Merge

hotspot/src/share/vm/classfile/classFileParser.cpp

@@ -232,7 +232,9 @@ constantPoolHandle ClassFileParser::parse_constant_pool(TRAPS) {
     length >= 1, "Illegal constant pool size %u in class file %s",
     length, CHECK_(nullHandle));
   constantPoolOop constant_pool =
-                      oopFactory::new_constantPool(length, CHECK_(nullHandle));
+                      oopFactory::new_constantPool(length,
+                                                   methodOopDesc::IsSafeConc,
+                                                   CHECK_(nullHandle));
   constantPoolHandle cp (THREAD, constant_pool);
 
   cp->set_partially_loaded();    // Enables heap verify to work on partial constantPoolOops
@@ -1675,7 +1677,8 @@ methodHandle ClassFileParser::parse_method(constantPoolHandle cp, bool is_interf
   // All sizing information for a methodOop is finally available, now create it
   methodOop m_oop  = oopFactory::new_method(
     code_length, access_flags, linenumber_table_length,
-    total_lvt_length, checked_exceptions_length, CHECK_(nullHandle));
+    total_lvt_length, checked_exceptions_length,
+    methodOopDesc::IsSafeConc, CHECK_(nullHandle));
   methodHandle m (THREAD, m_oop);
 
   ClassLoadingService::add_class_method_size(m_oop->size()*HeapWordSize);

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp

@@ -706,6 +706,30 @@ void CompactibleFreeListSpace::object_iterate(ObjectClosure* blk) {
   }
 }
 
+// Apply the given closure to each live object in the space
+//   The usage of CompactibleFreeListSpace
+// by the ConcurrentMarkSweepGeneration for concurrent GC's allows
+// objects in the space with references to objects that are no longer
+// valid.  For example, an object may reference another object
+// that has already been sweep up (collected).  This method uses
+// obj_is_alive() to determine whether it is safe to apply the closure to
+// an object.  See obj_is_alive() for details on how liveness of an
+// object is decided.
+
+void CompactibleFreeListSpace::safe_object_iterate(ObjectClosure* blk) {
+  assert_lock_strong(freelistLock());
+  NOT_PRODUCT(verify_objects_initialized());
+  HeapWord *cur, *limit;
+  size_t curSize;
+  for (cur = bottom(), limit = end(); cur < limit;
+       cur += curSize) {
+    curSize = block_size(cur);
+    if (block_is_obj(cur) && obj_is_alive(cur)) {
+      blk->do_object(oop(cur));
+    }
+  }
+}
+
 void CompactibleFreeListSpace::object_iterate_mem(MemRegion mr,
                                                   UpwardsObjectClosure* cl) {
   assert_locked();
@@ -861,7 +885,9 @@ const {
     } else {
       // must read from what 'p' points to in each loop.
       klassOop k = ((volatile oopDesc*)p)->klass_or_null();
-      if (k != NULL && ((oopDesc*)p)->is_parsable()) {
+      if (k != NULL &&
+          ((oopDesc*)p)->is_parsable() &&
+          ((oopDesc*)p)->is_conc_safe()) {
         assert(k->is_oop(), "Should really be klass oop.");
         oop o = (oop)p;
         assert(o->is_oop(), "Should be an oop");

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp

@@ -481,6 +481,15 @@ class CompactibleFreeListSpace: public CompactibleSpace {
   void oop_iterate(OopClosure* cl);
 
   void object_iterate(ObjectClosure* blk);
+  // Apply the closure to each object in the space whose references
+  // point to objects in the heap.  The usage of CompactibleFreeListSpace
+  // by the ConcurrentMarkSweepGeneration for concurrent GC's allows
+  // objects in the space with references to objects that are no longer
+  // valid.  For example, an object may reference another object
+  // that has already been sweep up (collected).  This method uses
+  // obj_is_alive() to determine whether it is safe to iterate of
+  // an object.
+  void safe_object_iterate(ObjectClosure* blk);
   void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);
 
   // Requires that "mr" be entirely within the space.

