8038212: Method::is_valid_method() check has performance regression impact for stackwalking

Summary: Only prune metaspace virtual spaces at safepoint so walking them is safe outside a safepoint.
Reviewed-by: mgerdin, mgronlun, hseigel, stefank

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

@@ -549,6 +549,8 @@ ClassLoaderData* ClassLoaderDataGraph::_head = NULL;
 ClassLoaderData* ClassLoaderDataGraph::_unloading = NULL;
 ClassLoaderData* ClassLoaderDataGraph::_saved_head = NULL;
 
+bool ClassLoaderDataGraph::_should_purge = false;
+
 // Add a new class loader data node to the list.  Assign the newly created
 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field
 ClassLoaderData* ClassLoaderDataGraph::add(Handle loader, bool is_anonymous, TRAPS) {
@@ -675,32 +677,6 @@ GrowableArray<ClassLoaderData*>* ClassLoaderDataGraph::new_clds() {
   return array;
 }
 
-// For profiling and hsfind() only.  Otherwise, this is unsafe (and slow).  This
-// is done lock free to avoid lock inversion problems.  It is safe because
-// new ClassLoaderData are added to the end of the CLDG, and only removed at
-// safepoint.  The _unloading list can be deallocated concurrently with CMS so
-// this doesn't look in metaspace for classes that have been unloaded.
-bool ClassLoaderDataGraph::contains(const void* x) {
-  if (DumpSharedSpaces) {
-    // There are only two metaspaces to worry about.
-    ClassLoaderData* ncld = ClassLoaderData::the_null_class_loader_data();
-    return (ncld->ro_metaspace()->contains(x) || ncld->rw_metaspace()->contains(x));
-  }
-
-  if (UseSharedSpaces && MetaspaceShared::is_in_shared_space(x)) {
-    return true;
-  }
-
-  for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
-    if (cld->metaspace_or_null() != NULL && cld->metaspace_or_null()->contains(x)) {
-      return true;
-    }
-  }
-
-  // Do not check unloading list because deallocation can be concurrent.
-  return false;
-}
-
 #ifndef PRODUCT
 bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {
   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
@@ -759,6 +735,7 @@ bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure) {
 }
 
 void ClassLoaderDataGraph::purge() {
+  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
   ClassLoaderData* list = _unloading;
   _unloading = NULL;
   ClassLoaderData* next = list;

hotspot/src/share/vm/classfile/classLoaderData.hpp

@@ -66,6 +66,7 @@ class ClassLoaderDataGraph : public AllStatic {
   static ClassLoaderData* _unloading;
   // CMS support.
   static ClassLoaderData* _saved_head;
+  static bool _should_purge;
 
   static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
   static void post_class_unload_events(void);
@@ -87,12 +88,20 @@ class ClassLoaderDataGraph : public AllStatic {
   static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
   static GrowableArray<ClassLoaderData*>* new_clds();
 
+  static void set_should_purge(bool b) { _should_purge = b; }
+  static void purge_if_needed() {
+    // Only purge the CLDG for CMS if concurrent sweep is complete.
+    if (_should_purge) {
+      purge();
+      // reset for next time.
+      set_should_purge(false);
+    }
+  }
+
   static void dump_on(outputStream * const out) PRODUCT_RETURN;
   static void dump() { dump_on(tty); }
   static void verify();
 
-  // expensive test for pointer in metaspace for debugging
-  static bool contains(const void* x);
 #ifndef PRODUCT
   static bool contains_loader_data(ClassLoaderData* loader_data);
 #endif

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

@@ -6362,7 +6362,9 @@ void CMSCollector::sweep(bool asynch) {
   verify_overflow_empty();
 
   if (should_unload_classes()) {
-    ClassLoaderDataGraph::purge();
+    // Delay purge to the beginning of the next safepoint.  Metaspace::contains
+    // requires that the virtual spaces are stable and not deleted.
+    ClassLoaderDataGraph::set_should_purge(true);
   }
 
   _intra_sweep_timer.stop();

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

@@ -5401,7 +5401,7 @@ public:
       if (_g1h->is_in_g1_reserved(p)) {
         _par_scan_state->push_on_queue(p);
       } else {
-        assert(!ClassLoaderDataGraph::contains((address)p),
+        assert(!Metaspace::contains((const void*)p),
                err_msg("Otherwise need to call _copy_metadata_obj_cl->do_oop(p) "
                               PTR_FORMAT, p));
           _copy_non_heap_obj_cl->do_oop(p);

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

@@ -75,7 +75,7 @@ bool MetaspaceObj::is_shared() const {
 }
 
 bool MetaspaceObj::is_metaspace_object() const {
-  return ClassLoaderDataGraph::contains((void*)this);
+  return Metaspace::contains((void*)this);
 }
 
 void MetaspaceObj::print_address_on(outputStream* st) const {

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

@@ -316,6 +316,8 @@ class VirtualSpaceNode : public CHeapObj<mtClass> {
   MetaWord* bottom() const { return (MetaWord*) _virtual_space.low(); }
   MetaWord* end() const { return (MetaWord*) _virtual_space.high(); }
 
