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--- eeros_architecture:sequencer:monitors [2017/08/10 08:28] – created graf
+++ eeros_architecture:sequencer:monitors [2019/03/28 13:22] – [Define your own Condition] graf
@@ Line 1: / Line 1: @@
 ====== Conditions and Monitors ======
+A monitor allows to supervise certain conditions of a robot during a sequence. Examples could include the following situations:
+  * A sequence steers a robot along a given path. A monitors checks for obstacles. As soon as an obstacle is close enough, the monitor causes a predefined exception sequence to be executed.
+  * A sequence takes too long to run due to some erroneous behavior. A monitor checks for timeout and either restarts or aborts the sequence or switches to an exception sequence.
+  * A sequence moves a robot arm. While moving the arm looses its load. A monitor checks for this load to be present and aborts the sequence.
+All these situations have in common, that a user does want to check for a given set of conditions during the running of the sequence (including subsequences or steps).
+===== Define your own Condition =====
+Implement your condition by extending the class ''Condition'' as given below:
+<code cpp>
+class MyCondition : public Condition {
+public:
+  MyCondition() : { }                 // initialize any attributes necessary
+  bool validate() {return yourTest;}  // implement whatever your condition should check
+};
+</code>
+The method //validate// must return ''true'' in order for the monitor checking this condition to fire.
+IMPORTANT Every Sequence or step already has a timeout condition (of class ''ConditionTimeout''). It allows for checking a maximum duration of execution. Also, every sequence has an abort condition (of class ''ConditionAbort''). This condition makes it possible to abort a sequence, e.g. by pressing ''Ctrl-C''.
+===== Assign a Condition to a Monitor =====
+The second step is to define a monitor and assign it a condition.
+<code cpp>
+SequenceA seq(...);                                                 // define a sequence
+MyCondition myCondition;                                            // and a condition
+Monitor myMonitor("myMon", &seq, myCondition, SequenceProp::abort); // create an associated monitor
+setExceptionSequence(exceptionSeq);                                 // choose a sequence to run in case of a condition to become false
+seq.addMonitor(&myMonitor);                                         // and add it to the sequence
+</code>
+IMPORTANT Here again, every sequence or step already has a timeout monitor which helps to check its associated timeout condition. A second monitor checks the abort condition.