fix issue 305: CodeConverter.replaceArrayAccess leads to java.util.ConcurrentModificationException

src/main/javassist/bytecode/analysis/Type.java

@@ -15,9 +15,7 @@
  */
 package javassist.bytecode.analysis;
 
-import java.util.HashMap;
-import java.util.IdentityHashMap;
-import java.util.Map;
+import java.util.*;
 
 import javassist.ClassPool;
 import javassist.CtClass;
@@ -496,24 +494,26 @@ Map<String,CtClass> findCommonInterfaces(Map<String,CtClass> typeMap, Map<String
         if (typeMap == null||typeMap.isEmpty())
             alterMap.clear();
 
-        for (String name:alterMap.keySet())
+        Iterator<String> it = alterMap.keySet().iterator();
+        while (it.hasNext()) {
+            String name = it.next();
             if (!typeMap.containsKey(name))
-                alterMap.remove(name);
+                it.remove();
+        }
 
         // Reduce to subinterfaces
         // This does not need to be recursive since we make a copy,
         // and that copy contains all super types for the whole hierarchy
-        for (CtClass intf:alterMap.values()) {
-            CtClass[] interfaces;
+        Collection<CtClass> interfaces = new ArrayList<>();
+        for (CtClass intf : alterMap.values()) {
             try {
-                interfaces = intf.getInterfaces();
+                interfaces.addAll(Arrays.asList(intf.getInterfaces()));
             } catch (NotFoundException e) {
                 throw new RuntimeException(e);
             }
-
-            for (CtClass c:interfaces)
-                alterMap.remove(c.getName());
         }
+        for (CtClass c : interfaces)
+            alterMap.remove(c.getName());
 
         return alterMap;
     }

src/test/javassist/JvstTest.java

@@ -1179,6 +1179,7 @@ public static Test suite() {
         suite.addTestSuite(test.javassist.proxy.ProxySimpleTest.class);
         suite.addTestSuite(test.javassist.bytecode.analysis.AnalyzerTest.class);
         suite.addTestSuite(test.javassist.convert.ArrayAccessReplaceTest.class);
+        suite.addTestSuite(test.javassist.convert.ArrayAccessReplaceTest2.class);
         suite.addTestSuite(test.javassist.bytecode.analysis.DomTreeTest.class);
         return suite;
     }

src/test/test/javassist/convert/ArrayAccessReplaceTest2.java

@@ -0,0 +1,21 @@
+package test.javassist.convert;
+
+import javassist.ClassPool;
+import javassist.CodeConverter;
+import javassist.CtClass;
+import junit.framework.TestCase;
+
+public class ArrayAccessReplaceTest2 extends TestCase {
+
+    public void testAdvancedInstrumentation() throws Exception {
+        ClassPool pool = new ClassPool(true);
+        CtClass monitoringClass = pool.get(ArrayAccessReplaceTest2.class.getName());
+        CtClass targetClass = pool.get(InstrumentationTarget.class.getName());
+        CodeConverter converter = new CodeConverter();
+        // we just test if the instrumentation works, the monitoring class does not need to actually contain the replacer methods
+        // what is only relevant when code gets executed
+        converter.replaceArrayAccess(monitoringClass, new CodeConverter.DefaultArrayAccessReplacementMethodNames());
+        targetClass.instrument(converter);
+    }
+
+}