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4.3.16 Discrete Event Actor Libraries A library of actors is provided to particularly support discrete-event models. In discrete-event models, signals consist of events placed in time, where time is a double. Events are processed in chronological order. EventButton: Output a token in response to the click of a button. EventFilter: An actor that filters a stream of boolean tokens. Every true input token that it receives is reproduced on the output port. False tokens are discarded. This is usually used to properly trigger other discrete event actors (such as inhibit and select) based on boolean values. Inhibit: Output a received input token, unless the inhibit port receives a token. Merge: Merge input events into a single signal. PreemptableTask: Simulate a preemptable task. Previous: On each iteration, this actor produces the token received on the previous iteration. On the first iteration, it produces the token given by the initialValue parameter, if such a value has been set. Queue: This actor implements an event queue. When a token is received on the input port, it is stored in the queue. When the trigger port receives a token, the oldest element in the queue is output. If there is no element in the queue when a token is received on the trigger port, then no output is produced. QueueWithNextOut: This actor is like the Queue actor above. An additional output port, nextOut, has been added which allows the model to know what's next to come out. This new output produces a token whenever the queue has been empty and a new token is queued. It also produces an output whenever a token is taken from the queue and at least one token remains. Otherwise, no output token is produced at nextOut. The token produced is the oldest token remaining in the queue. Sampler: On each trigger input, produce at the output the most recently seen input. Server: Delay input events until they have been “served” for the specified amount of time. SingleEvent: Produce a single event with the specified time and value. TimedDelay: Delay input events by the specified amount. TimeGap: Produce at the output the amount of time between input events. Timer: Given an input time value, produce value on the output that amount of time in the future. VariableDelay: Delay input events by the specified amount. WaitingTime: Measure the amount of time that one event (arriving on waiter) has to wait for an event to arrive on waitee. There is an output event for every event that arrives on waiter, where the value of that output is the time spent waiting, and the time of the output is time of the arriving waitee event. 4.4 Data Polymorphism A data polymorphic actor is one that can operate on any of a number of input data types. For example, AddSubtract can accept any numeric type of input. 148 Ptolemy <strong>II</strong>
Actor Libraries Figure 4.4 shows the methods defined in the base class Token. Any data exchanged between actors in Ptolemy <strong>II</strong> is wrapped in an instance of Token (or more precisely, in an instance of a class derived from Token). Notice that add() and subtract() are methods of this base class. This makes it easy to implement a data polymorphic adder. It is instructive to examine the code in an actor that performs data polymorphic operations. The fire() method of the AddSubtract actor is shown in figure 4.5. In this code, we first iterate through the channels of plus input. The first token read (by the get() method) is assigned to sum. Subsequently, the polymorphic add() method of that token is used to add additional tokens. The second iteration, over the channels at the minus input port, is slightly trickier. If no tokens were read from the plus input, then the variable sum is initialized by calling the polymorphic zero() method of the first token read at the minus port. The zero() method returns whatever a zero value is for the token in question. Not all classes derived from Token override all its methods. For example, StringToken overrides add() but not subtract(). Adding strings means simply concatenating them, but it is hard to assign a rea- FIGURE 4.4. The Token class defines a polymorphic interface that includes basic arithmetic operations. Token +Token() +add(rightArg : Token) : Token +addReverse(leftArg : Token) : Token +convert(token : Token) : Token +divide(divisor : Token) : Token +divideReverse(dividend : Token) : Token +getType() : Type +isCloseTo(token : Token) : BooleanToken +isCloseTo(token : Token, epsilon : double) : BooleanToken +isEqualTo(token : Token) : BooleanToken +modulo(rightArg : Token) : Token +moduloReverse(leftArg : Token) : Token +multiply(rightFactor : Token) : Token +multiplyReverse(leftFactor : Token) : Token +one() : Token +subtract(rightArg : Token) : Token +subtractReverse(leftArg : Token) : Token +zero() : Token public void fire() throws IllegalActionException { Token sum = null; for (int i = 0; i < plus.getWidth(); i++) { if (plus.hasToken(i)) { if (sum == null) { sum = plus.get(i); } else { sum = sum.add(plus.get(i)); } } } for (int i = 0; i < minus.getWidth(); i++) { if (minus.hasToken(i)) { Token in = minus.get(i); if (sum == null) { sum = in.zero(); } sum = sum.subtract(in); } } if (sum != null) { output.send(0, sum); } } FIGURE 4.5. The fire() method of the AddSubtract shows the use of polymorphic add() and subtract() methods in the Token class (see figure 4.4). Heterogeneous Concurrent Modeling and Design 149
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PTOLEMY II HETEROGENEOUS CONCURRENT
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VOLUME 1 INTRODUCTION TO PTOLEMY II
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Volume 1 Contents Introduction to P
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2.10.3. Constructing Modal Models 8
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7. MoML 191 7.1. Introduction 191 7
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1 Introduction Author: Edward A. Le
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Introduction heterochronous dataflo
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Introduction A major emphasis in Pt
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Introduction determine when actors
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Introduction provides levels of vis
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Introduction is a guard, and the se
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Introduction well. All of these are
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Introduction clients to update thei
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Introduction will be supplied with
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Introduction 1.3.12 Synchronous Dat
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Introduction FIGURE 1.10. Refinemen
