public class PetriNetDirector extends Director
This domain implements the basic Petri Net model where Places and Transitions form a bipartite graph and enabled Transitions can fire randomly. It also allows Transitions to be replaced by any other Actors in Ptolemy. It implements two forms of Hierarchical and compositional Petri nets. The first form of hierarchical and compositional Petri net semantics comes from the fact that a Transition can contain a sub-Petri-net which is invisible to the director of the container of the Transition. The second form of hierarchical and compositional Petri net semantics comes from a new Actor called PetriNetActor which is a collection of Places and Transitions, and those Places and Transitions are visible to the director of the container of the PetriNetActor. The users can choose which form of models to use, and/or mix them together.
The basic Petri net is a directed, weighted, bipartite graph consisting of two kinds of nodes, called Places and Transitions, where arcs are either from a Place to a Transition or from a Transition to a Place. In graphical representation, Places are drawn as circles, Transitions as bars or boxes. Arcs are labeled with their weights (positive integers). Labels of unity weight are usually omitted. Multiple arcs can exist between a Place and a Transition. A marking assigns to each Place p an nonnegative integer k, we say that p is marked with k tokens.
Please note here the term token is used differently from the general Ptolemy term token. Here a token is really the integer 1. k tokens is represented by the integer k.
A Transition t is said to be enabled if each input Place p of t is marked with at least the sum of w(p, t) tokens, where w(p, t) are the weights of the arcs from p to t.
An enabled Transition may or may not fire. When there are multiple enabled Transitions, any of them can fire randomly. A firing of an enabled Transition t removes w(p, t) tokens from each input Place p of t, and adds w(t, p) tokens to each output Place p of t, where w(t, p) and w(p, t) are the weights of the arcs from and to the Transition respectively.
A Transition without any input Place is called a source Transition, and one without any output Place is called a sink Transition. Note that a source Transition is unconditionally enabled, and that the firing of a sink Transition consumes tokens, but does not produce any.
Many variations of Petri net exist in the literature including: hierarchical Petri nets, colored Petri nets, timed Petri nets, fuzzy Petri nets, stochastic Petri nets, compositional Petri nets, and many of the combinations.
As pointed out earlier, in Ptolemy we implement the basic Petri net model plus two kinds of hierarchical and compositional Petri nets. This is made possible by defining the PetriNetActor. The PetriNetActor is a directed and weighted graph just like the basic Petri Net model. However, a PetriNetActor graph G = (V, E) contains three kinds of nodes: Places p_i, Transitions t_i, and PetriNetActors PA_i, i.e., V = {p_i} union {t_i} union {PA_i} , where each PA_i itself is again defined as a PetriNetActor. Places are assigned with non-negative integer markings. The default marking is 0. A Place is implemented by the atomic actor Place. A PetriNetActor is a TypedCompositeActor contains Places, Transitions and/or PetriNetActors.
Each node of V is called a component of the PetriNetActor G. Therefore the vertex set V of G is also called the component set of the PetriNetActor G. The concept of component is a key difference between the basic Petri net model and the hierarchical Petri net model defined here. In Ptolemy term, a component is an element in the entityList of the PetriNetActor. A PetriNetActor consists of components. A component can be a Place, a Transition, and a PetriNetActor component. A component can be enabled and fires if it is a Transition or it is a PetriNetActor component that contains other Transitions. When the firing method _fireHierarchicalPetriNetOnce() fires, it chooses one component to fire.
The definition of PetriNetActor defines one form of hierarchical and compositional Petri nets. It defines a hierarchical Petri net since the PetriNetActor G can contain other PetriNetActors PA_i as components. It defines a compositional Petri net since two PetriNetActors PA_1 and PA_2 of V can be connected through their ports to form a bigger Petri net G.
The second form of Hierarchical and compositional Petri net comes from the fact that a Transition can be any TypedCompositeActor in Ptolemy domains, which can have its own firing director. The content of the Transition is invisible to the director of the container of the Transition. Therefore it is possible to have a Transition contains other Places and Transitions and has a PetriNetDirector as the local director for the Transition.
The set of Transitions of the PetriNetActor G, or the Transition set of G, is defined to be the union of the Transitions t_i with the sets of Transitions of each PetriNetActor component PA_i. A member of the Transition set of G is therefore contained in G itself in which case the Transition is also a component of G, or it is contained in some PetriNetActor component PA_i. Therefore a Transition is a different concept from a Component in PetriNetActor graph. The method findTransitions() returns the Transition set of G.
