lockf.rb provides Ruby bindings for lockf(3).
Blocking
Lock::File#lock can be used to acquire a lock. Lock::File.temporary_file returns a lock for an unlinked temporary file. Lock::File#lock will block when another process has acquired a lock beforehand:
#!/usr/bin/env ruby
require "lock/file"
lockf = Lock::File.temporary_file
lockf.lock
print "Lock acquired by parent process (#{Time.now.utc})", "\n"
fork do
print "Child process waiting on lock (#{Time.now.utc})", "\n"
lockf.lock
print "Lock acquired by child process (#{Time.now.utc})", "\n"
end
sleep(3)
lockf.release
Process.wait
##
# Lock acquired by parent process (2023-02-11 16:43:15 UTC)
# Child process waiting on lock (2023-02-11 16:43:15 UTC)
# Lock acquired by child process (2023-02-11 16:43:18 UTC)Non-blocking
Lock::File#lock_nonblock
can be used to acquire a lock without blocking. When it is found
that acquiring a lock would block the method will raise an
exception (Errno::EAGAIN / Errno::EWOULDBLOCK) instead:
#!/usr/bin/env ruby
require "lock/file"
lockf = Lock::File.temporary_file
lockf.lock_nonblock
print "Lock acquired by parent process (#{Time.now.utc})", "\n"
fork do
lockf.lock_nonblock
print "Lock acquired by child process (#{Time.now.utc})", "\n"
rescue Errno::EWOULDBLOCK
sleep 1
print "Lock would block", "\n"
retry
end
sleep 3
lockf.release
Process.wait
##
# Lock acquired by parent process (2023-02-11 19:03:05 UTC)
# Lock would block
# Lock would block
# Lock would block
# Lock acquired by child process (2023-02-11 19:03:08 UTC)lockf
Lock::File::FFI.lockf provides a direct interface to lockf(3) that is more or less equivalent to how the function would be called from C:
#!/usr/bin/env ruby
require "lock/file"
require "tempfile"
file = Tempfile.new("lockf-ffi").tap(&:unlink)
Lock::File::FFI.lockf(file, Lock::File::F_LOCK, 0)
print "Lock acquired", "\n"
Lock::File::FFI.lockf(file, Lock::File::F_ULOCK, 0)
print "Lock released", "\n"
file.close
##
# Lock acquired
# Lock releasedA complete API reference is available at 0x1eef.github.io/x/lockf.rb
lockf.rb can be installed via rubygems.org:
gem install lockf.rb