# HG changeset patch
# User Peter Mehlitz <Peter.C.Mehlitz@nasa.gov>
# Date 1429601655 25200
# Node ID 6774e2e08d377af16d070ed6c537bf3f5ae4808d
# Parent  db918c531e6df8a1a11ee7f6b5857913e98aa278
the fix I would have liked to avoid - apparently hotspot internally does nested locking during class init, which can lead to deadlocks such as described in http://ternarysearch.blogspot.ru/2013/07/static-initialization-deadlock.html. Actually, it's not a regular deadlock since core dumps still list the threads as runnable, althouth it doesn't seem to be a livelock either. In any case, it can be simulated by nested locking and clinit execution, and it is such a serious defect that we want to be able to catch it. The general mechanism is to replace the disparate (but properly ordered) direct clinit calls of the generic ClassInfo.initializeClass() with a single sythetic method that includes all required locking (bottom up), clinit calls / class status change (top down), and unlocking (top down). We also need to add a synthetic insn to defer changing the class status of classes that don't have clinits(), or otherwise the correct lock/unlock order will not amount to anything if the hierarchy is entered through one of the clinit-absent classes. Now we get proper deadlocks if there are concurrent cyclic dependencies during class resolution. However, this can be such a state exploder that we certainly don't want this as the default behavior, especially since it probably is hotspot specific. Nested class init locking is therefore controlled by jvm.nested_init and respective jvm.nested_init.include/exclude options. Added a NestedInitTest to demonstrate use. Thanks to Lilia Abdulina for bringing this long forgotten issue up

In the wake of nested locks, there were a number of cases to fix that implicitly relied on absent clinits because clients were not properly checking for re-execution (most notably java.util.Exchanger). This mostly came in through MJIEnv.newObject/ElementInfo. We might turn ClinitRequired into a handled exception at some point, to catch such cases during compilation.

Added a UnknownJPFClass exception (in analogy to ClinitRequired), to make clients aware of failed class load attempts/reasons.

fixed Exchanger peer, which was not giving up the lock when timing out. This is an example of a lockfree wait op that can time out. Basically, ThreadInfo.isWaiting() needs to be complemented by a isWaitingOrTimedOut(), and ElementInfo.notifies0() has to be aware of it

fixed NPE when setting report.probe_interval in tests, which was missing that it had to create a stat object

diff -r db918c531e6d -r 6774e2e08d37 .idea/codeStyleSettings.xml
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/.idea/codeStyleSettings.xml	Tue Apr 21 00:34:15 2015 -0700
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectCodeStyleSettingsManager">
+    <option name="PER_PROJECT_SETTINGS">
+      <value>
+        <XML>
+          <option name="XML_LEGACY_SETTINGS_IMPORTED" value="true" />
+        </XML>
+      </value>
+    </option>
+    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default (1)" />
+  </component>
+</project>
\ No newline at end of file
diff -r db918c531e6d -r 6774e2e08d37 jpf.properties
--- a/jpf.properties	Wed Apr 15 22:40:21 2015 -0700
+++ b/jpf.properties	Tue Apr 21 00:34:15 2015 -0700
@@ -301,6 +301,17 @@
 # if this is set to true, overriden finalize() methods execute upon objects garbage collections
 vm.process_finalizers = false
 
+
+### jvm specifics
+
+# di=o we model nested locks during class init (to detect possible hotspot dealocks during init)
+# (off by default since it can cause state explosion)
+jvm.nested_init=false
+
+# if so, for which classes (default is to exclude system classes)
+jvm.nested_init.exclude=java.*,javax.*,sun.misc.*
+
+
 ############################### 3. CG part ###############################
 
 # choice randomization policy in effect:
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/JVMClassInfo.java
--- a/src/main/gov/nasa/jpf/jvm/JVMClassInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/JVMClassInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -18,34 +18,11 @@
 
 package gov.nasa.jpf.jvm;
 
