2 * Copyright (C) 2014, United States Government, as represented by the
3 * Administrator of the National Aeronautics and Space Administration.
6 * The Java Pathfinder core (jpf-core) platform is licensed under the
7 * Apache License, Version 2.0 (the "License"); you may not use this file except
8 * in compliance with the License. You may obtain a copy of the License at
10 * http://www.apache.org/licenses/LICENSE-2.0.
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
18 package gov.nasa.jpf.listener;
20 import gov.nasa.jpf.Config;
21 import gov.nasa.jpf.JPF;
22 import gov.nasa.jpf.ListenerAdapter;
23 import gov.nasa.jpf.jvm.bytecode.INVOKEINTERFACE;
24 import gov.nasa.jpf.jvm.bytecode.JVMFieldInstruction;
25 import gov.nasa.jpf.search.Search;
26 import gov.nasa.jpf.vm.*;
27 import gov.nasa.jpf.vm.bytecode.ReadInstruction;
28 import gov.nasa.jpf.vm.bytecode.WriteInstruction;
29 import gov.nasa.jpf.vm.choice.IntChoiceFromSet;
30 import gov.nasa.jpf.vm.choice.IntIntervalGenerator;
32 import java.io.FileWriter;
33 import java.io.IOException;
34 import java.io.PrintWriter;
36 import java.util.logging.Logger;
39 * This a DPOR implementation for event-driven applications with loops that create cycles of state matching
40 * In this new DPOR algorithm/implementation, each run is terminated iff:
41 * - we find a state that matches a state in a previous run, or
42 * - we have a matched state in the current run that consists of cycles that contain all choices/events.
44 public class DPORStateReducerWithSummary extends ListenerAdapter {
46 // Information printout fields for verbose mode
47 private boolean verboseMode;
48 private boolean stateReductionMode;
49 private final PrintWriter out;
50 private PrintWriter fileWriter;
51 private String detail;
54 private Transition transition;
56 // DPOR-related fields
58 private Integer[] choices;
59 private Integer[] refChoices; // Second reference to a copy of choices (choices may be modified for fair scheduling)
60 private int choiceCounter;
61 private int maxEventChoice;
62 // Data structure to track the events seen by each state to track cycles (containing all events) for termination
63 private HashMap<Integer,Integer> currVisitedStates; // States visited in the current execution (maps to frequency)
64 private HashSet<Integer> justVisitedStates; // States just visited in the previous choice/event
65 private HashSet<Integer> prevVisitedStates; // States visited in the previous execution
66 private HashSet<ClassInfo> nonRelevantClasses;// Class info objects of non-relevant classes
67 private HashSet<FieldInfo> nonRelevantFields; // Field info objects of non-relevant fields
68 private HashSet<FieldInfo> relevantFields; // Field info objects of relevant fields
69 private HashMap<Integer, HashSet<Integer>> stateToEventMap;
70 // Data structure to analyze field Read/Write accesses and conflicts
71 private HashMap<Integer, LinkedList<BacktrackExecution>> backtrackMap; // Track created backtracking points
72 private PriorityQueue<Integer> backtrackStateQ; // Heap that returns the latest state
73 private Execution currentExecution; // Holds the information about the current execution
74 private HashMap<Integer, HashSet<Integer>> doneBacktrackMap; // Record state ID and trace already constructed
75 private MainSummary mainSummary; // Main summary (M) for state ID, event, and R/W set
76 private HashMap<Integer, PredecessorInfo> stateToPredInfo; // Predecessor info indexed by state ID
77 private HashMap<Integer, RestorableVMState> restorableStateMap; // Maps state IDs to the restorable state object
78 private RGraph rGraph; // R-Graph for past executions
81 private boolean isBooleanCGFlipped;
82 private boolean isEndOfExecution;
83 private boolean isNotCheckedForEventsYet;
86 private int numOfTransitions;
88 public DPORStateReducerWithSummary(Config config, JPF jpf) {
89 verboseMode = config.getBoolean("printout_state_transition", false);
90 stateReductionMode = config.getBoolean("activate_state_reduction", true);
92 out = new PrintWriter(System.out, true);
96 String outputFile = config.getString("file_output");
97 if (!outputFile.isEmpty()) {
99 fileWriter = new PrintWriter(new FileWriter(outputFile, true), true);
100 } catch (IOException e) {
103 isBooleanCGFlipped = false;
104 isNotCheckedForEventsYet = true;
105 mainSummary = new MainSummary();
106 numOfTransitions = 0;
107 nonRelevantClasses = new HashSet<>();
108 nonRelevantFields = new HashSet<>();
109 relevantFields = new HashSet<>();
110 restorableStateMap = new HashMap<>();
111 stateToPredInfo = new HashMap<>();
112 initializeStatesVariables();
116 public void stateRestored(Search search) {
118 id = search.getStateId();
119 depth = search.getDepth();
120 transition = search.getTransition();
122 out.println("\n==> DEBUG: The state is restored to state with id: " + id + " -- Transition: " + transition +
123 " and depth: " + depth + "\n");
128 public void searchStarted(Search search) {
130 out.println("\n==> DEBUG: ----------------------------------- search started" + "\n");
135 public void stateAdvanced(Search search) {
137 id = search.getStateId();
138 depth = search.getDepth();
139 transition = search.getTransition();
140 if (search.isNewState()) {
146 if (search.isEndState()) {
147 out.println("\n==> DEBUG: This is the last state!\n");
150 out.println("\n==> DEBUG: The state is forwarded to state with id: " + id + " with depth: " + depth +
151 " which is " + detail + " Transition: " + transition + "\n");
153 if (stateReductionMode) {
154 updateStateInfo(search);
159 public void stateBacktracked(Search search) {
161 id = search.getStateId();
162 depth = search.getDepth();
163 transition = search.getTransition();
166 out.println("\n==> DEBUG: The state is backtracked to state with id: " + id + " -- Transition: " + transition +
167 " and depth: " + depth + "\n");
169 if (stateReductionMode) {
170 updateStateInfo(search);
174 static Logger log = JPF.getLogger("report");
177 public void searchFinished(Search search) {
