Disallow null in QueueReader to handle concurrency correctly

Before that, it could happen that the QueueReader's hasNext method is called, and then the corresponding element gets invalidated by another thread. In that case, the next method throw a NoSuchElement exce>
Instead (and conforming to to the JavaDoc), we allow null to be returned in these cases.
This means that ChunkedQueues may not contain actual nulls anymore.

Author: MarcMil

src/main/java/soot/MethodToContexts.java

@@ -55,7 +55,9 @@ public MethodToContexts(Iterator<MethodOrMethodContext> it) {
   public void add(Iterator<MethodOrMethodContext> it) {
     while (it.hasNext()) {
       MethodOrMethodContext momc = it.next();
-      add(momc);
+      if (momc != null) {
+        add(momc);
+      }
     }
   }
 

src/main/java/soot/jimple/spark/builder/ContextInsensitiveBuilder.java

@@ -104,11 +104,14 @@ public void build() {
     }
     while (callEdges.hasNext()) {
       Edge e = callEdges.next();
+      if (e == null) {
+        continue;
+      }
       if (!e.isInvalid()) {
         if (e.tgt().isConcrete() || e.tgt().isNative()) {
-	  MethodPAG mpag = MethodPAG.v(pag, e.tgt());
-	  mpag.build();
-	  mpag.addToPAG(null);
+          MethodPAG mpag = MethodPAG.v(pag, e.tgt());
+          mpag.build();
+          mpag.addToPAG(null);
         }
         pag.addCallTarget(e);
       }

src/main/java/soot/jimple/spark/geom/geomPA/GeomPointsTo.java

@@ -359,7 +359,11 @@ private void preprocess() {
     CallGraph soot_callgraph = Scene.v().getCallGraph();
 
     while (smList.hasNext()) {
-      final SootMethod func = smList.next().method();
+      MethodOrMethodContext n = smList.next();
+      if (n == null) {
+        continue;
+      }
+      final SootMethod func = n.method();
       func2int.put(func, id);
       int2func.put(id, func);
 
@@ -385,7 +389,7 @@ private void preprocess() {
     QueueReader<Edge> edgeList = Scene.v().getCallGraph().listener();
     while (edgeList.hasNext()) {
       Edge edge = edgeList.next();
-      if (edge.isClinit()) {
+      if (edge == null || edge.isClinit()) {
         continue;
       }
 

src/main/java/soot/jimple/spark/internal/TypeManager.java

@@ -115,6 +115,9 @@ final public BitVector get(Type type) {
     final Scene sc = Scene.v();
     while (allocNodeListener.hasNext()) {
       AllocNode n = allocNodeListener.next();
+      if (n == null) {
+        continue;
+      }
       Type nt = n.getType();
       Iterable<Type> types;
       if (nt instanceof NullType || nt instanceof AnySubType) {

src/main/java/soot/jimple/spark/solver/OnFlyCallGraph.java

@@ -111,6 +111,9 @@ private void processReachables() {
     reachableMethods.update();
     while (reachablesReader.hasNext()) {
       MethodOrMethodContext m = reachablesReader.next();
+      if (m == null) {
+        continue;
+      }
       MethodPAG mpag = MethodPAG.v(pag, m.method());
       try {
         mpag.build();
@@ -129,6 +132,9 @@ private void processReachables() {
   private void processCallEdges() {
     while (callEdges.hasNext()) {
       Edge e = callEdges.next();
+      if (e == null) {
+        continue;
+      }
       MethodPAG amp = MethodPAG.v(pag, e.tgt());
       amp.build();
       amp.addToPAG(e.tgtCtxt());

src/main/java/soot/jimple/toolkits/callgraph/CallGraph.java

@@ -29,6 +29,7 @@
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.NoSuchElementException;
 import java.util.Set;
 
 import soot.Kind;
@@ -99,7 +100,7 @@ public boolean removeAllEdgesOutOf(Unit u) {
     Set<Edge> edgesToRemove = new HashSet<>();
     for (QueueReader<Edge> edgeRdr = listener(); edgeRdr.hasNext();) {
       Edge e = edgeRdr.next();
-      if (e.srcUnit() == u) {
+      if (e != null && e.srcUnit() == u) {
         e.remove();
         removeEdge(e, false);
         edgesToRemove.add(e);
@@ -395,7 +396,9 @@ public String toString() {
     StringBuilder out = new StringBuilder();
     for (QueueReader<Edge> reader = listener(); reader.hasNext();) {
       Edge e = reader.next();
-      out.append(e.toString()).append('\n');
+      if (e != null) {
+        out.append(e.toString()).append('\n');
+      }
     }
     return out.toString();
   }

