1 /*
2 * Copyright (c) 2018, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.inline.hpp"
27 #include "classfile/dictionary.hpp"
28 #include "classfile/javaClasses.hpp"
29 #include "classfile/metadataOnStackMark.hpp"
30 #include "classfile/moduleEntry.hpp"
31 #include "classfile/packageEntry.hpp"
32 #include "code/dependencyContext.hpp"
33 #include "logging/log.hpp"
34 #include "logging/logStream.hpp"
35 #include "memory/allocation.inline.hpp"
36 #include "memory/metaspace.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "runtime/atomic.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/mutex.hpp"
41 #include "runtime/safepoint.hpp"
42 #include "runtime/safepointVerifiers.hpp"
43 #include "utilities/growableArray.hpp"
44 #include "utilities/macros.hpp"
45 #include "utilities/ostream.hpp"
46
47 volatile size_t ClassLoaderDataGraph::_num_array_classes = 0;
48 volatile size_t ClassLoaderDataGraph::_num_instance_classes = 0;
49
50 void ClassLoaderDataGraph::clear_claimed_marks() {
51 // The claimed marks of the CLDs in the ClassLoaderDataGraph are cleared
52 // outside a safepoint and without locking the ClassLoaderDataGraph_lock.
53 // This is required to avoid a deadlock between concurrent GC threads and safepointing.
54 //
55 // We need to make sure that the CLD contents are fully visible to the
56 // reader thread. This is accomplished by acquire/release of the _head,
57 // and is sufficient.
58 //
59 // Any ClassLoaderData added after or during walking the list are prepended to
60 // _head. Their claim mark need not be handled here.
61 for (ClassLoaderData* cld = Atomic::load_acquire(&_head); cld != NULL; cld = cld->next()) {
62 cld->clear_claim();
63 }
64 }
65
66 void ClassLoaderDataGraph::clear_claimed_marks(int claim) {
67 for (ClassLoaderData* cld = Atomic::load_acquire(&_head); cld != NULL; cld = cld->next()) {
68 cld->clear_claim(claim);
69 }
70 }
71 // Class iterator used by the compiler. It gets some number of classes at
72 // a safepoint to decay invocation counters on the methods.
73 class ClassLoaderDataGraphKlassIteratorStatic {
74 ClassLoaderData* _current_loader_data;
75 Klass* _current_class_entry;
76 public:
77
78 ClassLoaderDataGraphKlassIteratorStatic() : _current_loader_data(NULL), _current_class_entry(NULL) {}
79
80 InstanceKlass* try_get_next_class() {
81 assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
82 size_t max_classes = ClassLoaderDataGraph::num_instance_classes();
83 assert(max_classes > 0, "should not be called with no instance classes");
84 for (size_t i = 0; i < max_classes; ) {
85
86 if (_current_class_entry != NULL) {
87 Klass* k = _current_class_entry;
88 _current_class_entry = _current_class_entry->next_link();
89
90 if (k->is_instance_klass()) {
91 InstanceKlass* ik = InstanceKlass::cast(k);
92 i++; // count all instance classes found
93 // Not yet loaded classes are counted in max_classes
94 // but only return loaded classes.
95 if (ik->is_loaded()) {
96 return ik;
97 }
98 }
99 } else {
100 // Go to next CLD
101 if (_current_loader_data != NULL) {
102 _current_loader_data = _current_loader_data->next();
103 }
104 // Start at the beginning
105 if (_current_loader_data == NULL) {
106 _current_loader_data = ClassLoaderDataGraph::_head;
107 }
108
109 _current_class_entry = _current_loader_data->klasses();
110 }
111 }
112 // Should never be reached unless all instance classes have failed or are not fully loaded.
113 // Caller handles NULL.
114 return NULL;
115 }
116
117 // If the current class for the static iterator is a class being unloaded or
118 // deallocated, adjust the current class.
