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 (stateReductionMode) {
194 if (isNotCheckedForEventsYet) {
195 // Check if this benchmark has no events
196 if (nextCG instanceof IntChoiceFromSet) {
197 IntChoiceFromSet icsCG = (IntChoiceFromSet) nextCG;
198 Integer[] cgChoices = icsCG.getAllChoices();
199 if (cgChoices.length == 2 && cgChoices[0] == 0 && cgChoices[1] == -1) {
200 // This means the benchmark only has 2 choices, i.e., 0 and -1 which means that it has no events
201 stateReductionMode = false;
203 isNotCheckedForEventsYet = false;
206 // Initialize with necessary information from the CG
207 if (nextCG instanceof IntChoiceFromSet) {
208 IntChoiceFromSet icsCG = (IntChoiceFromSet) nextCG;
209 // Tell JPF that we are performing DPOR
211 if (!isEndOfExecution) {
212 // Check if CG has been initialized, otherwise initialize it
213 Integer[] cgChoices = icsCG.getAllChoices();
214 // Record the events (from choices)
215 if (choices == null) {
217 // Make a copy of choices as reference
218 refChoices = copyChoices(choices);
219 // Record the max event choice (the last element of the choice array)
220 maxEventChoice = choices[choices.length - 1];
222 icsCG.setNewValues(choices);
224 // Use a modulo since choiceCounter is going to keep increasing
225 int choiceIndex = choiceCounter % choices.length;
226 icsCG.advance(choices[choiceIndex]);
228 // Set done all CGs while transitioning to a new execution
237 public void choiceGeneratorAdvanced(VM vm, ChoiceGenerator<?> currentCG) {
238 if (stateReductionMode) {
239 // Check the boolean CG and if it is flipped, we are resetting the analysis
240 if (currentCG instanceof BooleanChoiceGenerator) {
241 if (!isBooleanCGFlipped) {
242 isBooleanCGFlipped = true;
244 // Allocate new objects for data structure when the boolean is flipped from "false" to "true"
245 initializeStatesVariables();
248 // Check every choice generated and ensure fair scheduling!
249 if (currentCG instanceof IntChoiceFromSet) {
250 IntChoiceFromSet icsCG = (IntChoiceFromSet) currentCG;
251 // If this is a new CG then we need to update data structures
252 resetStatesForNewExecution(icsCG, vm);
253 // If we don't see a fair scheduling of events/choices then we have to enforce it
254 ensureFairSchedulingAndSetupTransition(icsCG, vm);
255 // Update backtrack set of an executed event (transition): one transition before this one
256 updateBacktrackSet(currentExecution, choiceCounter - 1);
257 // Explore the next backtrack point:
258 // 1) if we have seen this state or this state contains cycles that involve all events, and
259 // 2) after the current CG is advanced at least once
260 if (choiceCounter > 0 && terminateCurrentExecution()) {
261 exploreNextBacktrackPoints(vm, icsCG);
265 // Map state to event
266 mapStateToEvent(icsCG.getNextChoice());
267 justVisitedStates.clear();
276 public void instructionExecuted(VM vm, ThreadInfo ti, Instruction nextInsn, Instruction executedInsn) {
277 if (stateReductionMode) {
278 if (!isEndOfExecution) {
279 // Has to be initialized and it is a integer CG
280 ChoiceGenerator<?> cg = vm.getChoiceGenerator();
281 if (cg instanceof IntChoiceFromSet || cg instanceof IntIntervalGenerator) {
282 int currentChoice = choiceCounter - 1; // Accumulative choice w.r.t the current trace
283 if (currentChoice < 0) { // If choice is -1 then skip
286 currentChoice = checkAndAdjustChoice(currentChoice, vm);
287 // Record accesses from executed instructions
288 if (executedInsn instanceof JVMFieldInstruction) {
289 // We don't care about libraries
290 if (!isFieldExcluded(executedInsn)) {
291 analyzeReadWriteAccesses(executedInsn, currentChoice);
293 } else if (executedInsn instanceof INVOKEINTERFACE) {
294 // Handle the read/write accesses that occur through iterators
295 analyzeReadWriteAccesses(executedInsn, ti, currentChoice);
307 // This class compactly stores backtrack execution:
308 // 1) backtrack choice list, and
309 // 2) first backtrack point (linking with predecessor execution)
310 private class BacktrackExecution {
311 private Integer[] choiceList;
312 private TransitionEvent firstTransition;
314 public BacktrackExecution(Integer[] choList, TransitionEvent fTransition) {
315 choiceList = choList;
316 firstTransition = fTransition;
319 public Integer[] getChoiceList() {
323 public TransitionEvent getFirstTransition() {
324 return firstTransition;
328 // This class stores a representation of an execution
329 // TODO: We can modify this class to implement some optimization (e.g., clock-vector)
330 // TODO: We basically need to keep track of:
331 // TODO: (1) last read/write access to each memory location
332 // TODO: (2) last state with two or more incoming events/transitions
333 private class Execution {
334 private HashMap<IntChoiceFromSet, Integer> cgToChoiceMap; // Map between CG to choice numbers for O(1) access
335 private ArrayList<TransitionEvent> executionTrace; // The BacktrackPoint objects of this execution
336 private boolean isNew; // Track if this is the first time it is accessed
337 private HashMap<Integer, ReadWriteSet> readWriteFieldsMap; // Record fields that are accessed
340 cgToChoiceMap = new HashMap<>();
