src/hotspot/share/classfile/classLoaderData.hpp

/*
 * Copyright (c) 2012, 2018, 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
 * 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 www.oracle.com if you need additional information or have any
 * questions.
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#ifndef SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP
#define SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP

#include "memory/allocation.hpp"
#include "memory/memRegion.hpp"
#include "memory/metaspace.hpp"
#include "oops/oopHandle.hpp"
#include "oops/weakHandle.hpp"
#include "runtime/mutex.hpp"
#include "utilities/growableArray.hpp"
#include "utilities/macros.hpp"
#if INCLUDE_JFR
#include "jfr/support/jfrTraceIdExtension.hpp"
#endif


//
// 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 provides iterators for root tracing and other GC operations.

class ClassLoaderData;
class JNIMethodBlock;
class Metadebug;
class ModuleEntry;
class PackageEntry;
class ModuleEntryTable;
class PackageEntryTable;
class DictionaryEntry;
class Dictionary;

// GC root for walking class loader data created

class ClassLoaderDataGraph : public AllStatic {
  friend class ClassLoaderData;
  friend class ClassLoaderDataGraphMetaspaceIterator;
  friend class ClassLoaderDataGraphKlassIteratorAtomic;
  friend class ClassLoaderDataGraphKlassIteratorStatic;
  friend class VMStructs;
 private:
  // 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* _saved_unloading;
  static bool _should_purge;
  // OOM has been seen in metaspace allocation. Used to prevent some
  // allocations until class unloading
  static bool _metaspace_oom;

  static volatile size_t  _num_instance_classes;
  static volatile size_t  _num_array_classes;

  static ClassLoaderData* add_to_graph(Handle class_loader, bool anonymous);
  static ClassLoaderData* add(Handle class_loader, bool anonymous);
 public:
  static ClassLoaderData* find_or_create(Handle class_loader);
  static void purge();
  static void clear_claimed_marks();
  // oops do
  static void oops_do(OopClosure* f, bool must_claim);
  static void keep_alive_oops_do(OopClosure* blk, bool must_claim);
  static void always_strong_oops_do(OopClosure* blk, bool must_claim);
  // cld do
  static void cld_do(CLDClosure* cl);
  static void cld_unloading_do(CLDClosure* cl);
  static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
  static void keep_alive_cld_do(CLDClosure* cl);
  static void always_strong_cld_do(CLDClosure* cl);
  // klass do
  // Walking classes through the ClassLoaderDataGraph include array classes.  It also includes
  // classes that are allocated but not loaded, classes that have errors, and scratch classes
  // for redefinition.  These classes are removed during the next class unloading.
  // Walking the ClassLoaderDataGraph also includes anonymous classes.
  static void classes_do(KlassClosure* klass_closure);
  static void classes_do(void f(Klass* const));
  static void methods_do(void f(Method*));
  static void modules_do(void f(ModuleEntry*));
  static void modules_unloading_do(void f(ModuleEntry*));
  static void packages_do(void f(PackageEntry*));
  static void packages_unloading_do(void f(PackageEntry*));
  static void loaded_classes_do(KlassClosure* klass_closure);
  static void classes_unloading_do(void f(Klass* const));
  static bool do_unloading(bool clean_previous_versions);

  // dictionary do
  // Iterate over all klasses in dictionary, but
  // just the classes from defining class loaders.
  static void dictionary_classes_do(void f(InstanceKlass*));
  // Added for initialize_itable_for_klass to handle exceptions.
  static void dictionary_classes_do(void f(InstanceKlass*, TRAPS), TRAPS);

  // Iterate all classes and their class loaders, including initiating class loaders.
  static void dictionary_all_entries_do(void f(InstanceKlass*, ClassLoaderData*));

  // VM_CounterDecay iteration support
  static InstanceKlass* try_get_next_class();

  static void verify_dictionary();
  static void print_dictionary(outputStream* st);
  static void print_dictionary_statistics(outputStream* st);

