[PATCH v2 2/5] provide fiddle-based eventfd implementation

[Eric Wong <e@80x24.org>]

sleepy_penguin requires a compiler and development headers to
install, so it could be a PITA to install for users on
distro-provided Ruby.  Allow fiddle since it's part of the Ruby
standard library since 1.9.2 and users won't have to install
anything else.
---
 lib/dtas.rb                     |  8 +++++++
 lib/dtas/sigevent.rb            |  7 ++++--
 lib/dtas/sigevent/efd.rb        |  2 ++
 lib/dtas/sigevent/fiddle_efd.rb | 38 +++++++++++++++++++++++++++++++++
 lib/dtas/sigevent/pipe.rb       |  2 +-
 test/test_sigevent.rb           | 20 +++++++++++++++++
 6 files changed, 74 insertions(+), 3 deletions(-)
 create mode 100644 lib/dtas/sigevent/fiddle_efd.rb
 create mode 100644 test/test_sigevent.rb

diff --git a/lib/dtas.rb b/lib/dtas.rb
index 7e9c0d5..ae2f815 100644
--- a/lib/dtas.rb
+++ b/lib/dtas.rb
@@ -25,6 +25,14 @@ def self.null # :nodoc:
     @null ||= File.open('/dev/null', 'r+')
   end
 
+  @libc = nil
+  def self.libc
+    @libc ||= begin
+      require 'fiddle'
+      Fiddle.dlopen(nil)
+    end
+  end
+
   # String#-@ will deduplicate strings when Ruby 2.5 is released (Dec 2017)
   # https://bugs.ruby-lang.org/issues/13077
   if RUBY_VERSION.to_f >= 2.5
diff --git a/lib/dtas/sigevent.rb b/lib/dtas/sigevent.rb
index d4a96d7..74d22df 100644
--- a/lib/dtas/sigevent.rb
+++ b/lib/dtas/sigevent.rb
@@ -3,8 +3,11 @@
 # frozen_string_literal: true
 begin
   raise LoadError, "no eventfd with _DTAS_POSIX" if ENV["_DTAS_POSIX"]
-  require 'sleepy_penguin'
-  require_relative 'sigevent/efd'
+  begin
+    require_relative 'sigevent/efd'
+  rescue LoadError
+    require_relative 'sigevent/fiddle_efd'
+  end
 rescue LoadError
   require_relative 'sigevent/pipe'
 end
diff --git a/lib/dtas/sigevent/efd.rb b/lib/dtas/sigevent/efd.rb
index 4be2c84..22772ee 100644
--- a/lib/dtas/sigevent/efd.rb
+++ b/lib/dtas/sigevent/efd.rb
@@ -3,6 +3,8 @@
 
 # used in various places for safe wakeups from IO.select via signals
 # This requires a modern Linux system and the "sleepy_penguin" RubyGem
+require 'sleepy_penguin'
+
 class DTAS::Sigevent < SleepyPenguin::EventFD # :nodoc:
   def self.new
     super(0, :CLOEXEC)
diff --git a/lib/dtas/sigevent/fiddle_efd.rb b/lib/dtas/sigevent/fiddle_efd.rb
new file mode 100644
index 0000000..e29f6ca
--- /dev/null
+++ b/lib/dtas/sigevent/fiddle_efd.rb
@@ -0,0 +1,38 @@
+# Copyright (C) 2013-2019 all contributors <dtas-all@nongnu.org>
+# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
+# frozen_string_literal: true
+
+# used in various places for safe wakeups from IO.select via signals
+# This requires a modern GNU/Linux system with eventfd(2) support
+require_relative '../nonblock'
+require 'fiddle'
+class DTAS::Sigevent # :nodoc:
+
+  EventFD = Fiddle::Function.new(DTAS.libc['eventfd'],
+    [ Fiddle::TYPE_INT, Fiddle::TYPE_INT ], # initval, flags
+    Fiddle::TYPE_INT) # fd
+
+  attr_reader :to_io
+  ONE = [ 1 ].pack('Q').freeze
+
+  def initialize
+    fd = EventFD.call(0, 02000000|00004000) # EFD_CLOEXEC|EFD_NONBLOCK
+    raise "eventfd failed: #{Fiddle.last_error}" if fd < 0
+    @to_io = DTAS::Nonblock.for_fd(fd)
+    @buf = ''.b
+  end
+
+  def signal
+    @to_io.syswrite(ONE)
+  end
+
+  def readable_iter
+    @to_io.read_nonblock(8, @buf, exception: false)
+    yield self, nil # calls DTAS::Process.reaper
+    :wait_readable
+  end
+
+  def close
+    @to_io.close
+  end
+end
diff --git a/lib/dtas/sigevent/pipe.rb b/lib/dtas/sigevent/pipe.rb
index 921a5b3..0ea9d31 100644
--- a/lib/dtas/sigevent/pipe.rb
+++ b/lib/dtas/sigevent/pipe.rb
@@ -3,7 +3,7 @@
 # frozen_string_literal: true
 
 # used in various places for safe wakeups from IO.select via signals
-# A fallback for non-Linux systems lacking the "sleepy_penguin" RubyGem
+# A fallback for non-Linux systems lacking the "splice" syscall
 require_relative '../nonblock'
 class DTAS::Sigevent # :nodoc:
   attr_reader :to_io
diff --git a/test/test_sigevent.rb b/test/test_sigevent.rb
new file mode 100644
index 0000000..6cfe528
--- /dev/null
+++ b/test/test_sigevent.rb
@@ -0,0 +1,20 @@
+# Copyright (C) 2019 all contributors <dtas-all@nongnu.org>
+# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
+# frozen_string_literal: true
+require_relative 'helper'
+require 'dtas'
+require 'dtas/sigevent'
+
+class TestSigevent < Testcase
+  def test_sigevent
+    io = DTAS::Sigevent.new
+    io.signal
+    assert IO.select([io]), 'IO.select returns'
+    res = io.readable_iter do |f,arg|
+      assert_same io, f
+      assert_nil arg
+    end
+    assert_equal :wait_readable, res
+    assert_nil io.close
+  end
+end