test/ruby/test_io.rb: fix timing sensitive test

For systems with sleepy timer thread disabled, the signal
handler does not fire soon enough and we need to ensure the
signal is received before we check its value.  So use a
self-pipe here.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63708 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -85,11 +85,16 @@ class TestIO < Test::Unit::TestCase
   end
 
   def trapping_usr2
-    @usr1_rcvd  = 0
-    trap(:USR2) { @usr1_rcvd += 1 }
-    yield
+    @usr2_rcvd  = 0
+    r, w = IO.pipe
+    trap(:USR2) do
+      w.write([@usr2_rcvd += 1].pack('L'))
+    end
+    yield r
   ensure
     trap(:USR2, "DEFAULT")
+    w&.close
+    r&.close
   end
 
   def test_pipe
@@ -864,7 +869,7 @@ class TestIO < Test::Unit::TestCase
         rescue Errno::EBADF
           skip "nonblocking IO for pipe is not implemented"
         end
-        trapping_usr2 do
+        trapping_usr2 do |rd|
           nr = 30
           begin
             pid = fork do
@@ -878,7 +883,7 @@ class TestIO < Test::Unit::TestCase
             nr.times do
               assert_equal megacontent.bytesize, IO.copy_stream("megasrc", s1)
             end
-            assert_equal(1, @usr1_rcvd)
+            assert_equal(1, rd.read(4).unpack1('L'))
           ensure
             s1.close
             _, status = Process.waitpid2(pid) if pid