1 /*
2 * Copyright (c) 2012, 2026, 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 // A ClassLoaderData identifies the full set of class types that a class
26 // loader's name resolution strategy produces for a given configuration of the
27 // class loader.
28 // Class types in the ClassLoaderData may be defined by from class file binaries
29 // provided by the class loader, or from other class loader it interacts with
30 // according to its name resolution strategy.
31 //
32 // Class loaders that implement a deterministic name resolution strategy
33 // (including with respect to their delegation behavior), such as the boot, the
34 // platform, and the system loaders of the JDK's built-in class loader
35 // hierarchy, always produce the same linkset for a given configuration.
36 //
37 // ClassLoaderData carries information related to a linkset (e.g.,
38 // metaspace holding its klass definitions).
39 // The System Dictionary and related data structures (e.g., placeholder table,
40 // loader constraints table) as well as the runtime representation of classes
41 // only reference ClassLoaderData.
42 //
43 // Instances of java.lang.ClassLoader holds a pointer to a ClassLoaderData that
44 // that represent the loader's "linking domain" in the JVM.
45 //
46 // The bootstrap loader (represented by null) also has a ClassLoaderData,
47 // the singleton class the_null_class_loader_data().
48
49 #include "cds/heapShared.hpp"
50 #include "classfile/classLoaderData.inline.hpp"
51 #include "classfile/classLoaderDataGraph.inline.hpp"
52 #include "classfile/dictionary.hpp"
53 #include "classfile/javaClasses.inline.hpp"
54 #include "classfile/moduleEntry.hpp"
55 #include "classfile/packageEntry.hpp"
56 #include "classfile/symbolTable.hpp"
57 #include "classfile/systemDictionary.hpp"
58 #include "classfile/systemDictionaryShared.hpp"
59 #include "classfile/vmClasses.hpp"
60 #include "logging/log.hpp"
61 #include "logging/logStream.hpp"
62 #include "memory/allocation.inline.hpp"
63 #include "memory/classLoaderMetaspace.hpp"
64 #include "memory/metadataFactory.hpp"
65 #include "memory/metaspace.hpp"
66 #include "memory/resourceArea.hpp"
67 #include "memory/universe.hpp"
68 #include "oops/access.inline.hpp"
69 #include "oops/inlineKlass.inline.hpp"
70 #include "oops/jmethodIDTable.hpp"
71 #include "oops/klass.inline.hpp"
72 #include "oops/oop.inline.hpp"
73 #include "oops/oopHandle.inline.hpp"
74 #include "oops/verifyOopClosure.hpp"
75 #include "oops/weakHandle.inline.hpp"
76 #include "runtime/arguments.hpp"
77 #include "runtime/atomicAccess.hpp"
78 #include "runtime/handles.inline.hpp"
79 #include "runtime/mutex.hpp"
80 #include "runtime/safepoint.hpp"
81 #include "utilities/growableArray.hpp"
82 #include "utilities/macros.hpp"
83 #include "utilities/ostream.hpp"
84
85 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = nullptr;
86
87 void ClassLoaderData::init_null_class_loader_data() {
88 assert(_the_null_class_loader_data == nullptr, "cannot initialize twice");
89 assert(ClassLoaderDataGraph::_head == nullptr, "cannot initialize twice");
90
91 _the_null_class_loader_data = new ClassLoaderData(Handle(), false);
92 ClassLoaderDataGraph::_head = _the_null_class_loader_data;
93 assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
94
95 LogTarget(Trace, class, loader, data) lt;
96 if (lt.is_enabled()) {
97 ResourceMark rm;
98 LogStream ls(lt);
99 ls.print("create ");
100 _the_null_class_loader_data->print_value_on(&ls);
101 ls.cr();
102 }
103 }
104
105 // Obtain and set the class loader's name within the ClassLoaderData so
106 // it will be available for error messages, logging, JFR, etc. The name
107 // and klass are available after the class_loader oop is no longer alive,
108 // during unloading.
109 void ClassLoaderData::initialize_name(Handle class_loader) {
110 ResourceMark rm;
111
112 // Obtain the class loader's name. If the class loader's name was not
113 // explicitly set during construction, the CLD's _name field will be null.
114 oop cl_name = java_lang_ClassLoader::name(class_loader());
115 if (cl_name != nullptr) {
116 const char* cl_instance_name = java_lang_String::as_utf8_string(cl_name);
117
118 if (cl_instance_name != nullptr && cl_instance_name[0] != '\0') {
119 _name = SymbolTable::new_symbol(cl_instance_name);
120 }
121 }
122
123 // Obtain the class loader's name and identity hash. If the class loader's
124 // name was not explicitly set during construction, the class loader's name and id
125 // will be set to the qualified class name of the class loader along with its
126 // identity hash.
127 // If for some reason the ClassLoader's constructor has not been run, instead of
128 // leaving the _name_and_id field null, fall back to the external qualified class
129 // name. Thus CLD's _name_and_id field should never have a null value.
130 oop cl_name_and_id = java_lang_ClassLoader::nameAndId(class_loader());
131 const char* cl_instance_name_and_id =
132 (cl_name_and_id == nullptr) ? _class_loader_klass->external_name() :
133 java_lang_String::as_utf8_string(cl_name_and_id);
134 assert(cl_instance_name_and_id != nullptr && cl_instance_name_and_id[0] != '\0', "class loader has no name and id");
135 _name_and_id = SymbolTable::new_symbol(cl_instance_name_and_id);
136 }
137
138 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder) :
139 _metaspace(nullptr),
140 _metaspace_lock(new Mutex(Mutex::nosafepoint-2, "MetaspaceAllocation_lock")),
141 _unloading(false), _has_class_mirror_holder(has_class_mirror_holder),
142 _modified_oops(true),
143 // A non-strong hidden class loader data doesn't have anything to keep
144 // it from being unloaded during parsing of the non-strong hidden class.