341 executionTrace = new ArrayList<>();
343 readWriteFieldsMap = new HashMap<>();
346 public void addTransition(TransitionEvent newBacktrackPoint) {
347 executionTrace.add(newBacktrackPoint);
350 public void clearCGToChoiceMap() {
351 cgToChoiceMap = null;
354 public int getChoiceFromCG(IntChoiceFromSet icsCG) {
355 return cgToChoiceMap.get(icsCG);
358 public ArrayList<TransitionEvent> getExecutionTrace() {
359 return executionTrace;
362 public TransitionEvent getFirstTransition() {
363 return executionTrace.get(0);
366 public TransitionEvent getLastTransition() {
367 return executionTrace.get(executionTrace.size() - 1);
370 public HashMap<Integer, ReadWriteSet> getReadWriteFieldsMap() {
371 return readWriteFieldsMap;
374 public boolean isNew() {
376 // Right after this is accessed, it is no longer new
383 public void mapCGToChoice(IntChoiceFromSet icsCG, int choice) {
384 cgToChoiceMap.put(icsCG, choice);
388 // This class compactly stores a predecessor
389 // 1) a predecessor execution
390 // 2) the predecessor choice in that predecessor execution
391 private class Predecessor {
392 private int choice; // Predecessor choice
393 private Execution execution; // Predecessor execution
395 public Predecessor(int predChoice, Execution predExec) {
397 execution = predExec;
400 public int getChoice() {
404 public Execution getExecution() {
409 // This class represents a R-Graph (in the paper it is a state transition graph R)
410 // This implementation stores reachable transitions from and connects with past executions
411 private class RGraph {
412 private int hiStateId; // Maximum state Id
413 private HashMap<Integer, HashSet<TransitionEvent>> graph; // Reachable transitions from past executions
417 graph = new HashMap<>();
420 public void addReachableTransition(int stateId, TransitionEvent transition) {
421 HashSet<TransitionEvent> transitionSet;
422 if (graph.containsKey(stateId)) {
423 transitionSet = graph.get(stateId);
425 transitionSet = new HashSet<>();
426 graph.put(stateId, transitionSet);
428 // Insert into the set if it does not contain it yet
429 if (!transitionSet.contains(transition)) {
430 transitionSet.add(transition);
432 // Update highest state ID
433 if (hiStateId < stateId) {
438 public HashSet<TransitionEvent> getReachableTransitionsAtState(int stateId) {
439 if (!graph.containsKey(stateId)) {
440 // This is a loop from a transition to itself, so just return the current transition
441 HashSet<TransitionEvent> transitionSet = new HashSet<>();
442 transitionSet.add(currentExecution.getLastTransition());
443 return transitionSet;
445 return graph.get(stateId);
448 public HashSet<TransitionEvent> getReachableTransitions(int stateId) {
449 HashSet<TransitionEvent> reachableTransitions = new HashSet<>();
450 // All transitions from states higher than the given state ID (until the highest state ID) are reachable
451 for(int stId = stateId; stId <= hiStateId; stId++) {
452 // We might encounter state IDs from the first round of Boolean CG
453 // The second round of Boolean CG should consider these new states
454 if (graph.containsKey(stId)) {
455 reachableTransitions.addAll(graph.get(stId));
458 return reachableTransitions;
462 // This class compactly stores Read and Write field sets
463 // We store the field name and its object ID
464 // Sharing the same field means the same field name and object ID
465 private class ReadWriteSet {
466 private HashMap<String, Integer> readMap;
467 private HashMap<String, Integer> writeMap;
469 public ReadWriteSet() {
470 readMap = new HashMap<>();
471 writeMap = new HashMap<>();
474 public void addReadField(String field, int objectId) {
475 readMap.put(field, objectId);
478 public void addWriteField(String field, int objectId) {
479 writeMap.put(field, objectId);
482 public void removeReadField(String field) {
483 readMap.remove(field);
486 public void removeWriteField(String field) {
487 writeMap.remove(field);
490 public boolean isEmpty() {
491 return readMap.isEmpty() && writeMap.isEmpty();
494 public ReadWriteSet getCopy() {
495 ReadWriteSet copyRWSet = new ReadWriteSet();
496 // Copy the maps in the set into the new object copy
497 copyRWSet.setReadMap(new HashMap<>(this.getReadMap()));
498 copyRWSet.setWriteMap(new HashMap<>(this.getWriteMap()));
502 public Set<String> getReadSet() {
503 return readMap.keySet();
506 public Set<String> getWriteSet() {
507 return writeMap.keySet();
510 public boolean readFieldExists(String field) {
511 return readMap.containsKey(field);
514 public boolean writeFieldExists(String field) {
515 return writeMap.containsKey(field);
518 public int readFieldObjectId(String field) {
519 return readMap.get(field);
522 public int writeFieldObjectId(String field) {
523 return writeMap.get(field);
526 private HashMap<String, Integer> getReadMap() {
530 private HashMap<String, Integer> getWriteMap() {
534 private void setReadMap(HashMap<String, Integer> rMap) {
538 private void setWriteMap(HashMap<String, Integer> wMap) {
543 // This class is a representation of a state.
544 // It stores the predecessors to a state.
545 // TODO: We also have stateToEventMap, restorableStateMap, and doneBacktrackMap that has state Id as HashMap key.