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp

@@ -3017,6 +3017,16 @@ ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
   }
 }
 
+void
+ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
+  if (freelistLock()->owned_by_self()) {
+    Generation::safe_object_iterate(cl);
+  } else {
+    MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
+    Generation::safe_object_iterate(cl);
+  }
+}
+
 void
 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
 }
@@ -6623,7 +6633,11 @@ size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
   if (_bitMap->isMarked(addr)) {
     // it's marked; is it potentially uninitialized?
     if (p->klass_or_null() != NULL) {
-      if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
+      // If is_conc_safe is false, the object may be undergoing
+      // change by the VM outside a safepoint.  Don't try to
+      // scan it, but rather leave it for the remark phase.
+      if (CMSPermGenPrecleaningEnabled &&
+          (!p->is_conc_safe() || !p->is_parsable())) {
         // Signal precleaning to redirty the card since
         // the klass pointer is already installed.
         assert(size == 0, "Initial value");
@@ -7001,7 +7015,6 @@ void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
       _mut->clear_range(mr);
     }
   DEBUG_ONLY(})
-
   // Note: the finger doesn't advance while we drain
   // the stack below.
   PushOrMarkClosure pushOrMarkClosure(_collector,
@@ -8062,9 +8075,13 @@ size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
     #ifdef DEBUG
       if (oop(addr)->klass_or_null() != NULL &&
           (   !_collector->should_unload_classes()
-           || oop(addr)->is_parsable())) {
+           || (oop(addr)->is_parsable()) &&
+               oop(addr)->is_conc_safe())) {
         // Ignore mark word because we are running concurrent with mutators
         assert(oop(addr)->is_oop(true), "live block should be an oop");
+        // is_conc_safe is checked before performing this assertion
+        // because an object that is not is_conc_safe may yet have
+        // the return from size() correct.
         assert(size ==
                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
                "P-mark and computed size do not agree");
@@ -8077,6 +8094,13 @@ size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
            (!_collector->should_unload_classes()
             || oop(addr)->is_parsable()),
            "Should be an initialized object");
+    // Note that there are objects used during class redefinition
+    // (e.g., merge_cp in VM_RedefineClasses::merge_cp_and_rewrite()
+    // which are discarded with their is_conc_safe state still
+    // false.  These object may be floating garbage so may be
+    // seen here.  If they are floating garbage their size
+    // should be attainable from their klass.  Do not that
+    // is_conc_safe() is true for oop(addr).
     // Ignore mark word because we are running concurrent with mutators
     assert(oop(addr)->is_oop(true), "live block should be an oop");
     // Verify that the bit map has no bits marked between

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp

@@ -1212,6 +1212,7 @@ class ConcurrentMarkSweepGeneration: public CardGeneration {
   // More iteration support
   virtual void oop_iterate(MemRegion mr, OopClosure* cl);
   virtual void oop_iterate(OopClosure* cl);
+  virtual void safe_object_iterate(ObjectClosure* cl);
   virtual void object_iterate(ObjectClosure* cl);
 
   // Need to declare the full complement of closures, whether we'll

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

@@ -850,6 +850,7 @@ public:
 
   // Iterate over all objects, calling "cl.do_object" on each.
   virtual void object_iterate(ObjectClosure* cl);
+  virtual void safe_object_iterate(ObjectClosure* cl) { object_iterate(cl); }
 
   // Iterate over all objects allocated since the last collection, calling
   // "cl.do_object" on each.  The heap must have been initialized properly

hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp

@@ -200,6 +200,7 @@ class ParallelScavengeHeap : public CollectedHeap {
 
   void oop_iterate(OopClosure* cl);
   void object_iterate(ObjectClosure* cl);
+  void safe_object_iterate(ObjectClosure* cl) { object_iterate(cl); }
   void permanent_oop_iterate(OopClosure* cl);
   void permanent_object_iterate(ObjectClosure* cl);
 

hotspot/src/share/vm/gc_interface/collectedHeap.hpp

@@ -466,6 +466,10 @@ class CollectedHeap : public CHeapObj {
   // This includes objects in permanent memory.
   virtual void object_iterate(ObjectClosure* cl) = 0;
 
+  // Similar to object_iterate() except iterates only
+  // over live objects.
+  virtual void safe_object_iterate(ObjectClosure* cl) = 0;
+
   // Behaves the same as oop_iterate, except only traverses
   // interior pointers contained in permanent memory. If there
   // is no permanent memory, does nothing.

hotspot/src/share/vm/memory/genCollectedHeap.cpp

@@ -910,6 +910,13 @@ void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
   perm_gen()->object_iterate(cl);
 }
 