179 out.println("\n==> DEBUG: ----------------------------------- search finished");
180 out.println("\n==> DEBUG: State reduction mode : " + stateReductionMode);
181 out.println("\n==> DEBUG: Number of transitions : " + numOfTransitions);
182 out.println("\n==> DEBUG: ----------------------------------- search finished" + "\n");
184 fileWriter.println("==> DEBUG: State reduction mode : " + stateReductionMode);
185 fileWriter.println("==> DEBUG: Number of transitions : " + numOfTransitions);
186 fileWriter.println();
192 public void choiceGeneratorRegistered(VM vm, ChoiceGenerator<?> nextCG, ThreadInfo currentThread, Instruction executedInstruction) {
193 if (isNotCheckedForEventsYet) {
194 // Check if this benchmark has no events
195 if (nextCG instanceof IntChoiceFromSet) {
196 IntChoiceFromSet icsCG = (IntChoiceFromSet) nextCG;
197 Integer[] cgChoices = icsCG.getAllChoices();
198 if (cgChoices.length == 2 && cgChoices[0] == 0 && cgChoices[1] == -1) {
199 stateReductionMode = false;
201 isNotCheckedForEventsYet = false;
204 if (stateReductionMode) {
205 // Initialize with necessary information from the CG
206 if (nextCG instanceof IntChoiceFromSet) {
207 IntChoiceFromSet icsCG = (IntChoiceFromSet) nextCG;
208 // Tell JPF that we are performing DPOR
210 if (!isEndOfExecution) {
211 // Check if CG has been initialized, otherwise initialize it
212 Integer[] cgChoices = icsCG.getAllChoices();
213 // Record the events (from choices)
214 if (choices == null) {
216 // Make a copy of choices as reference
217 refChoices = copyChoices(choices);
218 // Record the max event choice (the last element of the choice array)
219 maxEventChoice = choices[choices.length - 1];
221 icsCG.setNewValues(choices);
223 // Use a modulo since choiceCounter is going to keep increasing
224 int choiceIndex = choiceCounter % choices.length;
225 icsCG.advance(choices[choiceIndex]);
227 // Set done all CGs while transitioning to a new execution
235 public void choiceGeneratorAdvanced(VM vm, ChoiceGenerator<?> currentCG) {
236 if (stateReductionMode) {
237 // Check the boolean CG and if it is flipped, we are resetting the analysis
238 if (currentCG instanceof BooleanChoiceGenerator) {
239 if (!isBooleanCGFlipped) {
240 isBooleanCGFlipped = true;
242 // Allocate new objects for data structure when the boolean is flipped from "false" to "true"
243 initializeStatesVariables();
246 // Check every choice generated and ensure fair scheduling!
247 if (currentCG instanceof IntChoiceFromSet) {
248 IntChoiceFromSet icsCG = (IntChoiceFromSet) currentCG;
249 // If this is a new CG then we need to update data structures
250 resetStatesForNewExecution(icsCG, vm);
251 // If we don't see a fair scheduling of events/choices then we have to enforce it
252 ensureFairSchedulingAndSetupTransition(icsCG, vm);
253 // Update backtrack set of an executed event (transition): one transition before this one
254 updateBacktrackSet(currentExecution, choiceCounter - 1);
255 // Explore the next backtrack point:
256 // 1) if we have seen this state or this state contains cycles that involve all events, and
257 // 2) after the current CG is advanced at least once
258 if (choiceCounter > 0 && terminateCurrentExecution()) {
259 exploreNextBacktrackPoints(vm, icsCG);
263 // Map state to event
264 mapStateToEvent(icsCG.getNextChoice());
265 justVisitedStates.clear();
274 public void instructionExecuted(VM vm, ThreadInfo ti, Instruction nextInsn, Instruction executedInsn) {
275 if (stateReductionMode) {
276 if (!isEndOfExecution) {
277 // Has to be initialized and it is a integer CG
278 ChoiceGenerator<?> cg = vm.getChoiceGenerator();
279 if (cg instanceof IntChoiceFromSet || cg instanceof IntIntervalGenerator) {
280 int currentChoice = choiceCounter - 1; // Accumulative choice w.r.t the current trace
281 if (currentChoice < 0) { // If choice is -1 then skip
284 currentChoice = checkAndAdjustChoice(currentChoice, vm);
285 // Record accesses from executed instructions
286 if (executedInsn instanceof JVMFieldInstruction) {
287 // We don't care about libraries
288 if (!isFieldExcluded(executedInsn)) {
289 analyzeReadWriteAccesses(executedInsn, currentChoice);
291 } else if (executedInsn instanceof INVOKEINTERFACE) {
292 // Handle the read/write accesses that occur through iterators
293 analyzeReadWriteAccesses(executedInsn, ti, currentChoice);
305 // This class compactly stores backtrack execution:
306 // 1) backtrack choice list, and
307 // 2) first backtrack point (linking with predecessor execution)
308 private class BacktrackExecution {
309 private Integer[] choiceList;
310 private TransitionEvent firstTransition;
312 public BacktrackExecution(Integer[] choList, TransitionEvent fTransition) {
313 choiceList = choList;
314 firstTransition = fTransition;
317 public Integer[] getChoiceList() {
321 public TransitionEvent getFirstTransition() {
322 return firstTransition;
326 // This class stores a representation of an execution
327 // TODO: We can modify this class to implement some optimization (e.g., clock-vector)
328 // TODO: We basically need to keep track of:
329 // TODO: (1) last read/write access to each memory location
330 // TODO: (2) last state with two or more incoming events/transitions
331 private class Execution {
332 private HashMap<IntChoiceFromSet, Integer> cgToChoiceMap; // Map between CG to choice numbers for O(1) access
333 private ArrayList<TransitionEvent> executionTrace; // The BacktrackPoint objects of this execution
334 private boolean isNew; // Track if this is the first time it is accessed
335 private HashMap<Integer, ReadWriteSet> readWriteFieldsMap; // Record fields that are accessed
338 cgToChoiceMap = new HashMap<>();
339 executionTrace = new ArrayList<>();
341 readWriteFieldsMap = new HashMap<>();
344 public void addTransition(TransitionEvent newBacktrackPoint) {
345 executionTrace.add(newBacktrackPoint);
348 public void clearCGToChoiceMap() {
349 cgToChoiceMap = null;
352 public int getChoiceFromCG(IntChoiceFromSet icsCG) {
353 return cgToChoiceMap.get(icsCG);
