Mon, 07 Jul 2014 10:12:40 +0200
8049421: G1 Class Unloading after completing a concurrent mark cycle
Reviewed-by: tschatzl, ehelin, brutisso, coleenp, roland, iveresov
Contributed-by: stefan.karlsson@oracle.com, mikael.gerdin@oracle.com
1 /*
2 * Copyright (c) 2012, 2014, 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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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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23 */
25 #ifndef SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP
26 #define SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP
28 #include "memory/allocation.hpp"
29 #include "memory/memRegion.hpp"
30 #include "memory/metaspace.hpp"
31 #include "memory/metaspaceCounters.hpp"
32 #include "runtime/mutex.hpp"
33 #include "utilities/growableArray.hpp"
34 #if INCLUDE_TRACE
35 # include "utilities/ticks.hpp"
36 #endif
38 //
39 // A class loader represents a linkset. Conceptually, a linkset identifies
40 // the complete transitive closure of resolved links that a dynamic linker can
41 // produce.
42 //
43 // A ClassLoaderData also encapsulates the allocation space, called a metaspace,
44 // used by the dynamic linker to allocate the runtime representation of all
45 // the types it defines.
46 //
47 // ClassLoaderData are stored in the runtime representation of classes and the
48 // system dictionary, are roots of garbage collection, and provides iterators
49 // for root tracing and other GC operations.
51 class ClassLoaderData;
52 class JNIMethodBlock;
53 class JNIHandleBlock;
54 class Metadebug;
56 // GC root for walking class loader data created
58 class ClassLoaderDataGraph : public AllStatic {
59 friend class ClassLoaderData;
60 friend class ClassLoaderDataGraphMetaspaceIterator;
61 friend class ClassLoaderDataGraphKlassIteratorAtomic;
62 friend class VMStructs;
63 private:
64 // All CLDs (except the null CLD) can be reached by walking _head->_next->...
65 static ClassLoaderData* _head;
66 static ClassLoaderData* _unloading;
67 // CMS support.
68 static ClassLoaderData* _saved_head;
69 static ClassLoaderData* _saved_unloading;
70 static bool _should_purge;
72 static ClassLoaderData* add(Handle class_loader, bool anonymous, TRAPS);
73 static void post_class_unload_events(void);
74 public:
75 static ClassLoaderData* find_or_create(Handle class_loader, TRAPS);
76 static void purge();
77 static void clear_claimed_marks();
78 // oops do
79 static void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
80 static void keep_alive_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
81 static void always_strong_oops_do(OopClosure* blk, KlassClosure* klass_closure, bool must_claim);
82 // cld do
83 static void cld_do(CLDClosure* cl);
84 static void roots_cld_do(CLDClosure* strong, CLDClosure* weak);
85 static void keep_alive_cld_do(CLDClosure* cl);
86 static void always_strong_cld_do(CLDClosure* cl);
87 // klass do
88 static void classes_do(KlassClosure* klass_closure);
89 static void classes_do(void f(Klass* const));
90 static void loaded_classes_do(KlassClosure* klass_closure);
91 static void classes_unloading_do(void f(Klass* const));
92 static bool do_unloading(BoolObjectClosure* is_alive);
94 // CMS support.
95 static void remember_new_clds(bool remember) { _saved_head = (remember ? _head : NULL); }
96 static GrowableArray<ClassLoaderData*>* new_clds();
98 static void set_should_purge(bool b) { _should_purge = b; }
99 static void purge_if_needed() {
100 // Only purge the CLDG for CMS if concurrent sweep is complete.
101 if (_should_purge) {
102 purge();
103 // reset for next time.