A component has ports through which connections to other components are made. A Place or a Transition each has one input port and one output port, where multiple connections can be made. In our model, a PetriNetActor component can have multiple ports. A PetriNetActor component PA_j can be connected to Places p_i, Transitions t_i, or other PetriNetActor components PA_i through ports. A Place p_i can be connected to Transitions t_i, or to ports of PetriNetActor components PA_i. A Transition t_i can be connected to Places p_i or to ports of PetriNetActor components PA_i.
One restriction is that a port of a PetriNetActor component PA_i is either connected to Places or to Transitions, but not both. Another restriction is that a Place (Transition) is not allowed to be connected to another Place (Transition) through ports. Though no verification of these two conditions is checked, any violation of these two conditions will be reported by appropriate methods during the execution.
Multiple arcs can exist between any two components. The arcs can be marked by an nonnegative integer as their weights. Weight 1 can be omitted. The method _getWeightNumber(arc) obtains the weight assigned to the arc. If no weight is assigned, the default weight is 1.
For a Transition t, all Places p that can reach t through ports or without ports are the input Places of t. All Places that can be reached from t through ports or without ports are the output Places of t. Given a Transition t, the methods _findBackwardConnectedPlaces() and _findForwardConnectedPlaces() find the input and output Places of the Transition respectively.
A Transition t is enabled or ready in the PetriNetActor if for each input Place p of t, the marking of p is bigger than the sum of the weights of all arcs connecting p to t. The method isTransitionReady(transition) tests whether the given Transition is enabled/ready or not.
If a Transition t is enabled and t is contained in a PetriNetActor component PA_i, then the PetriNetActor component PA_i is also an enabled component. On the other hand, for any PetriNetActor component PA_i, if it contains an enabled Transition, then the PetriNetActor component PA_i is enabled. The method PetriNetActor.prefire() tests whether there is any enabled Transitions contained in the PetriNetActor component.
An enabled Transition may or may not fire. For the given PetriNetActor G, all its enabled components including Transitions t_i and PetriNetActor components PA_i are collected together in a list returned by _readyComponentList(). Suppose the list has n components of t_i and PA_i, each component has 1/n probability to be chosen to fire. The method _fireHierarchicalPetriNetOnce() chooses one component from the list to fire.
If an enabled Transition is chosen to fire, the method fireTransition() is called to fire the Transition and update the input and output Places of the Transition. The firing of the Transition is determined by its own director, if there is one, otherwise no action is needed. For each input Place of the Transition, its marking has to be decreased by the weight of each arc connecting the Place to the Transition. For each output Place, the marking will be increased by the weight of each arc connecting the Transition to the Place.
If a PetriNetActor component PA_i is chosen to fire, the director then recursively repeats the same procedure for PA_i as for the top level PetriNetActor G.
Finally, the firing of the hierarchical Petri net is continued until there is no more Transitions and components to fire, or it goes to infinite loop. Currently no action is taken for infinite loops.
Other form of firing sequence can be defined as well. We could randomly fire all the deeply contained Transitions. We could randomly fire the components in each hierarchy. [1] T. Murata, "Petri nets: properties, analysis and applications", Proceedings of the IEEE, VOl. 77, NO. 4, April 1989, pp. 541-579. [2] J. L. Peterson, "Petri Net Theory and the modeling of systems", Prentice Hall, 1981.
NamedObj.ContainedObjectsIterator| Modifier and Type | Field and Description |
|---|---|
(package private) Parameter |
iterations
This parameter represents the maximum number of times the PetriNet
should fire.
|
SharedParameter |
resetOnEachRun
If true, this parameter specifies that the random number
generator should be reset on each run of the model (in
the initialize() method).
|
SharedParameter |
seed
The seed that controls the random number generator that
determines which component is fired.
