1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_MEMORY_METASPACECLOSURE_HPP
26 #define SHARE_MEMORY_METASPACECLOSURE_HPP
27
28 #include "logging/log.hpp"
29 #include "memory/allocation.hpp"
30 #include "metaprogramming/enableIf.hpp"
31 #include "oops/array.hpp"
32 #include "utilities/debug.hpp"
33 #include "utilities/globalDefinitions.hpp"
34 #include "utilities/growableArray.hpp"
35 #include "utilities/macros.hpp"
36 #include "utilities/resizeableResourceHash.hpp"
37 #include <type_traits>
38
39 // The metadata hierarchy is separate from the oop hierarchy
40 class MetaspaceObj; // no C++ vtable
41 //class Array; // no C++ vtable
42 class Annotations; // no C++ vtable
43 class ConstantPoolCache; // no C++ vtable
44 class ConstMethod; // no C++ vtable
45 class MethodCounters; // no C++ vtable
46 class Symbol; // no C++ vtable
47 class Metadata; // has C++ vtable (so do all subclasses)
48 class ConstantPool;
49 class MethodData;
50 class Method;
51 class Klass;
52 class InstanceKlass;
53 class InstanceMirrorKlass;
54 class InstanceClassLoaderKlass;
55 class InstanceRefKlass;
56 class ArrayKlass;
57 class ObjArrayKlass;
58 class TypeArrayKlass;
59
60 // class MetaspaceClosure --
61 //
62 // This class is used for iterating the objects in the HotSpot Metaspaces. It
63 // provides an API to walk all the reachable objects starting from a set of
64 // root references (such as all Klass'es in the SystemDictionary).
65 //
66 // Currently it is used for compacting the CDS archive by eliminate temporary
67 // objects allocated during archive creation time. See ArchiveBuilder for an example.
68 //
69 // To support MetaspaceClosure, each subclass of MetaspaceObj must provide
70 // a method of the type void metaspace_pointers_do(MetaspaceClosure*). This method
71 // should call MetaspaceClosure::push() on every pointer fields of this
72 // class that points to a MetaspaceObj. See Annotations::metaspace_pointers_do()
73 // for an example.
74 class MetaspaceClosure {
75 public:
76 enum Writability {
77 _writable,
78 _not_writable,
79 _default
80 };
81
82 // class MetaspaceClosure::Ref --
83 //
84 // MetaspaceClosure can be viewed as a very simple type of copying garbage
85 // collector. For it to function properly, it requires each subclass of
86 // MetaspaceObj to provide two methods:
87 //
88 // size_t size(); -- to determine how much data to copy
89 // void metaspace_pointers_do(MetaspaceClosure*); -- to locate all the embedded pointers
90 //
91 // Calling these methods would be trivial if these two were virtual methods.
92 // However, to save space, MetaspaceObj has NO vtable. The vtable is introduced
93 // only in the Metadata class.
94 //
95 // To work around the lack of a vtable, we use the Ref class with templates
96 // (see MSORef, OtherArrayRef, MSOArrayRef, and MSOPointerArrayRef)
97 // so that we can statically discover the type of a object. The use of Ref
98 // depends on the fact that:
99 //
100 // [1] We don't use polymorphic pointers for MetaspaceObj's that are not subclasses
101 // of Metadata. I.e., we don't do this:
102 // class Klass {
103 // MetaspaceObj *_obj;
104 // Array<int>* foo() { return (Array<int>*)_obj; }
105 // Symbol* bar() { return (Symbol*) _obj; }
106 //
107 // [2] All Array<T> dimensions are statically declared.
108 //
109 // Pointer Tagging
110 //
111 // All metaspace pointers are at least 4 byte aligned. Therefore, it's possible for
112 // certain pointers to contain "tags" in their lowest 2 bits.
113 //
114 // Ref::obj() clears the tag bits in the return values. As a result, most
115 // callers who just want walk a closure of metaspace objects do not need to worry
116 // about the tag bits.
