Execution proceeds as follows. The director checks each actor to determine whether it is strict or not by calling its isStrict() method (here, "strict" means that all inputs must be known before the actor can specify any outputs). By default, actors are strict. Strict actors are fired only once in an iteration. Their inputs are all known (and may absent) when prefire() is invoked. If prefire() returns true, the fire() and postfire() are invoked exactly once.
Specialized actors may be non-strict, meaning that they are able to produce outputs even their inputs are not known. Such actors must conform to certain requirements in order to ensure determinacy. First, such actors should check input ports by calling their isKnown() method before calling hasToken() to determine whether the port is "absent." Only if both isKnown() and hasToken() return true should the actor call get() on that port. A non-strict actor may be prefired and fired repeatedly in an iteration if some of the inputs are unknown. Once an actor is fired with all its inputs known, it will not be fired again in the same iteration. A composite actor containing this director is a non-strict actor.
Each actor's fire() method implements a (possibly state-dependent) function from input ports to output ports. At each tick of the clock, the fire() method of each non-strict actor may be evaluated multiple times, and each time, it must implement the same function. Thus, the actors are required to conform with the strict actor semantics, which means that they do not change their state in the prefire() or fire() methods, and only change their state in postfire(). This helps ensure that the actor is monotonic. Montonicity implies three constraints on the actor. First, if prefire() ever returns true during an iteration, then it will return true on all subsequent invocations of prefire() in the same iteration(). In subsequent iterations, inputs may become known, but once they are known, the value of the input and whether it is present cannot change in subsequent firings in the same iteration. Second, if either prefire() or fire() call clear() on an output port, then no subsequent invocation in the same iteration can call put() on the port. Third, if prefire() or fire() call put() on an output port with some token, then no subsequent invocation in the same iteration can call clear() or put() with a token with a different value. These constraints ensure determinacy.
If synchronizeToRealTime is set to true,
then the postfire() method stalls until the real time elapsed
since the model started matches the current time.
This ensures that the director does not get ahead of real time. However,
of course, this does not ensure that the director keeps up with real time.
Note that this synchronization occurs after actors have been fired,
but before they have been postfired.
The SR director has a period parameter which specifies the amount of model time that elapses per iteration. If the value of period is 0.0 (the default), then it has no effect, and this director never increments time nor calls fireAt() on the enclosing director. If the period is greater than 0.0, then if this director is at the top level, it increments time by this amount in each invocation of postfire(). If it is not at the top level, then it refuses to fire at times that do not match a multiple of the period (by returning false in prefire()). If it fires, then in postfire() it calls fireAt(currentTime + period) in postfire() to request the next firing.
Note that currentTime, as usual, means local time. If this director is inside a modal model, then that current time may lag behind the time of the environment in which the modal model executes because time does not elapse while a mode is inactive. In fact, time may bounce around, since if a startTime is specified and the modal model has a reset transition, then local time may be reinitialized to the start time during execution. Moreover, if the startTime of this director inside a modal is greater than the start time of the enclosing director, then local time may actually be ahead of environment time.
This behavior gives an interesting use of SR within DE or Continuous. In particular, if set a period other than 0.0, the composite actor with this SR director will fire periodically with the specified period.
If period is greater than 0.0 and the parameter
synchronizeToRealTime is set to true,
then the prefire() method stalls until the real time elapsed
since the model started matches the period multiplied by
the iteration count.
This ensures that the director does not get ahead of real time. However,
of course, this does not ensure that the director keeps up with real time.
@author Paul Whitaker, Edward A. Lee, Contributor: Ivan Jeukens, Haiyang Zheng
@version $Id: SRDirector.java 70402 2014-10-23 00:52:20Z cxh $
@since Ptolemy II 2.0
@Pt.ProposedRating Green (pwhitake)
@Pt.AcceptedRating Green (pwhitake)
*/
public class SRDirector extends FixedPointDirector implements PeriodicDirector {
/** Construct a director in the default workspace with an empty string
* as its name. The director is added to the list of objects in
* the workspace. Increment the version number of the workspace.
* @exception IllegalActionException If the name has a period in it, or
* the director is not compatible with the specified container.
* @exception NameDuplicationException If the container already contains
* an entity with the specified name.
*/
public SRDirector() throws IllegalActionException, NameDuplicationException {
super();
_init();
}
/** Construct a director in the given workspace with an empty name.