+import gov.nasa.jpf.Config;
 import gov.nasa.jpf.util.Misc;
-import gov.nasa.jpf.vm.AbstractTypeAnnotationInfo;
-import gov.nasa.jpf.vm.AnnotationInfo;
-import gov.nasa.jpf.vm.BootstrapMethodInfo;
-import gov.nasa.jpf.vm.BytecodeAnnotationInfo;
-import gov.nasa.jpf.vm.BytecodeTypeParameterAnnotationInfo;
-import gov.nasa.jpf.vm.ClassInfo;
-import gov.nasa.jpf.vm.ClassLoaderInfo;
-import gov.nasa.jpf.vm.ClassParseException;
-import gov.nasa.jpf.vm.DirectCallStackFrame;
-import gov.nasa.jpf.vm.ExceptionHandler;
-import gov.nasa.jpf.vm.ExceptionParameterAnnotationInfo;
-import gov.nasa.jpf.vm.FieldInfo;
-import gov.nasa.jpf.vm.FormalParameterAnnotationInfo;
-import gov.nasa.jpf.vm.GenericSignatureHolder;
-import gov.nasa.jpf.vm.InfoObject;
-import gov.nasa.jpf.vm.LocalVarInfo;
-import gov.nasa.jpf.vm.MethodInfo;
-import gov.nasa.jpf.vm.NativeMethodInfo;
-import gov.nasa.jpf.vm.StackFrame;
-import gov.nasa.jpf.vm.SuperTypeAnnotationInfo;
-import gov.nasa.jpf.vm.ThreadInfo;
-import gov.nasa.jpf.vm.ThrowsAnnotationInfo;
-import gov.nasa.jpf.vm.TypeAnnotationInfo;
-import gov.nasa.jpf.vm.TypeParameterAnnotationInfo;
-import gov.nasa.jpf.vm.TypeParameterBoundAnnotationInfo;
-import gov.nasa.jpf.vm.Types;
-import gov.nasa.jpf.vm.VariableAnnotationInfo;
+import gov.nasa.jpf.util.StringSetMatcher;
+import gov.nasa.jpf.vm.*;
+
 import java.lang.reflect.Modifier;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
@@ -610,7 +587,22 @@
       }
     }
   }
-  
+
+  // since nested class init locking can explode the state space, we make it optional and controllable
+  protected static boolean nestedInit;
+  protected static StringSetMatcher includeNestedInit;
+  protected static StringSetMatcher excludeNestedInit;
+
+  protected static boolean init (Config config){
+    nestedInit = config.getBoolean("jvm.nested_init", false);
+    if (nestedInit){
+      includeNestedInit =  StringSetMatcher.getNonEmpty(config.getStringArray("jvm.nested_init.include"));
+      excludeNestedInit = StringSetMatcher.getNonEmpty(config.getStringArray("jvm.nested_init.exclude"));
+    }
+
+    return true;
+  }
+
   JVMClassInfo (String name, ClassLoaderInfo cli, ClassFile cf, String srcUrl, JVMCodeBuilder cb) throws ClassParseException {
     super( name, cli, srcUrl);
     
@@ -668,7 +660,79 @@
       // the interfaces are already loaded.
     }
   }
-  
+
+  /**
+   * perform initialization of this class and its not-yet-initialized superclasses (top down),
+   * which includes calling clinit() methods
+   *
+   * This is overridden here to model a questionable yet consequential behavior of hotspot, which
+   * is holding derived class locks when initializing base classes. The generic implementation in
+   * ClassInfo uses non-nested locks (i.e. A.clinit() only synchronizes on A.class) and hence cannot
+   * produce the same static init deadlocks as hotspot. In order to catch such defects we implement
+   * nested locking here.
+   *
+   * The main difference is that the generic implementation only pushes DCSFs for required clinits
+   * and otherwise doesn't lock anything. Here, we create one static init specific DCSF which wraps
+   * all clinits in nested monitorenter/exits. We create this even if there is no clinit so that we
+   * mimic hotspot locking.
+   *
+   * Note this scheme also enables us to get rid of the automatic clinit sync (they don't have
+   * a 0x20 sync modifier in classfiles)
+   *
+   * @return true if client needs to re-execute because we pushed DirectCallStackFrames
+   */
+  @Override
+  public boolean initializeClass(ThreadInfo ti) {
+    if (needsInitialization(ti)) {
+      if (nestedInit && StringSetMatcher.isMatch(name, includeNestedInit, excludeNestedInit)) {
+        registerClass(ti); // this is recursively upwards
+        int nOps = 2 * (getNumberOfSuperClasses() + 1); // this is just an upper bound for the number of operands we need
+
+        MethodInfo miInitialize = new MethodInfo("[initializeClass]", "()V", Modifier.STATIC, 0, nOps);
+        JVMDirectCallStackFrame frame = new JVMDirectCallStackFrame(miInitialize, null);
+        JVMCodeBuilder cb = getSystemCodeBuilder(null, miInitialize);
+
+        addClassInit(ti, frame, cb); // this is recursively upwards until we hit a initialized superclass
+        cb.directcallreturn();
+        cb.installCode();
+
+        // this is normally initialized in the ctor, but at that point we don't have the code yet
+        frame.setPC(miInitialize.getFirstInsn());
+
+        ti.pushFrame(frame);
+        return true; // client has to re-execute, we pushed a stackframe
+
+
+      } else { // use generic initialization without nested locks (directly calling clinits)
+        return super.initializeClass(ti);
+      }
+
+    } else {
+      return false; // nothing to do
+    }
+  }
+
+  protected void addClassInit (ThreadInfo ti, JVMDirectCallStackFrame frame, JVMCodeBuilder cb){
+    int clsObjRef = getClassObjectRef();
+
+    frame.pushRef(clsObjRef);
+    cb.monitorenter();
+
+    if (superClass != null && superClass.needsInitialization(ti)) {
+      ((JVMClassInfo) superClass).addClassInit(ti, frame, cb);      // go recursive
+    }
+
+    if (getMethod("<clinit>()V", false) != null) { // do we have a clinit
+      cb.invokeclinit(this);
+    } else {
+      cb.finishclinit(this);
+      // we can't just do call ci.setInitialized() since that has to be deferred
+    }
+
+    frame.pushRef(clsObjRef);
+    cb.monitorexit();
+  }
+
   //--- call processing
   
   protected JVMCodeBuilder getSystemCodeBuilder (ClassFile cf, MethodInfo mi){
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/JVMCodeBuilder.java
--- a/src/main/gov/nasa/jpf/jvm/JVMCodeBuilder.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/JVMCodeBuilder.java	Tue Apr 21 00:34:15 2015 -0700
@@ -88,7 +88,11 @@
     Instruction[] a = code.toArray( new Instruction[code.size()]);
     mi.setCode(a);
   }
-  
+
+  public int getCodeSize(){
+    return code.size();
+  }
+
   //--- the factory methods
 
