Ruby/File Directory/flock

# Returns false if File::LOCK_NB is specified and the operation would otherwise have blocked. 
# Not available on all platforms. 
puts File.new("testfile").flock(File::LOCK_UN)   
# Lock code constants 
# LOCK_EX        Exclusive lock. 
# LOCK_NB        Don"t block when locking. 
# LOCK_SH        Shared lock. 
# LOCK_UN        Unlock.