356 public ArrayList<TransitionEvent> getExecutionTrace() {
357 return executionTrace;
360 public TransitionEvent getFirstTransition() {
361 return executionTrace.get(0);
364 public TransitionEvent getLastTransition() {
365 return executionTrace.get(executionTrace.size() - 1);
368 public HashMap<Integer, ReadWriteSet> getReadWriteFieldsMap() {
369 return readWriteFieldsMap;
372 public boolean isNew() {
374 // Right after this is accessed, it is no longer new
381 public void mapCGToChoice(IntChoiceFromSet icsCG, int choice) {
382 cgToChoiceMap.put(icsCG, choice);
386 // This class compactly stores a predecessor
387 // 1) a predecessor execution
388 // 2) the predecessor choice in that predecessor execution
389 private class Predecessor {
390 private int choice; // Predecessor choice
391 private Execution execution; // Predecessor execution
393 public Predecessor(int predChoice, Execution predExec) {
395 execution = predExec;
398 public int getChoice() {
402 public Execution getExecution() {
407 // This class represents a R-Graph (in the paper it is a state transition graph R)
408 // This implementation stores reachable transitions from and connects with past executions
409 private class RGraph {
410 private int hiStateId; // Maximum state Id
411 private HashMap<Integer, HashSet<TransitionEvent>> graph; // Reachable transitions from past executions
415 graph = new HashMap<>();
418 public void addReachableTransition(int stateId, TransitionEvent transition) {
419 HashSet<TransitionEvent> transitionSet;
420 if (graph.containsKey(stateId)) {
421 transitionSet = graph.get(stateId);
423 transitionSet = new HashSet<>();
424 graph.put(stateId, transitionSet);
426 // Insert into the set if it does not contain it yet
427 if (!transitionSet.contains(transition)) {
428 transitionSet.add(transition);
430 // Update highest state ID
431 if (hiStateId < stateId) {
436 public HashSet<TransitionEvent> getReachableTransitionsAtState(int stateId) {
437 if (!graph.containsKey(stateId)) {
438 // This is a loop from a transition to itself, so just return the current transition
439 HashSet<TransitionEvent> transitionSet = new HashSet<>();
440 transitionSet.add(currentExecution.getLastTransition());
441 return transitionSet;
443 return graph.get(stateId);
446 public HashSet<TransitionEvent> getReachableTransitions(int stateId) {
447 HashSet<TransitionEvent> reachableTransitions = new HashSet<>();
448 // All transitions from states higher than the given state ID (until the highest state ID) are reachable
449 for(int stId = stateId; stId <= hiStateId; stId++) {
450 // We might encounter state IDs from the first round of Boolean CG
451 // The second round of Boolean CG should consider these new states
452 if (graph.containsKey(stId)) {
453 reachableTransitions.addAll(graph.get(stId));
456 return reachableTransitions;
460 // This class compactly stores Read and Write field sets
461 // We store the field name and its object ID
462 // Sharing the same field means the same field name and object ID
463 private class ReadWriteSet {
464 private HashMap<String, Integer> readMap;
465 private HashMap<String, Integer> writeMap;
467 public ReadWriteSet() {
468 readMap = new HashMap<>();
469 writeMap = new HashMap<>();
472 public void addReadField(String field, int objectId) {
473 readMap.put(field, objectId);
476 public void addWriteField(String field, int objectId) {
477 writeMap.put(field, objectId);
480 public void removeReadField(String field) {
481 readMap.remove(field);
484 public void removeWriteField(String field) {
485 writeMap.remove(field);
488 public boolean isEmpty() {
489 return readMap.isEmpty() && writeMap.isEmpty();
492 public ReadWriteSet getCopy() {
493 ReadWriteSet copyRWSet = new ReadWriteSet();
494 // Copy the maps in the set into the new object copy
495 copyRWSet.setReadMap(new HashMap<>(this.getReadMap()));
496 copyRWSet.setWriteMap(new HashMap<>(this.getWriteMap()));
500 public Set<String> getReadSet() {
501 return readMap.keySet();
504 public Set<String> getWriteSet() {
505 return writeMap.keySet();
508 public boolean readFieldExists(String field) {
509 return readMap.containsKey(field);
512 public boolean writeFieldExists(String field) {
513 return writeMap.containsKey(field);
516 public int readFieldObjectId(String field) {
517 return readMap.get(field);
520 public int writeFieldObjectId(String field) {
521 return writeMap.get(field);
524 private HashMap<String, Integer> getReadMap() {
528 private HashMap<String, Integer> getWriteMap() {
532 private void setReadMap(HashMap<String, Integer> rMap) {
536 private void setWriteMap(HashMap<String, Integer> wMap) {
541 // This class is a representation of a state.
542 // It stores the predecessors to a state.
543 // TODO: We also have stateToEventMap, restorableStateMap, and doneBacktrackMap that has state Id as HashMap key.
544 private class PredecessorInfo {
545 private HashSet<Predecessor> predecessors; // Maps incoming events/transitions (execution and choice)
546 private HashMap<Execution, HashSet<Integer>> recordedPredecessors;
547 // Memorize event and choice number to not record them twice
549 public PredecessorInfo() {
550 predecessors = new HashSet<>();
551 recordedPredecessors = new HashMap<>();
554 public HashSet<Predecessor> getPredecessors() {
558 private boolean isRecordedPredecessor(Execution execution, int choice) {
559 // See if we have recorded this predecessor earlier
560 HashSet<Integer> recordedChoices;
561 if (recordedPredecessors.containsKey(execution)) {
562 recordedChoices = recordedPredecessors.get(execution);
563 if (recordedChoices.contains(choice)) {
567 recordedChoices = new HashSet<>();
568 recordedPredecessors.put(execution, recordedChoices);
570 // Record the choice if we haven't seen it
571 recordedChoices.add(choice);
576 public void recordPredecessor(Execution execution, int choice) {
577 if (!isRecordedPredecessor(execution, choice)) {
578 predecessors.add(new Predecessor(choice, execution));
583 // This class compactly stores transitions:
587 // 4) predecessors (for backward DFS).
