[ruby-core:83578] [Ruby trunk Feature#14042] IO#puts: use writev if available

Issue #14042 has been updated by Eregon (Benoit Daloze).


Correction, it only breaks one spec, not mspec.
The spec is "IO.popen raises IOError when writing a read-only pipe" in popen_spec.rb.

I reduced the code and this behaves differently:

~~~
$ chruby trunk
$ ruby -e 'IO.popen(["ruby", "-e", "sleep 1; puts :a"], "r").close'
Traceback (most recent call last):
    3: from -e:1:in `<main>'
    2: from -e:1:in `puts'
    1: from -e:1:in `puts'
-e:1:in `write': Broken pipe @ io_writev - <STDOUT> (Errno::EPIPE)

$ chruby 2.4.2                                                     
$ ruby -e 'IO.popen(["ruby", "-e", "sleep 1; puts :a"], "r").close'
~~~

I don't understand why though.

----------------------------------------
Feature #14042: IO#puts: use writev if available
https://bugs.ruby-lang.org/issues/14042#change-67606

* Author: rohitpaulk (Paul Kuruvilla)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Hi, 

I've attached a patch to make IO#puts use writev if available. Currently, IO#puts calls `write` twice: Once to write the string, and the second to write a newline (if the string doesn't end with one already). With this patch, those two calls are replaced with a single `writev` call.


A test has been added that demonstrates the problem. 

For a bit of background: 

* A related issue: https://bugs.ruby-lang.org/issues/9420. (I couldn't figure out a way to 'attach' my patch to that issue, so I'm creating a new one)
* A blog post I wrote a while back about this: https://hackernoon.com/rubys-puts-is-not-atomic-889c57fc9a28

Command I used to run the test I added: `make test-all TESTS='ruby/test_io.rb -n test_puts_parallel'`


I'm a first time contributor, a bit confused as to where a changelog entry should be added. Is the `NEWS` file the right place?

Regards,
Paul

---Files--------------------------------
ruby-changes.patch (2.83 KB)


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