546 private class PredecessorInfo {
547 private HashSet<Predecessor> predecessors; // Maps incoming events/transitions (execution and choice)
548 private HashMap<Execution, HashSet<Integer>> recordedPredecessors;
549 // Memorize event and choice number to not record them twice
551 public PredecessorInfo() {
552 predecessors = new HashSet<>();
553 recordedPredecessors = new HashMap<>();
556 public HashSet<Predecessor> getPredecessors() {
560 private boolean isRecordedPredecessor(Execution execution, int choice) {
561 // See if we have recorded this predecessor earlier
562 HashSet<Integer> recordedChoices;
563 if (recordedPredecessors.containsKey(execution)) {
564 recordedChoices = recordedPredecessors.get(execution);
565 if (recordedChoices.contains(choice)) {
569 recordedChoices = new HashSet<>();
570 recordedPredecessors.put(execution, recordedChoices);
572 // Record the choice if we haven't seen it
573 recordedChoices.add(choice);
578 public void recordPredecessor(Execution execution, int choice) {
579 if (!isRecordedPredecessor(execution, choice)) {
580 predecessors.add(new Predecessor(choice, execution));
585 // This class compactly stores transitions:
589 // 4) predecessors (for backward DFS).
590 private class TransitionEvent {
591 private int choice; // Choice chosen at this transition
592 private int choiceCounter; // Choice counter at this transition
593 private Execution execution; // The execution where this transition belongs
594 private int stateId; // State at this transition
595 private IntChoiceFromSet transitionCG; // CG at this transition
597 public TransitionEvent() {
605 public int getChoice() {
609 public int getChoiceCounter() {
610 return choiceCounter;
613 public Execution getExecution() {
617 public int getStateId() {
621 public IntChoiceFromSet getTransitionCG() { return transitionCG; }
623 public void setChoice(int cho) {
627 public void setChoiceCounter(int choCounter) {
628 choiceCounter = choCounter;
631 public void setExecution(Execution exec) {
635 public void setStateId(int stId) {
639 public void setTransitionCG(IntChoiceFromSet cg) {
644 // -- PRIVATE CLASSES RELATED TO SUMMARY
645 // This class stores the main summary of states
646 // 1) Main mapping between state ID and state summary
647 // 2) State summary is a mapping between events (i.e., event choices) and their respective R/W sets
648 private class MainSummary {
649 private HashMap<Integer, HashMap<Integer, ReadWriteSet>> mainSummary;
651 public MainSummary() {
652 mainSummary = new HashMap<>();
655 public Set<Integer> getEventChoicesAtStateId(int stateId) {
656 HashMap<Integer, ReadWriteSet> stateSummary = mainSummary.get(stateId);
657 // Return a new set since this might get updated concurrently
658 return new HashSet<>(stateSummary.keySet());
661 public ReadWriteSet getRWSetForEventChoiceAtState(int eventChoice, int stateId) {
662 HashMap<Integer, ReadWriteSet> stateSummary = mainSummary.get(stateId);
663 return stateSummary.get(eventChoice);
666 public Set<Integer> getStateIds() {
667 return mainSummary.keySet();
670 private ReadWriteSet performUnion(ReadWriteSet recordedRWSet, ReadWriteSet rwSet) {
671 // Combine the same write accesses and record in the recordedRWSet
672 HashMap<String, Integer> recordedWriteMap = recordedRWSet.getWriteMap();
673 HashMap<String, Integer> writeMap = rwSet.getWriteMap();
674 for(Map.Entry<String, Integer> entry : recordedWriteMap.entrySet()) {
675 String writeField = entry.getKey();
676 // Remove the entry from rwSet if both field and object ID are the same
677 if (writeMap.containsKey(writeField) &&
678 (writeMap.get(writeField).equals(recordedWriteMap.get(writeField)))) {
679 writeMap.remove(writeField);
682 // Then add the rest (fields in rwSet but not in recordedRWSet)
683 // into the recorded map because these will be traversed
684 recordedWriteMap.putAll(writeMap);
685 // Combine the same read accesses and record in the recordedRWSet
686 HashMap<String, Integer> recordedReadMap = recordedRWSet.getReadMap();
687 HashMap<String, Integer> readMap = rwSet.getReadMap();
688 for(Map.Entry<String, Integer> entry : recordedReadMap.entrySet()) {
689 String readField = entry.getKey();
690 // Remove the entry from rwSet if both field and object ID are the same
691 if (readMap.containsKey(readField) &&
692 (readMap.get(readField).equals(recordedReadMap.get(readField)))) {
693 readMap.remove(readField);
696 // Then add the rest (fields in rwSet but not in recordedRWSet)
697 // into the recorded map because these will be traversed
698 recordedReadMap.putAll(readMap);
703 public ReadWriteSet updateStateSummary(int stateId, int eventChoice, ReadWriteSet rwSet) {
704 // If the state Id has not existed, insert the StateSummary object
705 // If the state Id has existed, find the event choice:
706 // 1) If the event choice has not existed, insert the ReadWriteSet object
707 // 2) If the event choice has existed, perform union between the two ReadWriteSet objects
708 if (!rwSet.isEmpty()) {
709 HashMap<Integer, ReadWriteSet> stateSummary;
710 if (!mainSummary.containsKey(stateId)) {
711 stateSummary = new HashMap<>();
712 stateSummary.put(eventChoice, rwSet.getCopy());
713 mainSummary.put(stateId, stateSummary);