145 // The null-class-loader should always be kept alive.
146 _keep_alive_ref_count((has_class_mirror_holder || h_class_loader.is_null()) ? 1 : 0),
147 _claim(0),
148 _handles(),
149 _klasses(nullptr), _packages(nullptr), _modules(nullptr), _unnamed_module(nullptr), _dictionary(nullptr),
150 _jmethod_ids(nullptr),
151 _deallocate_list(nullptr),
152 _next(nullptr),
153 _unloading_next(nullptr),
154 _class_loader_klass(nullptr), _name(nullptr), _name_and_id(nullptr) {
155
156 if (!h_class_loader.is_null()) {
157 _class_loader = _handles.add(h_class_loader());
158 _class_loader_klass = h_class_loader->klass();
159 initialize_name(h_class_loader);
160 }
161
162 if (!has_class_mirror_holder) {
163 // The holder is initialized later for non-strong hidden classes,
164 // and before calling anything that call class_loader().
165 initialize_holder(h_class_loader);
166
167 // A ClassLoaderData created solely for a non-strong hidden class should never
168 // have a ModuleEntryTable or PackageEntryTable created for it.
169 _packages = new PackageEntryTable();
170 if (h_class_loader.is_null()) {
171 // Create unnamed module for boot loader
172 _unnamed_module = ModuleEntry::create_boot_unnamed_module(this);
173 } else {
174 // Create unnamed module for all other loaders
175 _unnamed_module = ModuleEntry::create_unnamed_module(this);
176 }
177 _dictionary = create_dictionary();
178 }
179
180 NOT_PRODUCT(_dependency_count = 0); // number of class loader dependencies
181
182 JFR_ONLY(INIT_ID(this);)
183 }
184
185 ClassLoaderData::ChunkedHandleList::~ChunkedHandleList() {
186 Chunk* c = _head;
187 while (c != nullptr) {
188 Chunk* next = c->_next;
189 delete c;
190 c = next;
191 }
192 }
193
194 OopHandle ClassLoaderData::ChunkedHandleList::add(oop o) {
195 if (_head == nullptr || _head->_size == Chunk::CAPACITY) {
196 Chunk* next = new Chunk(_head);
197 AtomicAccess::release_store(&_head, next);
198 }
199 oop* handle = &_head->_data[_head->_size];
200 NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, o);
201 AtomicAccess::release_store(&_head->_size, _head->_size + 1);
202 return OopHandle(handle);
203 }
204
205 int ClassLoaderData::ChunkedHandleList::count() const {
206 int count = 0;
207 Chunk* chunk = AtomicAccess::load_acquire(&_head);
208 while (chunk != nullptr) {
209 count += AtomicAccess::load(&chunk->_size);
210 chunk = chunk->_next;
211 }
212 return count;
213 }
214
215 inline void ClassLoaderData::ChunkedHandleList::oops_do_chunk(OopClosure* f, Chunk* c, const juint size) {
216 for (juint i = 0; i < size; i++) {
217 f->do_oop(&c->_data[i]);
218 }
219 }
220
221 void ClassLoaderData::ChunkedHandleList::oops_do(OopClosure* f) {
222 Chunk* head = AtomicAccess::load_acquire(&_head);
223 if (head != nullptr) {
224 // Must be careful when reading size of head
225 oops_do_chunk(f, head, AtomicAccess::load_acquire(&head->_size));
226 for (Chunk* c = head->_next; c != nullptr; c = c->_next) {
227 oops_do_chunk(f, c, c->_size);
228 }
229 }
230 }
231
232 class VerifyContainsOopClosure : public OopClosure {
233 oop _target;
234 bool _found;
235
236 public:
237 VerifyContainsOopClosure(oop target) : _target(target), _found(false) {}
238
239 void do_oop(oop* p) {
240 if (p != nullptr && NativeAccess<AS_NO_KEEPALIVE>::oop_load(p) == _target) {
241 _found = true;
242 }
243 }
244
245 void do_oop(narrowOop* p) {
246 // The ChunkedHandleList should not contain any narrowOop
247 ShouldNotReachHere();
248 }
249
250 bool found() const {
251 return _found;
252 }
253 };
254
255 bool ClassLoaderData::ChunkedHandleList::contains(oop p) {
256 VerifyContainsOopClosure cl(p);
257 oops_do(&cl);
258 return cl.found();
259 }
260
261 #ifndef PRODUCT
262 bool ClassLoaderData::ChunkedHandleList::owner_of(oop* oop_handle) {
263 Chunk* chunk = AtomicAccess::load_acquire(&_head);
264 while (chunk != nullptr) {
265 if (&(chunk->_data[0]) <= oop_handle && oop_handle < &(chunk->_data[AtomicAccess::load(&chunk->_size)])) {
266 return true;
267 }
268 chunk = chunk->_next;
269 }
270 return false;
271 }
272 #endif // PRODUCT
273
274 void ClassLoaderData::clear_claim(int claim) {
275 for (;;) {
276 int old_claim = AtomicAccess::load(&_claim);
277 if ((old_claim & claim) == 0) {
278 return;
279 }
280 int new_claim = old_claim & ~claim;
281 if (AtomicAccess::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
282 return;
283 }
284 }
285 }
286
287 #ifdef ASSERT
288 void ClassLoaderData::verify_not_claimed(int claim) {
289 assert((_claim & claim) == 0, "Found claim: %d bits in _claim: %d", claim, _claim);
290 }
291 #endif
292
293 bool ClassLoaderData::try_claim(int claim) {
294 for (;;) {
295 int old_claim = AtomicAccess::load(&_claim);
296 if ((old_claim & claim) == claim) {
297 return false;
298 }
299 int new_claim = old_claim | claim;
300 if (AtomicAccess::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
301 return true;
302 }
303 }
304 }
305
306 void ClassLoaderData::demote_strong_roots() {
307 // The oop handle area contains strong roots that the GC traces from. We are about
308 // to demote them to strong native oops that the GC does *not* trace from. Conceptually,
309 // we are retiring a rather normal strong root, and creating a strong non-root handle,
310 // which happens to reuse the same address as the normal strong root had.
