[ruby-core:105590] [Ruby master Bug#18244] Unexpected errors output order

Issue #18244 has been updated by inversion (Yura Babak).


> Do you have any reason to make `stderr` unbuffered?

I do add records to stdout within a cycle, so it is better to have it buffered for better overall performance. Also, I have few parallel workers in threads with such cycles. As a result, when some worker crashes (and app terminated) — in the log there is an error output and after it a lot of regular outputs from other workers, so it is very hard to find out in which iteration error actually happened.


----------------------------------------
Bug #18244: Unexpected errors output order
https://bugs.ruby-lang.org/issues/18244#change-94058

* Author: inversion (Yura Babak)
* Status: Feedback
* Priority: Normal
* ruby -v: Ruby v3.0.2.107 (2021-07-07) [x64-mingw32]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
Having this code:
```ruby
# $stderr.sync = false
warn 'warn'
$stderr.puts 'err'
fail
```
When I run it like this `ruby test.rb 2>err.log`, output is ok:
```
warn
err
test.rb:3:in `<main>': unhandled exception
```

But when I uncomment the first line — the output is different:
```
warn
test.rb:3:in `<main>': unhandled exception
err
```
Why buffered output to the `$stderr` redirected to file has the **wrong order**?
If we do not redirect to the file — the order is ok (exception is the last line of the output).

Checked platforms:
`Windows10: Ruby v3.0.2.107 (2021-07-07) [x64-mingw32]`
`Linux: Ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]`



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