[ruby-core:104329] [Ruby master Bug#17996] Cygwin: thread + pipe behavior since Ruby 2.6

[xtkoba+ruby@gmail.com]

Issue #17996 has been reported by xtkoba (Tee KOBAYASHI).

----------------------------------------
Bug #17996: Cygwin: thread + pipe behavior since Ruby 2.6
https://bugs.ruby-lang.org/issues/17996

* Author: xtkoba (Tee KOBAYASHI)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.1.0dev (2021-06-10T23:31:51Z master 9210f8df7f) [x86_64-cygwin]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
The following one-liner is the repro named `thread-pipe-read-close.rb` the aim of which is essentially the same as that of "IO#close raises an IOError with a clear message" test in `spec/ruby/core/io/close_spec.rb`.

```ruby
r, w = IO.pipe; Thread.new{ r.read }; sleep 0.5; r.close
```

Run on Cygwin with Ruby 2.6 or later, this hangs up indefinitely consuming a full core. On the other hand, with Ruby 2.5.9p229 it works as expected.

```
$ miniruby25 -v
ruby 2.5.9p229 (2021-04-05 revision 67939) [x86_64-cygwin]

$ miniruby25 thread-pipe-read-close.rb
#<Thread:0x000000080006c9f0@thread-pipe-read-close.rb:2 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
        1: from thread-pipe-read-close.rb:2:in `block in <main>'
thread-pipe-read-close.rb:2:in `read': IOError

$ miniruby -v
ruby 3.1.0dev (2021-06-10T23:31:51Z master 9210f8df7f) [x86_64-cygwin]

$ miniruby thread-pipe-read-close.rb
```



-- 
https://bugs.ruby-lang.org/