1 /*
2 * Copyright (c) 2012, 2025, 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 "classfile/classLoaderData.inline.hpp"
50 #include "classfile/classLoaderDataGraph.inline.hpp"
51 #include "classfile/dictionary.hpp"
52 #include "classfile/javaClasses.inline.hpp"
53 #include "classfile/moduleEntry.hpp"
54 #include "classfile/packageEntry.hpp"
55 #include "classfile/symbolTable.hpp"
56 #include "classfile/systemDictionary.hpp"
57 #include "classfile/systemDictionaryShared.hpp"
58 #include "classfile/vmClasses.hpp"
59 #include "logging/log.hpp"
60 #include "logging/logStream.hpp"
61 #include "memory/allocation.inline.hpp"
62 #include "memory/classLoaderMetaspace.hpp"
63 #include "memory/metadataFactory.hpp"
64 #include "memory/metaspace.hpp"
65 #include "memory/resourceArea.hpp"
66 #include "memory/universe.hpp"
67 #include "oops/access.inline.hpp"
68 #include "oops/klass.inline.hpp"
69 #include "oops/oop.inline.hpp"
70 #include "oops/oopHandle.inline.hpp"
71 #include "oops/verifyOopClosure.hpp"
72 #include "oops/weakHandle.inline.hpp"
73 #include "runtime/arguments.hpp"
74 #include "runtime/atomic.hpp"
75 #include "runtime/handles.inline.hpp"
76 #include "runtime/mutex.hpp"
77 #include "runtime/safepoint.hpp"
78 #include "utilities/growableArray.hpp"
79 #include "utilities/macros.hpp"
80 #include "utilities/ostream.hpp"
81
82 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = nullptr;
83
84 void ClassLoaderData::init_null_class_loader_data() {
85 assert(_the_null_class_loader_data == nullptr, "cannot initialize twice");
86 assert(ClassLoaderDataGraph::_head == nullptr, "cannot initialize twice");
87
88 _the_null_class_loader_data = new ClassLoaderData(Handle(), false);
89 ClassLoaderDataGraph::_head = _the_null_class_loader_data;
90 assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
91
92 LogTarget(Trace, class, loader, data) lt;
93 if (lt.is_enabled()) {
94 ResourceMark rm;
95 LogStream ls(lt);
96 ls.print("create ");
97 _the_null_class_loader_data->print_value_on(&ls);
98 ls.cr();
99 }
100 }
101
102 // Obtain and set the class loader's name within the ClassLoaderData so
103 // it will be available for error messages, logging, JFR, etc. The name
104 // and klass are available after the class_loader oop is no longer alive,
105 // during unloading.
106 void ClassLoaderData::initialize_name(Handle class_loader) {
107 ResourceMark rm;
108
109 // Obtain the class loader's name. If the class loader's name was not
110 // explicitly set during construction, the CLD's _name field will be null.
111 oop cl_name = java_lang_ClassLoader::name(class_loader());
112 if (cl_name != nullptr) {
113 const char* cl_instance_name = java_lang_String::as_utf8_string(cl_name);
114
115 if (cl_instance_name != nullptr && cl_instance_name[0] != '\0') {
116 _name = SymbolTable::new_symbol(cl_instance_name);
117 }
118 }
119
120 // Obtain the class loader's name and identity hash. If the class loader's
121 // name was not explicitly set during construction, the class loader's name and id
122 // will be set to the qualified class name of the class loader along with its
123 // identity hash.
124 // If for some reason the ClassLoader's constructor has not been run, instead of
125 // leaving the _name_and_id field null, fall back to the external qualified class
126 // name. Thus CLD's _name_and_id field should never have a null value.
127 oop cl_name_and_id = java_lang_ClassLoader::nameAndId(class_loader());
128 const char* cl_instance_name_and_id =
129 (cl_name_and_id == nullptr) ? _class_loader_klass->external_name() :
130 java_lang_String::as_utf8_string(cl_name_and_id);
131 assert(cl_instance_name_and_id != nullptr && cl_instance_name_and_id[0] != '\0', "class loader has no name and id");
132 _name_and_id = SymbolTable::new_symbol(cl_instance_name_and_id);
133 }
134
135 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool has_class_mirror_holder) :
136 _metaspace(nullptr),
137 _metaspace_lock(new Mutex(Mutex::nosafepoint-2, "MetaspaceAllocation_lock")),
138 _unloading(false), _has_class_mirror_holder(has_class_mirror_holder),
139 _modified_oops(true),
140 // A non-strong hidden class loader data doesn't have anything to keep
141 // it from being unloaded during parsing of the non-strong hidden class.
142 // The null-class-loader should always be kept alive.
143 _keep_alive_ref_count((has_class_mirror_holder || h_class_loader.is_null()) ? 1 : 0),
144 _claim(0),
145 _handles(),
146 _klasses(nullptr), _packages(nullptr), _modules(nullptr), _unnamed_module(nullptr), _dictionary(nullptr),
147 _jmethod_ids(nullptr),
148 _deallocate_list(nullptr),
149 _next(nullptr),
150 _unloading_next(nullptr),
151 _class_loader_klass(nullptr), _name(nullptr), _name_and_id(nullptr) {
152
153 if (!h_class_loader.is_null()) {
154 _class_loader = _handles.add(h_class_loader());
155 _class_loader_klass = h_class_loader->klass();
156 initialize_name(h_class_loader);
157 }
158
159 if (!has_class_mirror_holder) {
160 // The holder is initialized later for non-strong hidden classes,
161 // and before calling anything that call class_loader().
