view hotspot/src/share/vm/classfile/classLoaderData.hpp @ 15847:f9ce2cd20dee

8008549: NPG: SystemDictionary::find(...) unnecessarily keeps class loaders alive Summary: SystemDictionary::find(...) should not create and register ClassLoaderData objects for class loaders. Reviewed-by: coleenp, acorn Contributed-by: Stefan Karlsson <>, Erik Helin <>
author stefank
date Thu, 21 Feb 2013 17:22:15 +0100
parents eabd4555d072
children 6235d2c7549f
line wrap: on
line source
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit if you need additional information or have any
 * questions.


#include "memory/allocation.hpp"
#include "memory/memRegion.hpp"
#include "memory/metaspace.hpp"
#include "memory/metaspaceCounters.hpp"
#include "runtime/mutex.hpp"
#include "utilities/growableArray.hpp"

// A class loader represents a linkset. Conceptually, a linkset identifies
// the complete transitive closure of resolved links that a dynamic linker can
// produce.
// A ClassLoaderData also encapsulates the allocation space, called a metaspace,
// used by the dynamic linker to allocate the runtime representation of all
// the types it defines.
// ClassLoaderData are stored in the runtime representation of classes and the
// system dictionary, are roots of garbage collection, and provides iterators
// for root tracing and other GC operations.

class ClassLoaderData;
class JNIMethodBlock;
class JNIHandleBlock;
class Metadebug;
// GC root for walking class loader data created

class ClassLoaderDataGraph : public AllStatic {
  friend class ClassLoaderData;
  friend class ClassLoaderDataGraphMetaspaceIterator;
  friend class VMStructs;
  // All CLDs (except the null CLD) can be reached by walking _head->_next->...
  static ClassLoaderData* _head;
  static ClassLoaderData* _unloading;
  // CMS support.
  static ClassLoaderData* _saved_head;

  static ClassLoaderData* add(ClassLoaderData** loader_data_addr, Handle class_loader, TRAPS);
  static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
  static void purge();
  static void clear_claimed_marks();
  static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
  static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
  static void classes_do(KlassClosure* klass_closure);
  static bool do_unloading(BoolObjectClosure* is_alive);

  // CMS support.
  static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
  static GrowableArray<ClassLoaderData*>* new_clds();

  static void dump_on(outputStream * const out) PRODUCT_RETURN;
  static void dump() { dump_on(tty); }
  static void verify();

#ifndef PRODUCT
  // expensive test for pointer in metaspace for debugging
  static bool contains(address x);
  static bool contains_loader_data(ClassLoaderData* loader_data);

// ClassLoaderData class

class ClassLoaderData : public CHeapObj<mtClass> {
  friend class VMStructs;
  friend class ClassLoaderDataGraph;
  friend class ClassLoaderDataGraphMetaspaceIterator;
  friend class MetaDataFactory;
  friend class Method;

  static ClassLoaderData * _the_null_class_loader_data;

  oop _class_loader;       // oop used to uniquely identify a class loader
                           // class loader or a canonical class path
  oop _dependencies;       // oop to hold dependencies from this class loader
                           // data to others.
  Metaspace * _metaspace;  // Meta-space where meta-data defined by the
                           // classes in the class loader are allocated.
  Mutex* _metaspace_lock;  // Locks the metaspace for allocations and setup.
  bool _unloading;         // true if this class loader goes away
  bool _keep_alive;        // if this CLD can be unloaded for anonymous loaders
  bool _is_anonymous;      // if this CLD is for an anonymous class
  volatile int _claimed;   // true if claimed, for example during GC traces.
                           // To avoid applying oop closure more than once.
                           // Has to be an int because we cas it.
  Klass* _klasses;         // The classes defined by the class loader.

