/* An actor that delays the input by the specified amount.
Copyright (c) 1998-2009 The Regents of the University of California.
All rights reserved.
Permission is hereby granted, without written agreement and without
license or royalty fees, to use, copy, modify, and distribute this
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of this software.
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*/
package ptolemy.domains.de.lib;
import java.util.HashSet;
import java.util.Set;
import ptolemy.actor.CausalityMarker;
import ptolemy.actor.Director;
import ptolemy.actor.util.CalendarQueue;
import ptolemy.actor.util.Time;
import ptolemy.actor.util.TimedEvent;
import ptolemy.data.DoubleToken;
import ptolemy.data.Token;
import ptolemy.data.expr.Parameter;
import ptolemy.data.type.BaseType;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.Port;
import ptolemy.kernel.util.Attribute;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.NameDuplicationException;
import ptolemy.kernel.util.Workspace;
//////////////////////////////////////////////////////////////////////////
//// TimedDelay
/**
This actor delays the input by a specified amount of time. The amount
of the time is required to be non-negative and has a default value 1.0.
The input and output types are unconstrained, except that the output type
must be the same as that of the input.
<p>
This actor keeps a local FIFO queue to store all received but not processed
inputs. The behavior of this actor on each firing is to read a token from
the input, if there is one, store it into the local queue, and output the
previously received token that is scheduled to be produced at the current
time.
<p> During the postfire() method, this actor schedules itself to fire again
to produce the just received token on the corresponding output channel after
the appropriate time delay. Note that if the value of delay is 0.0, the
actor schedules itself to fire at the current model time.
<p>
Occasionally, this actor is useful with the
delay parameter set to 0.0. The time stamp of the output will
equal that of the input, but there is a "microstep" delay.
The discrete-event domain in Ptolemy II has a "super dense" model
of time, meaning that a signal from one actor to another can
contain multiple events with the same time stamp. These events
are "simultaneous," but nonetheless
have a well-defined sequential ordering determined by the order
in which they are produced.
If \textit{delay} is 0.0, then the fire() method of this actor
always produces on its output port the event consumed in the
\textit{previous iteration} with the same time stamp, if there
was one. If there wasn't such a previous iteration, then it
produces no output. Its postfire() method consumes and
records the input for use in the next iteration, if there
is such an input, and also requests a refiring at the current
time. This refire request triggers the next iteration (at
the same time stamp), on which the output is produced.
<p>
A consequence of this strategy is that this actor is
able to produce an output (or assert that there is no output) before the
input with the same time is known. Hence, it can be used to break
causality loops in feedback systems. The DE director will leverage this when
determining the precedences of the actors. It is sometimes useful to think
of this zero-valued delay as an infinitesimal delay.
@see ptolemy.domains.de.lib.VariableDelay
@see ptolemy.domains.de.lib.Server
@author Edward A. Lee, Lukito Muliadi, Haiyang Zheng
@version $Id$
@since Ptolemy II 1.0
@Pt.ProposedRating Green (hyzheng)
@Pt.AcceptedRating Yellow (hyzheng)
*/
public class TimedDelay extends DETransformer {
/** Construct an actor with the specified container and name.
* Constrain that the output type to be the same as the input type.
* @param container The composite entity to contain this one.
* @param name The name of this actor.
* @exception IllegalActionException If the entity cannot be contained
* by the proposed container.
* @exception NameDuplicationException If the container already has an
* actor with this name.
*/
public TimedDelay(CompositeEntity container, String name)
throws NameDuplicationException, IllegalActionException {
super(container, name);
// NOTE: The _init method is used to allow classes that extend
// this class to reconfig their settings. This may not be a
// good pattern.
_init();
output.setTypeSameAs(input);
}
///////////////////////////////////////////////////////////////////
//// ports and parameters ////
/** The amount of delay. The default for this parameter is 1.0.
* This parameter must contain a DoubleToken
* with a non-negative value, or an exception will be thrown when
* it is set.
*/
public Parameter delay;
///////////////////////////////////////////////////////////////////
//// public methods ////
/** If the attribute is <i>delay</i>, then ensure that the value
* is non-negative.
* <p>NOTE: the newDelay may be 0.0, which may change the causality
* property of the model. We leave the model designers to decide
* whether the zero delay is really what they want.
* @param attribute The attribute that changed.
* @exception IllegalActionException If the delay is negative.
*/
public void attributeChanged(Attribute attribute)
throws IllegalActionException {
if (attribute == delay) {
double newDelay = ((DoubleToken) (delay.getToken())).doubleValue();
if (newDelay < 0.0) {
throw new IllegalActionException(this,
"Cannot have negative delay: " + newDelay);
} else {
_delay = newDelay;
}
} else {
super.attributeChanged(attribute);
}
}
/** Clone the actor into the specified workspace. Set a type
* constraint that the output type is the same as the that of input.
* @param workspace The workspace for the new object.
* @return A new actor.
* @exception CloneNotSupportedException If a derived class has
* has an attribute that cannot be cloned.
