Revert "bootstraptest/runner: speed up assert_finish by avoiding sleep"

This reverts commit r63754.
Many CI servers still use old ruby as base ruby which does not support
read_nonblock.

https://rubyci.org/logs/www.rubyist.net/~akr/chkbuild/debian/ruby-trunk/log/20180627T013100Z.fail.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63757 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 8 deletions

diff --git a/bootstraptest/runner.rb b/bootstraptest/runner.rb
index 29dfef771a..e807ce5b62 100755
--- a/bootstraptest/runner.rb
+++ b/bootstraptest/runner.rb
@@ -373,18 +373,13 @@ def assert_finish(timeout_seconds, testsrc, message = '')
     io = IO.popen("#{@ruby} -W0 #{filename}")
     pid = io.pid
     waited = false
-    tlimit = Process.clock_gettime(Process::CLOCK_MONOTONIC) + timeout_seconds
-    diff = timeout_seconds
-    while diff > 0
+    tlimit = Time.now + timeout_seconds
+    while Time.now < tlimit
       if Process.waitpid pid, Process::WNOHANG
         waited = true
         break
       end
-      if IO.select([io], nil, nil, diff)
-        while String === io.read_nonblock(1024, exception: false)
-        end
-      end
-      diff = tlimit - Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      sleep 0.1
     end
     if !waited
       Process.kill(:KILL, pid)