311 // Unless we invoke the right barriers, the GC might not notice that a strong root
312 // has been pulled from the system, and is left unprocessed by the GC. There can be
313 // several consequences:
314 // 1. A concurrently marking snapshot-at-the-beginning GC might assume that the contents
315 // of all strong roots get processed by the GC in order to keep them alive. Without
316 // barriers, some objects might not be kept alive.
317 // 2. A concurrently relocating GC might assume that after moving an object, a subsequent
318 // tracing from all roots can fix all the pointers in the system, which doesn't play
319 // well with roots racingly being pulled.
320 // 3. A concurrent GC using colored pointers, might assume that tracing the object graph
321 // from roots results in all pointers getting some particular color, which also doesn't
322 // play well with roots being pulled out from the system concurrently.
323
324 class TransitionRootsOopClosure : public OopClosure {
325 public:
326 virtual void do_oop(oop* p) {
327 // By loading the strong root with the access API, we can use the right barriers to
328 // store the oop as a strong non-root handle, that happens to reuse the same memory
329 // address as the strong root. The barriered store ensures that:
330 // 1. The concurrent SATB marking properties are satisfied as the store will keep
331 // the oop alive.
332 // 2. The concurrent object movement properties are satisfied as we store the address
333 // of the new location of the object, if any.
334 // 3. The colors if any will be stored as the new good colors.
335 oop obj = NativeAccess<>::oop_load(p); // Load the strong root
336 NativeAccess<>::oop_store(p, obj); // Store the strong non-root
337 }
338
339 virtual void do_oop(narrowOop* p) {
340 ShouldNotReachHere();
341 }
342 } cl;
343 oops_do(&cl, ClassLoaderData::_claim_none, false /* clear_mod_oops */);
344 }
345
346 // Non-strong hidden classes have their own ClassLoaderData that is marked to keep alive
347 // while the class is being parsed, and if the class appears on the module fixup list.
348 // Due to the uniqueness that no other class shares the hidden class' name or
349 // ClassLoaderData, no other non-GC thread has knowledge of the hidden class while
350 // it is being defined, therefore _keep_alive_ref_count is not volatile or atomic.
351 void ClassLoaderData::inc_keep_alive_ref_count() {
352 if (has_class_mirror_holder()) {
353 assert(_keep_alive_ref_count > 0, "Invalid keep alive increment count");
354 _keep_alive_ref_count++;
355 }
356 }
357
358 void ClassLoaderData::dec_keep_alive_ref_count() {
359 if (has_class_mirror_holder()) {
360 assert(_keep_alive_ref_count > 0, "Invalid keep alive decrement count");
361 if (_keep_alive_ref_count == 1) {
362 // When the keep_alive_ref_count counter is 1, the oop handle area is a strong root,
363 // acting as input to the GC tracing. Such strong roots are part of the
364 // snapshot-at-the-beginning, and can not just be pulled out from the
365 // system when concurrent GCs are running at the same time, without
366 // invoking the right barriers.
367 demote_strong_roots();
368 }
369 _keep_alive_ref_count--;
370 }
371 }
372
373 void ClassLoaderData::oops_do(OopClosure* f, int claim_value, bool clear_mod_oops) {
374 if (claim_value != ClassLoaderData::_claim_none && !try_claim(claim_value)) {
375 return;
376 }
377
378 // Only clear modified_oops after the ClassLoaderData is claimed.
379 if (clear_mod_oops) {
380 clear_modified_oops();
381 }
382
383 _handles.oops_do(f);
384 }
385
386 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {
387 // Lock-free access requires load_acquire
388 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
389 klass_closure->do_klass(k);
390 assert(k != k->next_link(), "no loops!");
391 }
392 }
393
394 void ClassLoaderData::classes_do(void f(Klass * const)) {
395 // Lock-free access requires load_acquire
396 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
397 f(k);
398 assert(k != k->next_link(), "no loops!");
399 }
400 }
401
402 void ClassLoaderData::methods_do(void f(Method*)) {
403 // Lock-free access requires load_acquire
404 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
405 if (k->is_instance_klass() && InstanceKlass::cast(k)->is_loaded()) {
406 InstanceKlass::cast(k)->methods_do(f);
407 }
408 }
409 }
410
411 void ClassLoaderData::loaded_classes_do(KlassClosure* klass_closure) {
412 // Lock-free access requires load_acquire
413 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
414 // Filter out InstanceKlasses (or their ObjArrayKlasses) that have not entered the
415 // loaded state.
416 if (k->is_instance_klass()) {
417 if (!InstanceKlass::cast(k)->is_loaded()) {
418 continue;
419 }
420 } else if (k->in_aot_cache() && k->is_objArray_klass()) {
421 Klass* bottom = ObjArrayKlass::cast(k)->bottom_klass();
422 if (bottom->is_instance_klass() && !InstanceKlass::cast(bottom)->is_loaded()) {
423 // This could happen if <bottom> is a shared class that has been restored
424 // but is not yet marked as loaded. All archived array classes of the
425 // bottom class are already restored and placed in the _klasses list.