+  bool contains(const void* ptr) { return ptr >= low() && ptr < high(); }
+
   size_t reserved_words() const  { return _virtual_space.reserved_size() / BytesPerWord; }
   size_t committed_words() const { return _virtual_space.actual_committed_size() / BytesPerWord; }
 
@@ -557,6 +559,8 @@ class VirtualSpaceList : public CHeapObj<mtClass> {
   void inc_virtual_space_count();
   void dec_virtual_space_count();
 
+  bool contains(const void* ptr);
+
   // Unlink empty VirtualSpaceNodes and free it.
   void purge(ChunkManager* chunk_manager);
 
@@ -641,8 +645,6 @@ class SpaceManager : public CHeapObj<mtClass> {
   // Accessors
   Metachunk* chunks_in_use(ChunkIndex index) const { return _chunks_in_use[index]; }
   void set_chunks_in_use(ChunkIndex index, Metachunk* v) {
-    // ensure lock-free iteration sees fully initialized node
-    OrderAccess::storestore();
     _chunks_in_use[index] = v;
   }
 
@@ -757,8 +759,6 @@ class SpaceManager : public CHeapObj<mtClass> {
   void print_on(outputStream* st) const;
   void locked_print_chunks_in_use_on(outputStream* st) const;
 
-  bool contains(const void *ptr);
-
   void verify();
   void verify_chunk_size(Metachunk* chunk);
   NOT_PRODUCT(void mangle_freed_chunks();)
@@ -1078,6 +1078,7 @@ void ChunkManager::remove_chunk(Metachunk* chunk) {
 // nodes with a 0 container_count.  Remove Metachunks in
 // the node from their respective freelists.
 void VirtualSpaceList::purge(ChunkManager* chunk_manager) {
+  assert(SafepointSynchronize::is_at_safepoint(), "must be called at safepoint for contains to work");
   assert_lock_strong(SpaceManager::expand_lock());
   // Don't use a VirtualSpaceListIterator because this
   // list is being changed and a straightforward use of an iterator is not safe.
@@ -1111,8 +1112,8 @@ void VirtualSpaceList::purge(ChunkManager* chunk_manager) {
   }
 #ifdef ASSERT
   if (purged_vsl != NULL) {
-  // List should be stable enough to use an iterator here.
-  VirtualSpaceListIterator iter(virtual_space_list());
+    // List should be stable enough to use an iterator here.
+    VirtualSpaceListIterator iter(virtual_space_list());
     while (iter.repeat()) {
       VirtualSpaceNode* vsl = iter.get_next();
       assert(vsl != purged_vsl, "Purge of vsl failed");
@@ -1121,6 +1122,23 @@ void VirtualSpaceList::purge(ChunkManager* chunk_manager) {
 #endif
 }
 
+
+// This function looks at the mmap regions in the metaspace without locking.
+// The chunks are added with store ordering and not deleted except for at
+// unloading time during a safepoint.
+bool VirtualSpaceList::contains(const void* ptr) {
+  // List should be stable enough to use an iterator here because removing virtual
+  // space nodes is only allowed at a safepoint.
+  VirtualSpaceListIterator iter(virtual_space_list());
+  while (iter.repeat()) {
+    VirtualSpaceNode* vsn = iter.get_next();
+    if (vsn->contains(ptr)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 void VirtualSpaceList::retire_current_virtual_space() {
   assert_lock_strong(SpaceManager::expand_lock());
 
@@ -1210,6 +1228,8 @@ bool VirtualSpaceList::create_new_virtual_space(size_t vs_word_size) {
   } else {
     assert(new_entry->reserved_words() == vs_word_size,
         "Reserved memory size differs from requested memory size");
+    // ensure lock-free iteration sees fully initialized node
+    OrderAccess::storestore();
     link_vs(new_entry);
     return true;
   }
@@ -2434,21 +2454,6 @@ MetaWord* SpaceManager::allocate_work(size_t word_size) {
   return result;
 }
 
-// This function looks at the chunks in the metaspace without locking.
-// The chunks are added with store ordering and not deleted except for at
-// unloading time.
-bool SpaceManager::contains(const void *ptr) {
-  for (ChunkIndex i = ZeroIndex; i < NumberOfInUseLists; i = next_chunk_index(i))
-  {
-    Metachunk* curr = chunks_in_use(i);
-    while (curr != NULL) {
-      if (curr->contains(ptr)) return true;
-      curr = curr->next();
-    }
-  }
-  return false;
-}
-
 void SpaceManager::verify() {
   // If there are blocks in the dictionary, then
   // verification of chunks does not work since
@@ -3538,11 +3543,15 @@ void Metaspace::print_on(outputStream* out) const {
 }
 
 bool Metaspace::contains(const void* ptr) {
-  if (vsm()->contains(ptr)) return true;
-  if (using_class_space()) {
-    return class_vsm()->contains(ptr);
+  if (UseSharedSpaces && MetaspaceShared::is_in_shared_space(ptr)) {
+    return true;
   }
-  return false;
+
+  if (using_class_space() && get_space_list(ClassType)->contains(ptr)) {
+     return true;
+  }
+
+  return get_space_list(NonClassType)->contains(ptr);
 }
 
 void Metaspace::verify() {
@@ -3787,5 +3796,4 @@ void TestVirtualSpaceNode_test() {
   TestVirtualSpaceNodeTest::test();
   TestVirtualSpaceNodeTest::test_is_available();
 }
-
 #endif