src/main/java/soot/jimple/toolkits/callgraph/CallGraphBuilder.java

@@ -111,7 +111,7 @@ public void build() {
         break;
       }
       final MethodOrMethodContext momc = worklist.next();
-      if (!process(momc)) {
+      if (momc != null && !process(momc)) {
         break;
       }
     }

src/main/java/soot/jimple/toolkits/callgraph/Filter.java

@@ -48,6 +48,9 @@ public Iterator<Edge> wrap(Iterator<Edge> source) {
   private void advance() {
     while (source.hasNext()) {
       next = source.next();
+      if (next == null) {
+    	continue;
+      }
       if (pred.want(next)) {
         return;
       }

src/main/java/soot/jimple/toolkits/callgraph/OnFlyCallGraphBuilder.java

@@ -279,6 +279,9 @@ public void processReachables() {
         }
       }
       MethodOrMethodContext momc = worklist.next();
+      if (momc == null) {
+        continue;
+      }
       SootMethod m = momc.method();
       if (appOnly && !m.getDeclaringClass().isApplicationClass()) {
         continue;

src/main/java/soot/jimple/toolkits/callgraph/ReachableMethods.java

@@ -25,6 +25,7 @@
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.NoSuchElementException;
 import java.util.Set;
 
 import soot.MethodOrMethodContext;
@@ -89,6 +90,9 @@ public void update() {
     }
     while (unprocessedMethods.hasNext()) {
       MethodOrMethodContext m = unprocessedMethods.next();
+      if (m == null) {
+    	continue;
+      }
       Iterator<Edge> targets = cg.edgesOutOf(m);
       if (filter != null) {
         targets = filter.wrap(targets);

src/main/java/soot/jimple/toolkits/callgraph/SlowCallGraph.java

@@ -134,7 +134,9 @@ public String toString() {
     StringBuilder out = new StringBuilder();
     for (QueueReader<Edge> rdr = listener(); rdr.hasNext();) {
       Edge e = rdr.next();
-      out.append(e.toString()).append('\n');
+      if (e != null) {
+        out.append(e.toString()).append('\n');
+      }
     }
     return out.toString();
   }

src/main/java/soot/util/queue/ChunkedQueue.java

@@ -33,7 +33,6 @@
 @SuppressWarnings("unchecked")
 public class ChunkedQueue<E> {
 
-  protected static final Object NULL_CONST = new Object();
   protected static final Object DELETED_CONST = new Object();
 
   protected static final int LENGTH = 60;
@@ -48,7 +47,7 @@ public ChunkedQueue() {
   /** Add an object to the queue. */
   public void add(E o) {
     if (o == null) {
-      o = (E) NULL_CONST;
+      throw new IllegalArgumentException("Null is not allowed");
     }
     if (index == LENGTH - 1) {
       Object[] temp = new Object[LENGTH];

src/main/java/soot/util/queue/QueueReader.java

@@ -35,6 +35,7 @@
  * been read by all the QueueReader's are kept. A QueueReader only receives the Object's added to the queue <b>after</b> the
  * QueueReader was created.
  *
+ * This QueueReader does <emph>not</emph> accept <code>null</code> values. 
  * @author Ondrej Lhotak
  */
 public class QueueReader<E> implements java.util.Iterator<E> {
@@ -54,19 +55,20 @@ public E next() {
     Object ret = null;
     do {
       if (q[index] == null) {
-        throw new NoSuchElementException();
+        //this is the case when someone concurrently invalidates 
+        //the rest of the elements
+        return null;
       }
       if (index == q.length - 1) {
         q = (E[]) q[index];
         index = 0;
         if (q[index] == null) {
-          throw new NoSuchElementException();
+          //this is the case when someone concurrently invalidates 
+          //the rest of the elements
+          return null;
         }
       }
       ret = q[index];
-      if (ret == ChunkedQueue.NULL_CONST) {
-        ret = null;
-      }
       index++;
     } while (skip(ret));
     return (E) ret;