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/*
* Copyright (c) 1997, 2022, 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_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 != (oop o) const { return obj() != o; }
bool operator == (const Handle& h) const { return obj() == h.obj(); }
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() const { return _handle; }
static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
inline void replace(oop obj);
};
// 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); \
type##Handle (oop *handle, bool dummy) : Handle(handle, dummy) {} \
\
/* 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(stackChunk , is_stackChunk_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) {
oop* handle = (oop*)internal_amalloc(oopSize);
*handle = obj;
return handle;
}
public:
#ifdef ASSERT
oop* allocate_handle(oop obj);
oop* allocate_null_handle();
#else
oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
oop* allocate_null_handle() { return allocate_handle(nullptr); }
#endif
// Garbage collection support
void oops_do(OopClosure* f);
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(THREAD);
// 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(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
};
// ResetNoHandleMark is called in a context where there is an enclosing
// NoHandleMark. A thread in _thread_in_native must not create handles so
// this is used when transitioning via ThreadInVMfromNative.
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
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