119 void adjust_saved_class(ClassLoaderData* cld) {
120 if (_current_loader_data == cld) {
121 _current_loader_data = cld->next();
122 if (_current_loader_data != NULL) {
123 _current_class_entry = _current_loader_data->klasses();
124 } // else try_get_next_class will start at the head
125 }
126 }
127
128 void adjust_saved_class(Klass* klass) {
129 if (_current_class_entry == klass) {
130 _current_class_entry = klass->next_link();
131 }
132 }
133 };
134
135 static ClassLoaderDataGraphKlassIteratorStatic static_klass_iterator;
136
137 InstanceKlass* ClassLoaderDataGraph::try_get_next_class() {
138 assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
139 return static_klass_iterator.try_get_next_class();
140 }
141
142 void ClassLoaderDataGraph::adjust_saved_class(ClassLoaderData* cld) {
143 return static_klass_iterator.adjust_saved_class(cld);
144 }
145
146 void ClassLoaderDataGraph::adjust_saved_class(Klass* klass) {
147 return static_klass_iterator.adjust_saved_class(klass);
148 }
149
150 void ClassLoaderDataGraph::clean_deallocate_lists(bool walk_previous_versions) {
151 assert(SafepointSynchronize::is_at_safepoint(), "must only be called at safepoint");
152 uint loaders_processed = 0;
153 for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
154 // is_alive check will be necessary for concurrent class unloading.
155 if (cld->is_alive()) {
156 // clean metaspace
157 if (walk_previous_versions) {
158 cld->classes_do(InstanceKlass::purge_previous_versions);
159 }
160 cld->free_deallocate_list();
161 loaders_processed++;
162 }
163 }
164 log_debug(class, loader, data)("clean_deallocate_lists: loaders processed %u %s",
165 loaders_processed, walk_previous_versions ? "walk_previous_versions" : "");
166 }
167
168 void ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces() {
169 assert(SafepointSynchronize::is_at_safepoint(), "must only be called at safepoint");
170
171 _should_clean_deallocate_lists = false; // assume everything gets cleaned
172
173 // Mark metadata seen on the stack so we can delete unreferenced entries.
174 // Walk all metadata, including the expensive code cache walk, only for class redefinition.
175 // The MetadataOnStackMark walk during redefinition saves previous versions if it finds old methods
176 // on the stack or in the code cache, so we only have to repeat the full walk if
177 // they were found at that time.
178 // TODO: have redefinition clean old methods out of the code cache. They still exist in some places.
179 bool walk_all_metadata = InstanceKlass::has_previous_versions_and_reset();
180
181 MetadataOnStackMark md_on_stack(walk_all_metadata, /*redefinition_walk*/false);
182 clean_deallocate_lists(walk_all_metadata);
183 }
184
185 // GC root of class loader data created.
186 ClassLoaderData* volatile ClassLoaderDataGraph::_head = NULL;
187 ClassLoaderData* ClassLoaderDataGraph::_unloading = NULL;
188
189 bool ClassLoaderDataGraph::_should_clean_deallocate_lists = false;
190 bool ClassLoaderDataGraph::_safepoint_cleanup_needed = false;
191 bool ClassLoaderDataGraph::_metaspace_oom = false;
192
193 // Add a new class loader data node to the list. Assign the newly created
194 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field
195 ClassLoaderData* ClassLoaderDataGraph::add_to_graph(Handle loader, bool has_class_mirror_holder) {
196
197 assert_lock_strong(ClassLoaderDataGraph_lock);
198
199 ClassLoaderData* cld;
200
201 // First check if another thread beat us to creating the CLD and installing
202 // it into the loader while we were waiting for the lock.
203 if (!has_class_mirror_holder && loader.not_null()) {
204 cld = java_lang_ClassLoader::loader_data_acquire(loader());
205 if (cld != NULL) {
206 return cld;
207 }
208 }
209
210 // We mustn't GC until we've installed the ClassLoaderData in the Graph since the CLD
211 // contains oops in _handles that must be walked. GC doesn't walk CLD from the
212 // loader oop in all collections, particularly young collections.
213 NoSafepointVerifier no_safepoints;
214
215 cld = new ClassLoaderData(loader, has_class_mirror_holder);
216
217 // First install the new CLD to the Graph.
218 cld->set_next(_head);
219 Atomic::release_store(&_head, cld);
220
221 // Next associate with the class_loader.