|
_actorsFinishedExecution, _aspectForActor, _aspectsPresent, _defaultMicrostep, _executionAspects, _finishRequested, _initializables, _nextScheduleTime, _stopRequested, _tokenSentToCommunicationAspect, _zeroTime, localClock, startTime, stopTime_changeListeners, _changeLock, _changeRequests, _debugging, _debugListeners, _deferChangeRequests, _elementName, _isPersistent, _verbose, _workspace, ATTRIBUTES, CLASSNAME, COMPLETE, CONTENTS, DEEP, FULLNAME, LINKSCOMPLETED, NOT_READY, STOP_ITERATING| Constructor and Description |
|---|
PetriNetDirector(CompositeEntity container,
java.lang.String name)
Construct a new Petri net director.
|
| Modifier and Type | Method and Description |
|---|---|
void |
attributeChanged(Attribute attribute)
If the attribute is seed
then create the base random number generator.
|
java.lang.Object |
clone(Workspace workspace)
Clone the director into the specified workspace.
|
java.util.LinkedList |
findTransitions(TypedCompositeActor container)
Find all Transitions of the given container, i.e., the
Transition set of the container, which is supposed to be a
PetriNetActor.
|
void |
fire()
Fire enabled components of the PetriNetActor by calling the
method _fireHierarchicalPetriNetOnce(), one at a time until
there is no more enabled components to fire.
|
void |
fireTransition(TypedCompositeActor transition)
Fire an enabled Transition.
|
boolean |
isTransitionReady(TypedCompositeActor transition)
Test whether a given Transition is enabled or not.
|
boolean |
postfire()
Return false, indicating that the director does not wish to be scheduled
for another iteration.
|
void |
preinitialize()
This method preinitializes the actors associated with this
director.
|
_actorFinished, _consultTimeRegulators, _description, _isEmbedded, _isTopLevel, _schedule, _transferInputs, _transferOutputs, addInitializable, createSchedule, defaultDependency, delayDependency, elapsedTimeSinceStart, finish, fireAt, fireAt, fireAt, fireAtCurrentTime, fireContainerAt, fireContainerAt, getCausalityInterface, getCurrentTime, getDeadline, getEnvironmentTime, getExecutionAspect, getGlobalTime, getModelNextIterationTime, getModelStartTime, getModelStopTime, getModelTime, getNextIterationTime, getStartTime, getStopTime, getTimeResolution, implementsStrictActorSemantics, initialize, initialize, invalidateResolvedTypes, invalidateSchedule, isEmbedded, isFireFunctional, isStopRequested, isStrict, iterate, mutexLockObject, newReceiver, notifyTokenSentToCommunicationAspect, prefire, preinitialize, removeInitializable, requestInitialization, resume, resumeActor, scheduleContainedActors, setContainer, setCurrentTime, setEmbedded, setModelTime, setTimeResolution, stop, stopFire, suggestedModalModelDirectors, supportMultirateFiring, suspend, terminate, transferInputs, transferOutputs, transferOutputs, wrapup_checkContainer, _getContainedObject, _propagateExistence, getContainer, moveDown, moveToFirst, moveToIndex, moveToLast, moveUp, setName, updateContent_addAttribute, _adjustOverride, _attachText, _cloneFixAttributeFields, _containedDecorators, _copyChangeRequestList, _debug, _debug, _debug, _debug, _debug, _executeChangeRequests, _exportMoMLContents, _getIndentPrefix, _isMoMLSuppressed, _markContentsDerived, _notifyHierarchyListenersAfterChange, _notifyHierarchyListenersBeforeChange, _propagateValue, _removeAttribute, _splitName, _stripNumericSuffix, _validateSettables, addChangeListener, addDebugListener, addHierarchyListener, attributeDeleted, attributeList, attributeList, attributeTypeChanged, clone, containedObjectsIterator, decorators, deepContains, depthInHierarchy, description, description, event, executeChangeRequests, exportMoML, exportMoML, exportMoML, exportMoML, exportMoML, exportMoMLPlain, getAttribute, getAttribute, getAttributes, getChangeListeners, getClassName, getDecoratorAttribute, getDecoratorAttributes, getDerivedLevel, getDerivedList, getDisplayName, getElementName, getFullName, getModelErrorHandler, getName, getName, getPrototypeList, getSource, handleModelError, isDeferringChangeRequests, isOverridden, isPersistent, lazyContainedObjectsIterator, message, notifyOfNameChange, propagateExistence, propagateValue, propagateValues, removeAttribute, removeChangeListener, removeDebugListener, removeHierarchyListener, requestChange, setClassName, setDeferringChangeRequests, setDerivedLevel, setDisplayName, setModelErrorHandler, setPersistent, setSource, sortContainedObjects, toplevel, toString, uniqueName, validateSettables, workspaceParameter iterations
public SharedParameter resetOnEachRun
public SharedParameter seed
This is a shared parameter, meaning that all instances of PetriNetDirector or derived classes in the same model share the same value. This parameter is used for testing so that a model has predictable results and can be compared against known good results.
