@bjhaid的回答可能会导致一个问题，那就是在Rubinius中，#timeout会导致一个解释器错误。这也是不必要的复杂。
这里有一个更简单的版本，使用非阻塞锁而不是超时：

def locked? lockfile_name
  f = File.open(lockfile_name, File::CREAT)

  # returns false if already locked, 0 if not
  ret = f.flock(File::LOCK_EX|File::LOCK_NB)

  # unlocks if possible, for cleanup; this is a noop if lock not acquired
  f.flock(File::LOCK_UN) 

  f.close
  !ret # ret == false means we *couldn't* get a lock, i.e. it was locked
end

当你对一个文件有一个排他锁时，试图在ruby中再次锁定它将无限期地等待，直到文件被解锁，所以你可以依靠它，并设置一个超时多长时间ruby应该等待，这可能不是最合适的方法，但我会这样做：

fh = File.open("/some/file/path", File::CREAT)
fh.flock(File::LOCK_EX)

require 'timeout'
def check_file_locked?(file)
  f = File.open(file, File::CREAT)
  Timeout::timeout(0.001) { f.flock(File::LOCK_EX) }
  f.flock(File::LOCK_UN)
  false
rescue 
  true
ensure
  f.close
end
f = File.open("/tmp/a.txt", "w+")
f.flock(File::LOCK_EX)
check_file_locked?("/tmp/a.txt") # => true
f.flock(File::LOCK_UN)
check_file_locked?("/tmp/a.txt") # => false

我为此创建了一个简单的Mutex类

class CrossProcessMutex
  def initialize(lock_filepath)
    @lock_filepath = lock_filepath
  end

  def synchronize
    # https://ruby-doc.org/3.2.0/File.html#method-i-flock
    f = File.open(@lock_filepath, File::RDWR|File::CREAT, 0644)
    f.flock File::LOCK_EX
    yield
  ensure
    f.flock File::LOCK_UN
  end
end