715 stateSummary = mainSummary.get(stateId);
716 if (!stateSummary.containsKey(eventChoice)) {
717 stateSummary.put(eventChoice, rwSet.getCopy());
719 rwSet = performUnion(stateSummary.get(eventChoice), rwSet);
728 private final static String DO_CALL_METHOD = "doCall";
729 // We exclude fields that come from libraries (Java and Groovy), and also the infrastructure
730 private final static String[] EXCLUDED_FIELDS_CONTAINS_LIST = {"_closure"};
731 private final static String[] EXCLUDED_FIELDS_ENDS_WITH_LIST =
732 // Groovy library created fields
733 {"stMC", "callSiteArray", "metaClass", "staticClassInfo", "__constructor__",
735 "sendEvent", "Object", "reference", "location", "app", "state", "log", "functionList", "objectList",
736 "eventList", "valueList", "settings", "printToConsole", "app1", "app2"};
737 private final static String[] EXCLUDED_FIELDS_STARTS_WITH_LIST =
738 // Java and Groovy libraries
739 { "java", "org", "sun", "com", "gov", "groovy"};
740 private final static String[] EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST = {"Event"};
741 private final static String GET_PROPERTY_METHOD =
742 "invokeinterface org.codehaus.groovy.runtime.callsite.CallSite.callGetProperty";
743 private final static String GROOVY_CALLSITE_LIB = "org.codehaus.groovy.runtime.callsite";
744 private final static String JAVA_INTEGER = "int";
745 private final static String JAVA_STRING_LIB = "java.lang.String";
748 private Integer[] copyChoices(Integer[] choicesToCopy) {
750 Integer[] copyOfChoices = new Integer[choicesToCopy.length];
751 System.arraycopy(choicesToCopy, 0, copyOfChoices, 0, choicesToCopy.length);
752 return copyOfChoices;
755 private void ensureFairSchedulingAndSetupTransition(IntChoiceFromSet icsCG, VM vm) {
756 // Check the next choice and if the value is not the same as the expected then force the expected value
757 int choiceIndex = choiceCounter % refChoices.length;
758 int nextChoice = icsCG.getNextChoice();
759 if (refChoices[choiceIndex] != nextChoice) {
760 int expectedChoice = refChoices[choiceIndex];
761 int currCGIndex = icsCG.getNextChoiceIndex();
762 if ((currCGIndex >= 0) && (currCGIndex < refChoices.length)) {
763 icsCG.setChoice(currCGIndex, expectedChoice);
766 // Get state ID and associate it with this transition
767 int stateId = vm.getStateId();
768 TransitionEvent transition = setupTransition(icsCG, stateId, choiceIndex);
769 // Add new transition to the current execution and map it in R-Graph
770 for (Integer stId : justVisitedStates) { // Map this transition to all the previously passed states
771 rGraph.addReachableTransition(stId, transition);
773 currentExecution.mapCGToChoice(icsCG, choiceCounter);
774 // Store restorable state object for this state (always store the latest)
775 if (!restorableStateMap.containsKey(stateId)) {
776 RestorableVMState restorableState = vm.getRestorableState();
777 restorableStateMap.put(stateId, restorableState);
781 private TransitionEvent setupTransition(IntChoiceFromSet icsCG, int stateId, int choiceIndex) {
782 // Get a new transition
783 TransitionEvent transition;
784 if (currentExecution.isNew()) {
785 // We need to handle the first transition differently because this has a predecessor execution
786 transition = currentExecution.getFirstTransition();
788 transition = new TransitionEvent();
789 currentExecution.addTransition(transition);
790 addPredecessors(stateId);
792 transition.setExecution(currentExecution);
793 transition.setTransitionCG(icsCG);
794 transition.setStateId(stateId);
795 transition.setChoice(refChoices[choiceIndex]);
796 transition.setChoiceCounter(choiceCounter);
801 // --- Functions related to cycle detection and reachability graph
803 // Detect cycles in the current execution/trace
804 // We terminate the execution iff:
805 // (1) the state has been visited in the current execution
806 // (2) the state has one or more cycles that involve all the events
807 // With simple approach we only need to check for a re-visited state.
808 // Basically, we have to check that we have executed all events between two occurrences of such state.
809 private boolean completeFullCycle(int stId) {
810 // False if the state ID hasn't been recorded
811 if (!stateToEventMap.containsKey(stId)) {
814 HashSet<Integer> visitedEvents = stateToEventMap.get(stId);
815 // Check if this set contains all the event choices
816 // If not then this is not the terminating condition
817 for(int i=0; i<=maxEventChoice; i++) {
818 if (!visitedEvents.contains(i)) {
825 private void initializeStatesVariables() {
832 if (!isBooleanCGFlipped) {
833 currVisitedStates = new HashMap<>();
834 justVisitedStates = new HashSet<>();
835 prevVisitedStates = new HashSet<>();
836 stateToEventMap = new HashMap<>();
838 currVisitedStates.clear();
839 justVisitedStates.clear();
840 prevVisitedStates.clear();
841 stateToEventMap.clear();
844 if (!isBooleanCGFlipped) {
845 backtrackMap = new HashMap<>();
847 backtrackMap.clear();
849 backtrackStateQ = new PriorityQueue<>(Collections.reverseOrder());
850 currentExecution = new Execution();
851 currentExecution.addTransition(new TransitionEvent()); // Always start with 1 backtrack point
852 if (!isBooleanCGFlipped) {
