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 /*

  * Copyright (c) 1997, 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

  * 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

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 #ifndef SHARE_VM_RUNTIME_HANDLES_HPP

 #define SHARE_VM_RUNTIME_HANDLES_HPP

 #include "oops/klass.hpp"

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

 // 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 ValueObj, 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 h1(obj);              // allocate new handle

 //   Handle h2(thread, obj);      // faster allocation when current thread is known

 //   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, e.g.

 //

 //   oop           Handle

 //   Method*       methodHandle

 //   instanceOop   instanceHandle

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

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

 // used operators for ease of use.

 class Handle VALUE_OBJ_CLASS_SPEC {

  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; }

   Handle(oop obj);

   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()                 {} \

     type##Handle (type##Oop obj) : Handle((oop)obj) {                         \

       assert(is_null() || ((oop)obj)->is_a(),                                 \

              "illegal type");                                                 \

     }                                                                         \

     type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \

       assert(is_null() || ((oop)obj)->is_a(), "illegal type");                \

     }                                                                         \

     \

     /* Operators for ease of use */              \

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

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

   };

 DEF_HANDLE(instance         , is_instance         )

 DEF_HANDLE(array            , is_array            )

 DEF_HANDLE(objArray         , is_objArray         )

 DEF_HANDLE(typeArray        , is_typeArray        )

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

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

 // from being reclaimed by RedefineClasses.

 // 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 (type* obj);                    \

     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)

 // Writing this class explicitly, since DEF_METADATA_HANDLE(klass) doesn't

 // provide the necessary Klass* <-> Klass* conversions. This Klass

 // could be removed when we don't have the Klass* typedef anymore.

 class KlassHandle : public StackObj {

   Klass* _value;

  protected:

    Klass* obj() const          { return _value; }

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

  public:

    KlassHandle()                                 : _value(NULL) {}

    KlassHandle(const Klass* obj)                 : _value(const_cast<Klass *>(obj)) {};

    KlassHandle(Thread* thread, const Klass* obj) : _value(const_cast<Klass *>(obj)) {};

    Klass* operator () () const { return obj(); }

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

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

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

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

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

 };

 class instanceKlassHandle : public KlassHandle {

  public:

   /* Constructors */

   instanceKlassHandle () : KlassHandle() {}

   instanceKlassHandle (const Klass* k) : KlassHandle(k) {

     assert(k == NULL || k->oop_is_instance(),

            "illegal type");

   }

   instanceKlassHandle (Thread* thread, const Klass* k) : KlassHandle(thread, k) {

     assert(k == NULL || k->oop_is_instance(),

            "illegal type");

   }

   /* Access to klass part */

   InstanceKlass*       operator () () const { return (InstanceKlass*)obj(); }

   InstanceKlass*       operator -> () const { return (InstanceKlass*)obj(); }

 };

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

 // 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

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

 // The following code will therefore NOT work:

 //

 //   Handle h;

 //   {

 //     HandleMark hm;

 //     h = Handle(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; }

  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

 };

 #endif // SHARE_VM_RUNTIME_HANDLES_HPP