Fix for JRuby: Fiber#new still creates new Threads

lib/database_cleaner/sequel/transaction.rb

@@ -3,7 +3,18 @@
 module DatabaseCleaner
   module Sequel
     class Transaction < Base
+      def self.check_fiber_brokenness
+        if !@checked_fiber_brokenness && Fiber.new { Thread.current }.resume != Thread.current
+          raise RuntimeError, "This ruby engine's Fibers are not compatible with Sequel's connection pool. " +
+            "To work around this, please use DatabaseCleaner.cleaning with a block instead of " +
+            "DatabaseCleaner.start and DatabaseCleaner.clean"
+        end
+        @checked_fiber_brokenness = true
+      end
+
       def start
+        self.class.check_fiber_brokenness
+
         @fibers ||= []
         db = self.db
         f = Fiber.new do
@@ -19,6 +30,10 @@ def clean
         f = @fibers.pop
         f.resume
       end
+
+      def cleaning
+        self.db.transaction(:rollback => :always, :savepoint => true, :auto_savepoint => true) { yield }
+      end
     end
   end
 end

lib/database_cleaner/sequel/version.rb

@@ -1,5 +1,5 @@
 module DatabaseCleaner
   module Sequel
-    VERSION = "2.0.0"
+    VERSION = "2.0.1"
   end
 end