162 initialize_holder(h_class_loader);
163
164 // A ClassLoaderData created solely for a non-strong hidden class should never
165 // have a ModuleEntryTable or PackageEntryTable created for it.
166 _packages = new PackageEntryTable();
167 if (h_class_loader.is_null()) {
168 // Create unnamed module for boot loader
169 _unnamed_module = ModuleEntry::create_boot_unnamed_module(this);
170 } else {
171 // Create unnamed module for all other loaders
172 _unnamed_module = ModuleEntry::create_unnamed_module(this);
173 }
174 _dictionary = create_dictionary();
175 }
176
177 NOT_PRODUCT(_dependency_count = 0); // number of class loader dependencies
178
179 JFR_ONLY(INIT_ID(this);)
180 }
181
182 ClassLoaderData::ChunkedHandleList::~ChunkedHandleList() {
183 Chunk* c = _head;
184 while (c != nullptr) {
185 Chunk* next = c->_next;
186 delete c;
187 c = next;
188 }
189 }
190
191 OopHandle ClassLoaderData::ChunkedHandleList::add(oop o) {
192 if (_head == nullptr || _head->_size == Chunk::CAPACITY) {
193 Chunk* next = new Chunk(_head);
194 Atomic::release_store(&_head, next);
195 }
196 oop* handle = &_head->_data[_head->_size];
197 NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, o);
198 Atomic::release_store(&_head->_size, _head->_size + 1);
199 return OopHandle(handle);
200 }
201
202 int ClassLoaderData::ChunkedHandleList::count() const {
203 int count = 0;
204 Chunk* chunk = Atomic::load_acquire(&_head);
205 while (chunk != nullptr) {
206 count += Atomic::load(&chunk->_size);
207 chunk = chunk->_next;
208 }
209 return count;
210 }
211
212 inline void ClassLoaderData::ChunkedHandleList::oops_do_chunk(OopClosure* f, Chunk* c, const juint size) {
213 for (juint i = 0; i < size; i++) {
214 f->do_oop(&c->_data[i]);
215 }
216 }
217
218 void ClassLoaderData::ChunkedHandleList::oops_do(OopClosure* f) {
219 Chunk* head = Atomic::load_acquire(&_head);
220 if (head != nullptr) {
221 // Must be careful when reading size of head
222 oops_do_chunk(f, head, Atomic::load_acquire(&head->_size));
223 for (Chunk* c = head->_next; c != nullptr; c = c->_next) {
224 oops_do_chunk(f, c, c->_size);
225 }
226 }
227 }
228
229 class VerifyContainsOopClosure : public OopClosure {
230 oop _target;
231 bool _found;
232
233 public:
234 VerifyContainsOopClosure(oop target) : _target(target), _found(false) {}
235
236 void do_oop(oop* p) {
237 if (p != nullptr && NativeAccess<AS_NO_KEEPALIVE>::oop_load(p) == _target) {
238 _found = true;
239 }
240 }
241
242 void do_oop(narrowOop* p) {
243 // The ChunkedHandleList should not contain any narrowOop
244 ShouldNotReachHere();
245 }
246
247 bool found() const {
248 return _found;
249 }
250 };
251
252 bool ClassLoaderData::ChunkedHandleList::contains(oop p) {
253 VerifyContainsOopClosure cl(p);
254 oops_do(&cl);
255 return cl.found();
256 }
257
258 #ifndef PRODUCT
259 bool ClassLoaderData::ChunkedHandleList::owner_of(oop* oop_handle) {
260 Chunk* chunk = Atomic::load_acquire(&_head);
261 while (chunk != nullptr) {
262 if (&(chunk->_data[0]) <= oop_handle && oop_handle < &(chunk->_data[Atomic::load(&chunk->_size)])) {
263 return true;
264 }
265 chunk = chunk->_next;
266 }
267 return false;
268 }
269 #endif // PRODUCT
270
271 void ClassLoaderData::clear_claim(int claim) {
272 for (;;) {
273 int old_claim = Atomic::load(&_claim);
274 if ((old_claim & claim) == 0) {
275 return;
276 }
277 int new_claim = old_claim & ~claim;
278 if (Atomic::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
279 return;
280 }
281 }
282 }
283
284 #ifdef ASSERT
285 void ClassLoaderData::verify_not_claimed(int claim) {
286 assert((_claim & claim) == 0, "Found claim: %d bits in _claim: %d", claim, _claim);
287 }
288 #endif
289
290 bool ClassLoaderData::try_claim(int claim) {
291 for (;;) {
292 int old_claim = Atomic::load(&_claim);
293 if ((old_claim & claim) == claim) {
294 return false;
295 }
296 int new_claim = old_claim | claim;
297 if (Atomic::cmpxchg(&_claim, old_claim, new_claim) == old_claim) {
298 return true;
299 }
300 }
301 }
302
303 void ClassLoaderData::demote_strong_roots() {
304 // The oop handle area contains strong roots that the GC traces from. We are about
305 // to demote them to strong native oops that the GC does *not* trace from. Conceptually,
306 // we are retiring a rather normal strong root, and creating a strong non-root handle,
307 // which happens to reuse the same address as the normal strong root had.
