/*

 * Copyright (c) 2017, 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.

 *

 */

#ifndef SHARE_VM_MEMORY_METASPACE_ITERATOR_HPP

#define SHARE_VM_MEMORY_METASPACE_ITERATOR_HPP

#include "logging/log.hpp"

#include "memory/allocation.hpp"

#include "oops/array.hpp"

#include "utilities/growableArray.hpp"

#include "utilities/resourceHash.hpp"

// The metadata hierarchy is separate from the oop hierarchy

  class MetaspaceObj;        // no C++ vtable

//class   Array;             // no C++ vtable

  class   Annotations;       // no C++ vtable

  class   ConstantPoolCache; // no C++ vtable

  class   ConstMethod;       // no C++ vtable

  class   MethodCounters;    // no C++ vtable

  class   Symbol;            // no C++ vtable

  class   Metadata;          // has C++ vtable (so do all subclasses)

  class     ConstantPool;

  class     MethodData;

  class     Method;

  class     Klass;

  class       InstanceKlass;

  class         InstanceMirrorKlass;

  class         InstanceClassLoaderKlass;

  class         InstanceRefKlass;

  class       ArrayKlass;

  class         ObjArrayKlass;

  class         TypeArrayKlass;

// class MetaspaceClosure --

//

// This class is used for iterating the objects in the HotSpot Metaspaces. It

// provides an API to walk all the reachable objects starting from a set of

// root references (such as all Klass'es in the SystemDictionary).

//

// Currently it is used for compacting the CDS archive by eliminate temporary

// objects allocated during archive creation time. See ArchiveCompactor in

// metaspaceShared.cpp for an example.

//

// To support MetaspaceClosure, each subclass of MetaspaceObj must provide

// a method of the type void metaspace_pointers_do(MetaspaceClosure*). This method

// should call MetaspaceClosure::push() on every pointer fields of this

// class that points to a MetaspaceObj. See Annotations::metaspace_pointers_do()

// for an example.

class MetaspaceClosure {

public:

  enum Writability {

    _writable,

    _not_writable,

    _default

  };

  // class MetaspaceClosure::Ref --

  //

  // MetaspaceClosure can be viewed as a very simple type of copying garbage

  // collector. For it to function properly, it requires each subclass of

  // MetaspaceObj to provide two methods:

  //

  //  size_t size();                                 -- to determine how much data to copy

  //  void metaspace_pointers_do(MetaspaceClosure*); -- to locate all the embedded pointers

  //

  // Calling these methods would be trivial if these two were virtual methods.

  // However, to save space, MetaspaceObj has NO vtable. The vtable is introduced

  // only in the Metadata class.

  //

  // To work around the lack of a vtable, we use Ref class with templates

  // (see ObjectRef, PrimitiveArrayRef and PointerArrayRef)

  // so that we can statically discover the type of a object. The use of Ref

  // depends on the fact that:

  //

  // [1] We don't use polymorphic pointers for MetaspaceObj's that are not subclasses

  //     of Metadata. I.e., we don't do this:

  //     class Klass {

  //         MetaspaceObj *_obj;

  //         Array<int>* foo() { return (Array<int>*)_obj; }

  //         Symbol*     bar() { return (Symbol*)    _obj; }

  //

  // [2] All Array<T> dimensions are statically declared.

  class Ref {

  protected:

    virtual void** mpp() const = 0;

  public:

    virtual bool not_null() const = 0;

    virtual int size() const = 0;

    virtual void metaspace_pointers_do(MetaspaceClosure *it) const = 0;

    virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const = 0;

    virtual MetaspaceObj::Type msotype() const = 0;

    virtual bool is_read_only_by_default() const = 0;

    address obj() const {

      // In some rare cases (see CPSlot in constantPool.hpp) we store some flags in the lowest

      // 2 bits of a MetaspaceObj pointer. Unmask these when manipulating the pointer.

      uintx p = (uintx)*mpp();

      return (address)(p & (~FLAG_MASK));

    }

    void update(address new_loc) const;

  private:

    static const uintx FLAG_MASK = 0x03;

    int flag_bits() const {

      uintx p = (uintx)*mpp();

      return (int)(p & FLAG_MASK);

    }

  };

private:

  // -------------------------------------------------- ObjectRef

  template <class T> class ObjectRef : public Ref {

    T** _mpp;

    T* dereference() const {

      return *_mpp;

    }

  protected:

    virtual void** mpp() const {

      return (void**)_mpp;

    }

  public:

    ObjectRef(T** mpp) : _mpp(mpp) {}

    virtual bool is_read_only_by_default() const { return T::is_read_only_by_default(); }

    virtual bool not_null()                const { return dereference() != NULL; }

    virtual int size()                     const { return dereference()->size(); }

    virtual MetaspaceObj::Type msotype()   const { return dereference()->type(); }

    virtual void metaspace_pointers_do(MetaspaceClosure *it) const {

      dereference()->metaspace_pointers_do(it);