+void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
+  for (int i = 0; i < _n_gens; i++) {
+    _gens[i]->safe_object_iterate(cl);
+  }
+  perm_gen()->safe_object_iterate(cl);
+}
+
 void GenCollectedHeap::object_iterate_since_last_GC(ObjectClosure* cl) {
   for (int i = 0; i < _n_gens; i++) {
     _gens[i]->object_iterate_since_last_GC(cl);

hotspot/src/share/vm/memory/genCollectedHeap.hpp

@@ -215,6 +215,7 @@ public:
   void oop_iterate(OopClosure* cl);
   void oop_iterate(MemRegion mr, OopClosure* cl);
   void object_iterate(ObjectClosure* cl);
+  void safe_object_iterate(ObjectClosure* cl);
   void object_iterate_since_last_GC(ObjectClosure* cl);
   Space* space_containing(const void* addr) const;
 

hotspot/src/share/vm/memory/generation.cpp

@@ -319,6 +319,21 @@ void Generation::object_iterate(ObjectClosure* cl) {
   space_iterate(&blk);
 }
 
+class GenerationSafeObjIterateClosure : public SpaceClosure {
+ private:
+  ObjectClosure* _cl;
+ public:
+  virtual void do_space(Space* s) {
+    s->safe_object_iterate(_cl);
+  }
+  GenerationSafeObjIterateClosure(ObjectClosure* cl) : _cl(cl) {}
+};
+
+void Generation::safe_object_iterate(ObjectClosure* cl) {
+  GenerationSafeObjIterateClosure blk(cl);
+  space_iterate(&blk);
+}
+
 void Generation::prepare_for_compaction(CompactPoint* cp) {
   // Generic implementation, can be specialized
   CompactibleSpace* space = first_compaction_space();

hotspot/src/share/vm/memory/generation.hpp

@@ -518,6 +518,11 @@ class Generation: public CHeapObj {
   // each.
   virtual void object_iterate(ObjectClosure* cl);
 
+  // Iterate over all safe objects in the generation, calling "cl.do_object" on
+  // each.  An object is safe if its references point to other objects in
+  // the heap.  This defaults to object_iterate() unless overridden.
+  virtual void safe_object_iterate(ObjectClosure* cl);
+
   // Iterate over all objects allocated in the generation since the last
   // collection, calling "cl.do_object" on each.  The generation must have
   // been initialized properly to support this function, or else this call

hotspot/src/share/vm/memory/heapInspection.cpp

@@ -263,6 +263,9 @@ void HeapInspection::heap_inspection(outputStream* st) {
   if (!cit.allocation_failed()) {
     // Iterate over objects in the heap
     RecordInstanceClosure ric(&cit);
+    // If this operation encounters a bad object when using CMS,
+    // consider using safe_object_iterate() which avoids perm gen
+    // objects that may contain bad references.
     Universe::heap()->object_iterate(&ric);
 
     // Report if certain classes are not counted because of
@@ -317,5 +320,8 @@ void HeapInspection::find_instances_at_safepoint(klassOop k, GrowableArray<oop>*
 
   // Iterate over objects in the heap
   FindInstanceClosure fic(k, result);
+  // If this operation encounters a bad object when using CMS,
+  // consider using safe_object_iterate() which avoids perm gen
+  // objects that may contain bad references.
   Universe::heap()->object_iterate(&fic);
 }

hotspot/src/share/vm/memory/oopFactory.cpp

@@ -82,9 +82,11 @@ objArrayOop oopFactory::new_system_objArray(int length, TRAPS) {
 }
 
 
-constantPoolOop oopFactory::new_constantPool(int length, TRAPS) {
+constantPoolOop oopFactory::new_constantPool(int length,
+                                             bool is_conc_safe,
+                                             TRAPS) {
   constantPoolKlass* ck = constantPoolKlass::cast(Universe::constantPoolKlassObj());
-  return ck->allocate(length, CHECK_NULL);
+  return ck->allocate(length, is_conc_safe, CHECK_NULL);
 }
 
 
@@ -105,11 +107,13 @@ constMethodOop oopFactory::new_constMethod(int byte_code_size,
                                            int compressed_line_number_size,
                                            int localvariable_table_length,
                                            int checked_exceptions_length,
+                                           bool is_conc_safe,
                                            TRAPS) {
   klassOop cmkObj = Universe::constMethodKlassObj();
   constMethodKlass* cmk = constMethodKlass::cast(cmkObj);
   return cmk->allocate(byte_code_size, compressed_line_number_size,
                        localvariable_table_length, checked_exceptions_length,
+                       is_conc_safe,
                        CHECK_NULL);
 }
 