222 if (!has_class_mirror_holder) {
223 // Use OrderAccess, since readers need to get the loader_data only after
224 // it's added to the Graph
225 java_lang_ClassLoader::release_set_loader_data(loader(), cld);
226 }
227
228 // Lastly log, if requested
229 LogTarget(Trace, class, loader, data) lt;
230 if (lt.is_enabled()) {
231 ResourceMark rm;
232 LogStream ls(lt);
233 ls.print("create ");
234 cld->print_value_on(&ls);
235 ls.cr();
236 }
237 return cld;
238 }
239
240 ClassLoaderData* ClassLoaderDataGraph::add(Handle loader, bool has_class_mirror_holder) {
241 MutexLocker ml(ClassLoaderDataGraph_lock);
242 ClassLoaderData* loader_data = add_to_graph(loader, has_class_mirror_holder);
243 return loader_data;
244 }
245
246 void ClassLoaderDataGraph::cld_unloading_do(CLDClosure* cl) {
247 assert_locked_or_safepoint_weak(ClassLoaderDataGraph_lock);
248 for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {
249 assert(cld->is_unloading(), "invariant");
250 cl->do_cld(cld);
251 }
252 }
253
254 // These are functions called by the GC, which require all of the CLDs, including the
255 // unloading ones.
256 void ClassLoaderDataGraph::cld_do(CLDClosure* cl) {
257 assert_locked_or_safepoint_weak(ClassLoaderDataGraph_lock);
258 for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->_next) {
259 cl->do_cld(cld);
260 }
261 }
262
263 void ClassLoaderDataGraph::roots_cld_do(CLDClosure* strong, CLDClosure* weak) {
264 assert_locked_or_safepoint_weak(ClassLoaderDataGraph_lock);
265 for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->_next) {
266 CLDClosure* closure = cld->keep_alive() ? strong : weak;
267 if (closure != NULL) {
268 closure->do_cld(cld);
269 }
270 }
271 }
272
273 void ClassLoaderDataGraph::always_strong_cld_do(CLDClosure* cl) {
274 assert_locked_or_safepoint_weak(ClassLoaderDataGraph_lock);
275 if (ClassUnloading) {
276 roots_cld_do(cl, NULL);
277 } else {
278 cld_do(cl);
279 }
280 }
281
282 // Closure for locking and iterating through classes. Only lock outside of safepoint.
283 LockedClassesDo::LockedClassesDo(classes_do_func_t f) : _function(f),
284 _do_lock(!SafepointSynchronize::is_at_safepoint()) {
285 if (_do_lock) {
286 ClassLoaderDataGraph_lock->lock();
287 }
288 }
289
290 LockedClassesDo::LockedClassesDo() : _function(NULL),
291 _do_lock(!SafepointSynchronize::is_at_safepoint()) {
292 // callers provide their own do_klass
293 if (_do_lock) {
294 ClassLoaderDataGraph_lock->lock();
295 }
296 }
297
298 LockedClassesDo::~LockedClassesDo() {
299 if (_do_lock) {
300 ClassLoaderDataGraph_lock->unlock();
301 }
302 }
303
304
305 // Iterating over the CLDG needs to be locked because
306 // unloading can remove entries concurrently soon.
307 class ClassLoaderDataGraphIterator : public StackObj {
308 ClassLoaderData* _next;
309 Thread* _thread;
310 HandleMark _hm; // clean up handles when this is done.
311 Handle _holder;
312 NoSafepointVerifier _nsv; // No safepoints allowed in this scope
313 // unless verifying at a safepoint.
314
315 public:
316 ClassLoaderDataGraphIterator() : _next(ClassLoaderDataGraph::_head), _thread(Thread::current()), _hm(_thread) {
317 _thread = Thread::current();
318 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
319 }
320
321 ClassLoaderData* get_next() {
322 ClassLoaderData* cld = _next;
323 // Skip already unloaded CLD for concurrent unloading.
324 while (cld != NULL && !cld->is_alive()) {
325 cld = cld->next();
326 }
327 if (cld != NULL) {
328 // Keep cld that is being returned alive.