853 doneBacktrackMap = new HashMap<>();
855 doneBacktrackMap.clear();
857 rGraph = new RGraph();
859 isEndOfExecution = false;
862 private void mapStateToEvent(int nextChoiceValue) {
863 // Update all states with this event/choice
864 // This means that all past states now see this transition
865 Set<Integer> stateSet = stateToEventMap.keySet();
866 for(Integer stateId : stateSet) {
867 HashSet<Integer> eventSet = stateToEventMap.get(stateId);
868 eventSet.add(nextChoiceValue);
872 private boolean terminateCurrentExecution() {
873 // We need to check all the states that have just been visited
874 // Often a transition (choice/event) can result into forwarding/backtracking to a number of states
875 boolean terminate = false;
876 Set<Integer> mainStateIds = mainSummary.getStateIds();
877 for(Integer stateId : justVisitedStates) {
878 // We exclude states that are produced by other CGs that are not integer CG
879 // When we encounter these states, then we should also encounter the corresponding integer CG state ID
880 if (mainStateIds.contains(stateId)) {
881 // We perform updates on backtrack sets for every
882 if (prevVisitedStates.contains(stateId) || completeFullCycle(stateId)) {
883 updateBacktrackSetsFromGraph(stateId, currentExecution, choiceCounter - 1);
886 // If frequency > 1 then this means we have visited this stateId more than once in the current execution
887 if (currVisitedStates.containsKey(stateId) && currVisitedStates.get(stateId) > 1) {
888 updateBacktrackSetsFromGraph(stateId, currentExecution, choiceCounter - 1);
895 private void updateStateInfo(Search search) {
896 // Update the state variables
897 int stateId = search.getStateId();
898 // Insert state ID into the map if it is new
899 if (!stateToEventMap.containsKey(stateId)) {
900 HashSet<Integer> eventSet = new HashSet<>();
901 stateToEventMap.put(stateId, eventSet);
903 addPredecessorToRevisitedState(stateId);
904 justVisitedStates.add(stateId);
905 if (!prevVisitedStates.contains(stateId)) {
906 // It is a currently visited states if the state has not been seen in previous executions
908 if (currVisitedStates.containsKey(stateId)) {
909 frequency = currVisitedStates.get(stateId);
911 currVisitedStates.put(stateId, frequency + 1); // Increment frequency counter
915 // --- Functions related to Read/Write access analysis on shared fields
917 private void addNewBacktrackPoint(int stateId, Integer[] newChoiceList, TransitionEvent conflictTransition) {
918 // Insert backtrack point to the right state ID
919 LinkedList<BacktrackExecution> backtrackExecList;
920 if (backtrackMap.containsKey(stateId)) {
921 backtrackExecList = backtrackMap.get(stateId);
923 backtrackExecList = new LinkedList<>();
924 backtrackMap.put(stateId, backtrackExecList);
926 // Add the new backtrack execution object
927 TransitionEvent backtrackTransition = new TransitionEvent();
928 backtrackExecList.addFirst(new BacktrackExecution(newChoiceList, backtrackTransition));
929 // Add to priority queue
930 if (!backtrackStateQ.contains(stateId)) {
931 backtrackStateQ.add(stateId);
935 private void addPredecessors(int stateId) {
936 PredecessorInfo predecessorInfo;
937 if (!stateToPredInfo.containsKey(stateId)) {
938 predecessorInfo = new PredecessorInfo();
939 stateToPredInfo.put(stateId, predecessorInfo);
940 } else { // This is a new state Id
941 predecessorInfo = stateToPredInfo.get(stateId);
943 predecessorInfo.recordPredecessor(currentExecution, choiceCounter - 1);
946 // Analyze Read/Write accesses that are directly invoked on fields
947 private void analyzeReadWriteAccesses(Instruction executedInsn, int currentChoice) {
948 // Get the field info
949 FieldInfo fieldInfo = ((JVMFieldInstruction) executedInsn).getFieldInfo();
950 // Analyze only after being initialized
951 String fieldClass = fieldInfo.getFullName();
952 // Do the analysis to get Read and Write accesses to fields
953 ReadWriteSet rwSet = getReadWriteSet(currentChoice);
954 int objectId = fieldInfo.getClassInfo().getClassObjectRef();
955 // Record the field in the map
956 if (executedInsn instanceof WriteInstruction) {
957 // We first check the non-relevant fields set
958 if (!nonRelevantFields.contains(fieldInfo)) {
959 // Exclude certain field writes because of infrastructure needs, e.g., Event class field writes
960 for (String str : EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST) {
961 if (fieldClass.startsWith(str)) {
962 nonRelevantFields.add(fieldInfo);
967 // If we have this field in the non-relevant fields set then we return right away
970 rwSet.addWriteField(fieldClass, objectId);
971 } else if (executedInsn instanceof ReadInstruction) {
972 rwSet.addReadField(fieldClass, objectId);
976 // Analyze Read accesses that are indirect (performed through iterators)
977 // These accesses are marked by certain bytecode instructions, e.g., INVOKEINTERFACE
978 private void analyzeReadWriteAccesses(Instruction instruction, ThreadInfo ti, int currentChoice) {
980 INVOKEINTERFACE insn = (INVOKEINTERFACE) instruction;
981 if (insn.toString().startsWith(GET_PROPERTY_METHOD) &&
982 insn.getMethodInfo().getName().equals(DO_CALL_METHOD)) {
983 // Extract info from the stack frame
984 StackFrame frame = ti.getTopFrame();
