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.search.Search;
24 import gov.nasa.jpf.jvm.bytecode.*;
25 import gov.nasa.jpf.vm.*;
26 import gov.nasa.jpf.vm.bytecode.ReadInstruction;
27 import gov.nasa.jpf.vm.bytecode.WriteInstruction;
28 import gov.nasa.jpf.vm.choice.IntChoiceFromSet;
30 import java.io.PrintWriter;
34 // TODO: Fix for Groovy's model-checking
35 // TODO: This is a setter to change the values of the ChoiceGenerator to implement POR
37 * Simple tool to log state changes.
39 * This DPOR implementation is augmented by the algorithm presented in this SPIN paper:
40 * http://spinroot.com/spin/symposia/ws08/spin2008_submission_33.pdf
42 * The algorithm is presented on page 11 of the paper. Basically, we create a graph G
43 * (i.e., visible operation dependency graph)
44 * that maps inter-related threads/sub-programs that trigger state changes.
45 * The key to this approach is that we evaluate graph G in every iteration/recursion to
46 * only update the backtrack sets of the threads/sub-programs that are reachable in graph G
47 * from the currently running thread/sub-program.
49 public class StateReducer extends ListenerAdapter {
52 private boolean debugMode;
53 private boolean stateReductionMode;
54 private final PrintWriter out;
55 private String detail;
58 private Transition transition;
60 // State reduction fields
61 private Integer[] choices;
62 private IntChoiceFromSet currCG;
63 private int choiceCounter;
64 private Integer choiceUpperBound;
65 private Integer maxUpperBound;
66 private boolean isInitialized;
67 private boolean isResetAfterAnalysis;
68 private boolean isBooleanCGFlipped;
69 private HashMap<IntChoiceFromSet, Integer> cgMap;
70 // Record the mapping between event number and field accesses (Read and Write)
71 private HashMap<Integer, ReadWriteSet> readWriteFieldsMap;
72 // The following is the backtrack map (set) that stores all the backtrack information
73 // e.g., event number 1 can have two backtrack sequences: {3,1,2,4,...} and {2,1,3,4,...}
74 private HashMap<Integer, LinkedList<Integer[]>> backtrackMap;
75 // Stores explored backtrack lists in the form of HashSet of Strings
76 private HashSet<String> backtrackSet;
77 private HashMap<Integer, HashSet<Integer>> conflictPairMap;
79 // Map that represents graph G
80 // (i.e., visible operation dependency graph (VOD Graph)
81 private HashMap<Integer, HashSet<Integer>> vodGraphMap;
82 // Set that represents hash table H
83 // (i.e., hash table that records encountered states)
84 // VOD graph is updated when the state has not yet been seen
87 // Previous choice number
88 private int prevChoiceValue;
89 // HashSet that stores references to unused CGs
90 private HashSet<IntChoiceFromSet> unusedCG;
92 // Reference to the state graph in the ConflictTracker class
93 private HashMap<Integer, ConflictTracker.Node> stateGraph;
94 // Visited states in the previous and current executions/traces for terminating condition
95 private HashSet<Integer> prevVisitedStates;
96 private HashSet<Integer> currVisitedStates;
98 public StateReducer(Config config, JPF jpf) {
99 debugMode = config.getBoolean("debug_state_transition", false);
100 stateReductionMode = config.getBoolean("activate_state_reduction", true);
102 out = new PrintWriter(System.out, true);
110 isBooleanCGFlipped = false;
111 vodGraphMap = new HashMap<>();
113 prevChoiceValue = -1;
114 cgMap = new HashMap<>();
115 readWriteFieldsMap = new HashMap<>();
116 backtrackMap = new HashMap<>();
117 backtrackSet = new HashSet<>();
118 conflictPairMap = new HashMap<>();
119 unusedCG = new HashSet<>();
120 // TODO: We are assuming that the StateReducer is always used together with the ConflictTracker
121 stateGraph = ConflictTracker.nodes;
122 prevVisitedStates = new HashSet<>();
123 currVisitedStates = new HashSet<>();
124 initializeStateReduction();
127 private void initializeStateReduction() {
128 if (stateReductionMode) {
132 choiceUpperBound = 0;
134 isInitialized = false;
135 isResetAfterAnalysis = false;
137 readWriteFieldsMap.clear();
138 backtrackMap.clear();
139 backtrackSet.clear();
140 conflictPairMap.clear();
145 public void stateRestored(Search search) {
147 id = search.getStateId();
148 depth = search.getDepth();
149 transition = search.getTransition();