426 continue;
427 }
428 }
429
430 #ifdef ASSERT
431 oop m = k->java_mirror();
432 assert(m != nullptr, "nullptr mirror");
433 assert(m->is_a(vmClasses::Class_klass()), "invalid mirror");
434 #endif
435 klass_closure->do_klass(k);
436 }
437 }
438
439 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {
440 // Lock-free access requires load_acquire
441 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
442 if (k->is_instance_klass()) {
443 f(InstanceKlass::cast(k));
444 }
445 assert(k != k->next_link(), "no loops!");
446 }
447 }
448
449 void ClassLoaderData::inline_classes_do(void f(InlineKlass*)) {
450 // Lock-free access requires load_acquire
451 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
452 if (k->is_inline_klass()) {
453 f(InlineKlass::cast(k));
454 }
455 assert(k != k->next_link(), "no loops!");
456 }
457 }
458
459 void ClassLoaderData::modules_do(void f(ModuleEntry*)) {
460 assert_locked_or_safepoint(Module_lock);
461 if (_unnamed_module != nullptr) {
462 f(_unnamed_module);
463 }
464 if (_modules != nullptr) {
465 _modules->modules_do(f);
466 }
467 }
468
469 void ClassLoaderData::packages_do(void f(PackageEntry*)) {
470 assert_locked_or_safepoint(Module_lock);
471 if (_packages != nullptr) {
472 _packages->packages_do(f);
473 }
474 }
475
476 void ClassLoaderData::record_dependency(const Klass* k) {
477 assert(k != nullptr, "invariant");
478
479 ClassLoaderData * const from_cld = this;
480 ClassLoaderData * const to_cld = k->class_loader_data();
481
482 // Do not need to record dependency if the dependency is to a class whose
483 // class loader data is never freed. (i.e. the dependency's class loader
484 // is one of the three builtin class loaders and the dependency's class
485 // loader data has a ClassLoader holder, not a Class holder.)
486 if (to_cld->is_permanent_class_loader_data()) {
487 return;
488 }
489
490 oop to;
491 if (to_cld->has_class_mirror_holder()) {
492 // Just return if a non-strong hidden class class is attempting to record a dependency
493 // to itself. (Note that every non-strong hidden class has its own unique class
494 // loader data.)
495 if (to_cld == from_cld) {
496 return;
497 }
498 // Hidden class dependencies are through the mirror.
499 to = k->java_mirror();
500 } else {
501 to = to_cld->class_loader();
502 oop from = from_cld->class_loader();
503
504 // Just return if this dependency is to a class with the same or a parent
505 // class_loader.
506 if (from == to || java_lang_ClassLoader::isAncestor(from, to)) {
507 return; // this class loader is in the parent list, no need to add it.
508 }
509 }
510
511 // It's a dependency we won't find through GC, add it.
512 if (!_handles.contains(to)) {
513 NOT_PRODUCT(AtomicAccess::inc(&_dependency_count));
514 LogTarget(Trace, class, loader, data) lt;
515 if (lt.is_enabled()) {
516 ResourceMark rm;
517 LogStream ls(lt);
518 ls.print("adding dependency from ");
519 print_value_on(&ls);
520 ls.print(" to ");
521 to_cld->print_value_on(&ls);
522 ls.cr();
523 }
524 Handle dependency(Thread::current(), to);
525 add_handle(dependency);
526 // Added a potentially young gen oop to the ClassLoaderData
527 record_modified_oops();
528 }
529 }
530
531 void ClassLoaderData::add_class(Klass* k, bool publicize /* true */) {
532 {
533 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
534 Klass* old_value = _klasses;
535 k->set_next_link(old_value);
536 // Link the new item into the list, making sure the linked class is stable
537 // since the list can be walked without a lock
538 AtomicAccess::release_store(&_klasses, k);
539 if (k->is_array_klass()) {
540 ClassLoaderDataGraph::inc_array_classes(1);
541 } else {
542 ClassLoaderDataGraph::inc_instance_classes(1);
543 }
544 }
545
546 if (publicize) {
547 LogTarget(Trace, class, loader, data) lt;
548 if (lt.is_enabled()) {
549 ResourceMark rm;
550 LogStream ls(lt);
551 ls.print("Adding k: " PTR_FORMAT " %s to ", p2i(k), k->external_name());
552 print_value_on(&ls);
553 ls.cr();
554 }
555 }
556 }
557
558 void ClassLoaderData::initialize_holder(Handle loader_or_mirror) {
559 if (loader_or_mirror() != nullptr) {
560 assert(_holder.is_null(), "never replace holders");
561 _holder = WeakHandle(Universe::vm_weak(), loader_or_mirror);
562 }
563 }
564
565 // Remove a klass from the _klasses list for scratch_class during redefinition
566 // or parsed class in the case of an error.