308 // Unless we invoke the right barriers, the GC might not notice that a strong root
309 // has been pulled from the system, and is left unprocessed by the GC. There can be
310 // several consequences:
311 // 1. A concurrently marking snapshot-at-the-beginning GC might assume that the contents
312 // of all strong roots get processed by the GC in order to keep them alive. Without
313 // barriers, some objects might not be kept alive.
314 // 2. A concurrently relocating GC might assume that after moving an object, a subsequent
315 // tracing from all roots can fix all the pointers in the system, which doesn't play
316 // well with roots racingly being pulled.
317 // 3. A concurrent GC using colored pointers, might assume that tracing the object graph
318 // from roots results in all pointers getting some particular color, which also doesn't
319 // play well with roots being pulled out from the system concurrently.
320
321 class TransitionRootsOopClosure : public OopClosure {
322 public:
323 virtual void do_oop(oop* p) {
324 // By loading the strong root with the access API, we can use the right barriers to
325 // store the oop as a strong non-root handle, that happens to reuse the same memory
326 // address as the strong root. The barriered store ensures that:
327 // 1. The concurrent SATB marking properties are satisfied as the store will keep
328 // the oop alive.
329 // 2. The concurrent object movement properties are satisfied as we store the address
330 // of the new location of the object, if any.
331 // 3. The colors if any will be stored as the new good colors.
332 oop obj = NativeAccess<>::oop_load(p); // Load the strong root
333 NativeAccess<>::oop_store(p, obj); // Store the strong non-root
334 }
335
336 virtual void do_oop(narrowOop* p) {
337 ShouldNotReachHere();
338 }
339 } cl;
340 oops_do(&cl, ClassLoaderData::_claim_none, false /* clear_mod_oops */);
341 }
342
343 // Non-strong hidden classes have their own ClassLoaderData that is marked to keep alive
344 // while the class is being parsed, and if the class appears on the module fixup list.
345 // Due to the uniqueness that no other class shares the hidden class' name or
346 // ClassLoaderData, no other non-GC thread has knowledge of the hidden class while
347 // it is being defined, therefore _keep_alive_ref_count is not volatile or atomic.
348 void ClassLoaderData::inc_keep_alive_ref_count() {
349 if (has_class_mirror_holder()) {
350 assert(_keep_alive_ref_count > 0, "Invalid keep alive increment count");
351 _keep_alive_ref_count++;
352 }
353 }
354
355 void ClassLoaderData::dec_keep_alive_ref_count() {
356 if (has_class_mirror_holder()) {
357 assert(_keep_alive_ref_count > 0, "Invalid keep alive decrement count");
358 if (_keep_alive_ref_count == 1) {
359 // When the keep_alive_ref_count counter is 1, the oop handle area is a strong root,
360 // acting as input to the GC tracing. Such strong roots are part of the
361 // snapshot-at-the-beginning, and can not just be pulled out from the
362 // system when concurrent GCs are running at the same time, without
363 // invoking the right barriers.
364 demote_strong_roots();
365 }
366 _keep_alive_ref_count--;
367 }
368 }
369
370 void ClassLoaderData::oops_do(OopClosure* f, int claim_value, bool clear_mod_oops) {
371 if (claim_value != ClassLoaderData::_claim_none && !try_claim(claim_value)) {
372 return;
373 }
374
375 // Only clear modified_oops after the ClassLoaderData is claimed.
376 if (clear_mod_oops) {
377 clear_modified_oops();
378 }
379
380 _handles.oops_do(f);
381 }
382
383 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {
384 // Lock-free access requires load_acquire
385 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
386 klass_closure->do_klass(k);
387 assert(k != k->next_link(), "no loops!");
388 }
389 }
390
391 void ClassLoaderData::classes_do(void f(Klass * const)) {
392 // Lock-free access requires load_acquire
393 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
394 f(k);
395 assert(k != k->next_link(), "no loops!");
396 }
397 }
398
399 void ClassLoaderData::methods_do(void f(Method*)) {
400 // Lock-free access requires load_acquire
401 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
402 if (k->is_instance_klass() && InstanceKlass::cast(k)->is_loaded()) {
403 InstanceKlass::cast(k)->methods_do(f);
404 }
405 }
406 }
407
408 void ClassLoaderData::loaded_classes_do(KlassClosure* klass_closure) {
409 // Lock-free access requires load_acquire
410 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
411 // Filter out InstanceKlasses (or their ObjArrayKlasses) that have not entered the
412 // loaded state.
413 if (k->is_instance_klass()) {
414 if (!InstanceKlass::cast(k)->is_loaded()) {
415 continue;
416 }
417 } else if (k->is_shared() && k->is_objArray_klass()) {
418 Klass* bottom = ObjArrayKlass::cast(k)->bottom_klass();
419 if (bottom->is_instance_klass() && !InstanceKlass::cast(bottom)->is_loaded()) {
420 // This could happen if <bottom> is a shared class that has been restored
421 // but is not yet marked as loaded. All archived array classes of the
422 // bottom class are already restored and placed in the _klasses list.
