in_tail: avoid unnecessary open()s

[dwoo4dwoo]

As discussed in https://groups.google.com/forum/#!topic/fluentd/BBRde4Lyl9E

[dwoo4dwoo]

The Travis CI build failures seem unrelated to my change ... (UdpInputTest EADDRINUSE)

[repeatedly]

Possible file rotation cases:

• File is rotated before stat = FileWrapper.stat(@path)

No problem.

• File is rotated ater stat = FileWrapper.stat(@path)
  • if @inode != inode || fsize < @fsize is false: No problem. Next trigger should detect file rotation.
  • if @inode != inode || fsize < @fsize is true: It seems no problem. on_rotate also checks stat info with previous file. So this patch should not effect existing behaviour.

Does anyone have any concern for this patch?

[repeatedly]

If there are no problem, I will merge this patch today.

[sonots]

When Errno::ENOENT occurs on FileWrapper.stat(@path), it seems Errno::ENOENT occurs again at here. Do not you need to handle it?

[repeatedly]

So adding rescue nil is better?
io = FileWrapper.open(@path) rescue nil
or

begin
  io = FileWrapper.open(@path)
rescue Errno::ENOENT
end

[dwoo4dwoo]

@sonots : good catch - thanks!
@repeatedly : I'll update the pull request with your suggestion

[repeatedly]

@sonots Could you check again?

[sonots]

Could you tell me when this io object will be closed? Or, not necessary to close? Why?

[sonots]

I am not sure why there was

 io = nil

before. Maybe, we need to keep previous io object as @io like @iNode and @fsize to ensure to close it.

[sonots]

You should ignore only Errno::ENOENT as repeatedly wrote.

[dwoo4dwoo]

Hi @sonots ,

Could you tell me when this io object will be closed?

The file descriptor is consumed here:

https://github.com/fluent/fluentd/blob/master/lib/fluent/plugin/in_tail.rb#L384

The first time through ... an io_handler is created here:

https://github.com/fluent/fluentd/blob/master/lib/fluent/plugin/in_tail.rb#L416

The file descriptor remains open until the next file rotation, removal, or fluentd shutdown. The logic to deal with some of these situations begins here:

https://github.com/fluent/fluentd/blob/master/lib/fluent/plugin/in_tail.rb#L420

Other cases are handled here:

https://github.com/fluent/fluentd/blob/master/lib/fluent/plugin/in_tail.rb#L188

For example, shutdown calls stop_watchers().

You should ignore only Errno::ENOENT as repeatedly wrote

Sorry, I thought @repeatedly was giving me a choice, and I picked the first option. I'll update the pull request using the second option. I'll also rebase against master.

David

[sonots]

LGTM

[repeatedly]

Thanks for the patch!