*/
public Object clone(Workspace workspace) throws CloneNotSupportedException {
TimedDelay newObject = (TimedDelay) super.clone(workspace);
newObject.output.setTypeSameAs(newObject.input);
newObject._causalityMarker = (CausalityMarker)newObject.getAttribute("causalityMarker");
return newObject;
}
/** Read one token from the input. Send out a token that is scheduled
* to produce at the current time to the output.
* @exception IllegalActionException If there is no director, or the
* input can not be read, or the output can not be sent.
*/
public void fire() throws IllegalActionException {
super.fire();
// consume input
if (input.hasToken(0)) {
_currentInput = input.get(0);
} else {
_currentInput = null;
}
// produce output
// NOTE: The amount of delay may be zero.
// In this case, if there is already some token scheduled to
// be produced at the current time before the current input
// arrives, that token is produced. While the current input
// is delayed to the next available firing at the current time.
Time currentTime = getDirector().getModelTime();
_currentOutput = null;
if (_delayedOutputTokens.size() > 0) {
TimedEvent earliestEvent = (TimedEvent) _delayedOutputTokens.get();
Time eventTime = earliestEvent.timeStamp;
if (eventTime.equals(currentTime)) {
_currentOutput = (Token) earliestEvent.contents;
output.send(0, _currentOutput);
}
}
}
/** Initialize the states of this actor.
* @exception IllegalActionException If a derived class throws it.
*/
public void initialize() throws IllegalActionException {
super.initialize();
_currentInput = null;
_currentOutput = null;
_delayedOutputTokens = new CalendarQueue(
new TimedEvent.TimeComparator());
}
/** Process the current input if it has not been processed. Schedule
* a firing to produce the earliest output token.
* @exception IllegalActionException If scheduling to refire cannot
* be performed or the superclass throws it.
*/
public boolean postfire() throws IllegalActionException {
Time currentTime = getDirector().getModelTime();
Time delayToTime = currentTime.add(_delay);
// Remove the token that is sent at the current time.
if (_delayedOutputTokens.size() > 0) {
if (_currentOutput != null) {
_delayedOutputTokens.take();
}
}
// Handle the refiring of the multiple tokens
// that are scheduled to be produced at the same time.
if (_delayedOutputTokens.size() > 0) {
TimedEvent earliestEvent = (TimedEvent) _delayedOutputTokens.get();
Time eventTime = earliestEvent.timeStamp;
if (eventTime.equals(currentTime)) {
_fireAt(currentTime);
}
}
// Process the current input.
if (_currentInput != null) {
_delayedOutputTokens
.put(new TimedEvent(delayToTime, _currentInput));
_fireAt(delayToTime);
}
return super.postfire();
}
/** Override the base class to declare that the <i>output</i>
* does not depend on the <i>input</i> in a firing.
* @exception IllegalActionException If the superclass throws it.
*/
public void preinitialize() throws IllegalActionException {
super.preinitialize();
declareDelayDependency(input, output, _delay);
}
///////////////////////////////////////////////////////////////////
//// protected method ////
/** Initialize the delay parameter.
* @exception IllegalActionException If delay parameter cannot be set.
* @exception NameDuplicationException If there already is a parameter
* named "delay".
*/
protected void _init() throws IllegalActionException,
NameDuplicationException {
delay = new Parameter(this, "delay", new DoubleToken(1.0));
delay.setTypeEquals(BaseType.DOUBLE);
_delay = ((DoubleToken) delay.getToken()).doubleValue();
Set<Port> dependentPorts = new HashSet<Port>();
_causalityMarker = new CausalityMarker(this, "causalityMarker");
_causalityMarker.addDependentPortSet(dependentPorts);
}
///////////////////////////////////////////////////////////////////
//// protected variables ////
/** Current input. */
protected Token _currentInput;
/** Current output. */
protected Token _currentOutput;
/** The amount of delay. */
protected double _delay;
/** A local event queue to store the delayed output tokens. */
protected CalendarQueue _delayedOutputTokens;
/** A causality marker to store information about how pure events are causally
* related to trigger events.
*/
protected CausalityMarker _causalityMarker;
///////////////////////////////////////////////////////////////////
//// protected methods ////
/** Request a firing of this actor at the specified time
* and throw an exception if the director does not agree to
* do it at the requested time. This is a convenience method
* provided because many actors need it.
* <p>
* If the executive director is a Ptides director, use
* fireAt(Actor, Time, IOPort) method because the pure event this
* actor generates is always safe to process.
* </p>
* @param time The requested time.
* @exception IllegalActionException If the director does not
* agree to fire the actor at the specified time, or if there
* is no director.
*/
protected void _fireAt(Time time) throws IllegalActionException {
Director director = getDirector();
if (director == null) {
throw new IllegalActionException(this, "No director.");
}
Time result = null;
result = director.fireAt(this, time);
if (!result.equals(time)) {
throw new IllegalActionException(this,
"Director is unable to fire the actor at the requested time: "
+ time + ". It responds it will fire it at: "
+ result);
}
}
}