423 continue;
424 }
425 }
426
427 #ifdef ASSERT
428 oop m = k->java_mirror();
429 assert(m != nullptr, "nullptr mirror");
430 assert(m->is_a(vmClasses::Class_klass()), "invalid mirror");
431 #endif
432 klass_closure->do_klass(k);
433 }
434 }
435
436 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {
437 // Lock-free access requires load_acquire
438 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
439 if (k->is_instance_klass()) {
440 f(InstanceKlass::cast(k));
441 }
442 assert(k != k->next_link(), "no loops!");
443 }
444 }
445
446 void ClassLoaderData::modules_do(void f(ModuleEntry*)) {
447 assert_locked_or_safepoint(Module_lock);
448 if (_unnamed_module != nullptr) {
449 f(_unnamed_module);
450 }
451 if (_modules != nullptr) {
452 _modules->modules_do(f);
453 }
454 }
455
456 void ClassLoaderData::packages_do(void f(PackageEntry*)) {
457 assert_locked_or_safepoint(Module_lock);
458 if (_packages != nullptr) {
459 _packages->packages_do(f);
460 }
461 }
462
463 void ClassLoaderData::record_dependency(const Klass* k) {
464 assert(k != nullptr, "invariant");
465
466 ClassLoaderData * const from_cld = this;
467 ClassLoaderData * const to_cld = k->class_loader_data();
468
469 // Do not need to record dependency if the dependency is to a class whose
470 // class loader data is never freed. (i.e. the dependency's class loader
471 // is one of the three builtin class loaders and the dependency's class
472 // loader data has a ClassLoader holder, not a Class holder.)
473 if (to_cld->is_permanent_class_loader_data()) {
474 return;
475 }
476
477 oop to;
478 if (to_cld->has_class_mirror_holder()) {
479 // Just return if a non-strong hidden class class is attempting to record a dependency
480 // to itself. (Note that every non-strong hidden class has its own unique class
481 // loader data.)
482 if (to_cld == from_cld) {
483 return;
484 }
485 // Hidden class dependencies are through the mirror.
486 to = k->java_mirror();
487 } else {
488 to = to_cld->class_loader();
489 oop from = from_cld->class_loader();
490
491 // Just return if this dependency is to a class with the same or a parent
492 // class_loader.
493 if (from == to || java_lang_ClassLoader::isAncestor(from, to)) {
494 return; // this class loader is in the parent list, no need to add it.
495 }
496 }
497
498 // It's a dependency we won't find through GC, add it.
499 if (!_handles.contains(to)) {
500 NOT_PRODUCT(Atomic::inc(&_dependency_count));
501 LogTarget(Trace, class, loader, data) lt;
502 if (lt.is_enabled()) {
503 ResourceMark rm;
504 LogStream ls(lt);
505 ls.print("adding dependency from ");
506 print_value_on(&ls);
507 ls.print(" to ");
508 to_cld->print_value_on(&ls);
509 ls.cr();
510 }
511 Handle dependency(Thread::current(), to);
512 add_handle(dependency);
513 // Added a potentially young gen oop to the ClassLoaderData
514 record_modified_oops();
515 }
516 }
517
518 void ClassLoaderData::add_class(Klass* k, bool publicize /* true */) {
519 {
520 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
521 Klass* old_value = _klasses;
522 k->set_next_link(old_value);
523 // Link the new item into the list, making sure the linked class is stable
524 // since the list can be walked without a lock
525 Atomic::release_store(&_klasses, k);
526 if (k->is_array_klass()) {
527 ClassLoaderDataGraph::inc_array_classes(1);
528 } else {
529 ClassLoaderDataGraph::inc_instance_classes(1);
530 }
531 }
532
533 if (publicize) {
534 LogTarget(Trace, class, loader, data) lt;
535 if (lt.is_enabled()) {
536 ResourceMark rm;
537 LogStream ls(lt);
538 ls.print("Adding k: " PTR_FORMAT " %s to ", p2i(k), k->external_name());
539 print_value_on(&ls);
540 ls.cr();
541 }
542 }
543 }
544
545 void ClassLoaderData::initialize_holder(Handle loader_or_mirror) {
546 if (loader_or_mirror() != nullptr) {
547 assert(_holder.is_null(), "never replace holders");
548 _holder = WeakHandle(Universe::vm_weak(), loader_or_mirror);
549 }
550 }
551
552 // Remove a klass from the _klasses list for scratch_class during redefinition
553 // or parsed class in the case of an error.
554 void ClassLoaderData::remove_class(Klass* scratch_class) {
555 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
556
557 Klass* prev = nullptr;
558 for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
559 if (k == scratch_class) {
560 if (prev == nullptr) {
561 _klasses = k->next_link();
562 } else {
563 Klass* next = k->next_link();
564 prev->set_next_link(next);
565 }
566
567 if (k->is_array_klass()) {
568 ClassLoaderDataGraph::dec_array_classes(1);
569 } else {
570 ClassLoaderDataGraph::dec_instance_classes(1);
571 }
572
573 return;
574 }
575 prev = k;
576 assert(k != k->next_link(), "no loops!");
577 }
578 ShouldNotReachHere(); // should have found this class!!
579 }
580
581 void ClassLoaderData::unload() {
582 _unloading = true;
583
584 LogTarget(Trace, class, loader, data) lt;
585 if (lt.is_enabled()) {
586 ResourceMark rm;
587 LogStream ls(lt);
588 ls.print("unload");
589 print_value_on(&ls);
590 ls.cr();
591 }
592
593 // Some items on the _deallocate_list need to free their C heap structures
594 // if they are not already on the _klasses list.