  JNIHandleBlock* _handles; // Handles to constant pool arrays

  // These method IDs are created for the class loader and set to NULL when the
  // class loader is unloaded.  They are rarely freed, only for redefine classes
  // and if they lose a data race in InstanceKlass.
  JNIMethodBlock*                  _jmethod_ids;

  // Metadata to be deallocated when it's safe at class unloading, when
  // this class loader isn't unloaded itself.
  GrowableArray<Metadata*>*      _deallocate_list;

  // Support for walking class loader data objects
  ClassLoaderData* _next; /// Next loader_datas created

  // ReadOnly and ReadWrite metaspaces (static because only on the null
  // class loader for now).
  static Metaspace* _ro_metaspace;
  static Metaspace* _rw_metaspace;

  void add_dependency(Handle dependency, TRAPS);
  void locked_add_dependency(objArrayHandle last, objArrayHandle new_dependency);

  void set_next(ClassLoaderData* next) { _next = next; }
  ClassLoaderData* next() const        { return _next; }

  ClassLoaderData(Handle h_class_loader, bool is_anonymous);

  void set_metaspace(Metaspace* m) { _metaspace = m; }

  JNIHandleBlock* handles() const;
  void set_handles(JNIHandleBlock* handles);

  Mutex* metaspace_lock() const { return _metaspace_lock; }

  // GC interface.
  void clear_claimed()          { _claimed = 0; }
  bool claimed() const          { return _claimed == 1; }
  bool claim();

  void unload();
  bool keep_alive() const       { return _keep_alive; }
  bool is_alive(BoolObjectClosure* is_alive_closure) const;

  void classes_do(void f(InstanceKlass*));

  // Deallocate free list during class unloading.
  void free_deallocate_list();

  // Allocate out of this class loader data
  MetaWord* allocate(size_t size);

  // Accessors
  Metaspace* metaspace_or_null() const     { return _metaspace; }

  static ClassLoaderData* the_null_class_loader_data() {
    return _the_null_class_loader_data;

  bool is_anonymous() const { return _is_anonymous; }

  static void init_null_class_loader_data() {
    assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
    assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
    _the_null_class_loader_data = new ClassLoaderData((oop)NULL, false);
    ClassLoaderDataGraph::_head = _the_null_class_loader_data;
    assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
    if (DumpSharedSpaces) {

  bool is_the_null_class_loader_data() const {
    return this == _the_null_class_loader_data;

  // The Metaspace is created lazily so may be NULL.  This
  // method will allocate a Metaspace if needed.
  Metaspace* metaspace_non_null();

  oop class_loader() const      { return _class_loader; }

  // Returns true if this class loader data is for a loader going away.
  bool is_unloading() const     {
    assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
    return _unloading;
  // Anonymous class loader data doesn't have anything to keep them from
  // being unloaded during parsing the anonymous class.
  void set_keep_alive(bool value) { _keep_alive = value; }

  unsigned int identity_hash() {
    return _class_loader == NULL ? 0 : _class_loader->identity_hash();

  // Used when tracing from klasses.
  void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);

  void classes_do(KlassClosure* klass_closure);

  JNIMethodBlock* jmethod_ids() const              { return _jmethod_ids; }
  void set_jmethod_ids(JNIMethodBlock* new_block)  { _jmethod_ids = new_block; }

  void print_value() { print_value_on(tty); }
  void print_value_on(outputStream* out) const;
  void dump(outputStream * const out) PRODUCT_RETURN;
  void verify();
  const char* loader_name();

  jobject add_handle(Handle h);
  void add_class(Klass* k);
  void remove_class(Klass* k);
  void record_dependency(Klass* to, TRAPS);
  void init_dependencies(TRAPS);

  void add_to_deallocate_list(Metadata* m);

  static ClassLoaderData* class_loader_data(oop loader);
  static ClassLoaderData* class_loader_data_or_null(oop loader);
  static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
  static void print_loader(ClassLoaderData *loader_data, outputStream *out);

  // CDS support
  Metaspace* ro_metaspace();
  Metaspace* rw_metaspace();
  void initialize_shared_metaspaces();

class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
  ClassLoaderData* _data;
  bool repeat() { return _data != NULL; }
  Metaspace* get_next() {
    assert(_data != NULL, "Should not be NULL in call to the iterator");
    Metaspace* result = _data->metaspace_or_null();
    _data = _data->next();
    // This result might be NULL for class loaders without metaspace
    // yet.  It would be nice to return only non-null results but
    // there is no guarantee that there will be a non-null result
    // down the list so the caller is going to have to check.
    return result;