Ensure that defer_stop resets state. (#339)

lib/async/task.rb

@@ -304,19 +304,23 @@ def defer_stop
 			# - false: defer_stop has been called and we are not stopping.
 			# - true: defer_stop has been called and we will stop when exiting the block.
 			if @defer_stop.nil?
-				# If we are not deferring stop already, we can defer it now:
-				@defer_stop = false
-
 				begin
+					# If we are not deferring stop already, we can defer it now:
+					@defer_stop = false
+
 					yield
 				rescue Stop
 					# If we are exiting due to a stop, we shouldn't try to invoke stop again:
 					@defer_stop = nil
 					raise
 				ensure
+					defer_stop = @defer_stop
+
+					# We need to ensure the state is reset before we exit the block:
+					@defer_stop = nil
+
 					# If we were asked to stop, we should do so now:
-					if @defer_stop
-						@defer_stop = nil
+					if defer_stop
 						raise Stop, "Stopping current task (was deferred)!"
 					end
 				end

test/async/task.rb

@@ -909,6 +909,18 @@ def sleep_forever
 			child_task.stop
 			expect(child_task).to be(:stopped?)
 		end
+
+		it "can defer stop and exit normally" do
+			child_task = reactor.async do |task|
+				task.defer_stop do
+					# Nothing.
+				end
+			end
+
+			reactor.run_once(0)
+
+			expect(child_task.stop_deferred?).to be == nil
+		end
 	end
 
 	with "failing task" do