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Introduction occlusions due to terr
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Introduction tion. The overall arch
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Introduction kernel.attributes This
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Introduction 1.5.2 Overview of Key
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Introduction Actor interfaces are k
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Heterogeneous Concurrent Modeling a
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Introduction actor actor.gui data.e
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Introduction cient, scalable, and u
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Introduction 1.5.8 Future Capabilit
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Introduction Appendix A: UML — Un
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Introduction grams, the only constr
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2 Using Vergil Authors: Edward A. L
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Using Vergil 2.2.2 Executing a Pre-
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Using Vergil The Lorenz attractor m
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Using Vergil The Continuous-Time (C
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Using Vergil box in figure 2.11. En
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Using Vergil Don’t panic! Excepti
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Using Vergil tions are a normal par
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Using Vergil 2.4 Hierarchy Ptolemy
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Using Vergil Then using these ports
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Using Vergil the default 0.1 to 0.0
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Using Vergil pan window, it is easy
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Using Vergil FIGURE 2.33. The pan w
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Using Vergil we have modified the c
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Using Vergil model, simply copy (or
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Using Vergil A key issue is to deci
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Using Vergil instances. This proble
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Using Vergil quick tour for more de
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Using Vergil uses the index in the
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Using Vergil AddSubtract actor, and
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Using Vergil If you look inside the
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Using Vergil If you look inside the
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Using Vergil transition (or right c
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Using Vergil Once you have created
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Using Vergil The grid is turned off
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Authors: Edward A. Lee Xiaojun Liu
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Expressions classes to create a gen
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Page 127 and 128: Expressions In the example in figur
Page 129 and 130: Expressions A.2 Basic Mathematical
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Page 135 and 136: Expressions TABLE 8: Functions perf
Page 137 and 138: 4 Actor Libraries Authors: Elaine C
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Page 161 and 162: 5 Designing Actors Authors: Christo
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MoML 7.3.3 Names and Classes Most M
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MoML Here, the element named
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MoML implement. 7.3.7 Doc Element S
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MoML It is also sometimes necess
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MoML then there will be a link t
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MoML found. For example, if the cla
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MoML it cannot collide with the nam
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MoML The rendering of the icon is d
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MoML 7.4.5 Deleting Entities, Relat
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MoML This unlinks a port from the s
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MoML model. The EntityLibrary class
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MoML Suppose that using incremental
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MoML Generate a sine wave.
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MoML
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MoML Number of iterations in
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MoML -P- The f
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MoML -P- The phase,
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8 Custom Applets Authors: Edward A.
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Custom Applets html code, see the J
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Custom Applets public class Tutoria
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Custom Applets then the result of
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Custom Applets 8.3.5 Using Model Pa
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Custom Applets ptolemy/domains/doma
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References [1] G. Agha, Actors: A M
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[33] S. A. Edwards, “The Specific
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[67] E. Kohler, The Click Modular R
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[95] J. Liu, X. Liu, T. J. Koo, B.
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[132]W. R. Sutherland, "The on-Line
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Glossary abstract syntax ..........
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Ptolemy II ........................
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Index Symbols - in UML 41 # in UML
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coin flips 142 Color class 173 colo
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entity in XML 198 EntityLibrary cla
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Director class 159 inverse FFT 124
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CompositeEntity class 206 nextPower
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safety 34 SampleDelay actor 78, 138
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type constraint 155 type constraint
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