% svn diff --diff-cmd diff -x '-u -p'
Index: test/etc/test_etc.rb
===================================================================
--- test/etc/test_etc.rb	(revision 47647)
+++ test/etc/test_etc.rb	(working copy)
@@ -159,4 +159,9 @@ class TestEtc < Test::Unit::TestCase
     }
   end if defined?(Etc::PC_PIPE_BUF)
 
+  def test_nprocessors
+    n = Etc.nprocessors
+    assert_operator(1, :<=, n)
+  end
+
 end
Index: ext/etc/etc.c
===================================================================
--- ext/etc/etc.c	(revision 47647)
+++ ext/etc/etc.c	(working copy)
@@ -891,6 +891,38 @@ io_pathconf(VALUE io, VALUE arg)
 #define io_pathconf rb_f_notimplement
 #endif
 
+#if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
+/*
+ * Returns the number of online processors.
+ *
+ * The result is intended as the number of processes to
+ * use all available processors.
+ *
+ * This method is implemented as:
+ * - sysconf(_SC_NPROCESSORS_ONLN): GNU/Linux, NetBSD, FreeBSD, OpenBSD, DragonFly BSD, OpenIndiana, Mac OS X, AIX
+ *
+ * Example:
+ *
+ *   require 'etc'
+ *   p Etc.nprocessors #=> 4
+ *
+ */
+static VALUE
+etc_nprocessors(VALUE obj)
+{
+    long ret;
+
+    errno = 0;
+    ret = sysconf(_SC_NPROCESSORS_ONLN);
+    if (ret == -1) {
+        rb_sys_fail("sysconf(_SC_NPROCESSORS_ONLN)");
+    }
+    return LONG2NUM(ret);
+}
+#else
+#define etc_nprocessors rb_f_notimplement
+#endif
+
 /*
  * The Etc module provides access to information typically stored in
  * files in the /etc directory on Unix systems.
@@ -946,6 +978,7 @@ Init_etc(void)
     rb_define_module_function(mEtc, "sysconf", etc_sysconf, 1);
     rb_define_module_function(mEtc, "confstr", etc_confstr, 1);
     rb_define_method(rb_cIO, "pathconf", io_pathconf, 1);
+    rb_define_module_function(mEtc, "nprocessors", etc_nprocessors, 0);
 
     sPasswd =  rb_struct_define_under(mEtc, "Passwd",
 				      "name",
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 47647)
+++ ChangeLog	(working copy)
@@ -1,3 +1,8 @@
+Sat Sep 20 10:22:17 2014  Tanaka Akira  <akr@fsij.org>
+
+	* ext/etc/etc.c (etc_nprocessors_online): New method.
+	  Accepted by matz at RubyKaigi 2014.
+
 Sat Sep 20 10:02:51 2014  Tanaka Akira  <akr@fsij.org>
 
 	* ext/openssl/lib/openssl/x509.rb (OpenSSL::X509::Name#pretty_print):