[ruby/singleton] Simplify implementation of `Singleton#instance`.

(https://github.com/ruby/singleton/pull/9)

- Add more tests to cover rails' usage.

1 files changed, 1 insertions, 6 deletions

diff --git a/lib/singleton.rb b/lib/singleton.rb
index 07420d2ea2..7ed17a769c 100644
--- a/lib/singleton.rb
+++ b/lib/singleton.rb
@@ -121,12 +121,7 @@ module Singleton
     end
 
     def instance # :nodoc:
-      return @singleton__instance__ if @singleton__instance__
-      @singleton__mutex__.synchronize {
-        return @singleton__instance__ if @singleton__instance__
-        @singleton__instance__ = new()
-      }
-      @singleton__instance__
+      @singleton__instance__ || @singleton__mutex__.synchronize { @singleton__instance__ ||= new }
     end
 
     private