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

 /*
- * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2014, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -232,7 +232,8 @@ class Metaspace : public CHeapObj<mtClass> {
   MetaWord* expand_and_allocate(size_t size,
                                 MetadataType mdtype);
 
-  bool contains(const void* ptr);
+  static bool contains(const void* ptr);
+
   void dump(outputStream* const out) const;
 
   // Free empty virtualspaces

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

@@ -640,7 +640,7 @@ void Klass::verify_on(outputStream* st) {
 
   // This can be expensive, but it is worth checking that this klass is actually
   // in the CLD graph but not in production.
-  assert(ClassLoaderDataGraph::contains((address)this), "Should be");
+  assert(Metaspace::contains((address)this), "Should be");
 
   guarantee(this->is_klass(),"should be klass");
 

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

@@ -1866,6 +1866,14 @@ void Method::clear_jmethod_ids(ClassLoaderData* loader_data) {
   loader_data->jmethod_ids()->clear_all_methods();
 }
 
+bool Method::has_method_vptr(const void* ptr) {
+  Method m;
+  // This assumes that the vtbl pointer is the first word of a C++ object.
+  // This assumption is also in universe.cpp patch_klass_vtble
+  void* vtbl2 = dereference_vptr((const void*)&m);
+  void* this_vtbl = dereference_vptr(ptr);
+  return vtbl2 == this_vtbl;
+}
 
 // Check that this pointer is valid by checking that the vtbl pointer matches
 bool Method::is_valid_method() const {
@@ -1874,12 +1882,7 @@ bool Method::is_valid_method() const {
   } else if (!is_metaspace_object()) {
     return false;
   } else {
-    Method m;
-    // This assumes that the vtbl pointer is the first word of a C++ object.
-    // This assumption is also in universe.cpp patch_klass_vtble
-    void* vtbl2 = dereference_vptr((void*)&m);
-    void* this_vtbl = dereference_vptr((void*)this);
-    return vtbl2 == this_vtbl;
+    return has_method_vptr((const void*)this);
   }
 }
 

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

@@ -861,6 +861,7 @@ class Method : public Metadata {
   const char* internal_name() const { return "{method}"; }
 
   // Check for valid method pointer
+  static bool has_method_vptr(const void* ptr);
   bool is_valid_method() const;
 
   // Verify

hotspot/src/share/vm/runtime/os.cpp

@@ -1097,11 +1097,15 @@ void os::print_location(outputStream* st, intptr_t x, bool verbose) {
 
   }
 
-  // Check if in metaspace.
-  if (ClassLoaderDataGraph::contains((address)addr)) {
-    // Use addr->print() from the debugger instead (not here)
-    st->print_cr(INTPTR_FORMAT
-                 " is pointing into metadata", addr);
+  // Check if in metaspace and print types that have vptrs (only method now)
+  if (Metaspace::contains(addr)) {
+    if (Method::has_method_vptr((const void*)addr)) {
+      ((Method*)addr)->print_value_on(st);
+      st->cr();
+    } else {
+      // Use addr->print() from the debugger instead (not here)
+      st->print_cr(INTPTR_FORMAT " is pointing into metadata", addr);
+    }
     return;
   }
 

hotspot/src/share/vm/runtime/safepoint.cpp

@@ -541,6 +541,13 @@ void SafepointSynchronize::do_cleanup_tasks() {
     gclog_or_tty->rotate_log(false);
   }
 
+  {
+    // CMS delays purging the CLDG until the beginning of the next safepoint and to
+    // make sure concurrent sweep is done
+    TraceTime t7("purging class loader data graph", TraceSafepointCleanupTime);
+    ClassLoaderDataGraph::purge_if_needed();
+  }
+
   if (MemTracker::is_on()) {
     MemTracker::sync();
   }

hotspot/src/share/vm/utilities/globalDefinitions.hpp

@@ -1385,7 +1385,7 @@ inline intptr_t p2i(const void * p) {
 // All C++ compilers that we know of have the vtbl pointer in the first
 // word.  If there are exceptions, this function needs to be made compiler
 // specific.
-static inline void* dereference_vptr(void* addr) {
+static inline void* dereference_vptr(const void* addr) {
   return *(void**)addr;
 }