  // CMS support.
  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 int resize_if_needed();

  static bool has_metaspace_oom()           { return _metaspace_oom; }
  static void set_metaspace_oom(bool value) { _metaspace_oom = value; }

  static void print_on(outputStream * const out) PRODUCT_RETURN;
  static void print() { print_on(tty); }
  static void verify();

  // instance and array class counters
  static inline size_t num_instance_classes();
  static inline size_t num_array_classes();
  static inline void inc_instance_classes(size_t count);
  static inline void dec_instance_classes(size_t count);
  static inline void inc_array_classes(size_t count);
  static inline void dec_array_classes(size_t count);

#ifndef PRODUCT
  static bool contains_loader_data(ClassLoaderData* loader_data);
#endif
};

// ClassLoaderData class

class ClassLoaderData : public CHeapObj<mtClass> {
  friend class VMStructs;

 private:
  class ChunkedHandleList {
    struct Chunk : public CHeapObj<mtClass> {
      static const size_t CAPACITY = 32;

      oop _data[CAPACITY];
      volatile juint _size;
      Chunk* _next;

      Chunk(Chunk* c) : _next(c), _size(0) { }
    };

    Chunk* volatile _head;

    void oops_do_chunk(OopClosure* f, Chunk* c, const juint size);

   public:
    ChunkedHandleList() : _head(NULL) {}
    ~ChunkedHandleList();

    // Only one thread at a time can add, guarded by ClassLoaderData::metaspace_lock().
    // However, multiple threads can execute oops_do concurrently with add.
    oop* add(oop o);
    bool contains(oop p);
    NOT_PRODUCT(bool owner_of(oop* p);)
    void oops_do(OopClosure* f);

    int count() const;
  };

  friend class ClassLoaderDataGraph;
  friend class ClassLoaderDataGraphKlassIteratorAtomic;
  friend class ClassLoaderDataGraphKlassIteratorStatic;
  friend class ClassLoaderDataGraphMetaspaceIterator;
  friend class InstanceKlass;
  friend class MetaDataFactory;
  friend class Method;

  static ClassLoaderData * _the_null_class_loader_data;

  WeakHandle<vm_class_loader_data> _holder; // The oop that determines lifetime of this class loader
  OopHandle _class_loader;    // The instance of java/lang/ClassLoader associated with
                              // this ClassLoaderData

  ClassLoaderMetaspace * volatile _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 _is_anonymous;      // if this CLD is for an anonymous class

  // Remembered sets support for the oops in the class loader data.
  bool _modified_oops;             // Card Table Equivalent (YC/CMS support)
  bool _accumulated_modified_oops; // Mod Union Equivalent (CMS support)

  s2 _keep_alive;          // if this CLD is kept alive.
                           // Used for anonymous classes and the boot class
                           // loader. _keep_alive does not need to be volatile or
                           // atomic since there is one unique CLD per 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.
  ChunkedHandleList _handles; // Handles to constant pool arrays, Modules, etc, which
                              // have the same life cycle of the corresponding ClassLoader.

  NOT_PRODUCT(volatile int _dependency_count;)  // number of class loader dependencies

  Klass* volatile _klasses;              // The classes defined by the class loader.
  PackageEntryTable* volatile _packages; // The packages defined by the class loader.
  ModuleEntryTable*  volatile _modules;  // The modules defined by the class loader.
  ModuleEntry* _unnamed_module;          // This class loader's unnamed module.
  Dictionary*  _dictionary;              // The loaded InstanceKlasses, including initiated by this class loader

  // 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

  // JFR support
  Klass*  _class_loader_klass;
  Symbol* _class_loader_name;
  JFR_ONLY(DEFINE_TRACE_ID_FIELD;)

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

  ClassLoaderData(Handle h_class_loader, bool is_anonymous);
  ~ClassLoaderData();