    }

    virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {

      ((T*)new_loc)->metaspace_pointers_do(it);

    }

  };

  // -------------------------------------------------- PrimitiveArrayRef

  template <class T> class PrimitiveArrayRef : public Ref {

    Array<T>** _mpp;

    Array<T>* dereference() const {

      return *_mpp;

    }

  protected:

    virtual void** mpp() const {

      return (void**)_mpp;

    }

  public:

    PrimitiveArrayRef(Array<T>** mpp) : _mpp(mpp) {}

    // all Arrays are read-only by default

    virtual bool is_read_only_by_default() const { return true; }

    virtual bool not_null()                const { return dereference() != NULL;  }

    virtual int size()                     const { return dereference()->size(); }

    virtual MetaspaceObj::Type msotype()   const { return MetaspaceObj::array_type(sizeof(T)); }

    virtual void metaspace_pointers_do(MetaspaceClosure *it) const {

      Array<T>* array = dereference();

      log_trace(cds)("Iter(PrimitiveArray): %p [%d]", array, array->length());

    }

    virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {

      Array<T>* array = (Array<T>*)new_loc;

      log_trace(cds)("Iter(PrimitiveArray): %p [%d]", array, array->length());

    }

  };

  // -------------------------------------------------- PointerArrayRef

  template <class T> class PointerArrayRef : public Ref {

    Array<T*>** _mpp;

    Array<T*>* dereference() const {

      return *_mpp;

    }

  protected:

    virtual void** mpp() const {

      return (void**)_mpp;

    }

  public:

    PointerArrayRef(Array<T*>** mpp) : _mpp(mpp) {}

    // all Arrays are read-only by default

    virtual bool is_read_only_by_default() const { return true; }

    virtual bool not_null()                const { return dereference() != NULL; }

    virtual int size()                     const { return dereference()->size(); }

    virtual MetaspaceObj::Type msotype()   const { return MetaspaceObj::array_type(sizeof(T*)); }

    virtual void metaspace_pointers_do(MetaspaceClosure *it) const {

      metaspace_pointers_do_at_impl(it, dereference());

    }

    virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {

      metaspace_pointers_do_at_impl(it, (Array<T*>*)new_loc);

    }

  private:

    void metaspace_pointers_do_at_impl(MetaspaceClosure *it, Array<T*>* array) const {

      log_trace(cds)("Iter(ObjectArray): %p [%d]", array, array->length());

      for (int i = 0; i < array->length(); i++) {

        T** mpp = array->adr_at(i);

        it->push(mpp);

      }

    }

  };

  void push_impl(Ref* ref, Writability w);

public:

  // returns true if we want to keep iterating the pointers embedded inside <ref>

  virtual bool do_ref(Ref* ref, bool read_only) = 0;

  // When you do:

  //     void MyType::metaspace_pointers_do(MetaspaceClosure* it) {

  //       it->push(_my_field)

  //

  // C++ will try to match the "most specific" template function. This one will

  // will be matched if possible (if mpp is an Array<> of any pointer type).

  template <typename T> void push(Array<T*>** mpp, Writability w = _default) {

    PointerArrayRef<T> ref(mpp);

    push_impl(&ref, w);

  }

  // If the above function doesn't match (mpp is an Array<>, but T is not a pointer type), then

  // this is the second choice.

  template <typename T> void push(Array<T>** mpp, Writability w = _default) {

    PrimitiveArrayRef<T> ref(mpp);

    push_impl(&ref, w);

  }

  // If the above function doesn't match (mpp is not an Array<> type), then

  // this will be matched by default.

  template <class T> void push(T** mpp, Writability w = _default) {

    ObjectRef<T> ref(mpp);

    push_impl(&ref, w);

  }

};

// This is a special MetaspaceClosure that visits each unique MetaspaceObj once.

class UniqueMetaspaceClosure : public MetaspaceClosure {

  // Do not override. Returns true if we are discovering ref->obj() for the first time.

  virtual bool do_ref(Ref* ref, bool read_only);

public:

  // Gets called the first time we discover an object.

  virtual void do_unique_ref(Ref* ref, bool read_only) = 0;

private:

  static unsigned my_hash(const address& a) {

    return primitive_hash<address>(a);

  }

  static bool my_equals(const address& a0, const address& a1) {

    return primitive_equals<address>(a0, a1);

  }

  ResourceHashtable<

      address, bool,

      UniqueMetaspaceClosure::my_hash,   // solaris compiler doesn't like: primitive_hash<address>

      UniqueMetaspaceClosure::my_equals, // solaris compiler doesn't like: primitive_equals<address>

};

#endif // SHARE_VM_MEMORY_METASPACE_ITERATOR_HPP