   @Override public void aconst_null() {
@@ -996,13 +1000,13 @@
     Object v = cf.getCpValue(cpIntOrFloatOrStringOrClassIndex);
     switch (cf.getCpTag(cpIntOrFloatOrStringOrClassIndex)){
       case ClassFile.CONSTANT_INTEGER:
-        add( insnFactory.ldc_w((Integer)v)); break;
+        add( insnFactory.ldc_w((Integer) v)); break;
       case ClassFile.CONSTANT_FLOAT:
-        add( insnFactory.ldc_w((Float)v)); break;
+        add( insnFactory.ldc_w((Float) v)); break;
       case ClassFile.CONSTANT_STRING:
-        add( insnFactory.ldc_w((String)v, false)); break;
+        add( insnFactory.ldc_w((String) v, false)); break;
       case ClassFile.CONSTANT_CLASS:
-        add( insnFactory.ldc_w((String)v, true)); break;
+        add( insnFactory.ldc_w((String) v, true)); break;
     }
     pc+=3;
   }
@@ -1290,6 +1294,11 @@
     pc++;
   }
 
+  public void finishclinit (ClassInfo ci){
+    add (insnFactory.finishclinit(ci));
+    pc++;
+  }
+
   public void directcallreturn(){
     add( insnFactory.directcallreturn());
     pc++;
@@ -1309,5 +1318,5 @@
     add( insnFactory.runstart(mi));
     pc++;
   }
-  
+
 }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/JVMInstructionFactory.java
--- a/src/main/gov/nasa/jpf/jvm/JVMInstructionFactory.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/JVMInstructionFactory.java	Tue Apr 21 00:34:15 2015 -0700
@@ -480,4 +480,6 @@
 
   // this is never part of MethodInfo stored code
   abstract public Instruction runstart (MethodInfo miRun);
+
+  abstract public Instruction finishclinit (ClassInfo ci);
 }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/JVMSystemClassLoaderInfo.java
--- a/src/main/gov/nasa/jpf/jvm/JVMSystemClassLoaderInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/JVMSystemClassLoaderInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -44,6 +44,8 @@
 
     defaultCodeBuilder = createDefaultCodeBuilder(config, appId);
 
+    JVMClassInfo.init(config);
+
     // now we can notify
     vm.registerClassLoader(this);
   }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/bytecode/FINISHCLINIT.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/gov/nasa/jpf/jvm/bytecode/FINISHCLINIT.java	Tue Apr 21 00:34:15 2015 -0700
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2015, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package gov.nasa.jpf.jvm.bytecode;
+
+import gov.nasa.jpf.vm.ClassInfo;
+import gov.nasa.jpf.vm.Instruction;
+import gov.nasa.jpf.vm.ThreadInfo;
+
+/**
+ * artificial bytecode to defer class status changes of classes that don't have
+ * a <clinit>(), simulating native VM specific behavior that involves nested locking
+ * during class init
+ */
+public class FINISHCLINIT extends Instruction {
+
+  protected ClassInfo ciInit;
+
+  public FINISHCLINIT (ClassInfo ci){
+    ciInit = ci;
+  }
+
+  @Override
+  public Instruction execute (ThreadInfo ti) {
+    ciInit.setInitialized();
+    return getNext(ti);
+  }
+
+  @Override
+  public boolean isExtendedInstruction() {
+    return true;
+  }
+
+  public static final int OPCODE = 262;
+
+  @Override
+  public int getByteCode () {
+    return OPCODE;
+  }
+}
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/bytecode/INVOKECLINIT.java
--- a/src/main/gov/nasa/jpf/jvm/bytecode/INVOKECLINIT.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/bytecode/INVOKECLINIT.java	Tue Apr 21 00:34:15 2015 -0700
@@ -64,6 +64,7 @@
     
     // if we get here we still have to execute the clinit method
     setupCallee( ti, callee); // this creates, initializes & pushes the callee StackFrame, then acquires the lock
+    ciClsObj.setInitializing(ti);
 
     return ti.getPC(); // we can't just return the first callee insn if a listener throws an exception
   }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/bytecode/InstructionFactory.java
--- a/src/main/gov/nasa/jpf/jvm/bytecode/InstructionFactory.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/bytecode/InstructionFactory.java	Tue Apr 21 00:34:15 2015 -0700
@@ -1112,4 +1112,9 @@
     return new RUNSTART();
   }
 
+  @Override
+  public Instruction finishclinit(ClassInfo ci) {
+    return new FINISHCLINIT(ci);
+  }
+
 }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/bytecode/MONITORENTER.java
--- a/src/main/gov/nasa/jpf/jvm/bytecode/MONITORENTER.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/bytecode/MONITORENTER.java	Tue Apr 21 00:34:15 2015 -0700
@@ -69,7 +69,6 @@
     frame.pop();
     
     ei.lock(ti);  // mark object as locked, increment the lockCount, and set the thread as owner
-    
     return getNext(ti);
   }  
 
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/jvm/bytecode/RETURN.java
--- a/src/main/gov/nasa/jpf/jvm/bytecode/RETURN.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/jvm/bytecode/RETURN.java	Tue Apr 21 00:34:15 2015 -0700
@@ -33,12 +33,7 @@
   @Override
   public Instruction execute (ThreadInfo ti) {
 
-    // Constructors don't return anything so this is the only instruction that can be used to return from a constructor.
-
-    //MethodInfo mi = ti.getMethod();  // Get the current method being executed (e.g. returned from).
-
     if (mi.isInit()) {  // Check to see if this method is a constructor.
-
       int objref = ti.getThis();
       ElementInfo ei = ti.getElementInfo(objref); // Get the object.
 
