[ruby-core:83529] [Ruby trunk Feature#14042] IO#puts: use writev if available

Issue #14042 has been updated by rohitpaulk (Paul Kuruvilla).


> Would it make sense to add a deprecation warning in this case? i.e. If the receiver doesn't accept multiple arguments, we emit a deprecation warning and make 2 calls instead of one. If the receiver accepts multiple arguments, we make a single call.

Something along the lines of...

~~~diff
 rb_io_writev(VALUE io, int argc, VALUE *argv)
 {
-    return rb_funcallv(io, id_write, argc, argv);
+    if (rb_obj_method_arity(io, id_write) == -1) {
+        rb_funcallv(io, id_write, argc, argv);
+    }
+    else {
+        /**
+         * Previously, IO#write only accepted one argument. This was changed
+         * to use multiple arguments in revision #60343.
+         *
+         * To play well with programs that might've mocked an IO object and are
+         * only expecting a single argument - let's make multiple calls with
+         * a single argument each.
+         */
+        rb_warn("IO#write has been changed to accept multiple arguments. \
+You are seeing this warning because an object expected to implement the IO \
+interface has a #write method that doesn't accept multiple arguments. Please \
+change the implementation to accept multiple arguments.");
+        for (int i = 0; i < argc; i++) {
+            rb_io_write(io, argv[i]);
+        }
+    }
 }
~~~

~~~diff
 
+  def test_puts_works_with_io_objects_that_only_accept_single_arg
+    klass = Class.new do
+      attr_reader :captured
+
+      def write(str)
+        (@captured ||= "") << str
+      end
+    end
+
+    mocked_io_obj = klass.new
+    old_stdout, $stdout = $stdout, mocked_io_obj
+    puts "hey" # Should write to the mocked class
+    assert_equal("hey\n", mocked_io_obj.captured)
+  ensure
+    $stdout = old_stdout
+  end
+
~~~

----------------------------------------
Feature #14042: IO#puts: use writev if available
https://bugs.ruby-lang.org/issues/14042#change-67555

* Author: rohitpaulk (Paul Kuruvilla)
* Status: Open
* 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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