588 private class TransitionEvent {
589 private int choice; // Choice chosen at this transition
590 private int choiceCounter; // Choice counter at this transition
591 private Execution execution; // The execution where this transition belongs
592 private int stateId; // State at this transition
593 private IntChoiceFromSet transitionCG; // CG at this transition
595 public TransitionEvent() {
603 public int getChoice() {
607 public int getChoiceCounter() {
608 return choiceCounter;
611 public Execution getExecution() {
615 public int getStateId() {
619 public IntChoiceFromSet getTransitionCG() { return transitionCG; }
621 public void setChoice(int cho) {
625 public void setChoiceCounter(int choCounter) {
626 choiceCounter = choCounter;
629 public void setExecution(Execution exec) {
633 public void setStateId(int stId) {
637 public void setTransitionCG(IntChoiceFromSet cg) {
642 // -- PRIVATE CLASSES RELATED TO SUMMARY
643 // This class stores the main summary of states
644 // 1) Main mapping between state ID and state summary
645 // 2) State summary is a mapping between events (i.e., event choices) and their respective R/W sets
646 private class MainSummary {
647 private HashMap<Integer, HashMap<Integer, ReadWriteSet>> mainSummary;
649 public MainSummary() {
650 mainSummary = new HashMap<>();
653 public Set<Integer> getEventChoicesAtStateId(int stateId) {
654 HashMap<Integer, ReadWriteSet> stateSummary = mainSummary.get(stateId);
655 // Return a new set since this might get updated concurrently
656 return new HashSet<>(stateSummary.keySet());
659 public ReadWriteSet getRWSetForEventChoiceAtState(int eventChoice, int stateId) {
660 HashMap<Integer, ReadWriteSet> stateSummary = mainSummary.get(stateId);
661 return stateSummary.get(eventChoice);
664 public Set<Integer> getStateIds() {
665 return mainSummary.keySet();
668 private ReadWriteSet performUnion(ReadWriteSet recordedRWSet, ReadWriteSet rwSet) {
669 // Combine the same write accesses and record in the recordedRWSet
670 HashMap<String, Integer> recordedWriteMap = recordedRWSet.getWriteMap();
671 HashMap<String, Integer> writeMap = rwSet.getWriteMap();
672 for(Map.Entry<String, Integer> entry : recordedWriteMap.entrySet()) {
673 String writeField = entry.getKey();
674 // Remove the entry from rwSet if both field and object ID are the same
675 if (writeMap.containsKey(writeField) &&
676 (writeMap.get(writeField).equals(recordedWriteMap.get(writeField)))) {
677 writeMap.remove(writeField);
680 // Then add the rest (fields in rwSet but not in recordedRWSet)
681 // into the recorded map because these will be traversed
682 recordedWriteMap.putAll(writeMap);
683 // Combine the same read accesses and record in the recordedRWSet
684 HashMap<String, Integer> recordedReadMap = recordedRWSet.getReadMap();
685 HashMap<String, Integer> readMap = rwSet.getReadMap();
686 for(Map.Entry<String, Integer> entry : recordedReadMap.entrySet()) {
687 String readField = entry.getKey();
688 // Remove the entry from rwSet if both field and object ID are the same
689 if (readMap.containsKey(readField) &&
690 (readMap.get(readField).equals(recordedReadMap.get(readField)))) {
691 readMap.remove(readField);
694 // Then add the rest (fields in rwSet but not in recordedRWSet)
695 // into the recorded map because these will be traversed
696 recordedReadMap.putAll(readMap);
701 public ReadWriteSet updateStateSummary(int stateId, int eventChoice, ReadWriteSet rwSet) {
702 // If the state Id has not existed, insert the StateSummary object
703 // If the state Id has existed, find the event choice:
704 // 1) If the event choice has not existed, insert the ReadWriteSet object
705 // 2) If the event choice has existed, perform union between the two ReadWriteSet objects
706 if (!rwSet.isEmpty()) {
707 HashMap<Integer, ReadWriteSet> stateSummary;
708 if (!mainSummary.containsKey(stateId)) {
709 stateSummary = new HashMap<>();
710 stateSummary.put(eventChoice, rwSet.getCopy());
711 mainSummary.put(stateId, stateSummary);
713 stateSummary = mainSummary.get(stateId);
714 if (!stateSummary.containsKey(eventChoice)) {
715 stateSummary.put(eventChoice, rwSet.getCopy());
717 rwSet = performUnion(stateSummary.get(eventChoice), rwSet);
726 private final static String DO_CALL_METHOD = "doCall";
727 // We exclude fields that come from libraries (Java and Groovy), and also the infrastructure
728 private final static String[] EXCLUDED_FIELDS_CONTAINS_LIST = {"_closure"};
729 private final static String[] EXCLUDED_FIELDS_ENDS_WITH_LIST =
730 // Groovy library created fields
731 {"stMC", "callSiteArray", "metaClass", "staticClassInfo", "__constructor__",
733 "sendEvent", "Object", "reference", "location", "app", "state", "log", "functionList", "objectList",
734 "eventList", "valueList", "settings", "printToConsole", "app1", "app2"};
735 private final static String[] EXCLUDED_FIELDS_STARTS_WITH_LIST =
736 // Java and Groovy libraries
737 { "java", "org", "sun", "com", "gov", "groovy"};
738 private final static String[] EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST = {"Event"};
739 private final static String GET_PROPERTY_METHOD =
740 "invokeinterface org.codehaus.groovy.runtime.callsite.CallSite.callGetProperty";
741 private final static String GROOVY_CALLSITE_LIB = "org.codehaus.groovy.runtime.callsite";
742 private final static String JAVA_INTEGER = "int";
743 private final static String JAVA_STRING_LIB = "java.lang.String";
746 private Integer[] copyChoices(Integer[] choicesToCopy) {
748 Integer[] copyOfChoices = new Integer[choicesToCopy.length];
749 System.arraycopy(choicesToCopy, 0, copyOfChoices, 0, choicesToCopy.length);
750 return copyOfChoices;
753 private void ensureFairSchedulingAndSetupTransition(IntChoiceFromSet icsCG, VM vm) {
754 // Check the next choice and if the value is not the same as the expected then force the expected value
755 int choiceIndex = choiceCounter % refChoices.length;
756 int nextChoice = icsCG.getNextChoice();
757 if (refChoices[choiceIndex] != nextChoice) {
758 int expectedChoice = refChoices[choiceIndex];
759 int currCGIndex = icsCG.getNextChoiceIndex();
760 if ((currCGIndex >= 0) && (currCGIndex < refChoices.length)) {
761 icsCG.setChoice(currCGIndex, expectedChoice);
764 // Get state ID and associate it with this transition
765 int stateId = vm.getStateId();
766 TransitionEvent transition = setupTransition(icsCG, stateId, choiceIndex);
767 // Add new transition to the current execution and map it in R-Graph
768 for (Integer stId : justVisitedStates) { // Map this transition to all the previously passed states
769 rGraph.addReachableTransition(stId, transition);
771 currentExecution.mapCGToChoice(icsCG, choiceCounter);
772 // Store restorable state object for this state (always store the latest)
773 if (!restorableStateMap.containsKey(stateId)) {
774 RestorableVMState restorableState = vm.getRestorableState();
775 restorableStateMap.put(stateId, restorableState);
779 private TransitionEvent setupTransition(IntChoiceFromSet icsCG, int stateId, int choiceIndex) {
780 // Get a new transition
781 TransitionEvent transition;
782 if (currentExecution.isNew()) {
783 // We need to handle the first transition differently because this has a predecessor execution
784 transition = currentExecution.getFirstTransition();
786 transition = new TransitionEvent();
787 currentExecution.addTransition(transition);
788 addPredecessors(stateId);
790 transition.setExecution(currentExecution);
791 transition.setTransitionCG(icsCG);
792 transition.setStateId(stateId);
793 transition.setChoice(refChoices[choiceIndex]);
794 transition.setChoiceCounter(choiceCounter);
799 // --- Functions related to cycle detection and reachability graph
801 // Detect cycles in the current execution/trace
802 // We terminate the execution iff:
803 // (1) the state has been visited in the current execution
804 // (2) the state has one or more cycles that involve all the events
805 // With simple approach we only need to check for a re-visited state.