104 set_should_purge(false);
105 }
106 }
108 static void dump_on(outputStream * const out) PRODUCT_RETURN;
109 static void dump() { dump_on(tty); }
110 static void verify();
112 static bool unload_list_contains(const void* x);
113 #ifndef PRODUCT
114 static bool contains_loader_data(ClassLoaderData* loader_data);
115 #endif
117 #if INCLUDE_TRACE
118 private:
119 static Ticks _class_unload_time;
120 static void class_unload_event(Klass* const k);
121 #endif
122 };
124 // ClassLoaderData class
126 class ClassLoaderData : public CHeapObj<mtClass> {
127 friend class VMStructs;
128 private:
129 class Dependencies VALUE_OBJ_CLASS_SPEC {
130 objArrayOop _list_head;
131 void locked_add(objArrayHandle last,
132 objArrayHandle new_dependency,
133 Thread* THREAD);
134 public:
135 Dependencies() : _list_head(NULL) {}
136 Dependencies(TRAPS) : _list_head(NULL) {
137 init(CHECK);
138 }
139 void add(Handle dependency, TRAPS);
140 void init(TRAPS);
141 void oops_do(OopClosure* f);
142 };
144 friend class ClassLoaderDataGraph;
145 friend class ClassLoaderDataGraphKlassIteratorAtomic;
146 friend class ClassLoaderDataGraphMetaspaceIterator;
147 friend class MetaDataFactory;
148 friend class Method;
150 static ClassLoaderData * _the_null_class_loader_data;
152 oop _class_loader; // oop used to uniquely identify a class loader
153 // class loader or a canonical class path
154 Dependencies _dependencies; // holds dependencies from this class loader
155 // data to others.
157 Metaspace * _metaspace; // Meta-space where meta-data defined by the
158 // classes in the class loader are allocated.
159 Mutex* _metaspace_lock; // Locks the metaspace for allocations and setup.
160 bool _unloading; // true if this class loader goes away
161 bool _keep_alive; // if this CLD is kept alive without a keep_alive_object().
162 bool _is_anonymous; // if this CLD is for an anonymous class
163 volatile int _claimed; // true if claimed, for example during GC traces.
164 // To avoid applying oop closure more than once.
165 // Has to be an int because we cas it.
166 Klass* _klasses; // The classes defined by the class loader.
168 JNIHandleBlock* _handles; // Handles to constant pool arrays
170 // These method IDs are created for the class loader and set to NULL when the
171 // class loader is unloaded. They are rarely freed, only for redefine classes
172 // and if they lose a data race in InstanceKlass.
173 JNIMethodBlock* _jmethod_ids;
175 // Metadata to be deallocated when it's safe at class unloading, when
176 // this class loader isn't unloaded itself.
177 GrowableArray<Metadata*>* _deallocate_list;
179 // Support for walking class loader data objects
180 ClassLoaderData* _next; /// Next loader_datas created
182 // ReadOnly and ReadWrite metaspaces (static because only on the null
183 // class loader for now).
184 static Metaspace* _ro_metaspace;
185 static Metaspace* _rw_metaspace;
187 void set_next(ClassLoaderData* next) { _next = next; }
188 ClassLoaderData* next() const { return _next; }
190 ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies);
191 ~ClassLoaderData();
193 void set_metaspace(Metaspace* m) { _metaspace = m; }
195 JNIHandleBlock* handles() const;
196 void set_handles(JNIHandleBlock* handles);
198 Mutex* metaspace_lock() const { return _metaspace_lock; }
200 // GC interface.
201 void clear_claimed() { _claimed = 0; }
202 bool claimed() const { return _claimed == 1; }
203 bool claim();
205 void unload();
206 bool keep_alive() const { return _keep_alive; }
207 void classes_do(void f(Klass*));
208 void loaded_classes_do(KlassClosure* klass_closure);
209 void classes_do(void f(InstanceKlass*));
211 // Deallocate free list during class unloading.