595 free_deallocate_list_C_heap_structures();
596
597 // Clean up class dependencies and tell serviceability tools
598 // these classes are unloading. This must be called
599 // after erroneous classes are released.
600 classes_do(InstanceKlass::unload_class);
601
602 // Method::clear_jmethod_ids only sets the jmethod_ids to null without
603 // releasing the memory for related JNIMethodBlocks and JNIMethodBlockNodes.
604 // This is done intentionally because native code (e.g. JVMTI agent) holding
605 // jmethod_ids may access them after the associated classes and class loader
606 // are unloaded. The Java Native Interface Specification says "method ID
607 // does not prevent the VM from unloading the class from which the ID has
608 // been derived. After the class is unloaded, the method or field ID becomes
609 // invalid". In real world usages, the native code may rely on jmethod_ids
610 // being null after class unloading. Hence, it is unsafe to free the memory
611 // from the VM side without knowing when native code is going to stop using
612 // them.
613 if (_jmethod_ids != nullptr) {
614 Method::clear_jmethod_ids(this);
615 }
616 }
617
618 ModuleEntryTable* ClassLoaderData::modules() {
619 // Lazily create the module entry table at first request.
620 // Lock-free access requires load_acquire.
621 ModuleEntryTable* modules = Atomic::load_acquire(&_modules);
622 if (modules == nullptr) {
623 MutexLocker m1(Module_lock);
624 // Check if _modules got allocated while we were waiting for this lock.
625 if ((modules = _modules) == nullptr) {
626 modules = new ModuleEntryTable();
627
628 {
629 MutexLocker m1(metaspace_lock(), Mutex::_no_safepoint_check_flag);
630 // Ensure _modules is stable, since it is examined without a lock
631 Atomic::release_store(&_modules, modules);
632 }
633 }
634 }
635 return modules;
636 }
637
638 const int _boot_loader_dictionary_size = 1009;
639 const int _default_loader_dictionary_size = 107;
640
641 Dictionary* ClassLoaderData::create_dictionary() {
642 assert(!has_class_mirror_holder(), "class mirror holder cld does not have a dictionary");
643 int size;
644 if (_the_null_class_loader_data == nullptr) {
645 size = _boot_loader_dictionary_size;
646 } else if (is_system_class_loader_data()) {
647 size = _boot_loader_dictionary_size;
648 } else {
649 size = _default_loader_dictionary_size;
650 }
651 return new Dictionary(this, size);
652 }
653
654 // Tell the GC to keep this klass alive. Needed while iterating ClassLoaderDataGraph,
655 // and any runtime code that uses klasses.
656 oop ClassLoaderData::holder() const {
657 // A klass that was previously considered dead can be looked up in the
658 // CLD/SD, and its _java_mirror or _class_loader can be stored in a root
659 // or a reachable object making it alive again. The SATB part of G1 needs
660 // to get notified about this potential resurrection, otherwise the marking
661 // might not find the object.
662 if (!_holder.is_null()) { // null class_loader
663 return _holder.resolve();
664 } else {
665 return nullptr;
666 }
667 }
668
669 // Let the GC read the holder without keeping it alive.
670 oop ClassLoaderData::holder_no_keepalive() const {
671 if (!_holder.is_null()) { // null class_loader
672 return _holder.peek();
673 } else {
674 return nullptr;
675 }
676 }
677
678 // Unloading support
679 bool ClassLoaderData::is_alive() const {
680 bool alive = (_keep_alive_ref_count > 0) // null class loader and incomplete non-strong hidden class.
681 || (_holder.peek() != nullptr); // and not cleaned by the GC weak handle processing.
682
683 return alive;
684 }
685
686 class ReleaseKlassClosure: public KlassClosure {
687 private:
688 size_t _instance_class_released;
689 size_t _array_class_released;
690 public:
691 ReleaseKlassClosure() : _instance_class_released(0), _array_class_released(0) { }
692
693 size_t instance_class_released() const { return _instance_class_released; }
694 size_t array_class_released() const { return _array_class_released; }
695
696 void do_klass(Klass* k) {
697 if (k->is_array_klass()) {
698 _array_class_released ++;
699 } else {
700 assert(k->is_instance_klass(), "Must be");
701 _instance_class_released ++;
702 }
703 k->release_C_heap_structures();
704 }
705 };
706
707 ClassLoaderData::~ClassLoaderData() {
708 // Release C heap structures for all the classes.
709 ReleaseKlassClosure cl;
710 classes_do(&cl);
711
712 ClassLoaderDataGraph::dec_array_classes(cl.array_class_released());
713 ClassLoaderDataGraph::dec_instance_classes(cl.instance_class_released());
714
715 // Release the WeakHandle
716 _holder.release(Universe::vm_weak());
717
718 // Release C heap allocated hashtable for all the packages.
719 if (_packages != nullptr) {
720 // Destroy the table itself
721 delete _packages;
722 _packages = nullptr;
723 }
724
725 // Release C heap allocated hashtable for all the modules.