@@ -52,6 +47,9 @@
           ei.setConstructed();
         }
       }
+
+    } else if (mi.isClinit()) {
+      mi.getClassInfo().setInitialized();
     }
 
     return super.execute(ti);
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/report/ConsolePublisher.java
--- a/src/main/gov/nasa/jpf/report/ConsolePublisher.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/report/ConsolePublisher.java	Tue Apr 21 00:34:15 2015 -0700
@@ -364,7 +364,7 @@
   // this can be used outside a publisher, to show the same info
   public static void printStatistics (PrintWriter pw, Reporter reporter){
     Statistics stat = reporter.getStatistics();
-    
+
     pw.println("elapsed time:       " + formatHMS(reporter.getElapsedTime()));
     pw.println("states:             new=" + stat.newStates + ",visited=" + stat.visitedStates
             + ",backtracked=" + stat.backtracked + ",end=" + stat.endStates);
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/report/Reporter.java
--- a/src/main/gov/nasa/jpf/report/Reporter.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/report/Reporter.java	Tue Apr 21 00:34:15 2015 -0700
@@ -62,7 +62,8 @@
     this.jpf = jpf;
     search = jpf.getSearch();
     vm = jpf.getVM();
-    boolean reportStats = conf.getBoolean("report.statistics", false);
+    int probeInterval = conf.getInt("report.probe_interval");
+    boolean reportStats = conf.getBoolean("report.statistics", false) || (probeInterval > 0);
 
     started = new Date();
 
@@ -82,7 +83,6 @@
       getRegisteredStatistics();
     }
     
-    int probeInterval = conf.getInt("report.probe_interval");
     if (probeInterval > 0){
       probeTimer = createProbeIntervalTimer(probeInterval);
     }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/util/json/JSONObject.java
--- a/src/main/gov/nasa/jpf/util/json/JSONObject.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/util/json/JSONObject.java	Tue Apr 21 00:34:15 2015 -0700
@@ -108,6 +108,12 @@
         if (requiresClinitExecution(ciField, ti)){
           return true;
         }
+        if (ciField.isArray()){
+          ClassInfo ciComp = ciField.getComponentClassInfo();
+          if (requiresClinitExecution(ciComp, ti)) {
+            return true;
+          }
+        }
       }
       
       ci = ci.getSuperClass();
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/ClassInfo.java
--- a/src/main/gov/nasa/jpf/vm/ClassInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/vm/ClassInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -1454,6 +1454,14 @@
       return null;
     }
   }
+
+  public int getNumberOfSuperClasses(){
+    int n = 0;
+    for (ClassInfo ci = superClass; ci != null; ci = ci.superClass){
+      n++;
+    }
+    return n;
+  }
   
   /**
    * beware - this loads (but not yet registers) the enclosing class
@@ -1961,13 +1969,13 @@
     return false;
   }
 
+  /**
+   * see getInitializedClassInfo() for restrictions.
+   */
   public static ClassInfo getInitializedSystemClassInfo (String clsName, ThreadInfo ti){
     ClassLoaderInfo systemLoader = ClassLoaderInfo.getCurrentSystemClassLoader();
     ClassInfo ci = systemLoader.getResolvedClassInfo(clsName);
-
-    if (ci.initializeClass(ti)) {
-      throw new ClinitRequired(ci);
-    }
+    ci.initializeClassAtomic(ti);
 
     return ci;
   }
@@ -1979,7 +1987,10 @@
    */
   public static ClassInfo getInitializedClassInfo (String clsName, ThreadInfo ti){
     ClassLoaderInfo cl = ClassLoaderInfo.getCurrentClassLoader();
-    return cl.getInitializedClassInfo(clsName, ti);
+    ClassInfo ci = cl.getResolvedClassInfo(clsName);
+    ci.initializeClassAtomic(ti);
+
+    return ci;
   }
 
   public boolean isRegistered () {
@@ -2131,9 +2142,16 @@
     return (!isObjectClassInfo() && superClass != null);
   }
 
-  public boolean needsInitialization () {
+  public boolean needsInitialization (ThreadInfo ti){
     StaticElementInfo sei = getStaticElementInfo();
-    return ((sei == null) || (sei.getStatus() > INITIALIZED));
+    if (sei != null){
+      int status = sei.getStatus();
+      if (status == INITIALIZED || status == ti.getId()){
+        return false;
+      }
+    }
+
+    return true;
   }
 