329 _holder = Handle(_thread, cld->holder_phantom());
330 _next = cld->next();
331 } else {
332 _next = NULL;
333 }
334 return cld;
335 }
336 };
337
338 void ClassLoaderDataGraph::loaded_cld_do(CLDClosure* cl) {
339 ClassLoaderDataGraphIterator iter;
340 while (ClassLoaderData* cld = iter.get_next()) {
341 cl->do_cld(cld);
342 }
343 }
344
345 // These functions assume that the caller has locked the ClassLoaderDataGraph_lock
346 // if they are not calling the function from a safepoint.
347 void ClassLoaderDataGraph::classes_do(KlassClosure* klass_closure) {
348 ClassLoaderDataGraphIterator iter;
349 while (ClassLoaderData* cld = iter.get_next()) {
350 cld->classes_do(klass_closure);
351 }
352 }
353
354 void ClassLoaderDataGraph::classes_do(void f(Klass* const)) {
355 ClassLoaderDataGraphIterator iter;
356 while (ClassLoaderData* cld = iter.get_next()) {
357 cld->classes_do(f);
358 }
359 }
360
361 void ClassLoaderDataGraph::methods_do(void f(Method*)) {
362 ClassLoaderDataGraphIterator iter;
363 while (ClassLoaderData* cld = iter.get_next()) {
364 cld->methods_do(f);
365 }
366 }
367
368 void ClassLoaderDataGraph::modules_do(void f(ModuleEntry*)) {
369 assert_locked_or_safepoint(Module_lock);
370 ClassLoaderDataGraphIterator iter;
371 while (ClassLoaderData* cld = iter.get_next()) {
372 cld->modules_do(f);
373 }
374 }
375
376 void ClassLoaderDataGraph::modules_unloading_do(void f(ModuleEntry*)) {
377 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
378 for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {
379 assert(cld->is_unloading(), "invariant");
380 cld->modules_do(f);
381 }
382 }
383
384 void ClassLoaderDataGraph::packages_do(void f(PackageEntry*)) {
385 assert_locked_or_safepoint(Module_lock);
386 ClassLoaderDataGraphIterator iter;
387 while (ClassLoaderData* cld = iter.get_next()) {
388 cld->packages_do(f);
389 }
390 }
391
392 void ClassLoaderDataGraph::packages_unloading_do(void f(PackageEntry*)) {
393 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
394 for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {
395 assert(cld->is_unloading(), "invariant");
396 cld->packages_do(f);
397 }
398 }
399
400 void ClassLoaderDataGraph::loaded_classes_do(KlassClosure* klass_closure) {
401 ClassLoaderDataGraphIterator iter;
402 while (ClassLoaderData* cld = iter.get_next()) {
403 cld->loaded_classes_do(klass_closure);
404 }
405 }
406
407 // This case can block but cannot do unloading (called from CDS)
408 void ClassLoaderDataGraph::unlocked_loaded_classes_do(KlassClosure* klass_closure) {
409 for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
410 cld->loaded_classes_do(klass_closure);
411 }
412 }
413
414
415 void ClassLoaderDataGraph::classes_unloading_do(void f(Klass* const)) {
416 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
417 for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {
418 assert(cld->is_unloading(), "invariant");
419 cld->classes_do(f);
420 }
421 }
422
423 #define FOR_ALL_DICTIONARY(X) ClassLoaderDataGraphIterator iter; \
424 while (ClassLoaderData* X = iter.get_next()) \
425 if (X->dictionary() != NULL)
426
427 // Walk classes in the loaded class dictionaries in various forms.
428 // Only walks the classes defined in this class loader.
429 void ClassLoaderDataGraph::dictionary_classes_do(void f(InstanceKlass*)) {
430 FOR_ALL_DICTIONARY(cld) {
431 cld->dictionary()->classes_do(f);
432 }
433 }
434
435 // Only walks the classes defined in this class loader.