* The director is added to the list of objects in the workspace.
* Increment the version number of the workspace.
* @param workspace The workspace for this object.
* @exception IllegalActionException If the name has a period in it, or
* the director is not compatible with the specified container.
* @exception NameDuplicationException If the container already contains
* an entity with the specified name.
*/
public SRDirector(Workspace workspace) throws IllegalActionException,
NameDuplicationException {
super(workspace);
_init();
}
/** Construct a director in the given container with the given name.
* The container argument must not be null, or a
* NullPointerException will be thrown.
* If the name argument is null, then the name is set to the
* empty string. Increment the version number of the workspace.
* @param container Container of the director.
* @param name Name of this director.
* @exception IllegalActionException If the director is not compatible
* with the specified container.
* @exception NameDuplicationException If the name collides with an
* attribute in the container.
*/
public SRDirector(CompositeEntity container, String name)
throws IllegalActionException, NameDuplicationException {
super(container, name);
_init();
}
///////////////////////////////////////////////////////////////////
//// parameters ////
/** The time period of each iteration. This parameter has type double
* and default value 0.0, which means that this director does not
* increment model time and does not request firings by calling
* fireAt() on any enclosing director. If the value is set to
* something greater than 0.0, then if this director is at the
* top level, it will increment model time by the specified
* amount in its postfire() method. If it is not at the top
* level, then it will call fireAt() on the enclosing executive
* director with the argument being the current time plus the
* specified period. In addition,
* if it is not at the top level, then it refuses to fire
* at times that do not match a multiple of the period
* (by returning false in prefire()).
*/
public Parameter period;
///////////////////////////////////////////////////////////////////
//// public methods ////
/** Clone the object into the specified workspace. The new object is
* not added to the directory of that workspace (you must do this
* yourself if you want it there).
* @param workspace The workspace for the cloned object.
* @exception CloneNotSupportedException Not thrown in this base class
* @return The new Attribute.
*/
@Override
public Object clone(Workspace workspace) throws CloneNotSupportedException {
SRDirector newObject = (SRDirector) super.clone(workspace);
try {
newObject._periodicDirectorHelper = new PeriodicDirectorHelper(
newObject);
} catch (IllegalActionException e) {
throw new CloneNotSupportedException("Failed to clone helper: " + e);
}
return newObject;
}
/** Request a firing of the given actor at the given absolute
* time, and return the time at which the specified will be
* fired. If the period is 0.0 and there is no enclosing
* director, then this method returns the current time. If
* the period is 0.0 and there is an enclosing director, then
* this method delegates to the enclosing director, returning
* whatever it returns. If the period is not 0.0, then
* this method checks to see whether the
* requested time is equal to the current time plus an integer
* multiple of the period. If so, it returns the requested time.
* If not, it returns current time plus the period.
* @param actor The actor scheduled to be fired.
* @param time The requested time.
* @param microstep The microstep (ignored by this director).
* @exception IllegalActionException If the operation is not
* permissible (e.g. the given time is in the past).
* @return Either the requested time or the current time plus the
* period.
*/
@Override
public Time fireAt(Actor actor, Time time, int microstep)
throws IllegalActionException {
return _periodicDirectorHelper.fireAt(actor, time);
}
/** Return the time value of the next iteration.
* If this director is at the top level, then the returned value
* is the current time plus the period. Otherwise, this method
* delegates to the executive director.
* @return The time of the next iteration.
* @exception IllegalActionException If time objects cannot be created.
*/
@Override
public Time getModelNextIterationTime() throws IllegalActionException {
if (!_isTopLevel()) {
return super.getModelNextIterationTime();
}
try {
double periodValue = periodValue();
if (periodValue > 0.0) {
return getModelTime().add(periodValue);
} else {
return getModelTime();
}
} catch (IllegalActionException exception) {
// This should have been caught by now.
throw new InternalErrorException(exception);
}
}
/** Initialize the director and all deeply contained actors by calling
* the super.initialize() method.
* If the period parameter is greater than zero, then
* request a first firing of the executive director, if there
* is one.
* @exception IllegalActionException If the superclass throws it.
*/
@Override
public void initialize() throws IllegalActionException {
super.initialize();
_periodicDirectorHelper.initialize();
// In preinitialize(), _startTime was set to the start time of
// the executive director. However, this invocation of initialize()
// may be occurring later in the execution of a model, as a result
// for example of a reset transition. In that case, _startTime
// may be in the past relative to the environment time.