117 //
118 // If you need to use the tags, you can access the tagged pointer with Ref::addr()
119 // and manipulate its parts with strip_tags(), decode_tags() and add_tags()
120 class Ref : public CHeapObj<mtMetaspace> {
121 Writability _writability;
122 address _enclosing_obj;
123 Ref* _next;
124 NONCOPYABLE(Ref);
125
126 protected:
127 virtual void** mpp() const = 0;
128 Ref(Writability w) : _writability(w), _enclosing_obj(nullptr), _next(nullptr) {}
129 public:
130 virtual bool not_null() const = 0;
131 virtual int size() const = 0;
132 virtual void metaspace_pointers_do(MetaspaceClosure *it) const = 0;
133 virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const = 0;
134 virtual MetaspaceObj::Type msotype() const = 0;
135 virtual bool is_read_only_by_default() const = 0;
136 virtual ~Ref() {}
137
138 address obj() const {
139 return strip_tags(*addr());
140 }
141
142 address* addr() const {
143 return (address*)mpp();
144 }
145
146 // See comments in ArchiveBuilder::remember_embedded_pointer_in_enclosing_obj()
147 address enclosing_obj() const {
148 return _enclosing_obj;
149 }
150 void set_enclosing_obj(address obj) {
151 _enclosing_obj = obj;
152 }
153
154 Writability writability() const { return _writability; };
155 void set_next(Ref* n) { _next = n; }
156 Ref* next() const { return _next; }
157 };
158
159 // Pointer tagging support
160 constexpr static uintx TAG_MASK = 0x03;
161
162 template <typename T>
163 static T strip_tags(T ptr_with_tags) {
164 uintx n = (uintx)ptr_with_tags;
165 return (T)(n & ~TAG_MASK);
166 }
167
168 template <typename T>
169 static uintx decode_tags(T ptr_with_tags) {
170 uintx n = (uintx)ptr_with_tags;
171 return (n & TAG_MASK);
172 }
173
174 template <typename T>
175 static T add_tags(T ptr, uintx tags) {
176 uintx n = (uintx)ptr;
177 assert((n & TAG_MASK) == 0, "sanity");
178 assert(tags <= TAG_MASK, "sanity");
179 return (T)(n | tags);
180 }
181
182 private:
183 // MSORef -- iterate an instance of MetaspaceObj
184 template <class T> class MSORef : public Ref {
185 T** _mpp;
186 T* dereference() const {
187 return strip_tags(*_mpp);
188 }
189 protected:
190 virtual void** mpp() const {
191 return (void**)_mpp;
192 }
193
194 public:
195 MSORef(T** mpp, Writability w) : Ref(w), _mpp(mpp) {}
196
197 virtual bool is_read_only_by_default() const { return T::is_read_only_by_default(); }
198 virtual bool not_null() const { return dereference() != nullptr; }
199 virtual int size() const { return dereference()->size(); }
200 virtual MetaspaceObj::Type msotype() const { return dereference()->type(); }
201
202 virtual void metaspace_pointers_do(MetaspaceClosure *it) const {
203 dereference()->metaspace_pointers_do(it);
204 }
205 virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {
206 ((T*)new_loc)->metaspace_pointers_do(it);
207 }
208 };
209
210 // abstract base class for MSOArrayRef, MSOPointerArrayRef and OtherArrayRef
211 template <class T> class ArrayRef : public Ref {
212 Array<T>** _mpp;
213 protected:
214 Array<T>* dereference() const {
215 return strip_tags(*_mpp);
216 }
217 virtual void** mpp() const {
218 return (void**)_mpp;
219 }
220
221 ArrayRef(Array<T>** mpp, Writability w) : Ref(w), _mpp(mpp) {}
222
223 // all Arrays are read-only by default
224 virtual bool is_read_only_by_default() const { return true; }
225 virtual bool not_null() const { return dereference() != nullptr; }
226 virtual int size() const { return dereference()->size(); }
227 virtual MetaspaceObj::Type msotype() const { return MetaspaceObj::array_type(sizeof(T)); }
228 };
229
230 // OtherArrayRef -- iterate an instance of Array<T>, where T is NOT a subtype of MetaspaceObj.