806 // Basically, we have to check that we have executed all events between two occurrences of such state.
807 private boolean completeFullCycle(int stId) {
808 // False if the state ID hasn't been recorded
809 if (!stateToEventMap.containsKey(stId)) {
812 HashSet<Integer> visitedEvents = stateToEventMap.get(stId);
813 // Check if this set contains all the event choices
814 // If not then this is not the terminating condition
815 for(int i=0; i<=maxEventChoice; i++) {
816 if (!visitedEvents.contains(i)) {
823 private void initializeStatesVariables() {
830 if (!isBooleanCGFlipped) {
831 currVisitedStates = new HashMap<>();
832 justVisitedStates = new HashSet<>();
833 prevVisitedStates = new HashSet<>();
834 stateToEventMap = new HashMap<>();
836 currVisitedStates.clear();
837 justVisitedStates.clear();
838 prevVisitedStates.clear();
839 stateToEventMap.clear();
842 if (!isBooleanCGFlipped) {
843 backtrackMap = new HashMap<>();
845 backtrackMap.clear();
847 backtrackStateQ = new PriorityQueue<>(Collections.reverseOrder());
848 currentExecution = new Execution();
849 currentExecution.addTransition(new TransitionEvent()); // Always start with 1 backtrack point
850 if (!isBooleanCGFlipped) {
851 doneBacktrackMap = new HashMap<>();
853 doneBacktrackMap.clear();
855 rGraph = new RGraph();
857 isEndOfExecution = false;
860 private void mapStateToEvent(int nextChoiceValue) {
861 // Update all states with this event/choice
862 // This means that all past states now see this transition
863 Set<Integer> stateSet = stateToEventMap.keySet();
864 for(Integer stateId : stateSet) {
865 HashSet<Integer> eventSet = stateToEventMap.get(stateId);
866 eventSet.add(nextChoiceValue);
870 private boolean terminateCurrentExecution() {
871 // We need to check all the states that have just been visited
872 // Often a transition (choice/event) can result into forwarding/backtracking to a number of states
873 boolean terminate = false;
874 Set<Integer> mainStateIds = mainSummary.getStateIds();
875 for(Integer stateId : justVisitedStates) {
876 // We exclude states that are produced by other CGs that are not integer CG
877 // When we encounter these states, then we should also encounter the corresponding integer CG state ID
878 if (mainStateIds.contains(stateId)) {
879 // We perform updates on backtrack sets for every
880 if (prevVisitedStates.contains(stateId) || completeFullCycle(stateId)) {
881 updateBacktrackSetsFromGraph(stateId, currentExecution, choiceCounter - 1);
884 // If frequency > 1 then this means we have visited this stateId more than once in the current execution
885 if (currVisitedStates.containsKey(stateId) && currVisitedStates.get(stateId) > 1) {
886 updateBacktrackSetsFromGraph(stateId, currentExecution, choiceCounter - 1);
893 private void updateStateInfo(Search search) {
894 // Update the state variables
895 int stateId = search.getStateId();
896 // Insert state ID into the map if it is new
897 if (!stateToEventMap.containsKey(stateId)) {
898 HashSet<Integer> eventSet = new HashSet<>();
899 stateToEventMap.put(stateId, eventSet);
901 addPredecessorToRevisitedState(stateId);
902 justVisitedStates.add(stateId);
903 if (!prevVisitedStates.contains(stateId)) {
904 // It is a currently visited states if the state has not been seen in previous executions
906 if (currVisitedStates.containsKey(stateId)) {
907 frequency = currVisitedStates.get(stateId);
909 currVisitedStates.put(stateId, frequency + 1); // Increment frequency counter
913 // --- Functions related to Read/Write access analysis on shared fields
915 private void addNewBacktrackPoint(int stateId, Integer[] newChoiceList, TransitionEvent conflictTransition) {
916 // Insert backtrack point to the right state ID
917 LinkedList<BacktrackExecution> backtrackExecList;
918 if (backtrackMap.containsKey(stateId)) {
919 backtrackExecList = backtrackMap.get(stateId);
921 backtrackExecList = new LinkedList<>();
922 backtrackMap.put(stateId, backtrackExecList);
924 // Add the new backtrack execution object
925 TransitionEvent backtrackTransition = new TransitionEvent();
926 backtrackExecList.addFirst(new BacktrackExecution(newChoiceList, backtrackTransition));
927 // Add to priority queue
928 if (!backtrackStateQ.contains(stateId)) {
929 backtrackStateQ.add(stateId);
933 private void addPredecessors(int stateId) {
934 PredecessorInfo predecessorInfo;
935 if (!stateToPredInfo.containsKey(stateId)) {
936 predecessorInfo = new PredecessorInfo();
937 stateToPredInfo.put(stateId, predecessorInfo);
938 } else { // This is a new state Id
939 predecessorInfo = stateToPredInfo.get(stateId);
941 predecessorInfo.recordPredecessor(currentExecution, choiceCounter - 1);
944 // Analyze Read/Write accesses that are directly invoked on fields
945 private void analyzeReadWriteAccesses(Instruction executedInsn, int currentChoice) {
946 // Get the field info
947 FieldInfo fieldInfo = ((JVMFieldInstruction) executedInsn).getFieldInfo();
948 // Analyze only after being initialized
949 String fieldClass = fieldInfo.getFullName();
950 // Do the analysis to get Read and Write accesses to fields