212 void free_deallocate_list();
214 // Allocate out of this class loader data
215 MetaWord* allocate(size_t size);
217 public:
219 bool is_alive(BoolObjectClosure* is_alive_closure) const;
221 // Accessors
222 Metaspace* metaspace_or_null() const { return _metaspace; }
224 static ClassLoaderData* the_null_class_loader_data() {
225 return _the_null_class_loader_data;
226 }
228 bool is_anonymous() const { return _is_anonymous; }
230 static void init_null_class_loader_data() {
231 assert(_the_null_class_loader_data == NULL, "cannot initialize twice");
232 assert(ClassLoaderDataGraph::_head == NULL, "cannot initialize twice");
234 // We explicitly initialize the Dependencies object at a later phase in the initialization
235 _the_null_class_loader_data = new ClassLoaderData((oop)NULL, false, Dependencies());
236 ClassLoaderDataGraph::_head = _the_null_class_loader_data;
237 assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
238 if (DumpSharedSpaces) {
239 _the_null_class_loader_data->initialize_shared_metaspaces();
240 }
241 }
243 bool is_the_null_class_loader_data() const {
244 return this == _the_null_class_loader_data;
245 }
246 bool is_ext_class_loader_data() const;
248 // The Metaspace is created lazily so may be NULL. This
249 // method will allocate a Metaspace if needed.
250 Metaspace* metaspace_non_null();
252 oop class_loader() const { return _class_loader; }
254 // The object the GC is using to keep this ClassLoaderData alive.
255 oop keep_alive_object() const;
257 // Returns true if this class loader data is for a loader going away.
258 bool is_unloading() const {
259 assert(!(is_the_null_class_loader_data() && _unloading), "The null class loader can never be unloaded");
260 return _unloading;
261 }
263 // Used to make sure that this CLD is not unloaded.
264 void set_keep_alive(bool value) { _keep_alive = value; }
266 unsigned int identity_hash() {
267 return _class_loader == NULL ? 0 : _class_loader->identity_hash();
268 }
270 // Used when tracing from klasses.
271 void oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim);
273 void classes_do(KlassClosure* klass_closure);
275 JNIMethodBlock* jmethod_ids() const { return _jmethod_ids; }
276 void set_jmethod_ids(JNIMethodBlock* new_block) { _jmethod_ids = new_block; }
278 void print_value() { print_value_on(tty); }
279 void print_value_on(outputStream* out) const;
280 void dump(outputStream * const out) PRODUCT_RETURN;
281 void verify();
282 const char* loader_name();
284 jobject add_handle(Handle h);
285 void add_class(Klass* k);
286 void remove_class(Klass* k);
287 bool contains_klass(Klass* k);
288 void record_dependency(Klass* to, TRAPS);
289 void init_dependencies(TRAPS);
291 void add_to_deallocate_list(Metadata* m);
293 static ClassLoaderData* class_loader_data(oop loader);
294 static ClassLoaderData* class_loader_data_or_null(oop loader);
295 static ClassLoaderData* anonymous_class_loader_data(oop loader, TRAPS);
296 static void print_loader(ClassLoaderData *loader_data, outputStream *out);
298 // CDS support
299 Metaspace* ro_metaspace();
300 Metaspace* rw_metaspace();
301 void initialize_shared_metaspaces();
302 };
304 // An iterator that distributes Klasses to parallel worker threads.
305 class ClassLoaderDataGraphKlassIteratorAtomic : public StackObj {
306 volatile Klass* _next_klass;
307 public:
308 ClassLoaderDataGraphKlassIteratorAtomic();
309 Klass* next_klass();
310 private:
311 static Klass* next_klass_in_cldg(Klass* klass);
312 };
314 class ClassLoaderDataGraphMetaspaceIterator : public StackObj {
315 ClassLoaderData* _data;
316 public:
317 ClassLoaderDataGraphMetaspaceIterator();
318 ~ClassLoaderDataGraphMetaspaceIterator();
319 bool repeat() { return _data != NULL; }
320 Metaspace* get_next() {
321 assert(_data != NULL, "Should not be NULL in call to the iterator");
322 Metaspace* result = _data->metaspace_or_null();
323 _data = _data->next();
324 // This result might be NULL for class loaders without metaspace
325 // yet. It would be nice to return only non-null results but
326 // there is no guarantee that there will be a non-null result
327 // down the list so the caller is going to have to check.
328 return result;
329 }
330 };
331 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_HPP