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Ira Leviton (talk | contribs) m Deleted 'interestingly' - see Wikipedia:Manual_of_Style/Words_to_watch#Editorializing. |
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This actor is clearly nondeterministic. As long as it has only input on one of its input ports, everything is unambiguous. But, just like NDMerge, as soon as input is available on both input ports, it could fire either of its two actions, and there is nothing in that actor specification which would predispose it to choose one over the other.
Suppose now that this actor processes, e.g., audio data that continuously streams in on its In input port, and that this processing depends on the value of its state variable c—imagine c containing the setting of the volume dial. Every now and then, the user turns that dial, and a new value for c is sent to this actor. Clearly, it is not irrelevant in which order the two actions fire. In fact, we would like to make sure that the first action fires as soon as possible, so that the new user setting will take effect. More precisely, we would like to express the requirement that, should both actions be able to fire, the first one will be fired next.
The basic idea is to add a number of inequalities that relate actions with respect to their firing precedence.11 In our example, this leads to the following solution:
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