   public void setInitializing(ThreadInfo ti) {
@@ -2193,14 +2211,44 @@
 
     return (pushedFrames > 0);
   }
-    
+
+  /**
+   * use this with care since it will throw a JPFException if we encounter a choice point
+   * during execution of clinits
+   * Use this mostly for wrapper exceptions and other system classes that are guaranteed to load
+   */
+  public void initializeClassAtomic (ThreadInfo ti){
+    for (ClassInfo ci = this; ci != null; ci = ci.getSuperClass()) {
+      StaticElementInfo sei = ci.getStaticElementInfo();
+      if (sei == null){
+        sei = ci.registerClass(ti);
+      }
+
+      int status = sei.getStatus();
+      if (status != INITIALIZED && status != ti.getId()){
+          MethodInfo mi = ci.getMethod("<clinit>()V", false);
+          if (mi != null) {
+            DirectCallStackFrame frame = ci.createDirectCallStackFrame(ti, mi, 0);
+            ti.executeMethodAtomic(frame);
+          } else {
+            ci.setInitialized();
+          }
+      } else {
+        break; // if this class is initialized, so are its superclasses
+      }
+    }
+  }
+
   public void setInitialized() {
-    StaticElementInfo sei = getModifiableStaticElementInfo();
-    sei.setStatus(INITIALIZED);
+    StaticElementInfo sei = getStaticElementInfo();
+    if (sei != null && sei.getStatus() != INITIALIZED){
+      sei = getModifiableStaticElementInfo();
+      sei.setStatus(INITIALIZED);
 
-    // we don't emit classLoaded() notifications for non-builtin classes
-    // here anymore because it would be confusing to get instructionExecuted()
-    // notifications from the <clinit> execution before the classLoaded()
+      // we don't emit classLoaded() notifications for non-builtin classes
+      // here anymore because it would be confusing to get instructionExecuted()
+      // notifications from the <clinit> execution before the classLoaded()
+    }
   }
 
   public StaticElementInfo getStaticElementInfo() {
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/ClassLoaderInfo.java
--- a/src/main/gov/nasa/jpf/vm/ClassLoaderInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/vm/ClassLoaderInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -480,11 +480,7 @@
    */
   public ClassInfo getInitializedClassInfo (String clsName, ThreadInfo ti){
     ClassInfo ci = getResolvedClassInfo(clsName);
-
-    if (ci.initializeClass(ti)) {
-      throw new ClinitRequired(ci);
-    }
-
+    ci.initializeClassAtomic(ti);
     return ci;
   }
 
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/ElementInfo.java
--- a/src/main/gov/nasa/jpf/vm/ElementInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/vm/ElementInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -1856,7 +1856,7 @@
   
   
   private void notifies0 (ThreadInfo tiWaiter){
-    if (tiWaiter.isWaiting()){
+    if (tiWaiter.isWaitingOrTimedOut()){
       if (tiWaiter.getLockCount() > 0) {
         // waiter did hold the lock, but gave it up in the wait,  so it can't run yet
         tiWaiter.setNotifiedState();
@@ -1881,7 +1881,7 @@
     int i, nWaiters=0, iWaiter=0;
 
     for (i=0; i<locked.length; i++) {
-      if (locked[i].isWaiting()) {
+      if (locked[i].isWaitingOrTimedOut() ) {
         nWaiters++;
         iWaiter = i;
       }
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/MJIEnv.java
--- a/src/main/gov/nasa/jpf/vm/MJIEnv.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/vm/MJIEnv.java	Tue Apr 21 00:34:15 2015 -0700
@@ -17,10 +17,12 @@
  */
 package gov.nasa.jpf.vm;
 
+import com.sun.org.apache.bcel.internal.generic.InstructionConstants;
 import gov.nasa.jpf.Config;
 import gov.nasa.jpf.JPF;
 import gov.nasa.jpf.JPFException;
 import gov.nasa.jpf.JPFListener;
+import gov.nasa.jpf.vm.serialize.UnknownJPFClass;
 
 import java.util.Date;
 import java.util.Locale;
@@ -698,7 +700,7 @@
 
   public long getStaticLongField (int clsRef, String fname) {
     ClassInfo ci = getReferredClassInfo(clsRef);
-    return getStaticLongField(ci,fname);
+    return getStaticLongField(ci, fname);
   }
 
   public long getStaticLongField (String clsName, String fname) {
@@ -1036,12 +1038,12 @@
 
     return heap.newArray(elementClsName, size, ti).getObjectRef();
   }
-  
-  public ElementInfo newElementInfo (ClassInfo ci){
+
+  public ElementInfo newElementInfo (ClassInfo ci) throws ClinitRequired {
     if (ci.initializeClass(ti)){
       throw new ClinitRequired(ci);
     }
-    
+
     return heap.newObject(ci, ti);
   }
   
@@ -1050,7 +1052,7 @@
    * if yes, create a new instance of it but don't call any ctor
    * if no, throw a ClinitRequired exception
    */
-  public int newObject (ClassInfo ci) {
+  public int newObject (ClassInfo ci)  throws ClinitRequired {
     ElementInfo ei = newElementInfo(ci);
     return ei.getObjectRef();
   }
@@ -1065,22 +1067,18 @@
     return ei.getObjectRef();    
   }
   
-  public ElementInfo newElementInfo (String clsName) {
+  public ElementInfo newElementInfo (String clsName)  throws ClinitRequired, UnknownJPFClass {
     ClassInfo ci = ClassLoaderInfo.getCurrentResolvedClassInfo(clsName);
     if (ci != null){
       return newElementInfo(ci);
     } else {
-      return null;
+      throw new UnknownJPFClass(clsName);
     }
   }
   
