question

pie-chart-dispatcher-variable-with-chart.fsm

This is a great example of a custom statistic! As you have noticed, FlexSim doesn't really track how many task sequences there are, at least not in the same way it tracks other statistics. But we can still get the statistic you wanted.

The basic steps are:

1. Derive the data from dispatcher events using a Process Flow, and store it on a token label
2. Create a table that reads the token's label using a Statistics Collector

So first, the Process Flow. The flow itself is not complicated, but there are two main things that it does. First, it creates a Tracked Variable label on a token. Since this is a kind of state, I chose a Categorical Tracked Variable, and I used a profile. This kind of Tracked Variable remembers how long its been in each category, which is perfect for this situation. The second thing the flow does is it listens to events when the Dispatcher's task sequence list could change. This could happen either when a task sequence is received, or when a Task Executer becomes available. When either of these things happen, we want to re-examine the list of task sequences, to see if it has anything in it. If it does, we set the token's label to 1. If not, set it back to 0.

Now we have a token that has a label that knows what is on the task sequence list, and how long it has either had something or nothing. All we have to do now is get it in to a table. This is where the Statistics Collector comes in. The Statistics Collector listens to the OnExit of CreateHasTasks. It creates one row per token, and uses the token as the row value. In our case, there is only one token, so there will only be one row. The token has a label that refers to the dispatcher it is observing, so we reference that in the Dispatcher column.

The next two columns are almost identical. They update Always, and they both have code that looks like this:

data.rowValue.labels["HasTasks"].as(TrackedVariable).getTotalTimeAt(0)

Here's the breakdown: data.rowValue is the token that we care about (because we set the Row Value to token). That token has a label that is a Tracked Variable. We don't just want the value, though. We want to know how long the label has been set to a certain value. If we said

data.rowValue.HasTasks

then we would just get a 1 or a 0 back, because that syntax gets the current value.

Instead, we want to get some different information from the label. This means we have to use the .labels property. This property can be used to get the label itself, rather than the value of the label. Then, since we know that this label is a Tracked Variable, we can access the Tracked Variable API using .as(TrackedVariable). Finally, we can as the Tracked Variable how long it has been at a certain value (0 in this case).

Hopefully, that makes some sense. Let me know if you have any questions!