151 out.println("\n==> DEBUG: The state is restored to state with id: " + id + " -- Transition: " + transition +
152 " and depth: " + depth + "\n");
156 //--- the ones we are interested in
158 public void searchStarted(Search search) {
160 out.println("\n==> DEBUG: ----------------------------------- search started" + "\n");
165 public void choiceGeneratorRegistered(VM vm, ChoiceGenerator<?> nextCG, ThreadInfo currentThread, Instruction executedInstruction) {
166 if (stateReductionMode) {
167 // Initialize with necessary information from the CG
168 if (nextCG instanceof IntChoiceFromSet) {
169 IntChoiceFromSet icsCG = (IntChoiceFromSet) nextCG;
170 // Check if CG has been initialized, otherwise initialize it
171 Integer[] cgChoices = icsCG.getAllChoices();
172 if (!isInitialized) {
173 // Get the upper bound from the last element of the choices
174 choiceUpperBound = cgChoices[cgChoices.length - 1];
175 isInitialized = true;
177 // Record the subsequent Integer CGs only until we hit the upper bound
178 if (!isResetAfterAnalysis) {
179 if (choiceCounter <= choiceUpperBound && !cgMap.containsValue(choiceCounter)) {
180 // Update the choices of the first CG and add '-1'
181 if (choices == null) {
182 // Initialize backtrack set that stores all the explored backtrack lists
183 maxUpperBound = cgChoices.length;
184 // All the choices are always the same so we only need to update it once
185 choices = new Integer[cgChoices.length + 1];
186 System.arraycopy(cgChoices, 0, choices, 0, cgChoices.length);
187 choices[choices.length - 1] = -1;
188 String firstChoiceListString = buildStringFromChoiceList(choices);
189 backtrackSet.add(firstChoiceListString);
191 icsCG.setNewValues(choices);
193 // Advance the current Integer CG
194 // This way we explore all the event numbers in the first pass
195 icsCG.advance(choices[choiceCounter]);
196 cgMap.put(icsCG, choices[choiceCounter]);
198 // We repeat the same trace if a state match is not found yet
199 icsCG.setNewValues(choices);
201 // Use a modulo since choiceCounter is going to keep increasing
202 int choiceIndex = choiceCounter % (choices.length - 1);
203 icsCG.advance(choices[choiceIndex]);
206 //choiceCounter = choiceCounter < choiceUpperBound ? choiceCounter + 1 : 0;
209 // Set new CGs to done so that the search algorithm explores the existing CGs
216 private void resetAllCGs() {
217 // Extract the event numbers that have backtrack lists
218 Set<Integer> eventSet = backtrackMap.keySet();
219 // Return if there is no conflict at all (highly unlikely)
220 if (eventSet.isEmpty()) {
221 // Set every CG to done!
222 for (IntChoiceFromSet cg : cgMap.keySet()) {
227 // Reset every CG with the first backtrack lists
228 for (IntChoiceFromSet cg : cgMap.keySet()) {
229 int event = cgMap.get(cg);
230 LinkedList<Integer[]> choiceLists = backtrackMap.get(event);
231 if (choiceLists != null && choiceLists.peekFirst() != null) {
232 Integer[] choiceList = choiceLists.removeFirst();
233 // Deploy the new choice list for this CG
234 cg.setNewValues(choiceList);
240 // Set done every CG in the unused CG set
241 for (IntChoiceFromSet cg : unusedCG) {
248 // Detect cycles in the current execution/trace
249 // We terminate the execution iff:
250 // (1) the state has been visited in the current execution
251 // (2) the state has one or more cycles that involve all the events
252 private boolean containsCyclesWithAllEvents(int stId) {
254 HashSet<ConflictTracker.Node> visitingStates = new HashSet<>();
255 HashSet<Integer> visitedEvents = new HashSet<>();
256 boolean containsCyclesWithAllEvts = false;
257 ConflictTracker.Node currNode = stateGraph.get(stId);
258 dfsFindCycles(currNode, visitingStates, visitedEvents, new HashSet<>());
259 if (checkIfAllEventsInvolved(visitedEvents)) {
260 containsCyclesWithAllEvts = true;
263 return containsCyclesWithAllEvts;
266 private void dfsFindCycles(ConflictTracker.Node currNode, HashSet<ConflictTracker.Node> visitingStates,
267 HashSet<Integer> visitedEvents, HashSet<Integer> visitingEvents) {
269 // Stop when there is a cycle and record all the events
270 if (visitingStates.contains(currNode)) {
271 visitedEvents.addAll(visitingEvents);
273 visitingStates.add(currNode);
274 for(ConflictTracker.Edge edge : currNode.getOutEdges()) {
275 visitingEvents.add(edge.getEventNumber());