985 int[] frameSlots = frame.getSlots();
986 // Get the Groovy callsite library at index 0
987 ElementInfo eiCallsite = VM.getVM().getHeap().get(frameSlots[0]);
988 if (!eiCallsite.getClassInfo().getName().startsWith(GROOVY_CALLSITE_LIB)) {
991 // Get the iterated object whose property is accessed
992 ElementInfo eiAccessObj = VM.getVM().getHeap().get(frameSlots[1]);
993 if (eiAccessObj == null) {
996 // We exclude library classes (they start with java, org, etc.) and some more
997 ClassInfo classInfo = eiAccessObj.getClassInfo();
998 String objClassName = classInfo.getName();
999 // Check if this class info is part of the non-relevant classes set already
1000 if (!nonRelevantClasses.contains(classInfo)) {
1001 if (excludeThisForItStartsWith(EXCLUDED_FIELDS_READ_WRITE_INSTRUCTIONS_STARTS_WITH_LIST, objClassName) ||
1002 excludeThisForItStartsWith(EXCLUDED_FIELDS_STARTS_WITH_LIST, objClassName)) {
1003 nonRelevantClasses.add(classInfo);
1007 // If it is part of the non-relevant classes set then return immediately
1010 // Extract fields from this object and put them into the read write
1011 int numOfFields = eiAccessObj.getNumberOfFields();
1012 for(int i=0; i<numOfFields; i++) {
1013 FieldInfo fieldInfo = eiAccessObj.getFieldInfo(i);
1014 if (fieldInfo.getType().equals(JAVA_STRING_LIB) || fieldInfo.getType().equals(JAVA_INTEGER)) {
1015 String fieldClass = fieldInfo.getFullName();
1016 ReadWriteSet rwSet = getReadWriteSet(currentChoice);
1017 int objectId = fieldInfo.getClassInfo().getClassObjectRef();
1018 // Record the field in the map
1019 rwSet.addReadField(fieldClass, objectId);
1025 private int checkAndAdjustChoice(int currentChoice, VM vm) {
1026 // If current choice is not the same, then this is caused by the firing of IntIntervalGenerator
1027 // for certain method calls in the infrastructure, e.g., eventSince()
1028 ChoiceGenerator<?> currentCG = vm.getChoiceGenerator();
1029 // This is the main event CG
1030 if (currentCG instanceof IntIntervalGenerator) {
1031 // This is the interval CG used in device handlers
1032 ChoiceGenerator<?> parentCG = ((IntIntervalGenerator) currentCG).getPreviousChoiceGenerator();
1033 // Iterate until we find the IntChoiceFromSet CG
1034 while (!(parentCG instanceof IntChoiceFromSet)) {
1035 parentCG = ((IntIntervalGenerator) parentCG).getPreviousChoiceGenerator();
1037 // Find the choice related to the IntIntervalGenerator CG from the map
1038 currentChoice = currentExecution.getChoiceFromCG((IntChoiceFromSet) parentCG);
1040 return currentChoice;
1043 private void createBacktrackingPoint(int eventChoice, Execution conflictExecution, int conflictChoice) {
1044 // Create a new list of choices for backtrack based on the current choice and conflicting event number
1045 // E.g. if we have a conflict between 1 and 3, then we create the list {3, 1, 0, 2}
1046 // for the original set {0, 1, 2, 3}
1048 // eventChoice represents the event/transaction that will be put into the backtracking set of
1049 // conflictExecution/conflictChoice
1050 Integer[] newChoiceList = new Integer[refChoices.length];
1051 ArrayList<TransitionEvent> conflictTrace = conflictExecution.getExecutionTrace();
1052 int stateId = conflictTrace.get(conflictChoice).getStateId();
1053 // Check if this trace has been done from this state
1054 if (isTraceAlreadyConstructed(eventChoice, stateId)) {
1057 // Put the conflicting event numbers first and reverse the order
1058 newChoiceList[0] = eventChoice;
1059 // Put the rest of the event numbers into the array starting from the minimum to the upper bound
1060 for (int i = 0, j = 1; i < refChoices.length; i++) {
1061 if (refChoices[i] != newChoiceList[0]) {
1062 newChoiceList[j] = refChoices[i];
1066 // Predecessor of the new backtrack point is the same as the conflict point's
1067 addNewBacktrackPoint(stateId, newChoiceList, conflictTrace.get(conflictChoice));
1070 private boolean excludeThisForItContains(String[] excludedStrings, String className) {
1071 for (String excludedField : excludedStrings) {
1072 if (className.contains(excludedField)) {
1079 private boolean excludeThisForItEndsWith(String[] excludedStrings, String className) {
1080 for (String excludedField : excludedStrings) {
1081 if (className.endsWith(excludedField)) {
1088 private boolean excludeThisForItStartsWith(String[] excludedStrings, String className) {
1089 for (String excludedField : excludedStrings) {
1090 if (className.startsWith(excludedField)) {
1097 private void exploreNextBacktrackPoints(VM vm, IntChoiceFromSet icsCG) {
1098 // Check if we are reaching the end of our execution: no more backtracking points to explore
1099 // cgMap, backtrackMap, backtrackStateQ are updated simultaneously (checking backtrackStateQ is enough)
1100 if (!backtrackStateQ.isEmpty()) {
1101 // Set done all the other backtrack points
1102 for (TransitionEvent backtrackTransition : currentExecution.getExecutionTrace()) {
1103 backtrackTransition.getTransitionCG().setDone();
1105 // Reset the next backtrack point with the latest state
1106 int hiStateId = backtrackStateQ.peek();
1107 // Restore the state first if necessary
1108 if (vm.getStateId() != hiStateId) {
1109 RestorableVMState restorableState = restorableStateMap.get(hiStateId);