@@ -117,14 +121,17 @@ constMethodOop oopFactory::new_constMethod(int byte_code_size,
 methodOop oopFactory::new_method(int byte_code_size, AccessFlags access_flags,
                                  int compressed_line_number_size,
                                  int localvariable_table_length,
-                                 int checked_exceptions_length, TRAPS) {
+                                 int checked_exceptions_length,
+                                 bool is_conc_safe,
+                                 TRAPS) {
   methodKlass* mk = methodKlass::cast(Universe::methodKlassObj());
   assert(!access_flags.is_native() || byte_code_size == 0,
          "native methods should not contain byte codes");
   constMethodOop cm = new_constMethod(byte_code_size,
                                       compressed_line_number_size,
                                       localvariable_table_length,
-                                      checked_exceptions_length, CHECK_NULL);
+                                      checked_exceptions_length,
+                                      is_conc_safe, CHECK_NULL);
   constMethodHandle rw(THREAD, cm);
   return mk->allocate(rw, access_flags, CHECK_NULL);
 }

hotspot/src/share/vm/memory/oopFactory.hpp

@@ -81,7 +81,9 @@ class oopFactory: AllStatic {
   static symbolHandle    new_symbol_handle(const char* name, TRAPS) { return new_symbol_handle(name, (int)strlen(name), CHECK_(symbolHandle())); }
 
   // Constant pools
-  static constantPoolOop      new_constantPool     (int length, TRAPS);
+  static constantPoolOop      new_constantPool     (int length,
+                                                    bool is_conc_safe,
+                                                    TRAPS);
   static constantPoolCacheOop new_constantPoolCache(int length, TRAPS);
 
   // Instance classes
@@ -93,9 +95,20 @@ private:
   static constMethodOop  new_constMethod(int byte_code_size,
                                          int compressed_line_number_size,
                                          int localvariable_table_length,
-                                         int checked_exceptions_length, TRAPS);
+                                         int checked_exceptions_length,
+                                         bool is_conc_safe,
+                                         TRAPS);
 public:
-  static methodOop       new_method(int byte_code_size, AccessFlags access_flags, int compressed_line_number_size, int localvariable_table_length, int checked_exceptions_length, TRAPS);
+  // Set is_conc_safe for methods which cannot safely be
+  // processed by concurrent GC even after the return of
+  // the method.
+  static methodOop       new_method(int byte_code_size,
+                                    AccessFlags access_flags,
+                                    int compressed_line_number_size,
+                                    int localvariable_table_length,
+                                    int checked_exceptions_length,
+                                    bool is_conc_safe,
+                                    TRAPS);
 
   // Method Data containers
   static methodDataOop   new_methodData(methodHandle method, TRAPS);

hotspot/src/share/vm/memory/space.cpp

@@ -569,7 +569,15 @@ void Space::object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl) {
   if (prev > mr.start()) {
     region_start_addr = prev;
     blk_start_addr    = prev;
-    assert(blk_start_addr == block_start(region_start_addr), "invariant");
+    // The previous invocation may have pushed "prev" beyond the
+    // last allocated block yet there may be still be blocks
+    // in this region due to a particular coalescing policy.
+    // Relax the assertion so that the case where the unallocated
+    // block is maintained and "prev" is beyond the unallocated
+    // block does not cause the assertion to fire.
+    assert((BlockOffsetArrayUseUnallocatedBlock &&
+            (!is_in(prev))) ||
+           (blk_start_addr == block_start(region_start_addr)), "invariant");
   } else {
     region_start_addr = mr.start();
     blk_start_addr    = block_start(region_start_addr);
@@ -705,6 +713,12 @@ void ContiguousSpace::object_iterate(ObjectClosure* blk) {
   object_iterate_from(bm, blk);
 }
 