A seed of zero is interpreted to mean that no seed is specified, which means that each execution of the model could result in distinct data. For the value 0, the seed is set to System.currentTimeMillis() + hashCode(), which means that with extremely high probability, two distinct directors will have distinct seeds. However, current time may not have enough resolution to ensure that two subsequent executions of the same model have distinct seeds. For a value other than zero, the seed is set to that value plus the hashCode() of the full name of the director. This means that with high probability, two distinct director will have distinct, but repeatable seeds.
This parameter contains a LongToken, initially with value 0.
public PetriNetDirector(CompositeEntity container, java.lang.String name) throws IllegalActionException, NameDuplicationException
container - The container.name - The name of the director.IllegalActionException - If the name has a period in it, or the director is not
compatible with the specified container.NameDuplicationException - If the container already contains an entity with the
specified name.public void attributeChanged(Attribute attribute) throws IllegalActionException
attributeChanged in class Directorattribute - The attribute that changed.IllegalActionException - If the change is not acceptable
to this container (not thrown in this base class).public java.lang.Object clone(Workspace workspace) throws java.lang.CloneNotSupportedException
clone in class Directorworkspace - The workspace for the new object.java.lang.CloneNotSupportedException - If a derived class contains
an attribute that cannot be cloned.NamedObj.exportMoML(Writer, int, String),
NamedObj.setDeferringChangeRequests(boolean)public java.util.LinkedList findTransitions(TypedCompositeActor container)
container - The container where the Transitions are contained.public void fire()
throws IllegalActionException
A description of the firing is sent to any actors that implement
the PetriNetDisplayer interface. If this director has a debug
listener, then the description is also sent to those listeners.
fire in interface Executablefire in class DirectorIllegalActionException - If the method
_fireHierarchicalPetriNetOnce() throws exceptions, which can
happen if the method isTransitionReady() or fireTransition()
throws exceptions.public void fireTransition(TypedCompositeActor transition) throws IllegalActionException
The transition argument to this method must be an enabled Transition. If the given Transition is Opaque, then it fires the Transition first, otherwise no action is taken for the Transition; the method then updates the markings of the input Places and output Places of the Transition. The update of the marking is done one relation at a time. The input Places and output Places are found by the methods _findForwardConnectedPlaces() and _findBackwardConnectedPlaces() respectively.
transition - The transition to be fired.IllegalActionException - If the method _getWeightNumber() throws an exception.public boolean isTransitionReady(TypedCompositeActor transition) throws IllegalActionException
A Transition is enabled if for each of the input Places, the marking of the Place is bigger than the sum of weights of edges connecting the Place to the Transition. The Transition itself is any TypedCompositeActor. The Transition can be a component of a PetriNetActor, or it is contained in some PetriNetActor component.
This is one of the key methods for hierarchical Petri Nets. It is equivalent to the prefire() method for a Transition. The method first finds all the input Places of the Transition by calling the method _findBackwardConnectedPlaces(), and sets the temporary marking of the Places equal to the real marking; then it enumerates all the arcs connecting Places to the Transition and decreases the temporaryMarking of the Places reachable from the arc. If after all arcs have been enumerated and the temporaryMarking of all input Places are greater than 0, then the Transition is ready to fire, otherwise it is not ready to fire. The reason that we use a temporaryMarking here is to keep the initialMarking of the places unchanged when we test a Transition is ready or not.
transition - Transition to be tested to be enabled or not.IllegalActionException - If the method "_getWeightNumber" throws exceptions, which
can happen if the arcs are not assigned to some other
value other than integers.public void preinitialize()
throws IllegalActionException
preinitialize in interface Initializablepreinitialize in class DirectorIllegalActionException - Exception is thrown if superclass throws it.public boolean postfire()
throws IllegalActionException
postfire in interface Executablepostfire in class DirectorIllegalActionException - Not thrown in this base class.