276 dfsFindCycles(edge.getDst(), visitingStates, visitedEvents, visitingEvents);
277 visitingEvents.remove(edge.getEventNumber());
279 visitingStates.remove(currNode);
283 private boolean checkIfAllEventsInvolved(HashSet<Integer> visitedEvents) {
285 // Check if this set contains all the event choices
286 // If not then this is not the terminating condition
287 for(int i=0; i<=choiceUpperBound; i++) {
288 if (!visitedEvents.contains(i)) {
295 private void saveVisitedStates() {
297 // Save all the visited states
298 prevVisitedStates.addAll(currVisitedStates);
299 currVisitedStates.clear();
303 public void choiceGeneratorAdvanced(VM vm, ChoiceGenerator<?> currentCG) {
305 if (stateReductionMode) {
306 // Check the boolean CG and if it is flipped, we are resetting the analysis
307 if (currentCG instanceof BooleanChoiceGenerator) {
308 if (!isBooleanCGFlipped) {
309 isBooleanCGFlipped = true;
311 initializeStateReduction();
314 // Check every choice generated and make sure that all the available choices
315 // are chosen first before repeating the same choice of value twice!
316 if (currentCG instanceof IntChoiceFromSet) {
317 IntChoiceFromSet icsCG = (IntChoiceFromSet) currentCG;
318 // Update the current pointer to the current set of choices
319 if (choices == null || choices != icsCG.getAllChoices()) {
321 choices = icsCG.getAllChoices();
322 // Reset a few things for the sub-graph
323 conflictPairMap.clear();
324 readWriteFieldsMap.clear();
327 // Check if we have seen this state or this state contains cycles that involve all events
328 if (prevVisitedStates.contains(stateId) || containsCyclesWithAllEvents(stateId)) {
329 // Traverse the sub-graphs
330 if (isResetAfterAnalysis) {
331 // Advance choice counter for sub-graphs
333 // Do this for every CG after finishing each backtrack list
334 // We try to update the CG with a backtrack list if the state has been visited multiple times
335 if ((icsCG.getNextChoice() == -1 || choiceCounter > 1) && cgMap.containsKey(icsCG)) {
336 int event = cgMap.get(icsCG);
337 LinkedList<Integer[]> choiceLists = backtrackMap.get(event);
338 if (choiceLists != null && choiceLists.peekFirst() != null) {
339 Integer[] choiceList = choiceLists.removeFirst();
340 // Deploy the new choice list for this CG
341 icsCG.setNewValues(choiceList);
344 // Set done if this was the last backtrack list
350 // Update and reset the CG if needed (do this for the first time after the analysis)
351 // Start backtracking if this is a visited state and it is not a repeating state
353 isResetAfterAnalysis = true;
356 // Update the VOD graph always with the latest
357 updateVODGraph(icsCG.getNextChoice());
362 private void updateVODGraph(int currChoiceValue) {
363 // Update the graph when we have the current choice value
364 updateVODGraph(prevChoiceValue, currChoiceValue);
365 prevChoiceValue = currChoiceValue;
368 private void updateVODGraph(int prevChoice, int currChoice) {
370 HashSet<Integer> choiceSet;
371 if (vodGraphMap.containsKey(prevChoice)) {
372 // If the key already exists, just retrieve it
373 choiceSet = vodGraphMap.get(prevChoice);
375 // Create a new entry
376 choiceSet = new HashSet<>();
377 vodGraphMap.put(prevChoice, choiceSet);
379 choiceSet.add(currChoice);
383 public void stateAdvanced(Search search) {
385 id = search.getStateId();
386 depth = search.getDepth();
387 transition = search.getTransition();
388 if (search.isNewState()) {
394 if (search.isEndState()) {
395 out.println("\n==> DEBUG: This is the last state!\n");
398 out.println("\n==> DEBUG: The state is forwarded to state with id: " + id + " with depth: " + depth +
399 " which is " + detail + " Transition: " + transition + "\n");
401 if (stateReductionMode) {
402 // Update the state ID variables
403 stateId = search.getStateId();
404 currVisitedStates.add(stateId);
409 public void stateBacktracked(Search search) {
411 id = search.getStateId();
412 depth = search.getDepth();
413 transition = search.getTransition();
416 // Update the state variables
417 // Line 19 in the paper page 11 (see the heading note above)
418 stateId = search.getStateId();
419 currVisitedStates.add(stateId);
421 out.println("\n==> DEBUG: The state is backtracked to state with id: " + id + " -- Transition: " + transition +
