semaphore.rb

module Semaphore
	extend self

	def lock(lock_number)
		hold(lock_number)
		yield
	ensure
		release(lock_number)
	end

	def connection
		DataMapper.repository(:default).adapter
	end

	def hold(lock_number)
		connection.select("SELECT pg_advisory_lock(#{lock_number})")
	end

	def release(lock_number)
		connection.select("SELECT pg_advisory_unlock(#{lock_number})")
	end
end