951 ReadWriteSet rwSet = getReadWriteSet(currentChoice);
952 int objectId = fieldInfo.getClassInfo().getClassObjectRef();
953 // Record the field in the map
954 if (executedInsn instanceof WriteInstruction) {
955 // We first check the non-relevant fields set
956 if (!nonRelevantFields.contains(fieldInfo)) {
957 // Exclude certain field writes because of infrastructure needs, e.g., Event class field writes
958 for (String str : EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST) {
959 if (fieldClass.startsWith(str)) {
960 nonRelevantFields.add(fieldInfo);
965 // If we have this field in the non-relevant fields set then we return right away
968 rwSet.addWriteField(fieldClass, objectId);
969 } else if (executedInsn instanceof ReadInstruction) {
970 rwSet.addReadField(fieldClass, objectId);
974 // Analyze Read accesses that are indirect (performed through iterators)
975 // These accesses are marked by certain bytecode instructions, e.g., INVOKEINTERFACE
976 private void analyzeReadWriteAccesses(Instruction instruction, ThreadInfo ti, int currentChoice) {
978 INVOKEINTERFACE insn = (INVOKEINTERFACE) instruction;
979 if (insn.toString().startsWith(GET_PROPERTY_METHOD) &&
980 insn.getMethodInfo().getName().equals(DO_CALL_METHOD)) {
981 // Extract info from the stack frame
982 StackFrame frame = ti.getTopFrame();
983 int[] frameSlots = frame.getSlots();
984 // Get the Groovy callsite library at index 0
985 ElementInfo eiCallsite = VM.getVM().getHeap().get(frameSlots[0]);
986 if (!eiCallsite.getClassInfo().getName().startsWith(GROOVY_CALLSITE_LIB)) {
989 // Get the iterated object whose property is accessed
990 ElementInfo eiAccessObj = VM.getVM().getHeap().get(frameSlots[1]);
991 if (eiAccessObj == null) {
994 // We exclude library classes (they start with java, org, etc.) and some more
995 ClassInfo classInfo = eiAccessObj.getClassInfo();
996 String objClassName = classInfo.getName();
997 // Check if this class info is part of the non-relevant classes set already
998 if (!nonRelevantClasses.contains(classInfo)) {
999 if (excludeThisForItStartsWith(EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST, objClassName) ||
1000 excludeThisForItStartsWith(EXCLUDED_FIELDS_STARTS_WITH_LIST, objClassName)) {
1001 nonRelevantClasses.add(classInfo);
1005 // If it is part of the non-relevant classes set then return immediately
1008 // Extract fields from this object and put them into the read write
1009 int numOfFields = eiAccessObj.getNumberOfFields();
1010 for(int i=0; i<numOfFields; i++) {
1011 FieldInfo fieldInfo = eiAccessObj.getFieldInfo(i);
1012 if (fieldInfo.getType().equals(JAVA_STRING_LIB) || fieldInfo.getType().equals(JAVA_INTEGER)) {
1013 String fieldClass = fieldInfo.getFullName();
1014 ReadWriteSet rwSet = getReadWriteSet(currentChoice);
1015 int objectId = fieldInfo.getClassInfo().getClassObjectRef();
1016 // Record the field in the map
1017 rwSet.addReadField(fieldClass, objectId);
1023 private int checkAndAdjustChoice(int currentChoice, VM vm) {
1024 // If current choice is not the same, then this is caused by the firing of IntIntervalGenerator
1025 // for certain method calls in the infrastructure, e.g., eventSince()
1026 ChoiceGenerator<?> currentCG = vm.getChoiceGenerator();
1027 // This is the main event CG
1028 if (currentCG instanceof IntIntervalGenerator) {
1029 // This is the interval CG used in device handlers
1030 ChoiceGenerator<?> parentCG = ((IntIntervalGenerator) currentCG).getPreviousChoiceGenerator();
1031 // Iterate until we find the IntChoiceFromSet CG
1032 while (!(parentCG instanceof IntChoiceFromSet)) {
1033 parentCG = ((IntIntervalGenerator) parentCG).getPreviousChoiceGenerator();
1035 // Find the choice related to the IntIntervalGenerator CG from the map
1036 currentChoice = currentExecution.getChoiceFromCG((IntChoiceFromSet) parentCG);
1038 return currentChoice;
1041 private void createBacktrackingPoint(int eventChoice, Execution conflictExecution, int conflictChoice) {
1042 // Create a new list of choices for backtrack based on the current choice and conflicting event number
1043 // E.g. if we have a conflict between 1 and 3, then we create the list {3, 1, 0, 2}
1044 // for the original set {0, 1, 2, 3}
1046 // eventChoice represents the event/transaction that will be put into the backtracking set of
1047 // conflictExecution/conflictChoice
1048 Integer[] newChoiceList = new Integer[refChoices.length];
1049 ArrayList<TransitionEvent> conflictTrace = conflictExecution.getExecutionTrace();
1050 int stateId = conflictTrace.get(conflictChoice).getStateId();
1051 // Check if this trace has been done from this state
1052 if (isTraceAlreadyConstructed(eventChoice, stateId)) {
1055 // Put the conflicting event numbers first and reverse the order
1056 newChoiceList[0] = eventChoice;
1057 // Put the rest of the event numbers into the array starting from the minimum to the upper bound
1058 for (int i = 0, j = 1; i < refChoices.length; i++) {
1059 if (refChoices[i] != newChoiceList[0]) {
1060 newChoiceList[j] = refChoices[i];