+// For a continguous space object_iterate() and safe_object_iterate()
+// are the same.
+void ContiguousSpace::safe_object_iterate(ObjectClosure* blk) {
+  object_iterate(blk);
+}
+
 void ContiguousSpace::object_iterate_from(WaterMark mark, ObjectClosure* blk) {
   assert(mark.space() == this, "Mark does not match space");
   HeapWord* p = mark.point();

hotspot/src/share/vm/memory/space.hpp

@@ -193,6 +193,9 @@ class Space: public CHeapObj {
   // each.  Objects allocated by applications of the closure are not
   // included in the iteration.
   virtual void object_iterate(ObjectClosure* blk) = 0;
+  // Similar to object_iterate() except only iterates over
+  // objects whose internal references point to objects in the space.
+  virtual void safe_object_iterate(ObjectClosure* blk) = 0;
 
   // Iterate over all objects that intersect with mr, calling "cl->do_object"
   // on each.  There is an exception to this: if this closure has already
@@ -843,6 +846,9 @@ class ContiguousSpace: public CompactibleSpace {
   void oop_iterate(OopClosure* cl);
   void oop_iterate(MemRegion mr, OopClosure* cl);
   void object_iterate(ObjectClosure* blk);
+  // For contiguous spaces this method will iterate safely over objects
+  // in the space (i.e., between bottom and top) when at a safepoint.
+  void safe_object_iterate(ObjectClosure* blk);
   void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);
   // iterates on objects up to the safe limit
   HeapWord* object_iterate_careful(ObjectClosureCareful* cl);

hotspot/src/share/vm/oops/constMethodKlass.cpp

@@ -49,10 +49,16 @@ bool constMethodKlass::oop_is_parsable(oop obj) const {
   return constMethodOop(obj)->object_is_parsable();
 }
 
+bool constMethodKlass::oop_is_conc_safe(oop obj) const {
+  assert(obj->is_constMethod(), "must be constMethod oop");
+  return constMethodOop(obj)->is_conc_safe();
+}
+
 constMethodOop constMethodKlass::allocate(int byte_code_size,
                                           int compressed_line_number_size,
                                           int localvariable_table_length,
                                           int checked_exceptions_length,
+                                          bool is_conc_safe,
                                           TRAPS) {
 
   int size = constMethodOopDesc::object_size(byte_code_size,
@@ -75,6 +81,7 @@ constMethodOop constMethodKlass::allocate(int byte_code_size,
                                 compressed_line_number_size,
                                 localvariable_table_length);
   assert(cm->size() == size, "wrong size for object");
+  cm->set_is_conc_safe(is_conc_safe);
   cm->set_partially_loaded();
   assert(cm->is_parsable(), "Is safely parsable by gc");
   return cm;

hotspot/src/share/vm/oops/constMethodKlass.hpp

@@ -32,12 +32,16 @@ public:
   // Testing
   bool oop_is_constMethod() const { return true; }
   virtual bool oop_is_parsable(oop obj) const;
+  virtual bool oop_is_conc_safe(oop obj) const;
+
 
   // Allocation
   DEFINE_ALLOCATE_PERMANENT(constMethodKlass);
   constMethodOop allocate(int byte_code_size, int compressed_line_number_size,
                           int localvariable_table_length,
-                          int checked_exceptions_length, TRAPS);
+                          int checked_exceptions_length,
+                          bool is_conc_safe,
+                          TRAPS);
   static klassOop create_klass(TRAPS);
 
   // Sizing

hotspot/src/share/vm/oops/constMethodOop.hpp

@@ -104,6 +104,7 @@ private:
   // loads and stores.  This value may updated and read without a lock by
   // multiple threads, so is volatile.
   volatile uint64_t _fingerprint;
+  volatile bool     _is_conc_safe; // if true, safe for concurrent GC processing
 
 public:
   oop* oop_block_beg() const { return adr_method(); }
@@ -273,6 +274,8 @@ public:
   oop*  adr_method() const             { return (oop*)&_method;          }
   oop*  adr_stackmap_data() const      { return (oop*)&_stackmap_data;   }
   oop*  adr_exception_table() const    { return (oop*)&_exception_table; }
+  bool is_conc_safe() { return _is_conc_safe; }
+  void set_is_conc_safe(bool v) { _is_conc_safe = v; }
 
   // Unique id for the method
   static const u2 MAX_IDNUM;

hotspot/src/share/vm/oops/constantPoolKlass.cpp

@@ -25,7 +25,7 @@
 # include "incls/_precompiled.incl"
 # include "incls/_constantPoolKlass.cpp.incl"
 
