Dynamic Dataflow Modeling in Ptolemy II - Ptolemy Project ...

course if there are more than one output channel satisfying destination actors, the actor is
still deferrable. However, it does not require that all output channels satisfy all
destinations actors to be a deferrable actor. Second, when one particular channel of a
destination actor is satisfied, it has two possible situations. One situation is that the
number of tokens buffered on that channel is greater than or equal to the number of
tokens required on that channel in order to fire the destination actor. Another situation is
that the destination actor does not consume a token on that channel during next firing.
Third, when one particular channel of a destination actor is satisfied, it does not mean the
destination actor is enabled. It may be still waiting for tokens on different channels to
enable the next firing. The consequence is that we cannot use the prefire() method of the
destination actors to check its deferability. Each actor must expose the number of tokens
consumed on each input channel as part of its interface, which may dynamically change
from one firing to another. This will have consequences in designing actors that can be
used in DDF domain.
Having defined the deferability of an actor, which is a key concept in our scheduler, we
now give the algorithm in the following pseudo-code:
At the start of each basic iteration compute {
E = set of enabled actors
D = set of deferrable and enabled actors
minimax(D) = subset of D as defined on the next page
}
One basic (default) iteration consists of {
If (E \ D != Ø)
fire (E \ D)
else if (D != Ø)
fire minimax(D)
else
declare deadlock
}
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