6689653: JMapPerm fails with UseConcMarkSweepIncGC and compressed oops off

Summary: Added safe_object_iterate() for use by JMapPerm.
Reviewed-by: tonyp

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();

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.

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() {
 }
@@ -7001,7 +7011,6 @@ 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,

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

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

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);
 

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.

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);

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;
 

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();

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

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);
 }

src/share/vm/memory/space.cpp

@@ -705,6 +705,12 @@ 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();

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);

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

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();