-constantPoolOop constantPoolKlass::allocate(int length, TRAPS) {
+constantPoolOop constantPoolKlass::allocate(int length, bool is_conc_safe, TRAPS) {
   int size = constantPoolOopDesc::object_size(length);
   KlassHandle klass (THREAD, as_klassOop());
   constantPoolOop c =
@@ -38,6 +38,9 @@ constantPoolOop constantPoolKlass::allocate(int length, TRAPS) {
   c->set_flags(0);
   // only set to non-zero if constant pool is merged by RedefineClasses
   c->set_orig_length(0);
+  // if constant pool may change during RedefineClasses, it is created
+  // unsafe for GC concurrent processing.
+  c->set_is_conc_safe(is_conc_safe);
   // all fields are initialized; needed for GC
 
   // initialize tag array
@@ -207,6 +210,11 @@ int constantPoolKlass::oop_oop_iterate_m(oop obj, OopClosure* blk, MemRegion mr)
   return size;
 }
 
+bool constantPoolKlass::oop_is_conc_safe(oop obj) const {
+  assert(obj->is_constantPool(), "must be constantPool");
+  return constantPoolOop(obj)->is_conc_safe();
+}
+
 #ifndef SERIALGC
 int constantPoolKlass::oop_update_pointers(ParCompactionManager* cm, oop obj) {
   assert (obj->is_constantPool(), "obj must be constant pool");

hotspot/src/share/vm/oops/constantPoolKlass.hpp

@@ -34,7 +34,7 @@ class constantPoolKlass : public Klass {
 
   // Allocation
   DEFINE_ALLOCATE_PERMANENT(constantPoolKlass);
-  constantPoolOop allocate(int length, TRAPS);
+  constantPoolOop allocate(int length, bool is_conc_safe, TRAPS);
   static klassOop create_klass(TRAPS);
 
   // Casting from klassOop
@@ -48,6 +48,8 @@ class constantPoolKlass : public Klass {
   int object_size() const        { return align_object_size(header_size()); }
 
   // Garbage collection
+  // Returns true is the object is safe for GC concurrent processing.
+  virtual bool oop_is_conc_safe(oop obj) const;
   void oop_follow_contents(oop obj);
   int oop_adjust_pointers(oop obj);
 

hotspot/src/share/vm/oops/constantPoolOop.hpp

@@ -43,6 +43,8 @@ class constantPoolOopDesc : public oopDesc {
   klassOop             _pool_holder;   // the corresponding class
   int                  _flags;         // a few header bits to describe contents for GC
   int                  _length; // number of elements in the array
+  volatile bool        _is_conc_safe; // if true, safe for concurrent
+                                      // GC processing
   // only set to non-zero if constant pool is merged by RedefineClasses
   int                  _orig_length;
 
@@ -379,6 +381,9 @@ class constantPoolOopDesc : public oopDesc {
   static int object_size(int length)   { return align_object_size(header_size() + length); }
   int object_size()                    { return object_size(length()); }
 
+  bool is_conc_safe()                  { return _is_conc_safe; }
+  void set_is_conc_safe(bool v)        { _is_conc_safe = v; }
+
   friend class constantPoolKlass;
   friend class ClassFileParser;
   friend class SystemDictionary;

hotspot/src/share/vm/oops/klass.hpp

@@ -606,8 +606,19 @@ class Klass : public Klass_vtbl {
   #undef assert_same_query
 
   // Unless overridden, oop is parsable if it has a klass pointer.
+  // Parsability of an object is object specific.
   virtual bool oop_is_parsable(oop obj) const { return true; }
 
+  // Unless overridden, oop is safe for concurrent GC processing
+  // after its allocation is complete.  The exception to
+  // this is the case where objects are changed after allocation.
+  // Class redefinition is one of the known exceptions. During
+  // class redefinition, an allocated class can changed in order
+  // order to create a merged class (the combiniation of the
+  // old class definition that has to be perserved and the new class
+  // definition which is being created.
+  virtual bool oop_is_conc_safe(oop obj) const { return true; }
+
   // Access flags
   AccessFlags access_flags() const         { return _access_flags;  }
   void set_access_flags(AccessFlags flags) { _access_flags = flags; }