1110 vm.restoreState(restorableState);
1112 // Set the backtrack CG
1113 IntChoiceFromSet backtrackCG = (IntChoiceFromSet) vm.getChoiceGenerator();
1114 setBacktrackCG(hiStateId, backtrackCG);
1116 // Set done this last CG (we save a few rounds)
1119 // Save all the visited states when starting a new execution of trace
1120 prevVisitedStates.addAll(currVisitedStates.keySet());
1121 // This marks a transitional period to the new CG
1122 isEndOfExecution = true;
1125 private boolean isConflictFound(int eventChoice, Execution conflictExecution, int conflictChoice,
1126 ReadWriteSet currRWSet) {
1127 // conflictExecution/conflictChoice represent a predecessor event/transaction that can potentially have a conflict
1128 ArrayList<TransitionEvent> conflictTrace = conflictExecution.getExecutionTrace();
1129 HashMap<Integer, ReadWriteSet> confRWFieldsMap = conflictExecution.getReadWriteFieldsMap();
1130 // Skip if this event does not have any Read/Write set or the two events are basically the same event (number)
1131 if (!confRWFieldsMap.containsKey(conflictChoice) || eventChoice == conflictTrace.get(conflictChoice).getChoice()) {
1134 // R/W set of choice/event that may have a potential conflict
1135 ReadWriteSet confRWSet = confRWFieldsMap.get(conflictChoice);
1136 // Check for conflicts with Read and Write fields for Write instructions
1137 Set<String> currWriteSet = currRWSet.getWriteSet();
1138 for(String writeField : currWriteSet) {
1139 int currObjId = currRWSet.writeFieldObjectId(writeField);
1140 if ((confRWSet.readFieldExists(writeField) && confRWSet.readFieldObjectId(writeField) == currObjId) ||
1141 (confRWSet.writeFieldExists(writeField) && confRWSet.writeFieldObjectId(writeField) == currObjId)) {
1142 // Remove this from the write set as we are tracking per memory location
1143 currRWSet.removeWriteField(writeField);
1147 // Check for conflicts with Write fields for Read instructions
1148 Set<String> currReadSet = currRWSet.getReadSet();
1149 for(String readField : currReadSet) {
1150 int currObjId = currRWSet.readFieldObjectId(readField);
1151 if (confRWSet.writeFieldExists(readField) && confRWSet.writeFieldObjectId(readField) == currObjId) {
1152 // Remove this from the read set as we are tracking per memory location
1153 currRWSet.removeReadField(readField);
1157 // Return false if no conflict is found
1161 private boolean isFieldExcluded(Instruction executedInsn) {
1162 // Get the field info
1163 FieldInfo fieldInfo = ((JVMFieldInstruction) executedInsn).getFieldInfo();
1164 // Check if the non-relevant fields set already has it
1165 if (nonRelevantFields.contains(fieldInfo)) {
1168 // Check if the relevant fields set already has it
1169 if (relevantFields.contains(fieldInfo)) {
1172 // Analyze only after being initialized
1173 String field = fieldInfo.getFullName();
1174 // Check against "starts-with", "ends-with", and "contains" list
1175 if (excludeThisForItStartsWith(EXCLUDED_FIELDS_STARTS_WITH_LIST, field) ||
1176 excludeThisForItEndsWith(EXCLUDED_FIELDS_ENDS_WITH_LIST, field) ||
1177 excludeThisForItContains(EXCLUDED_FIELDS_CONTAINS_LIST, field)) {
1178 nonRelevantFields.add(fieldInfo);
1181 relevantFields.add(fieldInfo);
1185 // Check if this trace is already constructed
1186 private boolean isTraceAlreadyConstructed(int firstChoice, int stateId) {
1187 // Concatenate state ID and only the first event in the string, e.g., "1:1 for the trace 10234 at state 1"
1188 // Check if the trace has been constructed as a backtrack point for this state
1189 // TODO: THIS IS AN OPTIMIZATION!
1190 HashSet<Integer> choiceSet;
1191 if (doneBacktrackMap.containsKey(stateId)) {
1192 choiceSet = doneBacktrackMap.get(stateId);
1193 if (choiceSet.contains(firstChoice)) {
1197 choiceSet = new HashSet<>();
1198 doneBacktrackMap.put(stateId, choiceSet);
1200 choiceSet.add(firstChoice);
1205 private HashSet<Predecessor> getPredecessors(int stateId) {
1206 // Get a set of predecessors for this state ID
1207 HashSet<Predecessor> predecessors;
1208 if (stateToPredInfo.containsKey(stateId)) {
1209 PredecessorInfo predecessorInfo = stateToPredInfo.get(stateId);
1210 predecessors = predecessorInfo.getPredecessors();
1212 predecessors = new HashSet<>();
1215 return predecessors;
1218 private ReadWriteSet getReadWriteSet(int currentChoice) {
1219 // Do the analysis to get Read and Write accesses to fields
1221 // We already have an entry
1222 HashMap<Integer, ReadWriteSet> currReadWriteFieldsMap = currentExecution.getReadWriteFieldsMap();
1223 if (currReadWriteFieldsMap.containsKey(currentChoice)) {
1224 rwSet = currReadWriteFieldsMap.get(currentChoice);
1225 } else { // We need to create a new entry
1226 rwSet = new ReadWriteSet();
1227 currReadWriteFieldsMap.put(currentChoice, rwSet);
1232 // Reset data structure for each new execution
1233 private void resetStatesForNewExecution(IntChoiceFromSet icsCG, VM vm) {
1234 if (choices == null || choices != icsCG.getAllChoices()) {
1235 // Reset state variables
1237 choices = icsCG.getAllChoices();
1238 refChoices = copyChoices(choices);
1239 // Clear data structures
1240 currVisitedStates.clear();
1241 stateToEventMap.clear();
1242 isEndOfExecution = false;
