ruby - 为什么当 File 对象是新对象时 flock() 的工作方式不同？

Question

这是代码，它可以工作:

f = File.new('test', File::CREAT | File::RDWR)
f.flock(File::LOCK_EX)
f.flock(File::LOCK_EX)
puts 'Works!'

但是，这个不起作用:

File.new('test', File::CREAT | File::RDWR).flock(File::LOCK_EX)
File.new('test', File::CREAT | File::RDWR).flock(File::LOCK_EX)
puts 'Works!'

你能解释一下这是为什么吗？我的实际问题是如何使第二个片段起作用？

Answer 1

how to make the second snippet work?

在尝试使用 LOCK_EX 重新锁定之前使用 LOCK_UN 解锁文件。或者不要使用 LOCK_EX。

至于为什么会发生这种情况，请参阅 documentation在 flock(2) 上。

If a process uses open(2) (or similar) to obtain more than one file descriptor for the same file, these file descriptors are treated independently by flock(). An attempt to lock the file using one of these file descriptors may be denied by a lock that the calling process has already placed via another file descriptor.