child_process: Plug file descriptor leak

[ashie]

Which issue(s) this PR fixes:
Fixes #3627

What this PR does / why we need it:
Pipes for child processes aren't closed explicitly after exiting child processes.
It might causes leave too many file descriptors opened on certain condition.

Docs Changes:
none

Release Note:
Same with the title.

[ashie]

Hmm, there is a new test failure case on Ruby head, it's not concerned with this patch though:

D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-api-0.4.5/lib/windows/api.rb:335:in `initialize': uninitialized constant Win32::API (NameError)

      @api = Win32::API.new(func, proto, rtype, dll)

                  ^^^^^
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/msvcrt/string.rb:12:in `new'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/msvcrt/string.rb:12:in `<module:String>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/msvcrt/string.rb:5:in `<module:MSVCRT>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/msvcrt/string.rb:4:in `<module:Windows>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/msvcrt/string.rb:3:in `<top (required)>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/unicode.rb:3:in `require'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/unicode.rb:3:in `<top (required)>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/file.rb:1:in `require'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-pr-1.2.6/lib/windows/file.rb:1:in `<top (required)>'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/file_wrapper.rb:39:in `require'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/file_wrapper.rb:39:in `<class:WindowsFile>'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/file_wrapper.rb:38:in `<module:Fluent>'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/file_wrapper.rb:17:in `<top (required)>'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/in_tail.rb:30:in `require_relative'
	from D:/a/fluentd/fluentd/lib/fluent/plugin/in_tail.rb:30:in `<top (required)>'
	from D:/a/fluentd/fluentd/test/plugin/in_tail/test_fifo.rb:3:in `require'
	from D:/a/fluentd/fluentd/test/plugin/in_tail/test_fifo.rb:3:in `<top (required)>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/rake-13.0.6/lib/rake/rake_test_loader.rb:21:in `require'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/rake-13.0.6/lib/rake/rake_test_loader.rb:21:in `block in <main>'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/rake-13.0.6/lib/rake/rake_test_loader.rb:6:in `select'
	from D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/rake-13.0.6/lib/rake/rake_test_loader.rb:6:in `<main>'
rake aborted!

[ashie]

Hmm, there is a new test failure case on Ruby head, it's not concerned with this patch though:

D:/rubyinstaller-head-x64/lib/ruby/gems/3.2.0+2/gems/windows-api-0.4.5/lib/windows/api.rb:335:in `initialize': uninitialized constant Win32::API (NameError)

      @api = Win32::API.new(func, proto, rtype, dll)

                  ^^^^^

Fixed in #3849

[ashie]

Although still it doesn't seem fix memory leak indicated in #3627 (comment), I believe this patch is needed to close pipes as soon as they aren't needed. Shouldn't rely on GC.

[kenhys]

It seems that it is good approach to do it
(Even though still linearly incremented objects exists, it improves situation.)

[ashie]

Thanks for you review!