merge revision(s) 3a3b19b2bba49e5d6f1cf13764eb6dd701397be9: [Backport #17827]

	Fix Monitor to lock per Fiber, like Mutex [Bug #17827]

	---
	 ext/monitor/monitor.c        | 10 +++++-----
	 test/monitor/test_monitor.rb |  7 +++++++
	 2 files changed, 12 insertions(+), 5 deletions(-)

1 files changed, 7 insertions, 0 deletions

diff --git a/test/monitor/test_monitor.rb b/test/monitor/test_monitor.rb
index 734b639d4c..0f17d58f71 100644
--- a/test/monitor/test_monitor.rb
+++ b/test/monitor/test_monitor.rb
@@ -10,6 +10,13 @@ class TestMonitor < Test::Unit::TestCase
     @monitor = Monitor.new
   end
 
+  def test_enter_in_different_fibers
+    @monitor.enter
+    Fiber.new {
+      assert_equal false, @monitor.try_enter
+    }.resume
+  end
+
   def test_enter
     ary = []
     queue = Queue.new