  // The CLD are not placed in the Heap, so the Card Table or
  // the Mod Union Table can't be used to mark when CLD have modified oops.
  // The CT and MUT bits saves this information for the whole class loader data.
  void clear_modified_oops()             { _modified_oops = false; }
 public:
  void record_modified_oops()            { _modified_oops = true; }
  bool has_modified_oops()               { return _modified_oops; }

  void accumulate_modified_oops()        { if (has_modified_oops()) _accumulated_modified_oops = true; }
  void clear_accumulated_modified_oops() { _accumulated_modified_oops = false; }
  bool has_accumulated_modified_oops()   { return _accumulated_modified_oops; }
 private:

  void unload();
  bool keep_alive() const       { return _keep_alive > 0; }

  oop holder_phantom() const;
  void classes_do(void f(Klass*));
  void loaded_classes_do(KlassClosure* klass_closure);
  void classes_do(void f(InstanceKlass*));
  void methods_do(void f(Method*));
  void modules_do(void f(ModuleEntry*));
  void packages_do(void f(PackageEntry*));

  // Deallocate free list during class unloading.
  void free_deallocate_list();      // for the classes that are not unloaded
  void unload_deallocate_list();    // for the classes that are unloaded

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

  Dictionary* create_dictionary();

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

  bool is_alive() const;

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

  static ClassLoaderData* the_null_class_loader_data() {
    return _the_null_class_loader_data;
  }

  Mutex* metaspace_lock() const { return _metaspace_lock; }

  bool is_anonymous() const { return _is_anonymous; }

  static void init_null_class_loader_data();

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

  // Returns true if this class loader data is for the system class loader.
  // (Note that the class loader data may be anonymous.)
  bool is_system_class_loader_data() const;

  // Returns true if this class loader data is for the platform class loader.
  // (Note that the class loader data may be anonymous.)
  bool is_platform_class_loader_data() const;

  // Returns true if this class loader data is for the boot class loader.
  // (Note that the class loader data may be anonymous.)
  inline bool is_boot_class_loader_data() const;

  bool is_builtin_class_loader_data() const;
  bool is_permanent_class_loader_data() const;

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

  inline oop class_loader() const;

  // 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;
  }

  // Used to refcount an anonymous class's CLD in order to
  // indicate their aliveness.
  void inc_keep_alive();
  void dec_keep_alive();

  void initialize_holder(Handle holder);

  inline unsigned int identity_hash() const { return (unsigned int)(((intptr_t)this) >> 3); }

  void oops_do(OopClosure* f, bool must_claim, bool clear_modified_oops = false);

  void classes_do(KlassClosure* klass_closure);
  Klass* klasses() { return _klasses; }

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

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

  OopHandle add_handle(Handle h);
  void remove_handle(OopHandle h);
  void init_handle_locked(OopHandle& pd, Handle h);  // used for concurrent access to ModuleEntry::_pd field
  void add_class(Klass* k, bool publicize = true);
  void remove_class(Klass* k);
  bool contains_klass(Klass* k);
  void record_dependency(const Klass* to);
  PackageEntryTable* packages() { return _packages; }
  ModuleEntry* unnamed_module() { return _unnamed_module; }
  ModuleEntryTable* modules();
  bool modules_defined() { return (_modules != NULL); }

  // Loaded class dictionary
  Dictionary* dictionary() const { return _dictionary; }

  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(Handle loader);


  Klass* class_loader_klass() const { return _class_loader_klass; }
  Symbol* class_loader_name() const { return _class_loader_name; }
  JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
};

// An iterator that distributes Klasses to parallel worker threads.
class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
 Klass* volatile _next_klass;
 public:
  ClassLoaderDataGraphKlassIteratorAtomic();
  Klass* next_klass();
 private:
  static Klass* next_klass_in_cldg(Klass* klass);
};

class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
  ClassLoaderData* _data;
 public:
  ClassLoaderDataGraphMetaspaceIterator();
  ~ClassLoaderDataGraphMetaspaceIterator();
  bool repeat() { return _data != NULL; }
  ClassLoaderMetaspace* get_next() {
    assert(_data != NULL, "Should not be NULL in call to the iterator");
    ClassLoaderMetaspace* 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;
  }
};
#endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP