/*

 * Copyright (c) 1997, 2019, 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

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 * questions.

 *

 */

#ifndef SHARE_RUNTIME_HANDLES_HPP

#define SHARE_RUNTIME_HANDLES_HPP

#include "memory/arena.hpp"

#include "oops/oop.hpp"

#include "oops/oopsHierarchy.hpp"

class InstanceKlass;

class Klass;

class Thread;

//------------------------------------------------------------------------------------------------------------------------

// In order to preserve oops during garbage collection, they should be

// allocated and passed around via Handles within the VM. A handle is

// simply an extra indirection allocated in a thread local handle area.

//

// A handle is a value object, so it can be passed around as a value, can

// be used as a parameter w/o using &-passing, and can be returned as a

// return value.

//

// oop parameters and return types should be Handles whenever feasible.

//

// Handles are declared in a straight-forward manner, e.g.

//

//   oop obj = ...;

//   Handle h2(thread, obj);      // allocate a new handle in thread

//   Handle h3;                   // declare handle only, no allocation occurs

//   ...

//   h3 = h1;                     // make h3 refer to same indirection as h1

//   oop obj2 = h2();             // get handle value

//   h1->print();                 // invoking operation on oop

//

// Handles are specialized for different oop types to provide extra type

// information and avoid unnecessary casting. For each oop type xxxOop

// there is a corresponding handle called xxxHandle.

//------------------------------------------------------------------------------------------------------------------------

// Base class for all handles. Provides overloading of frequently

// used operators for ease of use.

class Handle {

 private:

  oop* _handle;

 protected:

  oop     obj() const                            { return _handle == NULL ? (oop)NULL : *_handle; }

  oop     non_null_obj() const                   { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }

 public:

  // Constructors

  Handle()                                       { _handle = NULL; }

  inline Handle(Thread* thread, oop obj);

  // General access

  oop     operator () () const                   { return obj(); }

  oop     operator -> () const                   { return non_null_obj(); }

  bool operator == (oop o) const                 { return obj() == o; }

  bool operator == (const Handle& h) const       { return obj() == h.obj(); }

  // Null checks

  bool    is_null() const                        { return _handle == NULL; }

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

  // Debugging

  void    print()                                { obj()->print(); }

  // Direct interface, use very sparingly.

  // Used by JavaCalls to quickly convert handles and to create handles static data structures.

  // Constructor takes a dummy argument to prevent unintentional type conversion in C++.

  Handle(oop *handle, bool dummy)                { _handle = handle; }

  // Raw handle access. Allows easy duplication of Handles. This can be very unsafe

  // since duplicates is only valid as long as original handle is alive.

  oop* raw_value()                               { return _handle; }

  static oop raw_resolve(oop *handle)            { return handle == NULL ? (oop)NULL : *handle; }

};

// Specific Handles for different oop types

#define DEF_HANDLE(type, is_a)                   \

  class type##Handle: public Handle {            \

   protected:                                    \

    type##Oop    obj() const                     { return (type##Oop)Handle::obj(); } \

    type##Oop    non_null_obj() const            { return (type##Oop)Handle::non_null_obj(); } \

                                                 \

   public:                                       \

    /* Constructors */                           \

    type##Handle ()                              : Handle()                 {} \

    inline type##Handle (Thread* thread, type##Oop obj); \

    \

    /* Operators for ease of use */              \

    type##Oop    operator () () const            { return obj(); } \

    type##Oop    operator -> () const            { return non_null_obj(); } \

  };

DEF_HANDLE(instance         , is_instance_noinline         )

DEF_HANDLE(array            , is_array_noinline            )

DEF_HANDLE(objArray         , is_objArray_noinline         )

DEF_HANDLE(typeArray        , is_typeArray_noinline        )

//------------------------------------------------------------------------------------------------------------------------

// Metadata Handles.  Unlike oop Handles these are needed to prevent metadata

// from being reclaimed by RedefineClasses.

// Metadata Handles should be passed around as const references to avoid copy construction

// and destruction for parameters.

// Specific Handles for different oop types

#define DEF_METADATA_HANDLE(name, type)          \

  class name##Handle;                            \

  class name##Handle : public StackObj {         \

    type*     _value;                            \

    Thread*   _thread;                           \

   protected:                                    \

    type*        obj() const                     { return _value; } \

    type*        non_null_obj() const            { assert(_value != NULL, "resolving NULL _value"); return _value; } \

                                                 \

   public:                                       \

    /* Constructors */                           \

    name##Handle () : _value(NULL), _thread(NULL) {}   \

    name##Handle (Thread* thread, type* obj);    \

                                                 \

    name##Handle (const name##Handle &h);        \

    name##Handle& operator=(const name##Handle &s); \

                                                 \

    /* Destructor */                             \

    ~name##Handle ();                            \

    void remove();                               \

                                                 \

    /* Operators for ease of use */              \

    type*        operator () () const            { return obj(); } \

    type*        operator -> () const            { return non_null_obj(); } \

                                                 \

    bool    operator == (type* o) const          { return obj() == o; } \

    bool    operator == (const name##Handle& h) const  { return obj() == h.obj(); } \