726 if (_modules != nullptr) {
727 // Destroy the table itself
728 delete _modules;
729 _modules = nullptr;
730 }
731
732 // Release C heap allocated hashtable for the dictionary
733 if (_dictionary != nullptr) {
734 // Destroy the table itself
735 delete _dictionary;
736 _dictionary = nullptr;
737 }
738
739 if (_unnamed_module != nullptr) {
740 delete _unnamed_module;
741 _unnamed_module = nullptr;
742 }
743
744 // release the metaspace
745 ClassLoaderMetaspace *m = _metaspace;
746 if (m != nullptr) {
747 _metaspace = nullptr;
748 delete m;
749 }
750
751 // Delete lock
752 delete _metaspace_lock;
753
754 // Delete free list
755 if (_deallocate_list != nullptr) {
756 delete _deallocate_list;
757 }
758
759 // Decrement refcounts of Symbols if created.
760 if (_name != nullptr) {
761 _name->decrement_refcount();
762 }
763 if (_name_and_id != nullptr) {
764 _name_and_id->decrement_refcount();
765 }
766 }
767
768 // Returns true if this class loader data is for the app class loader
769 // or a user defined system class loader. (Note that the class loader
770 // data may have a Class holder.)
771 bool ClassLoaderData::is_system_class_loader_data() const {
772 return SystemDictionary::is_system_class_loader(class_loader());
773 }
774
775 // Returns true if this class loader data is for the platform class loader.
776 // (Note that the class loader data may have a Class holder.)
777 bool ClassLoaderData::is_platform_class_loader_data() const {
778 return SystemDictionary::is_platform_class_loader(class_loader());
779 }
780
781 // Returns true if the class loader for this class loader data is one of
782 // the 3 builtin (boot application/system or platform) class loaders,
783 // including a user-defined system class loader. Note that if the class
784 // loader data is for a non-strong hidden class then it may
785 // get freed by a GC even if its class loader is one of these loaders.
786 bool ClassLoaderData::is_builtin_class_loader_data() const {
787 return (is_boot_class_loader_data() ||
788 SystemDictionary::is_system_class_loader(class_loader()) ||
789 SystemDictionary::is_platform_class_loader(class_loader()));
790 }
791
792 // Returns true if this class loader data is a class loader data
793 // that is not ever freed by a GC. It must be the CLD for one of the builtin
794 // class loaders and not the CLD for a non-strong hidden class.
795 bool ClassLoaderData::is_permanent_class_loader_data() const {
796 return is_builtin_class_loader_data() && !has_class_mirror_holder();
797 }
798
799 ClassLoaderMetaspace* ClassLoaderData::metaspace_non_null() {
800 // If the metaspace has not been allocated, create a new one. Might want
801 // to create smaller arena for Reflection class loaders also.
802 // The reason for the delayed allocation is because some class loaders are
803 // simply for delegating with no metadata of their own.
804 // Lock-free access requires load_acquire.
805 ClassLoaderMetaspace* metaspace = Atomic::load_acquire(&_metaspace);
806 if (metaspace == nullptr) {
807 MutexLocker ml(_metaspace_lock, Mutex::_no_safepoint_check_flag);
808 // Check if _metaspace got allocated while we were waiting for this lock.
809 if ((metaspace = _metaspace) == nullptr) {
810 if (this == the_null_class_loader_data()) {
811 assert (class_loader() == nullptr, "Must be");
812 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::BootMetaspaceType);
813 } else if (has_class_mirror_holder()) {
814 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::ClassMirrorHolderMetaspaceType);
815 } else {
816 metaspace = new ClassLoaderMetaspace(_metaspace_lock, Metaspace::StandardMetaspaceType);
817 }
818 // Ensure _metaspace is stable, since it is examined without a lock
819 Atomic::release_store(&_metaspace, metaspace);
820 }
821 }
822 return metaspace;
823 }
824
825 OopHandle ClassLoaderData::add_handle(Handle h) {
826 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
827 record_modified_oops();
828 return _handles.add(h());
829 }
830
831 void ClassLoaderData::remove_handle(OopHandle h) {
832 assert(!is_unloading(), "Do not remove a handle for a CLD that is unloading");
833 if (!h.is_empty()) {
834 assert(_handles.owner_of(h.ptr_raw()),
835 "Got unexpected handle " PTR_FORMAT, p2i(h.ptr_raw()));
836 h.replace(oop(nullptr));
837 }
838 }
839
840 void ClassLoaderData::init_handle_locked(OopHandle& dest, Handle h) {
841 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
842 if (dest.resolve() != nullptr) {
843 return;
844 } else {
845 record_modified_oops();
846 dest = _handles.add(h());
847 }
848 }
849
850 // Add this metadata pointer to be freed when it's safe. This is only during
851 // a safepoint which checks if handles point to this metadata field.
852 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
853 // Metadata in shared region isn't deleted.
854 if (!m->is_shared()) {
855 MutexLocker ml(metaspace_lock(), Mutex::_no_safepoint_check_flag);
856 if (_deallocate_list == nullptr) {
857 _deallocate_list = new (mtClass) GrowableArray<Metadata*>(100, mtClass);
858 }
859 _deallocate_list->append_if_missing(m);
860 ResourceMark rm;
861 log_debug(class, loader, data)("deallocate added for %s", m->print_value_string());
862 ClassLoaderDataGraph::set_should_clean_deallocate_lists();
863 }
864 }
865
866 // Deallocate free metadata on the free list. How useful the PermGen was!
