1/*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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24
25#ifndef SHARE_RUNTIME_HANDLES_HPP
26#define SHARE_RUNTIME_HANDLES_HPP
27
28#include "memory/arena.hpp"
29#include "oops/oop.hpp"
30#include "oops/oopsHierarchy.hpp"
31
32class InstanceKlass;
33class Klass;
34class Thread;
35
36//------------------------------------------------------------------------------------------------------------------------
37// In order to preserve oops during garbage collection, they should be
38// allocated and passed around via Handles within the VM. A handle is
39// simply an extra indirection allocated in a thread local handle area.
40//
41// A handle is a value object, so it can be passed around as a value, can
42// be used as a parameter w/o using &-passing, and can be returned as a
43// return value.
44//
45// oop parameters and return types should be Handles whenever feasible.
46//
47// Handles are declared in a straight-forward manner, e.g.
48//
49// oop obj = ...;
50// Handle h2(thread, obj); // allocate a new handle in thread
51// Handle h3; // declare handle only, no allocation occurs
52// ...
53// h3 = h1; // make h3 refer to same indirection as h1
54// oop obj2 = h2(); // get handle value
55// h1->print(); // invoking operation on oop
56//
57// Handles are specialized for different oop types to provide extra type
58// information and avoid unnecessary casting. For each oop type xxxOop
59// there is a corresponding handle called xxxHandle.
60
61//------------------------------------------------------------------------------------------------------------------------
62// Base class for all handles. Provides overloading of frequently
63// used operators for ease of use.
64
65class Handle {
66 private:
67 oop* _handle;
68
69 protected:
70 oop obj() const { return _handle == NULL ? (oop)NULL : *_handle; }
71 oop non_null_obj() const { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
72
73 public:
74 // Constructors
75 Handle() { _handle = NULL; }
76 inline Handle(Thread* thread, oop obj);
77
78 // General access
79 oop operator () () const { return obj(); }
80 oop operator -> () const { return non_null_obj(); }
81
82 bool operator == (oop o) const { return oopDesc::equals(obj(), o); }
83 bool operator == (const Handle& h) const { return oopDesc::equals(obj(), h.obj()); }
84
85 // Null checks
86 bool is_null() const { return _handle == NULL; }
87 bool not_null() const { return _handle != NULL; }
88
89 // Debugging
90 void print() { obj()->print(); }
91
92 // Direct interface, use very sparingly.
93 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
94 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
95 Handle(oop *handle, bool dummy) { _handle = handle; }
96
97 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
98 // since duplicates is only valid as long as original handle is alive.
99 oop* raw_value() { return _handle; }
100 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
101};
102
103// Specific Handles for different oop types
104#define DEF_HANDLE(type, is_a) \
105 class type##Handle: public Handle { \
106 protected: \
107 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
108 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
109 \
110 public: \
111 /* Constructors */ \
112 type##Handle () : Handle() {} \
113 inline type##Handle (Thread* thread, type##Oop obj); \
114 \
115 /* Operators for ease of use */ \
116 type##Oop operator () () const { return obj(); } \
117 type##Oop operator -> () const { return non_null_obj(); } \
118 };
119
120
121DEF_HANDLE(instance , is_instance_noinline )
122DEF_HANDLE(array , is_array_noinline )
123DEF_HANDLE(objArray , is_objArray_noinline )
124DEF_HANDLE(typeArray , is_typeArray_noinline )
125
126//------------------------------------------------------------------------------------------------------------------------
127
128// Metadata Handles. Unlike oop Handles these are needed to prevent metadata
129// from being reclaimed by RedefineClasses.
130// Metadata Handles should be passed around as const references to avoid copy construction
131// and destruction for parameters.