567 void ClassLoaderData::remove_class(Klass* scratch_class) {
568 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
569
570 Klass* prev = nullptr;
571 for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
572 if (k == scratch_class) {
573 if (prev == nullptr) {
574 _klasses = k->next_link();
575 } else {
576 Klass* next = k->next_link();
577 prev->set_next_link(next);
578 }
579
580 if (k->is_array_klass()) {
581 ClassLoaderDataGraph::dec_array_classes(1);
582 } else {
583 ClassLoaderDataGraph::dec_instance_classes(1);
584 }
585
586 return;
587 }
588 prev = k;
589 assert(k != k->next_link(), "no loops!");
590 }
591 ShouldNotReachHere(); // should have found this class!!
592 }
593
594 void ClassLoaderData::add_jmethod_id(jmethodID mid) {
595 MutexLocker m1(metaspace_lock(), Mutex::_no_safepoint_check_flag);
596 if (_jmethod_ids == nullptr) {
597 _jmethod_ids = new (mtClass) GrowableArray<jmethodID>(32, mtClass);
598 }
599 _jmethod_ids->push(mid);
600 }
601
602 // Method::remove_jmethod_ids removes jmethodID entries from the table which
603 // releases memory.
604 // Because native code (e.g., JVMTI agent) holding jmethod_ids may access them
605 // after the associated classes and class loader are unloaded, subsequent lookups
606 // for these ids will return null since they are no longer found in the table.
607 // The Java Native Interface Specification says "method ID
608 // does not prevent the VM from unloading the class from which the ID has
609 // been derived. After the class is unloaded, the method or field ID becomes
610 // invalid".
611 void ClassLoaderData::remove_jmethod_ids() {
612 MutexLocker ml(JmethodIdCreation_lock, Mutex::_no_safepoint_check_flag);
613 for (int i = 0; i < _jmethod_ids->length(); i++) {
614 jmethodID mid = _jmethod_ids->at(i);
615 JmethodIDTable::remove(mid);
616 }
617 delete _jmethod_ids;
618 _jmethod_ids = nullptr;
619 }
620
621 void ClassLoaderData::unload() {
622 _unloading = true;
623
624 LogTarget(Trace, class, loader, data) lt;
625 if (lt.is_enabled()) {
626 ResourceMark rm;
627 LogStream ls(lt);
628 ls.print("unload");
629 print_value_on(&ls);
630 ls.cr();
631 }
632
633 // Some items on the _deallocate_list need to free their C heap structures
634 // if they are not already on the _klasses list.
635 free_deallocate_list_C_heap_structures();
636
637 inline_classes_do(InlineKlass::cleanup);
638
639 // Clean up class dependencies and tell serviceability tools
640 // these classes are unloading. This must be called
641 // after erroneous classes are released.
642 classes_do(InstanceKlass::unload_class);
643
644 if (_jmethod_ids != nullptr) {
645 remove_jmethod_ids();
646 }
647 }
648
649 ModuleEntryTable* ClassLoaderData::modules() {
650 // Lazily create the module entry table at first request.
651 // Lock-free access requires load_acquire.
652 ModuleEntryTable* modules = AtomicAccess::load_acquire(&_modules);
653 if (modules == nullptr) {
654 MutexLocker m1(Module_lock);
655 // Check if _modules got allocated while we were waiting for this lock.
656 if ((modules = _modules) == nullptr) {
657 modules = new ModuleEntryTable();
658
659 {
660 MutexLocker m1(metaspace_lock(), Mutex::_no_safepoint_check_flag);
661 // Ensure _modules is stable, since it is examined without a lock
662 AtomicAccess::release_store(&_modules, modules);
663 }
664 }
665 }
666 return modules;
667 }
668
669 const int _boot_loader_dictionary_size = 1009;
670 const int _default_loader_dictionary_size = 107;
671
672 Dictionary* ClassLoaderData::create_dictionary() {
673 assert(!has_class_mirror_holder(), "class mirror holder cld does not have a dictionary");
674 int size;
675 if (_the_null_class_loader_data == nullptr) {
676 size = _boot_loader_dictionary_size;
677 } else if (is_system_class_loader_data()) {
678 size = _boot_loader_dictionary_size;
679 } else {
680 size = _default_loader_dictionary_size;
681 }
682 return new Dictionary(this, size);
683 }
684
685 // Tell the GC to keep this klass alive. Needed while iterating ClassLoaderDataGraph,
686 // and any runtime code that uses klasses.
687 oop ClassLoaderData::holder() const {
688 // A klass that was previously considered dead can be looked up in the
689 // CLD/SD, and its _java_mirror or _class_loader can be stored in a root
690 // or a reachable object making it alive again. The SATB part of G1 needs
691 // to get notified about this potential resurrection, otherwise the marking
692 // might not find the object.
693 if (!_holder.is_null()) { // null class_loader
694 return _holder.resolve();
695 } else {
696 return nullptr;
697 }
698 }
699
700 // Let the GC read the holder without keeping it alive.
701 oop ClassLoaderData::holder_no_keepalive() const {
702 if (!_holder.is_null()) { // null class_loader
703 return _holder.peek();
704 } else {
705 return nullptr;
706 }
707 }
708
709 // Unloading support
710 bool ClassLoaderData::is_alive() const {
711 bool alive = (_keep_alive_ref_count > 0) // null class loader and incomplete non-strong hidden class.
712 || (_holder.peek() != nullptr); // and not cleaned by the GC weak handle processing.
713
714 return alive;
715 }
716
717 class ReleaseKlassClosure: public KlassClosure {
718 private:
719 size_t _instance_class_released;
720 size_t _array_class_released;
721 public:
722 ReleaseKlassClosure() : _instance_class_released(0), _array_class_released(0) { }
723
724 size_t instance_class_released() const { return _instance_class_released; }
725 size_t array_class_released() const { return _array_class_released; }
726
727 void do_klass(Klass* k) {
728 if (k->is_array_klass()) {
729 _array_class_released ++;
730 } else {
731 assert(k->is_instance_klass(), "Must be");
732 _instance_class_released ++;
733 }
734 k->release_C_heap_structures();
735 }
736 };
737
738 ClassLoaderData::~ClassLoaderData() {
739 // Release C heap structures for all the classes.