-  public int newObject (String clsName) {
+  public int newObject (String clsName)   throws ClinitRequired, UnknownJPFClass {
     ElementInfo ei = newElementInfo(clsName);
-    if (ei != null){
-      return ei.getObjectRef();
-    } else {
-      return NULL;
-    }
+    return (ei != null) ? ei.getObjectRef() : NULL;
   }
   
   public int newString (String s) {
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/ThreadInfo.java
--- a/src/main/gov/nasa/jpf/vm/ThreadInfo.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/main/gov/nasa/jpf/vm/ThreadInfo.java	Tue Apr 21 00:34:15 2015 -0700
@@ -819,6 +819,11 @@
     return (state == State.WAITING) || (state == State.TIMEOUT_WAITING);
   }
 
+  public boolean isWaitingOrTimedOut (){
+    State state = threadData.state;
+    return (state == State.WAITING) || (state == State.TIMEOUT_WAITING) || (state == State.TIMEDOUT);
+  }
+
   public boolean isNotified () {
     return (threadData.state == State.NOTIFIED);
   }
@@ -1775,9 +1780,10 @@
    * thrown by the VM (or a listener)
    */
   public Instruction createAndThrowException (ClassInfo ci, String details) {
-    if (ci.initializeClass(this)) {
-      return getPC();
-    }
+    //if (ci.initializeClass(this)) {
+    //  return getPC();
+    //}
+    ci.initializeClassAtomic(this);
 
     int objref = createException(ci,details, MJIEnv.NULL);
     return throwException(objref);
@@ -1872,40 +1878,6 @@
     }
   }
 
-  
-  protected void _executeTransition (SystemState ss) throws JPFException {
-    Instruction pc = getPC();
-    Instruction nextPc = null;
-
-    currentThread = this;
-    executedInstructions = 0;
-    pendingException = null;
-
-    if (isStopped()){
-      pc = throwStopException();
-      setPC(pc);
-    }
-    
-    // this constitutes the main transition loop. It gobbles up
-    // insns until someone registered a ChoiceGenerator, there are no insns left,
-    // the transition was explicitly marked as ignored, or we have reached a
-    // max insn count and preempt the thread upon the next available backjump
-    while (pc != null) {
-      nextPc = executeInstruction();
-      
-      if (ss.breakTransition()) {
-        if (executedInstructions == 0){ // a CG from a re-executed insn
-          if (isEmptyTransitionEnabled()){ // treat as a new state if empty transitions are enabled
-            ss.setForced(true);
-          }
-        }
-        break;
-        
-      } else {        
-        pc = nextPc;
-      }
-    }
-  }
 
   protected void resetTransientAttributes(){
     attributes &= ~(ATTR_SKIP_INSN_EXEC | ATTR_SKIP_INSN_LOG | ATTR_ENABLE_EMPTY_TRANSITION);
@@ -2236,10 +2208,6 @@
       ElementInfo ei = getModifiableElementInfo( oref);
       
       ei.lock(this);
-      
-      if (mi.isClinit()) {
-        mi.getClassInfo().setInitializing(this);
-      }
     }
 
     vm.notifyMethodEntered(this, mi);
@@ -2268,14 +2236,6 @@
         ei = ei.getModifiableInstance();
         didUnblock = ei.unlock(this);
       }
-      
-      if (mi.isClinit()) {
-        // we just released the lock on the class object, returning from a clinit
-        // now we can consider this class to be initialized.
-        // NOTE this is still part of the RETURN insn of clinit, so ClassInfo.isInitialized
-        // is protected
-        mi.getClassInfo().setInitialized();
-      }
     }
 
     vm.notifyMethodExited(this, mi);
@@ -2875,6 +2835,7 @@
     for (StackFrame frame = top; (frame != null) && (handlerFrame == null); frame = frame.getPrevious()) {
       // that means we have to turn the exception into an InvocationTargetException
       if (frame.isReflection()) {
+        // make sure it's in the startup class set since we are not able to re-execute here
         ciException = ClassInfo.getInitializedSystemClassInfo("java.lang.reflect.InvocationTargetException", this);
         exceptionObjRef  = createException(ciException, exceptionName, exceptionObjRef);
         exceptionName = ciException.getName();
diff -r db918c531e6d -r 6774e2e08d37 src/main/gov/nasa/jpf/vm/serialize/UnknownJPFClass.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/gov/nasa/jpf/vm/serialize/UnknownJPFClass.java	Tue Apr 21 00:34:15 2015 -0700
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2015, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package gov.nasa.jpf.vm.serialize;
+
+/**
+ * exception to indicate that JPF can't find a (model) class of a given name
+ * For native clients directly or indirectly cause class resolution
+ *
+ * <2do> we might turn this into an handled exception at some point
+ */
+public class UnknownJPFClass extends RuntimeException {
+  protected String clsName;
+
+  public UnknownJPFClass(String clsName){
+    this.clsName = clsName;
+  }
+
+  String getRequestedClassName() {
+    return clsName;
+  }
+
+  @Override
+  public String getMessage(){
+    return clsName;
+  }
+}
diff -r db918c531e6d -r 6774e2e08d37 src/peers/gov/nasa/jpf/vm/JPF_java_util_concurrent_Exchanger.java
--- a/src/peers/gov/nasa/jpf/vm/JPF_java_util_concurrent_Exchanger.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/peers/gov/nasa/jpf/vm/JPF_java_util_concurrent_Exchanger.java	Tue Apr 21 00:34:15 2015 -0700
@@ -48,7 +48,7 @@
     }
   }
   