867 void ClassLoaderData::free_deallocate_list() {
868 // This must be called at a safepoint because it depends on metadata walking at
869 // safepoint cleanup time.
870 assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
871 assert(!is_unloading(), "only called for ClassLoaderData that are not unloading");
872 if (_deallocate_list == nullptr) {
873 return;
874 }
875 // Go backwards because this removes entries that are freed.
876 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
877 Metadata* m = _deallocate_list->at(i);
878 if (!m->on_stack()) {
879 _deallocate_list->remove_at(i);
880 // There are only three types of metadata that we deallocate directly.
881 // Cast them so they can be used by the template function.
882 if (m->is_method()) {
883 MetadataFactory::free_metadata(this, (Method*)m);
884 } else if (m->is_constantPool()) {
885 MetadataFactory::free_metadata(this, (ConstantPool*)m);
886 } else if (m->is_klass()) {
887 MetadataFactory::free_metadata(this, (InstanceKlass*)m);
888 } else {
889 ShouldNotReachHere();
890 }
891 } else {
892 // Metadata is alive.
893 // If scratch_class is on stack then it shouldn't be on this list!
894 assert(!m->is_klass() || !((InstanceKlass*)m)->is_scratch_class(),
895 "scratch classes on this list should be dead");
896 // Also should assert that other metadata on the list was found in handles.
897 // Some cleaning remains.
898 ClassLoaderDataGraph::set_should_clean_deallocate_lists();
899 }
900 }
901 }
902
903 // This is distinct from free_deallocate_list. For class loader data that are
904 // unloading, this frees the C heap memory for items on the list, and unlinks
905 // scratch or error classes so that unloading events aren't triggered for these
906 // classes. The metadata is removed with the unloading metaspace.
907 // There isn't C heap memory allocated for methods, so nothing is done for them.
908 void ClassLoaderData::free_deallocate_list_C_heap_structures() {
909 assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
910 assert(is_unloading(), "only called for ClassLoaderData that are unloading");
911 if (_deallocate_list == nullptr) {
912 return;
913 }
914 // Go backwards because this removes entries that are freed.
915 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
916 Metadata* m = _deallocate_list->at(i);
917 _deallocate_list->remove_at(i);
918 if (m->is_constantPool()) {
919 ((ConstantPool*)m)->release_C_heap_structures();
920 } else if (m->is_klass()) {
921 InstanceKlass* ik = (InstanceKlass*)m;
922 // also releases ik->constants() C heap memory
923 ik->release_C_heap_structures();
924 // Remove the class so unloading events aren't triggered for
925 // this class (scratch or error class) in do_unloading().
926 remove_class(ik);
927 // But still have to remove it from the dumptime_table.
928 SystemDictionaryShared::handle_class_unloading(ik);
929 }
930 }
931 }
932
933 // Caller needs ResourceMark
934 // If the class loader's _name has not been explicitly set, the class loader's
935 // qualified class name is returned.
936 const char* ClassLoaderData::loader_name() const {
937 if (_class_loader_klass == nullptr) {
938 return BOOTSTRAP_LOADER_NAME;
939 } else if (_name != nullptr) {
940 return _name->as_C_string();
941 } else {
942 return _class_loader_klass->external_name();
943 }
944 }
945
946 // Caller needs ResourceMark
947 // Format of the _name_and_id is as follows:
948 // If the defining loader has a name explicitly set then '<loader-name>' @<id>
949 // If the defining loader has no name then <qualified-class-name> @<id>
950 // If built-in loader, then omit '@<id>' as there is only one instance.
951 const char* ClassLoaderData::loader_name_and_id() const {
952 if (_class_loader_klass == nullptr) {
953 return "'" BOOTSTRAP_LOADER_NAME "'";
954 } else if (_name_and_id != nullptr) {
955 return _name_and_id->as_C_string();
956 } else {
957 // May be called in a race before _name_and_id is initialized.
