issue guard#487: only call one of Thread#join, Thread#kill

lib/listen/adapter/base.rb

@@ -88,9 +88,8 @@ def stop
       private
 
       def _stop
-        if thread = @run_thread
-          thread.kill.join
-        end
+        @run_thread&.kill
+        @run_thread = nil
       end
 
       def _timed(title)

lib/listen/adapter/darwin.rb

@@ -80,7 +80,7 @@ def _run_worker(worker)
       end
 
       def _stop
-        @worker_thread.kill.join if (@worker_thread ||= nil)
+        @worker_thread&.kill
         super
       end
     end

lib/listen/event/loop.rb

@@ -68,7 +68,7 @@ def stop
         transition! :stopped
 
         if @wait_thread.alive?
-          @wait_thread.join.kill
+          @wait_thread.join
         end
         @wait_thread = nil
       end

spec/lib/listen/adapter/polling_spec.rb

@@ -61,7 +61,6 @@
         t = Thread.new { subject.start }
         sleep 0.25
         t.kill
-        t.join
       end
     end
 

spec/lib/listen/event/loop_spec.rb

@@ -84,15 +84,15 @@
 
     describe '#stop' do
       before do
-        allow(thread).to receive_message_chain(:join, :kill)
+        allow(thread).to receive(:join)
       end
 
       it 'frees the thread' do
         subject.stop
       end
 
       it 'waits for the thread to finish' do
-        expect(thread).to receive_message_chain(:join, :kill)
+        expect(thread).to receive(:join)
         subject.stop
       end