-  ElementInfo createExchangeObject (MJIEnv env, int waiterDataRef){
+  ElementInfo createExchangeObject (MJIEnv env, int waiterDataRef) throws ClinitRequired {
     ElementInfo ei = env.newElementInfo("java.util.concurrent.Exchanger$Exchange");
     ei.setReferenceField("waiterData", waiterDataRef);
     ei.setReferenceField("waiterThread", env.getThreadInfo().getThreadObjectRef());
@@ -75,26 +75,35 @@
     StackFrame frame = ti.getModifiableTopFrame();
     ExchangeState state = frame.getFrameAttr(ExchangeState.class);
     long to = (timeoutMillis <0) ? 0 : timeoutMillis;
-    
+
     if (state == null){ // first time for waiter or responder
       int eRef = env.getReferenceField(objRef, "exchange");
       
       if (eRef == MJIEnv.NULL){ // first waiter, this has to block unless there is a timeout value of 0
-        ElementInfo ei = createExchangeObject(env, dataRef);
-        eRef = ei.getObjectRef();
+        ElementInfo eiExchanger;
+
+        try {
+          eiExchanger = createExchangeObject(env, dataRef);
+        } catch (ClinitRequired x){
+          // need to come back after class init
+          env.repeatInvocation();
+          return MJIEnv.NULL;
+        }
+
+        eRef = eiExchanger.getObjectRef();
         env.setReferenceField(objRef, "exchange", eRef);
         
         // timeout semantics differ - Object.wait(0) waits indefinitely, whereas here it
         // should throw immediately. We use -1 as non-timeout value
-        if (timeoutMillis == 0){
+        if (timeoutMillis == 0) {
           env.throwException("java.util.concurrent.TimeoutException");
           return MJIEnv.NULL;
         }
-        
-        ei.wait(ti, to, false);
+
+        eiExchanger.wait(ti, to, false);  // lockfree wait
         
         if (ti.getScheduler().setsWaitCG(ti, to)) {
-          return repeatInvocation(env, frame, ei, ExchangeState.createWaiterState(env, eRef));
+          return repeatInvocation(env, frame, eiExchanger, ExchangeState.createWaiterState(env, eRef));
         } else {
           throw new JPFException("blocked exchange() waiter without transition break");
         }
@@ -128,7 +137,7 @@
       }
       
     } else { // re-execution(s)
-      ElementInfo ei = env.getElementInfo(state.exchangeRef);
+      ElementInfo eiExchanger = env.getElementInfo(state.exchangeRef);
 
       int retRef = MJIEnv.NULL;
       
@@ -136,20 +145,24 @@
         env.throwException("java.lang.InterruptedException");
 
       } else if (ti.isTimedOut()){
-        if (state.isWaiter){
-          ei = ei.getModifiableInstance();
-          ei.setBooleanField("waiterTimedOut", true);
+        if (state.isWaiter) {
+          eiExchanger = eiExchanger.getModifiableInstance();
+          eiExchanger.setBooleanField("waiterTimedOut", true);
+
+          // we are still lockfree waiting on the exChanger object
+          eiExchanger.notifies(env.getSystemState(), ti, false);
         }
+
         env.throwException("java.util.concurrent.TimeoutException");
         
       } else {
-        retRef = ei.getReferenceField( state.isWaiter ? "responderData" : "waiterData");
+        retRef = eiExchanger.getReferenceField( state.isWaiter ? "responderData" : "waiterData");
       }
       
       //-- processed
       frame.removeFrameAttr(state);
-      ei = ei.getModifiableInstance();
-      env.releasePinDown(ei);
+      eiExchanger = eiExchanger.getModifiableInstance();
+      env.releasePinDown(eiExchanger);
       return retRef;
     }
   }
diff -r db918c531e6d -r 6774e2e08d37 src/tests/gov/nasa/jpf/test/mc/data/JSONTest.java
--- a/src/tests/gov/nasa/jpf/test/mc/data/JSONTest.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/tests/gov/nasa/jpf/test/mc/data/JSONTest.java	Tue Apr 21 00:34:15 2015 -0700
@@ -265,11 +265,11 @@
     }
   }
 
-  class IC {
+  static class IC {
     int i;
   }
 
-  class ArrayOfObjects {
+  static class ArrayOfObjects {
     IC cls[];
   }
 
diff -r db918c531e6d -r 6774e2e08d37 src/tests/gov/nasa/jpf/test/mc/threads/ClinitTest.java
--- a/src/tests/gov/nasa/jpf/test/mc/threads/ClinitTest.java	Wed Apr 15 22:40:21 2015 -0700
+++ b/src/tests/gov/nasa/jpf/test/mc/threads/ClinitTest.java	Tue Apr 21 00:34:15 2015 -0700
@@ -29,58 +29,59 @@
 
