From: normalperson@...
Date: 2015-07-20T20:22:04+00:00
Subject: [ruby-core:70051] [Ruby trunk - Feature #11377] [Open] [PATCH] IO.copy_stream uses poll on Linux

Issue #11377 has been reported by Eric Wong.

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Feature #11377: [PATCH] IO.copy_stream uses poll on Linux
https://bugs.ruby-lang.org/issues/11377

* Author: Eric Wong
* Status: Open
* Priority: Normal
* Assignee: Eric Wong
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poll and ppoll have a superior API which doesn't require the
kernel to scan a potentially large bitmap to find a high-numbered
FD [ruby-core:35572].  So favor using poll in case IO.copy_stream
encounters a non-blocking FD.

We cannot reliably use poll on most OSes, because file types (e.g.
FIFOs) which work with select may not work with poll.  Fortunately,
Linux uses a common notification mechanism between all
select/poll/epoll variants, so all file types are equally supported
between the notification mechanisms.

Verified by watching strace on the following scripts:

*** maygvl_copy_stream_wait_read ***
require 'io/nonblock'
r, w = IO.pipe
r.nonblock = true
IO.copy_stream(r, "/dev/null")

*** nogvl_copy_stream_wait_write ***
require 'io/nonblock'
r, w = IO.pipe
w.nonblock = true
IO.copy_stream("/dev/zero", w)

* io.c (nogvl_wait_for_single_fd): new function for Linux
  (maygvl_copy_stream_wait_read): Linux-specific version
  (nogvl_copy_stream_wait_write): use nogvl_wait_for_single_fd


---Files--------------------------------
0001-io.c-IO.copy_stream-uses-poll-on-Linux.patch (3.75 KB)


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