436 void ClassLoaderDataGraph::dictionary_classes_do(void f(InstanceKlass*, TRAPS), TRAPS) {
437 FOR_ALL_DICTIONARY(cld) {
438 cld->dictionary()->classes_do(f, CHECK);
439 }
440 }
441
442 void ClassLoaderDataGraph::verify_dictionary() {
443 FOR_ALL_DICTIONARY(cld) {
444 cld->dictionary()->verify();
445 }
446 }
447
448 void ClassLoaderDataGraph::print_dictionary(outputStream* st) {
449 FOR_ALL_DICTIONARY(cld) {
450 st->print("Dictionary for ");
451 cld->print_value_on(st);
452 st->cr();
453 cld->dictionary()->print_on(st);
454 st->cr();
455 }
456 }
457
458 void ClassLoaderDataGraph::print_table_statistics(outputStream* st) {
459 FOR_ALL_DICTIONARY(cld) {
460 ResourceMark rm;
461 stringStream tempst;
462 tempst.print("System Dictionary for %s class loader", cld->loader_name_and_id());
463 cld->dictionary()->print_table_statistics(st, tempst.as_string());
464 }
465 }
466
467 #ifndef PRODUCT
468 bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {
469 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
470 for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
471 if (loader_data == data) {
472 return true;
473 }
474 }
475
476 return false;
477 }
478 #endif // PRODUCT
479
480 bool ClassLoaderDataGraph::is_valid(ClassLoaderData* loader_data) {
481 DEBUG_ONLY( if (!VMError::is_error_reported()) { assert_locked_or_safepoint(ClassLoaderDataGraph_lock); } )
482 if (loader_data != NULL) {
483 if (loader_data == ClassLoaderData::the_null_class_loader_data()) {
484 return true;
485 }
486 for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {
487 if (loader_data == data) {
488 return true;
489 }
490 }
491 }
492 return false;
493 }
494
495 // Move class loader data from main list to the unloaded list for unloading
496 // and deallocation later.
497 bool ClassLoaderDataGraph::do_unloading() {
498 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
499
500 // Indicate whether safepoint cleanup is needed.
501 _safepoint_cleanup_needed = true;
502
503 ClassLoaderData* data = _head;
504 ClassLoaderData* prev = NULL;
505 bool seen_dead_loader = false;
506 uint loaders_processed = 0;
507 uint loaders_removed = 0;
508
509 data = _head;
510 while (data != NULL) {
511 if (data->is_alive()) {
512 prev = data;
513 data = data->next();
514 loaders_processed++;
515 continue;
516 }
517 seen_dead_loader = true;
518 loaders_removed++;
519 ClassLoaderData* dead = data;
520 dead->unload();
521 data = data->next();
522 // Remove from loader list.
523 // This class loader data will no longer be found
524 // in the ClassLoaderDataGraph.
525 if (prev != NULL) {
526 prev->set_next(data);
527 } else {
528 assert(dead == _head, "sanity check");
529 _head = data;
530 }
531 dead->set_next(_unloading);
532 _unloading = dead;
533 }
534
535 log_debug(class, loader, data)("do_unloading: loaders processed %u, loaders removed %u", loaders_processed, loaders_removed);
536
537 return seen_dead_loader;
538 }
539
540 // There's at least one dead class loader. Purge refererences of healthy module
541 // reads lists and package export lists to modules belonging to dead loaders.
542 void ClassLoaderDataGraph::clean_module_and_package_info() {
543 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
544
545 ClassLoaderData* data = _head;
546 while (data != NULL) {
547 // Walk a ModuleEntry's reads, and a PackageEntry's exports
548 // lists to determine if there are modules on those lists that are now
549 // dead and should be removed. A module's life cycle is equivalent
550 // to its defining class loader's life cycle. Since a module is
551 // considered dead if its class loader is dead, these walks must
552 // occur after each class loader's aliveness is determined.