// The super.initialize() call above should have set our
// current time to match the environment time, so we use
// the maximum of _startTime and the current time as the
// first firing time.
// NOTE: If we are being reinitialized during execution (e.g. because
// of a reset transition), then our current local time is set to match
// the environment time if startTime is blank (the default), meaning that
// start time is inherited from the environment. Otherwise, the accumulated
// suspend time should be set to the difference between the current time
// of the environment and the start time. In either case, this is the
// difference between the current time and the environment time.
Time startTime = getModelStartTime();
Time currentTime = getModelTime();
if (startTime.compareTo(currentTime) >= 0) {
fireContainerAt(startTime, 1);
} else {
// Use a microstep of 1 here on the assumption
// that initialization could create discontinuities.
fireContainerAt(currentTime, 1);
}
}
/** Return the value of the period as a double.
* @return The value of the period as a double.
* @exception IllegalActionException If the period parameter
* cannot be evaluated
*/
@Override
public double periodValue() throws IllegalActionException {
return ((DoubleToken) period.getToken()).doubleValue();
}
/** Return true if we are ready to fire, meaning that either (1) we are
* at the top level, (2) the period parameter is zero (in which case we
* are always ready to fire, or (3) the period parameter is nonzero,
* the current time matches the next expected execution time, and the
* current microstep is 1. If this actor is enclosed within a director
* that does not understand microsteps, then we ignore the microstep value.
* This method will also synchronize to real time, if appropriate.
* @exception IllegalActionException If the period
* parameter cannot be evaluated.
* @return true If current time is appropriate for a firing.
*/
@Override
public boolean prefire() throws IllegalActionException {
// The first call below sets current time to match the environment
// time. The second call, _periodicDirectorHelper.prefire(), checks
// to see whether current time is the next expected firing time.
boolean result = super.prefire() && _periodicDirectorHelper.prefire();
// If we are going to fire, then set the microstep to match that
// of the enclosing director, or set it to 1 if the enclosing
// director does not understand superdense time.
if (result && isEmbedded()) {
Nameable container = getContainer();
if (container instanceof CompositeActor) {
Director executiveDirector = ((CompositeActor) container)
.getExecutiveDirector();
if (isEmbedded()
&& executiveDirector instanceof SuperdenseTimeDirector) {
_index = ((SuperdenseTimeDirector) executiveDirector)
.getIndex();
} else {
_index = 1;
}
if (_debugging) {
_debug("SRDirector: Set microstep to " + _index);
}
} else {
// No container. This should not happen.
throw new IllegalActionException(this,
"SRDirector needs a CompositeActor container to execute");
}
} else {
// If either we are not going to fire or are at the top level,
// set the microstep to 1.
_index = 1;
}
if (_debugging) {
_debug("Prefire returns " + result);
}
return result;
}
/** Call postfire() on all contained actors that were fired on the last
* invocation of fire(). Return false if the model
* has finished executing, either by reaching the iteration limit, or if
* no actors in the model return true in postfire(), or if stop has
* been requested. This method is called only once for each iteration.
* Note that actors are postfired in arbitrary order.
*
* If the period parameter is greater than 0.0, then * if this director is at the top level, then increment time * by the specified period, and otherwise request a refiring * at the current time plus the period. * @return True if the Director wants to be fired again in the * future. * @exception IllegalActionException If the iterations or * period parameter does not contain a legal value. */ @Override public boolean postfire() throws IllegalActionException { // The super.postfire() method increments the superdense time index. boolean result = super.postfire(); _periodicDirectorHelper.postfire(); return result; } /////////////////////////////////////////////////////////////////// //// private methods //// /** Initialize the object. In this case, we give the SDFDirector a * default scheduler of the class SDFScheduler, an iterations * parameter and a vectorizationFactor parameter. */ private void _init() throws IllegalActionException, NameDuplicationException { period = new Parameter(this, "period"); period.setTypeEquals(BaseType.DOUBLE); period.setExpression("0.0"); _periodicDirectorHelper = new PeriodicDirectorHelper(this); // Put the stopTime at the end parameters, to encourage use // of iterations instead. stopTime.moveToLast(); } /////////////////////////////////////////////////////////////////// //// private variables //// /** Helper class supporting the period parameter. */ private PeriodicDirectorHelper _periodicDirectorHelper; }