   static class X {
     static int x;
+
     static {
       Verify.threadPrintln("initializing X");
-      assertTrue( x == 0);
+      assertTrue(x == 0);
       x++;
     }
   }
-  
+
   @Test
-  public void testNoConcurrentClinit () {
+  public void testNoConcurrentClinit() {
     if (verifyNoPropertyViolation()) {
-   
+
       Runnable r = new Runnable() {
         @Override
-		public void run() {
+        public void run() {
           int x = X.x;
         }
       };
       Thread t = new Thread(r);
       t.start();
-      
+
       int x = X.x;
-      assertTrue( "x = " + x, x == 1);
+      assertTrue("x = " + x, x == 1);
     }
   }
-  
-  
+
+
   static class Y {
     static long y;
-    
+
     static {
       Thread t = Thread.currentThread();
-       Verify.threadPrintln("initializing Y");
+      Verify.threadPrintln("initializing Y");
       y = t.getId();
     }
   }
-  
+
   @Test
   public void testClinitChoices() {
     if (verifyAssertionErrorDetails("gotcha")) {
       Runnable r = new Runnable() {
         @Override
-		public void run() {
+        public void run() {
           long y = Y.y;
         }
       };
       Thread t = new Thread(r);
       t.start();
-      
+
       long y = Y.y;
       Thread tCur = Thread.currentThread();
       Verify.threadPrintln("testing Y.y");
-      assertTrue( "gotcha", y == tCur.getId());
+      assertTrue("gotcha", y == tCur.getId());
     }
   }
 }
diff -r db918c531e6d -r 6774e2e08d37 src/tests/gov/nasa/jpf/test/mc/threads/NestedInitTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/tests/gov/nasa/jpf/test/mc/threads/NestedInitTest.java	Tue Apr 21 00:34:15 2015 -0700
@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2015, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package gov.nasa.jpf.test.mc.threads;
+
+import gov.nasa.jpf.util.test.TestJPF;
+import org.junit.Test;
+
+/**
+ * test deadlock detection during concurrent class init.
+ *
+ * This models hotspot behavior that can explode the state space
+ * and hence needs to be explicitly configured to perform
+ * nested locking during class init
+ */
+public class NestedInitTest extends TestJPF {
+
+  //------------------------------------------------ check normal clinit execution
+  static class Root {
+    static int data;
+
+    static {
+      System.out.print( Thread.currentThread().getName());
+      System.out.println(" in Root.<clinit>()");
+      data = 40;
+    }
+  }
+
+  static class Base extends Root {
+    static int data;
+
+    static {
+      System.out.print( Thread.currentThread().getName());
+      System.out.println(" in Base.<clinit>()");
+      data = Root.data + 1;
+    }
+  }
+
+  static class Derived extends Base {
+    static int data;
+
+    static {
+      System.out.print( Thread.currentThread().getName());
+      System.out.println(" in Derived.<clinit>()");
+      data = Base.data + 1;
+    }
+  }
+
+  @Test
+  public void testNestedInitSingleOk() {
+    if (verifyNoPropertyViolation("+jvm.nested_init")){
+      new Derived(); // force clinit
+      System.out.print("Derived.data = ");
+      System.out.println(Derived.data);
+      assertTrue(Derived.data == 42);
+    }
+  }
+
+  @Test
+  public void testNestedInitConcurrentOk() {
+    if (verifyNoPropertyViolation("+jvm.nested_init")){
+      new Thread( new Runnable(){
+        public void run(){
+          new Derived();
+          System.out.print("t: Derived.data = ");
+          System.out.println(Derived.data);
+          assertTrue(Derived.data == 42);
+        }
+      }).start();
+
+      new Derived(); // force clinit
+      System.out.print("main: Derived.data = ");
+      System.out.println(Derived.data);
+      assertTrue(Derived.data == 42);
+    }
+  }
+
+  //--- and now the nasty cases
+
+  //------------------------------------------ symmetric case
+
+  static class A {
+    static final B b = new B();
+  }
+
+  static class B {
+    static final A a = new A();
+  }
+
+  @Test
+  public void testSymmetricDeadlock() {
+    if (verifyDeadlock("+jvm.nested_init")) {
+      new Thread() {
+        public void run() {
+          new A();
+        }
+      }.start();
+      new B();
+    }
+  }
+
+  //------------------------------------------- hierarchical case
+  public static class CyclicBase {
+    static CyclicDerived sub = new CyclicDerived();
+  }
+
+  public static class CyclicDerived extends CyclicBase {
+  }
+
+
+  @Test
+  public void testCyclicHierarchyDeadlock (){
+    if (verifyDeadlock("+jvm.nested_init")) {
+      new Thread() {
+        public void run() {
+          new CyclicDerived(); // causes class inits via CyclicDerived
+        }
+      }.start();
+
+      Object o = CyclicBase.sub; // causes class inits via CyclicBase
+    }
+  }
+
+}
diff -r db918c531e6d -r 6774e2e08d37 src/tests/gov/nasa/jpf/test/vm/basic/ClassInitTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/tests/gov/nasa/jpf/test/vm/basic/ClassInitTest.java	Tue Apr 21 00:34:15 2015 -0700
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2015, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package gov.nasa.jpf.test.vm.basic;
+
+import gov.nasa.jpf.util.test.TestJPF;
+import org.junit.Test;
+
+/**
+ * basic regression test for class initialization
+ */
+public class ClassInitTest extends TestJPF {
+
+    static class Root {
+        static int data;
+        static {
+            System.out.println("in Root.<clinit>()");
+            data = 42;
+        }
+    }
+
+    static class Base extends Root {
+        static int data;
+        static {
+            System.out.println("in Base.<clinit>()");
+            data = Root.data + 1;
+        }
+    }
+
+    static class Derived extends Base {
+        static int data;
+        static {
+            System.out.println("in Derived.<clinit>()");
+            data = Base.data + 1;
+        }
+    }
+
+    @Test
+    public void testClinits (){
+        if (verifyNoPropertyViolation()){
+            int n = Derived.data;
+            assertTrue(n == 44);
+        }
+    }
+}