Versions | v1.0 (td-agent3)

Child Process Plugin Helper API

child_process helper manages child processes life cycle.

Here is the code example with child_process helper:

require 'fluent/plugin/output'

module Fluent::Plugin
  class ExampleOutput < Output
    Fluent::Plugin.register_output('example', self)

    # 1. load child_process helper
    helpers :child_process

    # omit configure, shutdown and other plugin API

    def start
      # 2. execute child process with unique name
      child_process_execute(:exec_external_command, "external_command", immediate: true, mode: [:read]) do
        # ...

Launched child process is managed by the plugin. No need child process shutdown code in plugin’s shutdown. The plugin shutdowns launched child process automatically.

Table of Contents


child_process_execute(title, sub_process_name, arguments: nil, subprocess_name: nil, interval: nil, immediate: false, parallel: false, mode: [:read, :write], stderr: :discard, env: {}, unsetenv: false, chdir: nil, internal_encoding: ‘utf-8’, external_encoding: ‘ascii-8bit’, scrub: true, replace_string: nil, wait_timeout: nil, on_exit_callback: nil, &block)

This method executes child_process with given parameters and routine

  • title: unique symbol value
  • sub_process_name: sub process name value
  • interval: Second unit integer/float value.
  • immediate: true/false. Default is false.
  • parallel: true/false. Default is false.
  • mode: [:read, :write]. Default is [:read, :write].
  • stderr: Connect stderr or not. Default is :discard.
  • env: Environment valuables. Default is {}.
  • unsetenv: true/false. Default is false
  • chdir: Working directory. Default is nil.
  • internal_encoding: Internal character encoding. Default is utf-8.
  • external_encoding: External character encoding. Default is ascii-8bit'
  • scrub: true/false. Default is true.
  • replace_string: Replace invalid code point with specified character. Default is nil.
  • wait_timeout: Set timeout seconds. Default is nil.
  • on_exit_callback: Set callback function. Default is nil

Code examples:

# Pass block directly. block is executed in 10 second interval.
child_process_execute(:exec_awesome_command, @command, interval: 10, mode: [:read]) {|io|
  # ...

# Pass block with existing method. block is executed one-shot.
child_process_execute(:exec_awesome_command, @command, immediate: true, mode: [:read], &method(:run))
def run(io)
  # ...

child_process used plugins

Last updated: 2018-03-17 23:54:10 +0000

Versions | v1.0 (td-agent3)

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.