change MonitorState and document its behavior

smach_ros/src/smach_ros/monitor_state.py

@@ -10,9 +10,23 @@
 __all__ = ['MonitorState']
 
 class MonitorState(smach.State):
-    """A state that will check a given ROS topic with a condition function.
+    """
+    A state that will check a given ROS topic with a condition function.
     """
     def __init__(self, topic, msg_type, cond_cb, max_checks=-1,input_keys = [],output_keys=[]):
+        """State constructor
+        @type topic string
+        @param topic the topic to monitor
+
+        @type msg_type a ROS message type
+        @param msg_type determines the type of the monitored topic
+
+        @type max_checks int
+        @param max_checks the number of messages to receive and evaluate. If cond_cb returns False for any
+               of them, the state will finish with outcome 'invalid'. If cond_cb returns True for 
+               all of them, the outcome will be 'valid'
+        
+        """
         smach.State.__init__(
             self,
             outcomes=['valid','invalid','preempted'],
@@ -52,12 +66,16 @@ def execute(self, ud):
 
     def _cb(self,msg,ud) :
         try:
-            if (self._max_checks > 0 and self._n_checks >= self._max_checks) or not self._cond_cb(ud, msg):
+            if self._cond_cb(ud, msg):
+                self._n_checks +=1
+            else:
                 self._trigger_event.set()
         except Exception as e:
             rospy.logerr("Error thrown while executing condition callback %s: %s" % (str(self._cond_cb), e))
             self._trigger_event.set()
-        self._n_checks += 1
+
+        if (self._max_checks > 0 and self._n_checks >= self._max_checks):
+            self._trigger_event.set()
 
     def request_preempt(self):
         smach.State.request_preempt(self)