1246 // Set a backtrack point for a particular state
1247 private void setBacktrackCG(int stateId, IntChoiceFromSet backtrackCG) {
1248 // Set a backtrack CG based on a state ID
1249 LinkedList<BacktrackExecution> backtrackExecutions = backtrackMap.get(stateId);
1250 BacktrackExecution backtrackExecution = backtrackExecutions.removeLast();
1251 backtrackCG.setNewValues(backtrackExecution.getChoiceList()); // Get the last from the queue
1252 backtrackCG.setStateId(stateId);
1253 backtrackCG.reset();
1254 // Update current execution with this new execution
1255 Execution newExecution = new Execution();
1256 TransitionEvent firstTransition = backtrackExecution.getFirstTransition();
1257 newExecution.addTransition(firstTransition);
1258 // Try to free some memory since this map is only used for the current execution
1259 currentExecution.clearCGToChoiceMap();
1260 currentExecution = newExecution;
1261 // Remove from the queue if we don't have more backtrack points for that state
1262 if (backtrackExecutions.isEmpty()) {
1263 backtrackMap.remove(stateId);
1264 backtrackStateQ.remove(stateId);
1268 // Update backtrack sets
1269 // 1) recursively, and
1270 // 2) track accesses per memory location (per shared variable/field)
1271 private void updateBacktrackSet(Execution execution, int currentChoice) {
1272 // Copy ReadWriteSet object
1273 HashMap<Integer, ReadWriteSet> currRWFieldsMap = execution.getReadWriteFieldsMap();
1274 ReadWriteSet currRWSet = currRWFieldsMap.get(currentChoice);
1275 if (currRWSet == null) {
1278 currRWSet = currRWSet.getCopy();
1279 // Memorize visited TransitionEvent object while performing backward DFS to avoid getting caught up in a cycle
1280 HashSet<TransitionEvent> visited = new HashSet<>();
1281 // Conflict TransitionEvent is essentially the current TransitionEvent
1282 TransitionEvent confTrans = execution.getExecutionTrace().get(currentChoice);
1283 // Update backtrack set recursively
1284 updateBacktrackSetDFS(execution, currentChoice, confTrans.getChoice(), currRWSet, visited);
1287 private void updateBacktrackSetDFS(Execution execution, int currentChoice, int conflictEventChoice,
1288 ReadWriteSet currRWSet, HashSet<TransitionEvent> visited) {
1289 TransitionEvent currTrans = execution.getExecutionTrace().get(currentChoice);
1290 // Record this transition into the state summary of main summary
1291 currRWSet = mainSummary.updateStateSummary(currTrans.getStateId(), conflictEventChoice, currRWSet);
1292 // Halt when we have visited this transition (in a cycle)
1293 if (visited.contains(currTrans)) {
1296 visited.add(currTrans);
1297 // Check the predecessors only if the set is not empty
1298 if (!currRWSet.isEmpty()) {
1299 // Explore all predecessors
1300 for (Predecessor predecessor : getPredecessors(currTrans.getStateId())) {
1301 // Get the predecessor (previous conflict choice)
1302 int predecessorChoice = predecessor.getChoice();
1303 Execution predecessorExecution = predecessor.getExecution();
1304 // Push up one happens-before transition
1305 int newConflictEventChoice = conflictEventChoice;
1306 // Check if a conflict is found
1307 ReadWriteSet newCurrRWSet = currRWSet.getCopy();
1308 if (isConflictFound(conflictEventChoice, predecessorExecution, predecessorChoice, newCurrRWSet)) {
1309 createBacktrackingPoint(conflictEventChoice, predecessorExecution, predecessorChoice);
1310 // We need to extract the pushed happens-before event choice from the predecessor execution and choice
1311 newConflictEventChoice = predecessorExecution.getExecutionTrace().get(predecessorChoice).getChoice();
1313 // Continue performing DFS if conflict is not found
1314 updateBacktrackSetDFS(predecessorExecution, predecessorChoice, newConflictEventChoice,
1315 newCurrRWSet, visited);
1320 // --- Functions related to the reachability analysis when there is a state match
1322 private void addPredecessorToRevisitedState(int stateId) {
1323 // Perform this analysis only when:
1324 // 1) this is not during a switch to a new execution,
1325 // 2) at least 2 choices/events have been explored (choiceCounter > 1),
1326 // 3) state > 0 (state 0 is for boolean CG)
1327 if (!isEndOfExecution && choiceCounter > 1 && stateId > 0) {
1328 if ((currVisitedStates.containsKey(stateId) && currVisitedStates.get(stateId) > 1) ||
1329 prevVisitedStates.contains(stateId)) {
1330 // Record a new predecessor for a revisited state
1331 addPredecessors(stateId);
1336 // Update the backtrack sets from previous executions
1337 private void updateBacktrackSetsFromGraph(int stateId, Execution currExecution, int currChoice) {
1338 // Get events/choices at this state ID
1339 Set<Integer> eventChoicesAtStateId = mainSummary.getEventChoicesAtStateId(stateId);
1340 for (Integer eventChoice : eventChoicesAtStateId) {
1341 // Get the ReadWriteSet object for this event at state ID
1342 ReadWriteSet rwSet = mainSummary.getRWSetForEventChoiceAtState(eventChoice, stateId);
1343 // Memorize visited TransitionEvent object while performing backward DFS to avoid getting caught up in a cycle
1344 HashSet<TransitionEvent> visited = new HashSet<>();
1345 // Update the backtrack sets recursively
1346 updateBacktrackSetDFS(currExecution, currChoice, eventChoice, rwSet.getCopy(), visited);