hotspot/src/share/vm/oops/methodOop.cpp

@@ -792,15 +792,34 @@ methodHandle methodOopDesc:: clone_with_new_data(methodHandle m, u_char* new_cod
   AccessFlags flags = m->access_flags();
   int checked_exceptions_len = m->checked_exceptions_length();
   int localvariable_len = m->localvariable_table_length();
-  methodOop newm_oop = oopFactory::new_method(new_code_length, flags, new_compressed_linenumber_size, localvariable_len, checked_exceptions_len, CHECK_(methodHandle()));
+  // Allocate newm_oop with the is_conc_safe parameter set
+  // to IsUnsafeConc to indicate that newm_oop is not yet
+  // safe for concurrent processing by a GC.
+  methodOop newm_oop = oopFactory::new_method(new_code_length,
+                                              flags,
+                                              new_compressed_linenumber_size,
+                                              localvariable_len,
+                                              checked_exceptions_len,
+                                              IsUnsafeConc,
+                                              CHECK_(methodHandle()));
   methodHandle newm (THREAD, newm_oop);
   int new_method_size = newm->method_size();
   // Create a shallow copy of methodOopDesc part, but be careful to preserve the new constMethodOop
   constMethodOop newcm = newm->constMethod();
   int new_const_method_size = newm->constMethod()->object_size();
+
   memcpy(newm(), m(), sizeof(methodOopDesc));
   // Create shallow copy of constMethodOopDesc, but be careful to preserve the methodOop
+  // is_conc_safe is set to false because that is the value of
+  // is_conc_safe initialzied into newcm and the copy should
+  // not overwrite that value.  During the window during which it is
+  // tagged as unsafe, some extra work could be needed during precleaning
+  // or concurrent marking but those phases will be correct.  Setting and
+  // resetting is done in preference to a careful copying into newcm to
+  // avoid having to know the precise layout of a constMethodOop.
+  m->constMethod()->set_is_conc_safe(false);
   memcpy(newcm, m->constMethod(), sizeof(constMethodOopDesc));
+  m->constMethod()->set_is_conc_safe(true);
   // Reset correct method/const method, method size, and parameter info
   newcm->set_method(newm());
   newm->set_constMethod(newcm);
@@ -831,6 +850,10 @@ methodHandle methodOopDesc:: clone_with_new_data(methodHandle m, u_char* new_cod
            m->localvariable_table_start(),
            localvariable_len * sizeof(LocalVariableTableElement));
   }
+
+  // Only set is_conc_safe to true when changes to newcm are
+  // complete.
+  newcm->set_is_conc_safe(true);
   return newm;
 }
 

hotspot/src/share/vm/oops/methodOop.hpp

@@ -129,6 +129,10 @@ class methodOopDesc : public oopDesc {
   volatile address           _from_interpreted_entry; // Cache of _code ? _adapter->i2c_entry() : _i2i_entry
 
  public:
+
+  static const bool IsUnsafeConc         = false;
+  static const bool IsSafeConc           = true;
+
   // accessors for instance variables
   constMethodOop constMethod() const             { return _constMethod; }
   void set_constMethod(constMethodOop xconst)    { oop_store_without_check((oop*)&_constMethod, (oop)xconst); }

hotspot/src/share/vm/oops/oop.hpp

@@ -108,6 +108,13 @@ class oopDesc {
   // installation of their klass pointer.
   bool is_parsable();
 
+  // Some perm gen objects that have been allocated and initialized
+  // can be changed by the VM when not at a safe point (class rededfinition
+  // is an example).  Such objects should not be examined by the
+  // concurrent processing of a garbage collector if is_conc_safe()
+  // returns false.
+  bool is_conc_safe();
+
   // type test operations (inlined in oop.inline.h)
   bool is_instance()           const;
   bool is_instanceRef()        const;

hotspot/src/share/vm/oops/oop.inline.hpp

@@ -435,6 +435,10 @@ inline bool oopDesc::is_parsable() {
   return blueprint()->oop_is_parsable(this);
 }
 