740 ReleaseKlassClosure cl;
741 classes_do(&cl);
742
743 ClassLoaderDataGraph::dec_array_classes(cl.array_class_released());
744 ClassLoaderDataGraph::dec_instance_classes(cl.instance_class_released());
745
746 // Release the WeakHandle
747 _holder.release(Universe::vm_weak());
748
749 // Release C heap allocated hashtable for all the packages.
750 if (_packages != nullptr) {
751 // Destroy the table itself
752 delete _packages;
753 _packages = nullptr;
754 }
755
756 // Release C heap allocated hashtable for all the modules.
757 if (_modules != nullptr) {
758 // Destroy the table itself
759 delete _modules;
760 _modules = nullptr;
761 }
762
763 // Release C heap allocated hashtable for the dictionary
764 if (_dictionary != nullptr) {
765 // Destroy the table itself
766 delete _dictionary;
767 _dictionary = nullptr;
768 }
769
770 if (_unnamed_module != nullptr) {
771 delete _unnamed_module;
772 _unnamed_module = nullptr;
773 }
774
775 // release the metaspace
776 ClassLoaderMetaspace *m = _metaspace;
777 if (m != nullptr) {
778 _metaspace = nullptr;
779 delete m;
780 }
781
782 // Delete lock
783 delete _metaspace_lock;
784
785 // Delete free list
786 if (_deallocate_list != nullptr) {
787 delete _deallocate_list;
788 }
789
790 // Decrement refcounts of Symbols if created.
791 if (_name != nullptr) {
792 _name->decrement_refcount();
793 }
794 if (_name_and_id != nullptr) {
795 _name_and_id->decrement_refcount();
796 }
797 }
798
799 // Returns true if this class loader data is for the app class loader
800 // or a user defined system class loader. (Note that the class loader
801 // data may have a Class holder.)
802 bool ClassLoaderData::is_system_class_loader_data() const {
803 return SystemDictionary::is_system_class_loader(class_loader());
804 }
805
806 // Returns true if this class loader data is for the platform class loader.
807 // (Note that the class loader data may have a Class holder.)
808 bool ClassLoaderData::is_platform_class_loader_data() const {
809 return SystemDictionary::is_platform_class_loader(class_loader());
810 }
811
812 // Returns true if the class loader for this class loader data is one of
813 // the 3 builtin (boot application/system or platform) class loaders,
814 // including a user-defined system class loader. Note that if the class
815 // loader data is for a non-strong hidden class then it may
816 // get freed by a GC even if its class loader is one of these loaders.
817 bool ClassLoaderData::is_builtin_class_loader_data() const {
818 return (is_boot_class_loader_data() ||
819 SystemDictionary::is_system_class_loader(class_loader()) ||
820 SystemDictionary::is_platform_class_loader(class_loader()));
821 }
822
823 // Returns true if this class loader data is a class loader data
824 // that is not ever freed by a GC. It must be the CLD for one of the builtin
825 // class loaders and not the CLD for a non-strong hidden class.
826 bool ClassLoaderData::is_permanent_class_loader_data() const {
827 return is_builtin_class_loader_data() && !has_class_mirror_holder();
828 }
829
830 ClassLoaderMetaspace* ClassLoaderData::metaspace_non_null() {
831 // If the metaspace has not been allocated, create a new one. Might want
832 // to create smaller arena for Reflection class loaders also.
833 // The reason for the delayed allocation is because some class loaders are
834 // simply for delegating with no metadata of their own.
835 // Lock-free access requires load_acquire.
836 ClassLoaderMetaspace* metaspace = AtomicAccess::load_acquire(&_metaspace);
837 if (metaspace == nullptr) {
838 MutexLocker ml(_metaspace_lock, Mutex::_no_safepoint_check_flag);
839 // Check if _metaspace got allocated while we were waiting for this lock.
840 if ((metaspace = _metaspace) == nullptr) {
841 if (this == the_null_class_loader_data()) {
842 assert (class_loader() == nullptr, "Must be");
843 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::BootMetaspaceType);
844 } else if (has_class_mirror_holder()) {
845 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::ClassMirrorHolderMetaspaceType);
846 } else {
847 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::StandardMetaspaceType);
848 }
849 // Ensure _metaspace is stable, since it is examined without a lock
850 AtomicAccess::release_store(&_metaspace, metaspace);
851 }
852 }
853 return metaspace;
854 }
855
856 OopHandle ClassLoaderData::add_handle(Handle h) {
857 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
858 record_modified_oops();
859 return _handles.add(h());
860 }
861
862 void ClassLoaderData::remove_handle(OopHandle h) {
863 assert(!is_unloading(), "Do not remove a handle for a CLD that is unloading");
864 if (!h.is_empty()) {
865 assert(_handles.owner_of(h.ptr_raw()),
866 "Got unexpected handle " PTR_FORMAT, p2i(h.ptr_raw()));
867 h.replace(oop(nullptr));
868 }
869 }
870
871 void ClassLoaderData::init_handle_locked(OopHandle& dest, Handle h) {
872 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
873 if (dest.resolve() != nullptr) {
874 return;
875 } else {
876 record_modified_oops();
877 dest = _handles.add(h());
878 }
879 }
880
881 // Add this metadata pointer to be freed when it's safe. This is only during
882 // a safepoint which checks if handles point to this metadata field.
883 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
884 // Metadata in shared region isn't deleted.
