graceful shutdown looks like lose the received events

[HatsuneMiku3939]

• fluentd or td-agent version.
  fluentd 1.3.3

• Environment information
  linux
  ruby 2.5.1

• configuration

  <source>
    @type forward
  </source>
  <match test>
    @type file
    path "/tmp/fluent-shutdown-test/output/${tag}"
    append true
    <buffer tag>
      @type "memory"
      path /tmp/fluent-shutdown-test/output/${tag}
    </buffer>
  </match>

• test code - https://github.com/HatsuneMiku3939/fluent-shutdown-test/blob/master/test.rb
  • https://travis-ci.org/HatsuneMiku3939/fluent-shutdown-test/builds/477185717

graceful shutdown immediately after post a large number of events looks like lose received events.

• case 1
  post 10 events -> graceful shutdown immediately -> file output contains 10 events

• case 2
  post 100000 events -> graceful shutdown immediately -> file output doesn't contains 100000 events

• desired behavior of case 2
  post 100000 events -> graceful shutdown immediately -> file output contains 100000 events

[repeatedly]

Hmm.... looks like in_forward stops event loop to shutdown and it causes pending requests are ignored when at-most-once.
Need to check event loop handling.