are encouraged to use it if you develop gem that uses flock command, and care about running it on different ruby versions and platforms. Each has its own quirks with regard to flock command.

How it's different from lockfile gem?

Lockfile is filelocking solution handling NFS filesystems, based on homemade locking solution. Filelock uses flock UNIX command to handle filelocking on very low level. Also lockfile allows you to specify retry timeout. In case of Ruby's flock command this is hard-cored to 0.1 seconds.

How it's different from cleverua-lockfile gem?

Cleverua removes lockfile after unlocking it. Thas has been proven fatal both in my tests and in filelocking advices from the Internet. You could try find a way to remove lock file without breaking Filelock tests. I will be glad to accept such pull-request.

What happens if my ruby process gets killed while holding a lock? Can new processes acquire this lock?

Yes

Try to break Filelock in some way (note it doesn't support NFS).

Filelock is MIT-licensed. You are awesome.