                                                 \

    /* Null checks */                            \

    bool    is_null() const                      { return _value == NULL; } \

    bool    not_null() const                     { return _value != NULL; } \

  };

DEF_METADATA_HANDLE(method, Method)

DEF_METADATA_HANDLE(constantPool, ConstantPool)

//------------------------------------------------------------------------------------------------------------------------

// Thread local handle area

class HandleArea: public Arena {

  friend class HandleMark;

  friend class NoHandleMark;

  friend class ResetNoHandleMark;

#ifdef ASSERT

  int _handle_mark_nesting;

  int _no_handle_mark_nesting;

#endif

  HandleArea* _prev;          // link to outer (older) area

 public:

  // Constructor

  HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {

    debug_only(_handle_mark_nesting    = 0);

    debug_only(_no_handle_mark_nesting = 0);

    _prev = prev;

  }

  // Handle allocation

 private:

  oop* real_allocate_handle(oop obj) {

#ifdef ASSERT

    oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));

#else

    oop* handle = (oop*) Amalloc_4(oopSize);

#endif

    *handle = obj;

    return handle;

  }

 public:

#ifdef ASSERT

  oop* allocate_handle(oop obj);

#else

  oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }

#endif

  // Garbage collection support

  void oops_do(OopClosure* f);

  // Number of handles in use

  size_t used() const     { return Arena::used() / oopSize; }

  debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })

};

//------------------------------------------------------------------------------------------------------------------------

// Handles are allocated in a (growable) thread local handle area. Deallocation

// is managed using a HandleMark. It should normally not be necessary to use

// HandleMarks manually.

//

// A HandleMark constructor will record the current handle area top, and the

// destructor will reset the top, destroying all handles allocated in between.

// The following code will therefore NOT work:

//

//   Handle h;

//   {

//     HandleMark hm;

//     h = Handle(THREAD, obj);

//   }

//   h()->print();       // WRONG, h destroyed by HandleMark destructor.

//

// If h has to be preserved, it can be converted to an oop or a local JNI handle

// across the HandleMark boundary.

// The base class of HandleMark should have been StackObj but we also heap allocate

// a HandleMark when a thread is created. The operator new is for this special case.

class HandleMark {

 private:

  Thread *_thread;              // thread that owns this mark

  HandleArea *_area;            // saved handle area

  Chunk *_chunk;                // saved arena chunk

  char *_hwm, *_max;            // saved arena info

  size_t _size_in_bytes;        // size of handle area

  // Link to previous active HandleMark in thread

  HandleMark* _previous_handle_mark;

  void initialize(Thread* thread);                // common code for constructors

  void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }

  HandleMark* previous_handle_mark() const        { return _previous_handle_mark; }

  size_t size_in_bytes() const { return _size_in_bytes; }

  // remove all chunks beginning with the next

  void chop_later_chunks();

 public:

  HandleMark();                            // see handles_inline.hpp

  HandleMark(Thread* thread)                      { initialize(thread); }

  ~HandleMark();

  // Functions used by HandleMarkCleaner

  // called in the constructor of HandleMarkCleaner

  void push();

  // called in the destructor of HandleMarkCleaner

  void pop_and_restore();

  // overloaded operators

  void* operator new(size_t size) throw();

  void* operator new [](size_t size) throw();

  void operator delete(void* p);

  void operator delete[](void* p);

};

//------------------------------------------------------------------------------------------------------------------------

// A NoHandleMark stack object will verify that no handles are allocated

// in its scope. Enabled in debug mode only.

class NoHandleMark: public StackObj {

 public:

#ifdef ASSERT

  NoHandleMark();

  ~NoHandleMark();

#else

  NoHandleMark()  {}

  ~NoHandleMark() {}

#endif

};

class ResetNoHandleMark: public StackObj {

  int _no_handle_mark_nesting;

 public:

#ifdef ASSERT

  ResetNoHandleMark();

  ~ResetNoHandleMark();

#else

  ResetNoHandleMark()  {}

  ~ResetNoHandleMark() {}

#endif

};

// The HandleMarkCleaner is a faster version of HandleMark.

// It relies on the fact that there is a HandleMark further

// down the stack (in JavaCalls::call_helper), and just resets

// to the saved values in that HandleMark.

class HandleMarkCleaner: public StackObj {

 private:

  Thread* _thread;

 public:

  inline HandleMarkCleaner(Thread* thread);

  inline ~HandleMarkCleaner();

};

#endif // SHARE_RUNTIME_HANDLES_HPP