958 return _class_loader_klass->external_name();
959 }
960 }
961
962 void ClassLoaderData::print_value_on(outputStream* out) const {
963 if (!is_unloading() && class_loader() != nullptr) {
964 out->print("loader data: " INTPTR_FORMAT " for instance ", p2i(this));
965 class_loader()->print_value_on(out); // includes loader_name_and_id() and address of class loader instance
966 } else {
967 // loader data: 0xsomeaddr of 'bootstrap'
968 out->print("loader data: " INTPTR_FORMAT " of %s", p2i(this), loader_name_and_id());
969 }
970 if (_has_class_mirror_holder) {
971 out->print(" has a class holder");
972 }
973 }
974
975 void ClassLoaderData::print_value() const { print_value_on(tty); }
976
977 #ifndef PRODUCT
978 class PrintKlassClosure: public KlassClosure {
979 outputStream* _out;
980 public:
981 PrintKlassClosure(outputStream* out): _out(out) { }
982
983 void do_klass(Klass* k) {
984 ResourceMark rm;
985 _out->print("%s,", k->external_name());
986 }
987 };
988
989 void ClassLoaderData::print_on(outputStream* out) const {
990 ResourceMark rm;
991 out->print_cr("ClassLoaderData(" INTPTR_FORMAT ")", p2i(this));
992 out->print_cr(" - name %s", loader_name_and_id());
993 if (!_holder.is_null()) {
994 out->print (" - holder ");
995 _holder.print_on(out);
996 out->print_cr("");
997 }
998 if (!_unloading) {
999 out->print_cr(" - class loader " INTPTR_FORMAT, p2i(_class_loader.peek()));
1000 } else {
1001 out->print_cr(" - class loader <unloading, oop is bad>");
1002 }
1003 out->print_cr(" - metaspace " INTPTR_FORMAT, p2i(_metaspace));
1004 out->print_cr(" - unloading %s", _unloading ? "true" : "false");
1005 out->print_cr(" - class mirror holder %s", _has_class_mirror_holder ? "true" : "false");
1006 out->print_cr(" - modified oops %s", _modified_oops ? "true" : "false");
1007 out->print_cr(" - _keep_alive_ref_count %d", _keep_alive_ref_count);
1008 out->print (" - claim ");
1009 switch(_claim) {
1010 case _claim_none: out->print_cr("none"); break;
1011 case _claim_finalizable: out->print_cr("finalizable"); break;
1012 case _claim_strong: out->print_cr("strong"); break;
1013 case _claim_stw_fullgc_mark: out->print_cr("stw full gc mark"); break;
1014 case _claim_stw_fullgc_adjust: out->print_cr("stw full gc adjust"); break;
1015 case _claim_other: out->print_cr("other"); break;
1016 case _claim_other | _claim_finalizable: out->print_cr("other and finalizable"); break;
1017 case _claim_other | _claim_strong: out->print_cr("other and strong"); break;
1018 default: ShouldNotReachHere();
1019 }
1020 out->print_cr(" - handles %d", _handles.count());
1021 out->print_cr(" - dependency count %d", _dependency_count);
1022 out->print (" - klasses { ");
1023 if (Verbose) {
1024 PrintKlassClosure closure(out);
1025 ((ClassLoaderData*)this)->classes_do(&closure);
1026 } else {
1027 out->print("...");
1028 }
1029 out->print_cr(" }");
1030 out->print_cr(" - packages " INTPTR_FORMAT, p2i(_packages));
1031 out->print_cr(" - module " INTPTR_FORMAT, p2i(_modules));
1032 out->print_cr(" - unnamed module " INTPTR_FORMAT, p2i(_unnamed_module));
1033 if (_dictionary != nullptr) {
1034 out->print (" - dictionary " INTPTR_FORMAT " ", p2i(_dictionary));
1035 _dictionary->print_size(out);
1036 } else {
1037 out->print_cr(" - dictionary " INTPTR_FORMAT, p2i(_dictionary));
1038 }
1039 if (_jmethod_ids != nullptr) {
1040 out->print (" - jmethod count ");
1041 Method::print_jmethod_ids_count(this, out);
1042 out->print_cr("");
1043 }
1044 out->print_cr(" - deallocate list " INTPTR_FORMAT, p2i(_deallocate_list));
1045 out->print_cr(" - next CLD " INTPTR_FORMAT, p2i(_next));
1046 }
1047 #endif // PRODUCT
1048
1049 void ClassLoaderData::print() const { print_on(tty); }
1050
1051 class VerifyHandleOops : public OopClosure {
1052 VerifyOopClosure vc;
1053 public:
1054 virtual void do_oop(oop* p) {
1055 if (p != nullptr && *p != nullptr) {
1056 oop o = *p;
1057 if (!java_lang_Class::is_instance(o)) {
1058 // is_instance will assert for an invalid oop.
1059 // Walk the resolved_references array and other assorted oops in the
1060 // CLD::_handles field. The mirror oops are followed by other heap roots.
1061 o->oop_iterate(&vc);
1062 }
1063 }
1064 }
1065 virtual void do_oop(narrowOop* o) { ShouldNotReachHere(); }
1066 };
1067
1068 void ClassLoaderData::verify() {
1069 assert_locked_or_safepoint(_metaspace_lock);
1070 oop cl = class_loader();
1071
1072 guarantee(this == class_loader_data(cl) || has_class_mirror_holder(), "Must be the same");
1073 guarantee(cl != nullptr || this == ClassLoaderData::the_null_class_loader_data() || has_class_mirror_holder(), "must be");
1074
1075 // Verify the integrity of the allocated space.
1076 #ifdef ASSERT
1077 if (metaspace_or_null() != nullptr) {
1078 metaspace_or_null()->verify();
1079 }
1080 #endif
1081
1082 for (Klass* k = _klasses; k != nullptr; k = k->next_link()) {
1083 guarantee(k->class_loader_data() == this, "Must be the same");
1084 k->verify();
1085 assert(k != k->next_link(), "no loops!");
1086 }
1087
1088 if (_modules != nullptr) {
1089 _modules->verify();
1090 }
1091
1092 if (_deallocate_list != nullptr) {
1093 for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
1094 Metadata* m = _deallocate_list->at(i);
1095 if (m->is_klass()) {
1096 ((Klass*)m)->verify();
1097 }
1098 }
1099 }
1100
1101 // Check the oops in the handles area
1102 VerifyHandleOops vho;
1103 oops_do(&vho, _claim_none, false);
1104 }
1105
1106 bool ClassLoaderData::contains_klass(Klass* klass) {
1107 // Lock-free access requires load_acquire
1108 for (Klass* k = Atomic::load_acquire(&_klasses); k != nullptr; k = k->next_link()) {
1109 if (k == klass) return true;
1110 }
1111 return false;
1112 }