diff --git a/lib/guard/interactor.rb b/lib/guard/interactor.rb
index 0abbb5a..e660fe6 100644
--- a/lib/guard/interactor.rb
+++ b/lib/guard/interactor.rb
@@ -1,6 +1,9 @@
 module Guard
   class Interactor
 
+    class LockException < Exception; end
+    class UnlockException < Exception; end
+
     attr_reader :locked
 
     def initialize
@@ -11,35 +14,43 @@ module Guard
       return if ENV["GUARD_ENV"] == 'test'
       @thread = Thread.new do
         loop do
-          if (entry = $stdin.gets) && !@locked
-            entry.gsub! /\n/, ''
-            case entry
-            when 'stop', 'quit', 'exit', 's', 'q', 'e'
-              ::Guard.stop
-            when 'reload', 'r', 'z'
-              ::Guard.reload
-            when 'pause', 'p'
-              ::Guard.pause
-            else
-              ::Guard.run_all
+          begin
+            if !@locked && (entry = $stdin.gets)
+              entry.gsub! /\n/, ''
+              case entry
+              when 'stop', 'quit', 'exit', 's', 'q', 'e'
+                ::Guard.stop
+              when 'reload', 'r', 'z'
+                ::Guard.reload
+              when 'pause', 'p'
+                ::Guard.pause
+              else
+                ::Guard.run_all
+              end
             end
+          rescue LockException
+            lock
+          rescue UnlockException
+            unlock
           end
         end
       end
     end
 
-    def stop
-      @thread.kill
-    end
-
     def lock
-      @locked = true
-      stop
+      if @thread == Thread.current
+        @locked = true
+      else
+        @thread.raise(LockException)
+      end
     end
 
     def unlock
-      @locked = false
-      start
+      if @thread == Thread.current
+        @locked = false
+      else
+        @thread.raise(UnlockException)
+      end
     end
 
   end