553 if (data->packages() != NULL) {
554 data->packages()->purge_all_package_exports();
555 }
556 if (data->modules_defined()) {
557 data->modules()->purge_all_module_reads();
558 }
559 data = data->next();
560 }
561 }
562
563 void ClassLoaderDataGraph::purge() {
564 ClassLoaderData* list = _unloading;
565 _unloading = NULL;
566 ClassLoaderData* next = list;
567 bool classes_unloaded = false;
568 while (next != NULL) {
569 ClassLoaderData* purge_me = next;
570 next = purge_me->next();
571 delete purge_me;
572 classes_unloaded = true;
573 }
574 if (classes_unloaded) {
575 Metaspace::purge();
576 set_metaspace_oom(false);
577 }
578 DependencyContext::purge_dependency_contexts();
579 }
580
581 int ClassLoaderDataGraph::resize_dictionaries() {
582 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
583 int resized = 0;
584 assert (Dictionary::does_any_dictionary_needs_resizing(), "some dictionary should need resizing");
585 FOR_ALL_DICTIONARY(cld) {
586 if (cld->dictionary()->resize_if_needed()) {
587 resized++;
588 }
589 }
590 return resized;
591 }
592
593 ClassLoaderDataGraphKlassIteratorAtomic::ClassLoaderDataGraphKlassIteratorAtomic()
594 : _next_klass(NULL) {
595 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
596 ClassLoaderData* cld = ClassLoaderDataGraph::_head;
597 Klass* klass = NULL;
598
599 // Find the first klass in the CLDG.
600 while (cld != NULL) {
601 assert_locked_or_safepoint(cld->metaspace_lock());
602 klass = cld->_klasses;
603 if (klass != NULL) {
604 _next_klass = klass;
605 return;
606 }
607 cld = cld->next();
608 }
609 }
610
611 Klass* ClassLoaderDataGraphKlassIteratorAtomic::next_klass_in_cldg(Klass* klass) {
612 Klass* next = klass->next_link();
613 if (next != NULL) {
614 return next;
615 }
616
617 // No more klasses in the current CLD. Time to find a new CLD.
618 ClassLoaderData* cld = klass->class_loader_data();
619 assert_locked_or_safepoint(cld->metaspace_lock());
620 while (next == NULL) {
621 cld = cld->next();
622 if (cld == NULL) {
623 break;
624 }
625 next = cld->_klasses;
626 }
627
628 return next;
629 }
630
631 Klass* ClassLoaderDataGraphKlassIteratorAtomic::next_klass() {
632 Klass* head = _next_klass;
633
634 while (head != NULL) {
635 Klass* next = next_klass_in_cldg(head);
636
637 Klass* old_head = Atomic::cmpxchg(&_next_klass, head, next);
638
639 if (old_head == head) {
640 return head; // Won the CAS.
641 }
642
643 head = old_head;
644 }
645
646 // Nothing more for the iterator to hand out.
647 assert(head == NULL, "head is " PTR_FORMAT ", expected not null:", p2i(head));
648 return NULL;
649 }
650
651 ClassLoaderDataGraphMetaspaceIterator::ClassLoaderDataGraphMetaspaceIterator() {
652 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint!");
653 _data = ClassLoaderDataGraph::_head;
654 }
655
656 ClassLoaderDataGraphMetaspaceIterator::~ClassLoaderDataGraphMetaspaceIterator() {}
657
658 ClassLoaderMetaspace* ClassLoaderDataGraphMetaspaceIterator::get_next() {
659 assert(_data != NULL, "Should not be NULL in call to the iterator");
660 ClassLoaderMetaspace* result = _data->metaspace_or_null();
661 _data = _data->next();
662 // This result might be NULL for class loaders without metaspace
663 // yet. It would be nice to return only non-null results but
664 // there is no guarantee that there will be a non-null result
665 // down the list so the caller is going to have to check.
666 return result;
667 }
668
669 void ClassLoaderDataGraph::verify() {
670 ClassLoaderDataGraphIterator iter;
671 while (ClassLoaderData* cld = iter.get_next()) {
672 cld->verify();
673 }
674 }
675
676 #ifndef PRODUCT
677 // callable from debugger
678 extern "C" int print_loader_data_graph() {
679 ResourceMark rm;
680 ClassLoaderDataGraph::print_on(tty);
681 return 0;
682 }
683
684 void ClassLoaderDataGraph::print_on(outputStream * const out) {
685 ClassLoaderDataGraphIterator iter;
686 while (ClassLoaderData* cld = iter.get_next()) {
687 cld->print_on(out);
688 }
689 }
690 #endif // PRODUCT
691
692 void ClassLoaderDataGraph::print() { print_on(tty); }