885 if (!m->in_aot_cache()) {
886 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
887 if (_deallocate_list == nullptr) {
888 _deallocate_list = new (mtClass) GrowableArray<Metadata*>(100, mtClass);
889 }
890 _deallocate_list->append_if_missing(m);
891 ResourceMark rm;
892 log_debug(class, loader, data)("deallocate added for %s", m->print_value_string());
893 ClassLoaderDataGraph::set_should_clean_deallocate_lists();
894 }
895 }
896
897 // Deallocate free metadata on the free list. How useful the PermGen was!
898 void ClassLoaderData::free_deallocate_list() {
899 // This must be called at a safepoint because it depends on metadata walking at
900 // safepoint cleanup time.
901 assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
902 assert(!is_unloading(), "only called for ClassLoaderData that are not unloading");
903 if (_deallocate_list == nullptr) {
904 return;
905 }
906 // Go backwards because this removes entries that are freed.
907 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
908 Metadata* m = _deallocate_list->at(i);
909 if (!m->on_stack()) {
910 _deallocate_list->remove_at(i);
911 // There are only three types of metadata that we deallocate directly.
912 // Cast them so they can be used by the template function.
913 if (m->is_method()) {
914 MetadataFactory::free_metadata(this, (Method*)m);
915 } else if (m->is_constantPool()) {
916 HeapShared::remove_scratch_resolved_references((ConstantPool*)m);
917 MetadataFactory::free_metadata(this, (ConstantPool*)m);
918 } else if (m->is_klass()) {
919 if (!((Klass*)m)->is_inline_klass()) {
920 MetadataFactory::free_metadata(this, (InstanceKlass*)m);
921 } else {
922 MetadataFactory::free_metadata(this, (InlineKlass*)m);
923 }
924 } else {
925 ShouldNotReachHere();
926 }
927 } else {
928 // Metadata is alive.
929 // If scratch_class is on stack then it shouldn't be on this list!
930 assert(!m->is_klass() || !((InstanceKlass*)m)->is_scratch_class(),
931 "scratch classes on this list should be dead");
932 // Also should assert that other metadata on the list was found in handles.
933 // Some cleaning remains.
934 ClassLoaderDataGraph::set_should_clean_deallocate_lists();
935 }
936 }
937 }
938
939 // This is distinct from free_deallocate_list. For class loader data that are
940 // unloading, this frees the C heap memory for items on the list, and unlinks
941 // scratch or error classes so that unloading events aren't triggered for these
942 // classes. The metadata is removed with the unloading metaspace.
943 // There isn't C heap memory allocated for methods, so nothing is done for them.
944 void ClassLoaderData::free_deallocate_list_C_heap_structures() {
945 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
946 assert(is_unloading(), "only called for ClassLoaderData that are unloading");
947 if (_deallocate_list == nullptr) {
948 return;
949 }
950 // Go backwards because this removes entries that are freed.
951 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
952 Metadata* m = _deallocate_list->at(i);
953 _deallocate_list->remove_at(i);
954 if (m->is_constantPool()) {
955 ((ConstantPool*)m)->release_C_heap_structures();
956 } else if (m->is_klass()) {
957 InstanceKlass* ik = (InstanceKlass*)m;
958 // also releases ik->constants() C heap memory
959 ik->release_C_heap_structures();
960 // Remove the class so unloading events aren't triggered for
961 // this class (scratch or error class) in do_unloading().
962 remove_class(ik);
963 // But still have to remove it from the dumptime_table.
964 SystemDictionaryShared::handle_class_unloading(ik);
965 }
966 }
967 }
968
969 // Caller needs ResourceMark
970 // If the class loader's _name has not been explicitly set, the class loader's
971 // qualified class name is returned.
972 const char* ClassLoaderData::loader_name() const {
973 if (_class_loader_klass == nullptr) {
974 return BOOTSTRAP_LOADER_NAME;
975 } else if (_name != nullptr) {
976 return _name->as_C_string();
977 } else {
978 return _class_loader_klass->external_name();
979 }
980 }
981
982 // Caller needs ResourceMark
983 // Format of the _name_and_id is as follows:
984 // If the defining loader has a name explicitly set then '<loader-name>' @<id>
985 // If the defining loader has no name then <qualified-class-name> @<id>
986 // If built-in loader, then omit '@<id>' as there is only one instance.
987 const char* ClassLoaderData::loader_name_and_id() const {
988 if (_class_loader_klass == nullptr) {
989 return "'" BOOTSTRAP_LOADER_NAME "'";
990 } else if (_name_and_id != nullptr) {
991 return _name_and_id->as_C_string();
992 } else {
993 // May be called in a race before _name_and_id is initialized.