132
133// Specific Handles for different oop types
134#define DEF_METADATA_HANDLE(name, type) \
135 class name##Handle; \
136 class name##Handle : public StackObj { \
137 type* _value; \
138 Thread* _thread; \
139 protected: \
140 type* obj() const { return _value; } \
141 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \
142 \
143 public: \
144 /* Constructors */ \
145 name##Handle () : _value(NULL), _thread(NULL) {} \
146 name##Handle (type* obj); \
147 name##Handle (Thread* thread, type* obj); \
148 \
149 name##Handle (const name##Handle &h); \
150 name##Handle& operator=(const name##Handle &s); \
151 \
152 /* Destructor */ \
153 ~name##Handle (); \
154 void remove(); \
155 \
156 /* Operators for ease of use */ \
157 type* operator () () const { return obj(); } \
158 type* operator -> () const { return non_null_obj(); } \
159 \
160 bool operator == (type* o) const { return obj() == o; } \
161 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \
162 \
163 /* Null checks */ \
164 bool is_null() const { return _value == NULL; } \
165 bool not_null() const { return _value != NULL; } \
166 };
167
168
169DEF_METADATA_HANDLE(method, Method)
170DEF_METADATA_HANDLE(constantPool, ConstantPool)
171
172//------------------------------------------------------------------------------------------------------------------------
173// Thread local handle area
174class HandleArea: public Arena {
175 friend class HandleMark;
176 friend class NoHandleMark;
177 friend class ResetNoHandleMark;
178#ifdef ASSERT
179 int _handle_mark_nesting;
180 int _no_handle_mark_nesting;
181#endif
182 HandleArea* _prev; // link to outer (older) area
183 public:
184 // Constructor
185 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
186 debug_only(_handle_mark_nesting = 0);
187 debug_only(_no_handle_mark_nesting = 0);
188 _prev = prev;
189 }
190
191 // Handle allocation
192 private:
193 oop* real_allocate_handle(oop obj) {
194#ifdef ASSERT
195 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
196#else
197 oop* handle = (oop*) Amalloc_4(oopSize);
198#endif
199 *handle = obj;
200 return handle;
201 }
202 public:
203#ifdef ASSERT
204 oop* allocate_handle(oop obj);
205#else
206 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
207#endif
208
209 // Garbage collection support
210 void oops_do(OopClosure* f);
211
212 // Number of handles in use
213 size_t used() const { return Arena::used() / oopSize; }
214
215 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
216};
217
218
219//------------------------------------------------------------------------------------------------------------------------
220// Handles are allocated in a (growable) thread local handle area. Deallocation
221// is managed using a HandleMark. It should normally not be necessary to use
222// HandleMarks manually.
223//
224// A HandleMark constructor will record the current handle area top, and the
225// destructor will reset the top, destroying all handles allocated in between.
226// The following code will therefore NOT work:
227//
228// Handle h;
229// {
230// HandleMark hm;
231// h = Handle(THREAD, obj);
232// }
233// h()->print(); // WRONG, h destroyed by HandleMark destructor.
234//
235// If h has to be preserved, it can be converted to an oop or a local JNI handle
236// across the HandleMark boundary.
237
238// The base class of HandleMark should have been StackObj but we also heap allocate
239// a HandleMark when a thread is created. The operator new is for this special case.
240
241class HandleMark {
242 private:
243 Thread *_thread; // thread that owns this mark
244 HandleArea *_area; // saved handle area
245 Chunk *_chunk; // saved arena chunk
246 char *_hwm, *_max; // saved arena info
247 size_t _size_in_bytes; // size of handle area
248 // Link to previous active HandleMark in thread
249 HandleMark* _previous_handle_mark;
250
251 void initialize(Thread* thread); // common code for constructors
252 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
253 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
254
255 size_t size_in_bytes() const { return _size_in_bytes; }
256 // remove all chunks beginning with the next
257 void chop_later_chunks();
258 public:
259 HandleMark(); // see handles_inline.hpp
260 HandleMark(Thread* thread) { initialize(thread); }
261 ~HandleMark();
262
263 // Functions used by HandleMarkCleaner
264 // called in the constructor of HandleMarkCleaner
265 void push();
266 // called in the destructor of HandleMarkCleaner
267 void pop_and_restore();
268 // overloaded operators
269 void* operator new(size_t size) throw();
270 void* operator new [](size_t size) throw();
271 void operator delete(void* p);
272 void operator delete[](void* p);
273};
274
275//------------------------------------------------------------------------------------------------------------------------
276// A NoHandleMark stack object will verify that no handles are allocated
277// in its scope. Enabled in debug mode only.
278
279class NoHandleMark: public StackObj {
280 public:
281#ifdef ASSERT
282 NoHandleMark();
283 ~NoHandleMark();
284#else
285 NoHandleMark() {}
286 ~NoHandleMark() {}
287#endif
288};
289
290
291class ResetNoHandleMark: public StackObj {
292 int _no_handle_mark_nesting;
293 public:
294#ifdef ASSERT
295 ResetNoHandleMark();
296 ~ResetNoHandleMark();
297#else
298 ResetNoHandleMark() {}
299 ~ResetNoHandleMark() {}
300#endif
301};
302
303// The HandleMarkCleaner is a faster version of HandleMark.
304// It relies on the fact that there is a HandleMark further
305// down the stack (in JavaCalls::call_helper), and just resets
306// to the saved values in that HandleMark.
307
308class HandleMarkCleaner: public StackObj {
309 private:
310 Thread* _thread;
311 public:
312 inline HandleMarkCleaner(Thread* thread);
313 inline ~HandleMarkCleaner();
314};
315
316#endif // SHARE_RUNTIME_HANDLES_HPP
317