422 " and depth: " + depth + "\n");
427 public void searchFinished(Search search) {
429 out.println("\n==> DEBUG: ----------------------------------- search finished" + "\n");
433 // This class compactly stores Read and Write field sets
434 // We store the field name and its object ID
435 // Sharing the same field means the same field name and object ID
436 private class ReadWriteSet {
437 private HashMap<String, Integer> readSet;
438 private HashMap<String, Integer> writeSet;
440 public ReadWriteSet() {
441 readSet = new HashMap<>();
442 writeSet = new HashMap<>();
445 public void addReadField(String field, int objectId) {
446 readSet.put(field, objectId);
449 public void addWriteField(String field, int objectId) {
450 writeSet.put(field, objectId);
453 public boolean readFieldExists(String field) {
454 return readSet.containsKey(field);
457 public boolean writeFieldExists(String field) {
458 return writeSet.containsKey(field);
461 public int readFieldObjectId(String field) {
462 return readSet.get(field);
465 public int writeFieldObjectId(String field) {
466 return writeSet.get(field);
470 private void analyzeReadWriteAccesses(Instruction executedInsn, String fieldClass, int currentChoice) {
471 // Do the analysis to get Read and Write accesses to fields
473 // We already have an entry
474 if (readWriteFieldsMap.containsKey(choices[currentChoice])) {
475 rwSet = readWriteFieldsMap.get(choices[currentChoice]);
476 } else { // We need to create a new entry
477 rwSet = new ReadWriteSet();
478 readWriteFieldsMap.put(choices[currentChoice], rwSet);
480 int objectId = ((JVMFieldInstruction) executedInsn).getFieldInfo().getClassInfo().getClassObjectRef();
481 // Record the field in the map
482 if (executedInsn instanceof WriteInstruction) {
483 // Exclude certain field writes because of infrastructure needs, e.g., Event class field writes
484 for (String str : EXCLUDED_FIELDS_WRITE_INSTRUCTIONS_STARTS_WITH_LIST) {
485 if (fieldClass.startsWith(str)) {
489 rwSet.addWriteField(fieldClass, objectId);
490 } else if (executedInsn instanceof ReadInstruction) {
491 rwSet.addReadField(fieldClass, objectId);
495 private boolean recordConflictPair(int currentEvent, int eventNumber) {
496 HashSet<Integer> conflictSet;
497 if (!conflictPairMap.containsKey(currentEvent)) {
498 conflictSet = new HashSet<>();
499 conflictPairMap.put(currentEvent, conflictSet);
501 conflictSet = conflictPairMap.get(currentEvent);
503 // If this conflict has been recorded before, we return false because
504 // we don't want to service this backtrack point twice
505 if (conflictSet.contains(eventNumber)) {
508 // If it hasn't been recorded, then do otherwise
509 conflictSet.add(eventNumber);
513 private String buildStringFromChoiceList(Integer[] newChoiceList) {
515 // When we see a choice list shorter than the upper bound, e.g., [3,2] for choices 0,1,2, and 3,
516 // then we have to pad the beginning before we store it, because [3,2] actually means [0,1,3,2]
517 // First, calculate the difference between this choice list and the upper bound
518 // The actual list doesn't include '-1' at the end
519 int actualListLength = newChoiceList.length - 1;
520 int diff = maxUpperBound - actualListLength;
521 StringBuilder sb = new StringBuilder();
522 // Pad the beginning if necessary
523 for (int i = 0; i < diff; i++) {
526 // Then continue with the actual choice list
527 // We don't include the '-1' at the end
528 for (int i = 0; i < newChoiceList.length - 1; i++) {
529 sb.append(newChoiceList[i]);
531 return sb.toString();
534 private void checkAndAddBacktrackList(LinkedList<Integer[]> backtrackChoiceLists, Integer[] newChoiceList) {
536 String newChoiceListString = buildStringFromChoiceList(newChoiceList);
537 // Add only if we haven't seen this combination before
538 if (!backtrackSet.contains(newChoiceListString)) {
539 backtrackSet.add(newChoiceListString);
540 backtrackChoiceLists.addLast(newChoiceList);
544 private void createBacktrackChoiceList(int currentChoice, int conflictEventNumber) {
546 LinkedList<Integer[]> backtrackChoiceLists;
547 // Create a new list of choices for backtrack based on the current choice and conflicting event number
548 // If we have a conflict between 1 and 3, then we create the list {3, 1, 2, 4, 5} for backtrack