1064 // Predecessor of the new backtrack point is the same as the conflict point's
1065 addNewBacktrackPoint(stateId, newChoiceList, conflictTrace.get(conflictChoice));
1068 private boolean excludeThisForItContains(String[] excludedStrings, String className) {
1069 for (String excludedField : excludedStrings) {
1070 if (className.contains(excludedField)) {
1077 private boolean excludeThisForItEndsWith(String[] excludedStrings, String className) {
1078 for (String excludedField : excludedStrings) {
1079 if (className.endsWith(excludedField)) {
1086 private boolean excludeThisForItStartsWith(String[] excludedStrings, String className) {
1087 for (String excludedField : excludedStrings) {
1088 if (className.startsWith(excludedField)) {
1095 private void exploreNextBacktrackPoints(VM vm, IntChoiceFromSet icsCG) {
1096 // Check if we are reaching the end of our execution: no more backtracking points to explore
1097 // cgMap, backtrackMap, backtrackStateQ are updated simultaneously (checking backtrackStateQ is enough)
1098 if (!backtrackStateQ.isEmpty()) {
1099 // Set done all the other backtrack points
1100 for (TransitionEvent backtrackTransition : currentExecution.getExecutionTrace()) {
1101 backtrackTransition.getTransitionCG().setDone();
1103 // Reset the next backtrack point with the latest state
1104 int hiStateId = backtrackStateQ.peek();
1105 // Restore the state first if necessary
1106 if (vm.getStateId() != hiStateId) {
1107 RestorableVMState restorableState = restorableStateMap.get(hiStateId);
1108 vm.restoreState(restorableState);
1110 // Set the backtrack CG
1111 IntChoiceFromSet backtrackCG = (IntChoiceFromSet) vm.getChoiceGenerator();
1112 setBacktrackCG(hiStateId, backtrackCG);
1114 // Set done this last CG (we save a few rounds)
1117 // Save all the visited states when starting a new execution of trace
1118 prevVisitedStates.addAll(currVisitedStates.keySet());
1119 // This marks a transitional period to the new CG
1120 isEndOfExecution = true;
1123 private boolean isConflictFound(int eventChoice, Execution conflictExecution, int conflictChoice,
1124 ReadWriteSet currRWSet) {
1125 // conflictExecution/conflictChoice represent a predecessor event/transaction that can potentially have a conflict
1126 ArrayList<TransitionEvent> conflictTrace = conflictExecution.getExecutionTrace();
1127 HashMap<Integer, ReadWriteSet> confRWFieldsMap = conflictExecution.getReadWriteFieldsMap();
1128 // Skip if this event does not have any Read/Write set or the two events are basically the same event (number)
1129 if (!confRWFieldsMap.containsKey(conflictChoice) || eventChoice == conflictTrace.get(conflictChoice).getChoice()) {
1132 // R/W set of choice/event that may have a potential conflict
1133 ReadWriteSet confRWSet = confRWFieldsMap.get(conflictChoice);
1134 // Check for conflicts with Read and Write fields for Write instructions
1135 Set<String> currWriteSet = currRWSet.getWriteSet();
1136 for(String writeField : currWriteSet) {
1137 int currObjId = currRWSet.writeFieldObjectId(writeField);
1138 if ((confRWSet.readFieldExists(writeField) && confRWSet.readFieldObjectId(writeField) == currObjId) ||
1139 (confRWSet.writeFieldExists(writeField) && confRWSet.writeFieldObjectId(writeField) == currObjId)) {
1140 // Remove this from the write set as we are tracking per memory location
1141 currRWSet.removeWriteField(writeField);
1145 // Check for conflicts with Write fields for Read instructions
1146 Set<String> currReadSet = currRWSet.getReadSet();
1147 for(String readField : currReadSet) {
1148 int currObjId = currRWSet.readFieldObjectId(readField);
1149 if (confRWSet.writeFieldExists(readField) && confRWSet.writeFieldObjectId(readField) == currObjId) {
1150 // Remove this from the read set as we are tracking per memory location
1151 currRWSet.removeReadField(readField);
1155 // Return false if no conflict is found
1159 private boolean isFieldExcluded(Instruction executedInsn) {
1160 // Get the field info
1161 FieldInfo fieldInfo = ((JVMFieldInstruction) executedInsn).getFieldInfo();
1162 // Check if the non-relevant fields set already has it
1163 if (nonRelevantFields.contains(fieldInfo)) {
1166 // Check if the relevant fields set already has it
1167 if (relevantFields.contains(fieldInfo)) {
1170 // Analyze only after being initialized
1171 String field = fieldInfo.getFullName();
1172 // Check against "starts-with", "ends-with", and "contains" list
1173 if (excludeThisForItStartsWith(EXCLUDED_FIELDS_STARTS_WITH_LIST, field) ||
1174 excludeThisForItEndsWith(EXCLUDED_FIELDS_ENDS_WITH_LIST, field) ||
1175 excludeThisForItContains(EXCLUDED_FIELDS_CONTAINS_LIST, field)) {
1176 nonRelevantFields.add(fieldInfo);
1179 relevantFields.add(fieldInfo);
1183 // Check if this trace is already constructed
1184 private boolean isTraceAlreadyConstructed(int firstChoice, int stateId) {
1185 // Concatenate state ID and only the first event in the string, e.g., "1:1 for the trace 10234 at state 1"
1186 // Check if the trace has been constructed as a backtrack point for this state
1187 // TODO: THIS IS AN OPTIMIZATION!