231 // T can be a primitive type, such as int, or a structure. However, we do not scan
232 // the fields inside T, so you should not embed any pointers inside T.
233 template <class T> class OtherArrayRef : public ArrayRef<T> {
234 public:
235 OtherArrayRef(Array<T>** mpp, Writability w) : ArrayRef<T>(mpp, w) {}
236
237 virtual void metaspace_pointers_do(MetaspaceClosure *it) const {
238 Array<T>* array = ArrayRef<T>::dereference();
239 log_trace(cds)("Iter(OtherArray): %p [%d]", array, array->length());
240 }
241 virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {
242 Array<T>* array = (Array<T>*)new_loc;
243 log_trace(cds)("Iter(OtherArray): %p [%d]", array, array->length());
244 }
245 };
246
247 // MSOArrayRef -- iterate an instance of Array<T>, where T is a subtype of MetaspaceObj.
248 // We recursively call T::metaspace_pointers_do() for each element in this array.
249 template <class T> class MSOArrayRef : public ArrayRef<T> {
250 public:
251 MSOArrayRef(Array<T>** mpp, Writability w) : ArrayRef<T>(mpp, w) {}
252
253 virtual void metaspace_pointers_do(MetaspaceClosure *it) const {
254 metaspace_pointers_do_at_impl(it, ArrayRef<T>::dereference());
255 }
256 virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {
257 metaspace_pointers_do_at_impl(it, (Array<T>*)new_loc);
258 }
259 private:
260 void metaspace_pointers_do_at_impl(MetaspaceClosure *it, Array<T>* array) const {
261 log_trace(cds)("Iter(MSOArray): %p [%d]", array, array->length());
262 for (int i = 0; i < array->length(); i++) {
263 T* elm = array->adr_at(i);
264 elm->metaspace_pointers_do(it);
265 }
266 }
267 };
268
269 // MSOPointerArrayRef -- iterate an instance of Array<T*>, where T is a subtype of MetaspaceObj.
270 // We recursively call MetaspaceClosure::push() for each pointer in this array.
271 template <class T> class MSOPointerArrayRef : public ArrayRef<T*> {
272 public:
273 MSOPointerArrayRef(Array<T*>** mpp, Writability w) : ArrayRef<T*>(mpp, w) {}
274
275 virtual void metaspace_pointers_do(MetaspaceClosure *it) const {
276 metaspace_pointers_do_at_impl(it, ArrayRef<T*>::dereference());
277 }
278 virtual void metaspace_pointers_do_at(MetaspaceClosure *it, address new_loc) const {
279 metaspace_pointers_do_at_impl(it, (Array<T*>*)new_loc);
280 }
281 private:
282 void metaspace_pointers_do_at_impl(MetaspaceClosure *it, Array<T*>* array) const {
283 log_trace(cds)("Iter(MSOPointerArray): %p [%d]", array, array->length());
284 for (int i = 0; i < array->length(); i++) {
285 T** mpp = array->adr_at(i);
286 it->push(mpp);
287 }
288 }
289 };
290
291 // Normally, chains of references like a->b->c->d are iterated recursively. However,
292 // if recursion is too deep, we save the Refs in _pending_refs, and push them later in
293 // MetaspaceClosure::finish(). This avoids overflowing the C stack.
294 //
295 // When we are visting d, the _enclosing_ref is c,
296 // When we are visting c, the _enclosing_ref is b, ... and so on.