549 // The backtrack point is the CG for event number 1 and the list length is one less than the original list
550 // (originally of length 6) since we don't start from event number 0
551 if (!isResetAfterAnalysis) {
552 // Check if we have a list for this choice number
553 // If not we create a new one for it
554 if (!backtrackMap.containsKey(conflictEventNumber)) {
555 backtrackChoiceLists = new LinkedList<>();
556 backtrackMap.put(conflictEventNumber, backtrackChoiceLists);
558 backtrackChoiceLists = backtrackMap.get(conflictEventNumber);
560 int maxListLength = choiceUpperBound + 1;
561 int listLength = maxListLength - conflictEventNumber;
562 Integer[] newChoiceList = new Integer[listLength + 1];
563 // Put the conflicting event numbers first and reverse the order
564 newChoiceList[0] = choices[currentChoice];
565 newChoiceList[1] = choices[conflictEventNumber];
566 // Put the rest of the event numbers into the array starting from the minimum to the upper bound
567 for (int i = conflictEventNumber + 1, j = 2; j < listLength; i++) {
568 if (choices[i] != choices[currentChoice]) {
569 newChoiceList[j] = choices[i];
573 // Set the last element to '-1' as the end of the sequence
574 newChoiceList[newChoiceList.length - 1] = -1;
575 checkAndAddBacktrackList(backtrackChoiceLists, newChoiceList);
576 // The start index for the recursion is always 1 (from the main branch)
577 } else { // This is a sub-graph
578 // There is a case/bug that after a re-initialization, currCG is not yet initialized
579 if (currCG != null && cgMap.containsKey(currCG)) {
580 int backtrackListIndex = cgMap.get(currCG);
581 backtrackChoiceLists = backtrackMap.get(backtrackListIndex);
582 int listLength = choices.length;
583 Integer[] newChoiceList = new Integer[listLength];
584 // Copy everything before the conflict number
585 for (int i = 0; i < conflictEventNumber; i++) {
586 newChoiceList[i] = choices[i];
588 // Put the conflicting events
589 newChoiceList[conflictEventNumber] = choices[currentChoice];
590 newChoiceList[conflictEventNumber + 1] = choices[conflictEventNumber];
592 for (int i = conflictEventNumber + 1, j = conflictEventNumber + 2; j < listLength - 1; i++) {
593 if (choices[i] != choices[currentChoice]) {
594 newChoiceList[j] = choices[i];
598 // Set the last element to '-1' as the end of the sequence
599 newChoiceList[newChoiceList.length - 1] = -1;
600 checkAndAddBacktrackList(backtrackChoiceLists, newChoiceList);
605 // We exclude fields that come from libraries (Java and Groovy), and also the infrastructure
606 private final static String[] EXCLUDED_FIELDS_STARTS_WITH_LIST =
607 // Java and Groovy libraries
608 { "java", "org", "sun", "com", "gov", "groovy"};
609 private final static String[] EXCLUDED_FIELDS_ENDS_WITH_LIST =
610 // Groovy library created fields
611 {"stMC", "callSiteArray", "metaClass", "staticClassInfo", "__constructor__",
613 "sendEvent", "Object", "reference", "location", "app", "state", "log", "functionList", "objectList",
614 "eventList", "valueList", "settings", "printToConsole", "app1", "app2"};
615 private final static String[] EXCLUDED_FIELDS_CONTAINS_LIST = {"_closure"};
616 private final static String[] EXCLUDED_FIELDS_WRITE_INSTRUCTIONS_STARTS_WITH_LIST = {"Event"};
618 private boolean isFieldExcluded(String field) {
619 // Check against "starts-with" list
620 for(String str : EXCLUDED_FIELDS_STARTS_WITH_LIST) {
621 if (field.startsWith(str)) {
625 // Check against "ends-with" list
626 for(String str : EXCLUDED_FIELDS_ENDS_WITH_LIST) {
627 if (field.endsWith(str)) {
631 // Check against "contains" list
632 for(String str : EXCLUDED_FIELDS_CONTAINS_LIST) {
633 if (field.contains(str)) {
641 // This method checks whether a choice is reachable in the VOD graph from a reference choice
642 // This is a BFS search
643 private boolean isReachableInVODGraph(int checkedChoice, int referenceChoice) {
644 // Record visited choices as we search in the graph
645 HashSet<Integer> visitedChoice = new HashSet<>();
646 visitedChoice.add(referenceChoice);
647 LinkedList<Integer> nodesToVisit = new LinkedList<>();
648 // If the state doesn't advance as the threads/sub-programs are executed (basically there is no new state),
649 // there is a chance that the graph doesn't have new nodes---thus this check will return a null.
650 if (vodGraphMap.containsKey(referenceChoice)) {
651 nodesToVisit.addAll(vodGraphMap.get(referenceChoice));
652 while(!nodesToVisit.isEmpty()) {
653 int currChoice = nodesToVisit.getFirst();
654 if (currChoice == checkedChoice) {
657 if (visitedChoice.contains(currChoice)) {
658 // If there is a loop then we don't find it
661 // Continue searching
662 visitedChoice.add(currChoice);
663 HashSet<Integer> currChoiceNextNodes = vodGraphMap.get(currChoice);
664 if (currChoiceNextNodes != null) {
665 // Add only if there is a mapping for next nodes
666 for (Integer nextNode : currChoiceNextNodes) {
668 if (nextNode == currChoice) {
671 nodesToVisit.addLast(nextNode);
680 public void instructionExecuted(VM vm, ThreadInfo ti, Instruction nextInsn, Instruction executedInsn) {
681 if (stateReductionMode) {
683 if (choiceCounter <= 0 || choiceCounter > choices.length - 1) {
684 // We do not compute the conflicts for the choice '-1'
687 int currentChoice = choiceCounter - 1;
688 // Record accesses from executed instructions
689 if (executedInsn instanceof JVMFieldInstruction) {
690 // Analyze only after being initialized
691 String fieldClass = ((JVMFieldInstruction) executedInsn).getFieldInfo().getFullName();
692 // We don't care about libraries
693 if (!isFieldExcluded(fieldClass)) {
694 analyzeReadWriteAccesses(executedInsn, fieldClass, currentChoice);
697 // Analyze conflicts from next instructions
698 if (nextInsn instanceof JVMFieldInstruction) {
699 // The constructor is only called once when the object is initialized
700 // It does not have shared access with other objects
701 MethodInfo mi = nextInsn.getMethodInfo();
702 if (!mi.getName().equals("<init>")) {
703 String fieldClass = ((JVMFieldInstruction) nextInsn).getFieldInfo().getFullName();
704 // We don't care about libraries
705 if (!isFieldExcluded(fieldClass)) {
706 // Check for conflict (go backward from currentChoice and get the first conflict)
707 // If the current event has conflicts with multiple events, then these will be detected
708 // one by one as this recursively checks backward when backtrack set is revisited and executed.
709 for (int eventNumber = currentChoice - 1; eventNumber >= 0; eventNumber--) {
710 // Skip if this event number does not have any Read/Write set
711 if (!readWriteFieldsMap.containsKey(choices[eventNumber])) {
714 ReadWriteSet rwSet = readWriteFieldsMap.get(choices[eventNumber]);
715 int currObjId = ((JVMFieldInstruction) nextInsn).getFieldInfo().getClassInfo().getClassObjectRef();
716 // 1) Check for conflicts with Write fields for both Read and Write instructions
717 if (((nextInsn instanceof WriteInstruction || nextInsn instanceof ReadInstruction) &&
718 rwSet.writeFieldExists(fieldClass) && rwSet.writeFieldObjectId(fieldClass) == currObjId) ||
719 (nextInsn instanceof WriteInstruction && rwSet.readFieldExists(fieldClass) &&
720 rwSet.readFieldObjectId(fieldClass) == currObjId)) {
721 // We do not record and service the same backtrack pair/point twice!
722 // If it has been serviced before, we just skip this
723 if (recordConflictPair(currentChoice, eventNumber)) {
724 // Lines 4-8 of the algorithm in the paper page 11 (see the heading note above)
725 if (vm.isNewState() ||
726 (!vm.isNewState() && isReachableInVODGraph(choices[currentChoice], choices[currentChoice-1]))) {
727 createBacktrackChoiceList(currentChoice, eventNumber);
728 // Break if a conflict is found!