1188 HashSet<Integer> choiceSet;
1189 if (doneBacktrackMap.containsKey(stateId)) {
1190 choiceSet = doneBacktrackMap.get(stateId);
1191 if (choiceSet.contains(firstChoice)) {
1195 choiceSet = new HashSet<>();
1196 doneBacktrackMap.put(stateId, choiceSet);
1198 choiceSet.add(firstChoice);
1203 private HashSet<Predecessor> getPredecessors(int stateId) {
1204 // Get a set of predecessors for this state ID
1205 HashSet<Predecessor> predecessors;
1206 if (stateToPredInfo.containsKey(stateId)) {
1207 PredecessorInfo predecessorInfo = stateToPredInfo.get(stateId);
1208 predecessors = predecessorInfo.getPredecessors();
1210 predecessors = new HashSet<>();
1213 return predecessors;
1216 private ReadWriteSet getReadWriteSet(int currentChoice) {
1217 // Do the analysis to get Read and Write accesses to fields
1219 // We already have an entry
1220 HashMap<Integer, ReadWriteSet> currReadWriteFieldsMap = currentExecution.getReadWriteFieldsMap();
1221 if (currReadWriteFieldsMap.containsKey(currentChoice)) {
1222 rwSet = currReadWriteFieldsMap.get(currentChoice);
1223 } else { // We need to create a new entry
1224 rwSet = new ReadWriteSet();
1225 currReadWriteFieldsMap.put(currentChoice, rwSet);
1230 // Reset data structure for each new execution
1231 private void resetStatesForNewExecution(IntChoiceFromSet icsCG, VM vm) {
1232 if (choices == null || choices != icsCG.getAllChoices()) {
1233 // Reset state variables
1235 choices = icsCG.getAllChoices();
1236 refChoices = copyChoices(choices);
1237 // Clear data structures
1238 currVisitedStates.clear();
1239 stateToEventMap.clear();
1240 isEndOfExecution = false;
1244 // Set a backtrack point for a particular state
1245 private void setBacktrackCG(int stateId, IntChoiceFromSet backtrackCG) {
1246 // Set a backtrack CG based on a state ID
1247 LinkedList<BacktrackExecution> backtrackExecutions = backtrackMap.get(stateId);
1248 BacktrackExecution backtrackExecution = backtrackExecutions.removeLast();
1249 backtrackCG.setNewValues(backtrackExecution.getChoiceList()); // Get the last from the queue
1250 backtrackCG.setStateId(stateId);
1251 backtrackCG.reset();
1252 // Update current execution with this new execution
1253 Execution newExecution = new Execution();
1254 TransitionEvent firstTransition = backtrackExecution.getFirstTransition();
1255 newExecution.addTransition(firstTransition);
1256 // Try to free some memory since this map is only used for the current execution
1257 currentExecution.clearCGToChoiceMap();
1258 currentExecution = newExecution;
1259 // Remove from the queue if we don't have more backtrack points for that state
1260 if (backtrackExecutions.isEmpty()) {
1261 backtrackMap.remove(stateId);
1262 backtrackStateQ.remove(stateId);
1266 // Update backtrack sets
1267 // 1) recursively, and
1268 // 2) track accesses per memory location (per shared variable/field)
1269 private void updateBacktrackSet(Execution execution, int currentChoice) {
1270 // Copy ReadWriteSet object
1271 HashMap<Integer, ReadWriteSet> currRWFieldsMap = execution.getReadWriteFieldsMap();
1272 ReadWriteSet currRWSet = currRWFieldsMap.get(currentChoice);
1273 if (currRWSet == null) {
1276 currRWSet = currRWSet.getCopy();
1277 // Memorize visited TransitionEvent object while performing backward DFS to avoid getting caught up in a cycle
1278 HashSet<TransitionEvent> visited = new HashSet<>();
1279 // Conflict TransitionEvent is essentially the current TransitionEvent
1280 TransitionEvent confTrans = execution.getExecutionTrace().get(currentChoice);
1281 // Update backtrack set recursively
1282 updateBacktrackSetDFS(execution, currentChoice, confTrans.getChoice(), currRWSet, visited);
1285 private void updateBacktrackSetDFS(Execution execution, int currentChoice, int conflictEventChoice,
1286 ReadWriteSet currRWSet, HashSet<TransitionEvent> visited) {
1287 TransitionEvent currTrans = execution.getExecutionTrace().get(currentChoice);
1288 // Record this transition into the state summary of main summary
1289 currRWSet = mainSummary.updateStateSummary(currTrans.getStateId(), conflictEventChoice, currRWSet);
1290 // Halt when we have visited this transition (in a cycle)
1291 if (visited.contains(currTrans)) {
1294 visited.add(currTrans);
1295 // Check the predecessors only if the set is not empty
1296 if (!currRWSet.isEmpty()) {
1297 // Explore all predecessors
1298 for (Predecessor predecessor : getPredecessors(currTrans.getStateId())) {
1299 // Get the predecessor (previous conflict choice)
1300 int predecessorChoice = predecessor.getChoice();
1301 Execution predecessorExecution = predecessor.getExecution();
1302 // Push up one happens-before transition
1303 int newConflictEventChoice = conflictEventChoice;
1304 // Check if a conflict is found
1305 ReadWriteSet newCurrRWSet = currRWSet.getCopy();
1306 if (isConflictFound(conflictEventChoice, predecessorExecution, predecessorChoice, newCurrRWSet)) {
1307 createBacktrackingPoint(conflictEventChoice, predecessorExecution, predecessorChoice);
1308 // We need to extract the pushed happens-before event choice from the predecessor execution and choice
1309 newConflictEventChoice = predecessorExecution.getExecutionTrace().get(predecessorChoice).getChoice();
1311 // Continue performing DFS if conflict is not found
1312 updateBacktrackSetDFS(predecessorExecution, predecessorChoice, newConflictEventChoice,
1313 newCurrRWSet, visited);
1318 // --- Functions related to the reachability analysis when there is a state match
1320 private void addPredecessorToRevisitedState(int stateId) {
1321 // Perform this analysis only when:
1322 // 1) this is not during a switch to a new execution,
1323 // 2) at least 2 choices/events have been explored (choiceCounter > 1),
1324 // 3) state > 0 (state 0 is for boolean CG)
1325 if (!isEndOfExecution && choiceCounter > 1 && stateId > 0) {
1326 if ((currVisitedStates.containsKey(stateId) && currVisitedStates.get(stateId) > 1) ||
1327 prevVisitedStates.contains(stateId)) {
1328 // Record a new predecessor for a revisited state
1329 addPredecessors(stateId);
1334 // Update the backtrack sets from previous executions
1335 private void updateBacktrackSetsFromGraph(int stateId, Execution currExecution, int currChoice) {
1336 // Get events/choices at this state ID
1337 Set<Integer> eventChoicesAtStateId = mainSummary.getEventChoicesAtStateId(stateId);
1338 for (Integer eventChoice : eventChoicesAtStateId) {
1339 // Get the ReadWriteSet object for this event at state ID
1340 ReadWriteSet rwSet = mainSummary.getRWSetForEventChoiceAtState(eventChoice, stateId);
1341 // Memorize visited TransitionEvent object while performing backward DFS to avoid getting caught up in a cycle
1342 HashSet<TransitionEvent> visited = new HashSet<>();
1343 // Update the backtrack sets recursively
1344 updateBacktrackSetDFS(currExecution, currChoice, eventChoice, rwSet.getCopy(), visited);