994 return _class_loader_klass->external_name();
995 }
996 }
997
998 void ClassLoaderData::print_value_on(outputStream* out) const {
999 if (!is_unloading() && class_loader() != nullptr) {
1000 out->print("loader data: " INTPTR_FORMAT " for instance ", p2i(this));
1001 class_loader()->print_value_on(out); // includes loader_name_and_id() and address of class loader instance
1002 } else {
1003 // loader data: 0xsomeaddr of 'bootstrap'
1004 out->print("loader data: " INTPTR_FORMAT " of %s", p2i(this), loader_name_and_id());
1005 }
1006 if (_has_class_mirror_holder) {
1007 out->print(" has a class holder");
1008 }
1009 }
1010
1011 void ClassLoaderData::print_value() const { print_value_on(tty); }
1012
1013 #ifndef PRODUCT
1014 class PrintKlassClosure: public KlassClosure {
1015 outputStream* _out;
1016 public:
1017 PrintKlassClosure(outputStream* out): _out(out) { }
1018
1019 void do_klass(Klass* k) {
1020 ResourceMark rm;
1021 _out->print("%s,", k->external_name());
1022 }
1023 };
1024
1025 void ClassLoaderData::print_on(outputStream* out) const {
1026 ResourceMark rm;
1027 out->print_cr("ClassLoaderData(" INTPTR_FORMAT ")", p2i(this));
1028 out->print_cr(" - name %s", loader_name_and_id());
1029 if (!_holder.is_null()) {
1030 out->print (" - holder ");
1031 _holder.print_on(out);
1032 out->print_cr("");
1033 }
1034 if (!_unloading) {
1035 out->print_cr(" - class loader " INTPTR_FORMAT, p2i(_class_loader.peek()));
1036 } else {
1037 out->print_cr(" - class loader <unloading, oop is bad>");
1038 }
1039 out->print_cr(" - metaspace " INTPTR_FORMAT, p2i(_metaspace));
1040 out->print_cr(" - unloading %s", _unloading ? "true" : "false");
1041 out->print_cr(" - class mirror holder %s", _has_class_mirror_holder ? "true" : "false");
1042 out->print_cr(" - modified oops %s", _modified_oops ? "true" : "false");
1043 out->print_cr(" - _keep_alive_ref_count %d", _keep_alive_ref_count);
1044 out->print (" - claim ");
1045 switch(_claim) {
1046 case _claim_none: out->print_cr("none"); break;
1047 case _claim_finalizable: out->print_cr("finalizable"); break;
1048 case _claim_strong: out->print_cr("strong"); break;
1049 case _claim_stw_fullgc_mark: out->print_cr("stw full gc mark"); break;
1050 case _claim_stw_fullgc_adjust: out->print_cr("stw full gc adjust"); break;
1051 case _claim_other: out->print_cr("other"); break;
1052 case _claim_other | _claim_finalizable: out->print_cr("other and finalizable"); break;
1053 case _claim_other | _claim_strong: out->print_cr("other and strong"); break;
1054 default: ShouldNotReachHere();
1055 }
1056 out->print_cr(" - handles %d", _handles.count());
1057 out->print_cr(" - dependency count %d", _dependency_count);
1058 out->print (" - klasses { ");
1059 if (Verbose) {
1060 PrintKlassClosure closure(out);
1061 ((ClassLoaderData*)this)->classes_do(&closure);
1062 } else {
1063 out->print("...");
1064 }
1065 out->print_cr(" }");
1066 out->print_cr(" - packages " INTPTR_FORMAT, p2i(_packages));
1067 out->print_cr(" - module " INTPTR_FORMAT, p2i(_modules));
1068 out->print_cr(" - unnamed module " INTPTR_FORMAT, p2i(_unnamed_module));
1069 if (_dictionary != nullptr) {
1070 out->print (" - dictionary " INTPTR_FORMAT " ", p2i(_dictionary));
1071 _dictionary->print_size(out);
1072 } else {
1073 out->print_cr(" - dictionary " INTPTR_FORMAT, p2i(_dictionary));
1074 }
1075 if (_jmethod_ids != nullptr) {
1076 out->print_cr(" - jmethod count %d", _jmethod_ids->length());
1077 }
1078 out->print_cr(" - deallocate list " INTPTR_FORMAT, p2i(_deallocate_list));
1079 out->print_cr(" - next CLD " INTPTR_FORMAT, p2i(_next));
1080 }
1081 #endif // PRODUCT
1082
1083 void ClassLoaderData::print() const { print_on(tty); }
1084
1085 class VerifyHandleOops : public OopClosure {
1086 VerifyOopClosure vc;
1087 public:
1088 virtual void do_oop(oop* p) {
1089 if (p != nullptr && *p != nullptr) {
1090 oop o = *p;
1091 if (!java_lang_Class::is_instance(o)) {
1092 // is_instance will assert for an invalid oop.
1093 // Walk the resolved_references array and other assorted oops in the
1094 // CLD::_handles field. The mirror oops are followed by other heap roots.
1095 o->oop_iterate(&vc);
1096 }
1097 }
1098 }
1099 virtual void do_oop(narrowOop* o) { ShouldNotReachHere(); }
1100 };
1101
1102 void ClassLoaderData::verify() {
1103 assert_locked_or_safepoint(_metaspace_lock);
1104 oop cl = class_loader();
1105
1106 guarantee(this == class_loader_data(cl) || has_class_mirror_holder(), "Must be the same");
1107 guarantee(cl != nullptr || this == ClassLoaderData::the_null_class_loader_data() || has_class_mirror_holder(), "must be");
1108
1109 // Verify the integrity of the allocated space.
1110 #ifdef ASSERT
1111 if (metaspace_or_null() != nullptr) {
1112 metaspace_or_null()->verify();
1113 }
1114 #endif
1115
1116 for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
1117 guarantee(k->class_loader_data() == this, "Must be the same");
1118 k->verify();
1119 assert(k != k->next_link(), "no loops!");
1120 }
1121
1122 if (_modules != nullptr) {
1123 _modules->verify();
1124 }
1125
1126 if (_deallocate_list != nullptr) {
1127 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
1128 Metadata* m = _deallocate_list->at(i);
1129 if (m->is_klass()) {
1130 ((Klass*)m)->verify();
1131 }
1132 }
1133 }
1134
1135 // Check the oops in the handles area
1136 VerifyHandleOops vho;
1137 oops_do(&vho, _claim_none, false);
1138 }
1139
1140 bool ClassLoaderData::contains_klass(Klass* klass) {
1141 // Lock-free access requires load_acquire
1142 for (Klass* k = AtomicAccess::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
1143 if (k == klass) return true;
1144 }
1145 return false;
1146 }