+inline bool oopDesc::is_conc_safe() {
+  return blueprint()->oop_is_conc_safe(this);
+}
+
 inline void update_barrier_set(void* p, oop v) {
   assert(oopDesc::bs() != NULL, "Uninitialized bs in oop!");
   oopDesc::bs()->write_ref_field(p, v);

hotspot/src/share/vm/prims/jvmtiRedefineClasses.cpp

@@ -1230,8 +1230,14 @@ jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
 
   // Constant pools are not easily reused so we allocate a new one
   // each time.
+  // merge_cp is created unsafe for concurrent GC processing.  It
+  // should be marked safe before discarding it because, even if
+  // garbage.  If it crosses a card boundary, it may be scanned
+  // in order to find the start of the first complete object on the card.
   constantPoolHandle merge_cp(THREAD,
-    oopFactory::new_constantPool(merge_cp_length, THREAD));
+    oopFactory::new_constantPool(merge_cp_length,
+                                 methodOopDesc::IsUnsafeConc,
+                                 THREAD));
   int orig_length = old_cp->orig_length();
   if (orig_length == 0) {
     // This old_cp is an actual original constant pool. We save
@@ -1274,6 +1280,7 @@ jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
       // rewriting so we can't use the old constant pool with the new
       // class.
 
+      merge_cp()->set_is_conc_safe(true);
       merge_cp = constantPoolHandle();  // toss the merged constant pool
     } else if (old_cp->length() < scratch_cp->length()) {
       // The old constant pool has fewer entries than the new constant
@@ -1283,6 +1290,7 @@ jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
       // rewriting so we can't use the new constant pool with the old
       // class.
 
+      merge_cp()->set_is_conc_safe(true);
       merge_cp = constantPoolHandle();  // toss the merged constant pool
     } else {
       // The old constant pool has more entries than the new constant
@@ -1296,6 +1304,7 @@ jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
       set_new_constant_pool(scratch_class, merge_cp, merge_cp_length, true,
         THREAD);
       // drop local ref to the merged constant pool
+      merge_cp()->set_is_conc_safe(true);
       merge_cp = constantPoolHandle();
     }
   } else {
@@ -1325,7 +1334,10 @@ jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
     // GCed.
     set_new_constant_pool(scratch_class, merge_cp, merge_cp_length, true,
       THREAD);
+    merge_cp()->set_is_conc_safe(true);
   }
+  assert(old_cp()->is_conc_safe(), "Just checking");
+  assert(scratch_cp()->is_conc_safe(), "Just checking");
 
   return JVMTI_ERROR_NONE;
 } // end merge_cp_and_rewrite()
@@ -2314,13 +2326,16 @@ void VM_RedefineClasses::set_new_constant_pool(
     // worst case merge situation. We want to associate the minimum
     // sized constant pool with the klass to save space.
     constantPoolHandle smaller_cp(THREAD,
-      oopFactory::new_constantPool(scratch_cp_length, THREAD));
+      oopFactory::new_constantPool(scratch_cp_length,
+                                   methodOopDesc::IsUnsafeConc,
+                                   THREAD));
     // preserve orig_length() value in the smaller copy
     int orig_length = scratch_cp->orig_length();
     assert(orig_length != 0, "sanity check");
     smaller_cp->set_orig_length(orig_length);
     scratch_cp->copy_cp_to(1, scratch_cp_length - 1, smaller_cp, 1, THREAD);
     scratch_cp = smaller_cp;
+    smaller_cp()->set_is_conc_safe(true);
   }
 
   // attach new constant pool to klass
@@ -2516,6 +2531,7 @@ void VM_RedefineClasses::set_new_constant_pool(
 
     rewrite_cp_refs_in_stack_map_table(method, THREAD);
   } // end for each method
+  assert(scratch_cp()->is_conc_safe(), "Just checking");
 } // end set_new_constant_pool()
 
 

hotspot/src/share/vm/prims/jvmtiTagMap.cpp

@@ -1320,6 +1320,9 @@ class VM_HeapIterateOperation: public VM_Operation {
     }
 
     // do the iteration
+    // If this operation encounters a bad object when using CMS,
+    // consider using safe_object_iterate() which avoids perm gen
+    // objects that may contain bad references.
     Universe::heap()->object_iterate(_blk);
 
     // when sharing is enabled we must iterate over the shared spaces

hotspot/src/share/vm/services/heapDumper.cpp

@@ -1700,7 +1700,7 @@ void VM_HeapDumper::doit() {
   // The HPROF_GC_CLASS_DUMP and HPROF_GC_INSTANCE_DUMP are the vast bulk
   // of the heap dump.
   HeapObjectDumper obj_dumper(this, writer());
-  Universe::heap()->object_iterate(&obj_dumper);
+  Universe::heap()->safe_object_iterate(&obj_dumper);
 
   // HPROF_GC_ROOT_THREAD_OBJ + frames + jni locals
   do_threads();