297 static const int MAX_NEST_LEVEL = 5;
298 Ref* _pending_refs;
299 int _nest_level;
300 Ref* _enclosing_ref;
301
302 void push_impl(Ref* ref);
303 void do_push(Ref* ref);
304
305 public:
306 MetaspaceClosure(): _pending_refs(nullptr), _nest_level(0), _enclosing_ref(nullptr) {}
307 ~MetaspaceClosure();
308
309 void finish();
310
311 // returns true if we want to keep iterating the pointers embedded inside <ref>
312 virtual bool do_ref(Ref* ref, bool read_only) = 0;
313
314 private:
315 template <class REF_TYPE, typename T>
316 void push_with_ref(T** mpp, Writability w) {
317 // We cannot make stack allocation because the Ref may need to be saved in
318 // _pending_refs to avoid overflowing the C call stack
319 push_impl(new REF_TYPE(mpp, w));
320 }
321
322 public:
323 // When MetaspaceClosure::push(...) is called, pick the correct Ref subtype to handle it:
324 //
325 // MetaspaceClosure* it = ...;
326 // Klass* o = ...; it->push(&o); => MSORef
327 // Array<int>* a1 = ...; it->push(&a1); => OtherArrayRef
328 // Array<Annotation>* a2 = ...; it->push(&a2); => MSOArrayRef
329 // Array<Klass*>* a3 = ...; it->push(&a3); => MSOPointerArrayRef
330 // Array<Array<Klass*>*>* a4 = ...; it->push(&a4); => MSOPointerArrayRef
331 // Array<Annotation*>* a5 = ...; it->push(&a5); => MSOPointerArrayRef
332 //
333 // Note that the following will fail to compile (to prevent you from adding new fields
334 // into the MetaspaceObj subtypes that cannot be properly copied by CDS):
335 //
336 // MemoryPool* p = ...; it->push(&p); => MemoryPool is not a subclass of MetaspaceObj
337 // Array<MemoryPool*>* a6 = ...; it->push(&a6); => MemoryPool is not a subclass of MetaspaceObj
338 // Array<int*>* a7 = ...; it->push(&a7); => int is not a subclass of MetaspaceObj
339
340 template <typename T>
341 void push(T** mpp, Writability w = _default) {
342 static_assert(std::is_base_of<MetaspaceObj, T>::value, "Do not push pointers of arbitrary types");
343 push_with_ref<MSORef<T>>(mpp, w);
344 }
345
346 template <typename T, ENABLE_IF(!std::is_base_of<MetaspaceObj, T>::value)>
347 void push(Array<T>** mpp, Writability w = _default) {
348 push_with_ref<OtherArrayRef<T>>(mpp, w);
349 }
350
351 template <typename T, ENABLE_IF(std::is_base_of<MetaspaceObj, T>::value)>
352 void push(Array<T>** mpp, Writability w = _default) {
353 push_with_ref<MSOArrayRef<T>>(mpp, w);
354 }
355
356 template <typename T>
357 void push(Array<T*>** mpp, Writability w = _default) {
358 static_assert(std::is_base_of<MetaspaceObj, T>::value, "Do not push Arrays of arbitrary pointer types");
359 push_with_ref<MSOPointerArrayRef<T>>(mpp, w);
360 }
361 };
362
363 // This is a special MetaspaceClosure that visits each unique MetaspaceObj once.
364 class UniqueMetaspaceClosure : public MetaspaceClosure {
365 static const int INITIAL_TABLE_SIZE = 15889;
366 static const int MAX_TABLE_SIZE = 1000000;
367
368 // Do not override. Returns true if we are discovering ref->obj() for the first time.
369 virtual bool do_ref(Ref* ref, bool read_only);
370
371 public:
372 // Gets called the first time we discover an object.
373 virtual bool do_unique_ref(Ref* ref, bool read_only) = 0;
374 UniqueMetaspaceClosure() : _has_been_visited(INITIAL_TABLE_SIZE, MAX_TABLE_SIZE) {}
375
376 private:
377 ResizeableResourceHashtable<address, bool, AnyObj::C_HEAP,
378 mtClassShared> _has_been_visited;
379 };
380
381 #endif // SHARE_MEMORY_METASPACECLOSURE_HPP