1 /*
2 * Copyright (c) 1998, 2021, 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 "gc/shared/collectedHeap.hpp"
27 #include "gc/shared/oopStorage.inline.hpp"
28 #include "gc/shared/oopStorageSet.hpp"
29 #include "logging/log.hpp"
30 #include "memory/iterator.hpp"
31 #include "memory/universe.hpp"
32 #include "oops/access.inline.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/handles.inline.hpp"
35 #include "runtime/jniHandles.inline.hpp"
36 #include "runtime/mutexLocker.hpp"
37 #include "runtime/thread.inline.hpp"
38 #include "utilities/align.hpp"
39 #include "utilities/debug.hpp"
40
41 OopStorage* JNIHandles::global_handles() {
42 return _global_handles;
43 }
44
45 OopStorage* JNIHandles::weak_global_handles() {
46 return _weak_global_handles;
47 }
48
49 // Serviceability agent support.
50 OopStorage* JNIHandles::_global_handles = NULL;
51 OopStorage* JNIHandles::_weak_global_handles = NULL;
52
53 void jni_handles_init() {
54 JNIHandles::_global_handles = OopStorageSet::create_strong("JNI Global", mtInternal);
55 JNIHandles::_weak_global_handles = OopStorageSet::create_weak("JNI Weak", mtInternal);
56 }
57
58 jobject JNIHandles::make_local(oop obj) {
59 return make_local(JavaThread::current(), obj);
60 }
61
62 // Used by NewLocalRef which requires NULL on out-of-memory
63 jobject JNIHandles::make_local(JavaThread* thread, oop obj, AllocFailType alloc_failmode) {
64 if (obj == NULL) {
65 return NULL; // ignore null handles
66 } else {
67 assert(oopDesc::is_oop(obj), "not an oop");
68 assert(!current_thread_in_native(), "must not be in native");
69 return thread->active_handles()->allocate_handle(thread, obj, alloc_failmode);
70 }
71 }
72
73 static void report_handle_allocation_failure(AllocFailType alloc_failmode,
74 const char* handle_kind) {
75 if (alloc_failmode == AllocFailStrategy::EXIT_OOM) {
76 // Fake size value, since we don't know the min allocation size here.
77 vm_exit_out_of_memory(sizeof(oop), OOM_MALLOC_ERROR,
78 "Cannot create %s JNI handle", handle_kind);
79 } else {
80 assert(alloc_failmode == AllocFailStrategy::RETURN_NULL, "invariant");
81 }
82 }
83
84 jobject JNIHandles::make_global(Handle obj, AllocFailType alloc_failmode) {
85 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
86 assert(!current_thread_in_native(), "must not be in native");
87 jobject res = NULL;
88 if (!obj.is_null()) {
89 // ignore null handles
90 assert(oopDesc::is_oop(obj()), "not an oop");
91 oop* ptr = global_handles()->allocate();
92 // Return NULL on allocation failure.
93 if (ptr != NULL) {
94 assert(*ptr == NULL, "invariant");
95 NativeAccess<>::oop_store(ptr, obj());
96 res = reinterpret_cast<jobject>(ptr);
97 } else {
98 report_handle_allocation_failure(alloc_failmode, "global");
99 }
100 }
101
102 return res;
103 }
104
105 jobject JNIHandles::make_weak_global(Handle obj, AllocFailType alloc_failmode) {
106 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
107 assert(!current_thread_in_native(), "must not be in native");
108 jobject res = NULL;
109 if (!obj.is_null()) {
110 // ignore null handles
111 assert(oopDesc::is_oop(obj()), "not an oop");
112 oop* ptr = weak_global_handles()->allocate();
113 // Return NULL on allocation failure.
114 if (ptr != NULL) {
115 assert(*ptr == NULL, "invariant");
116 NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(ptr, obj());
117 char* tptr = reinterpret_cast<char*>(ptr) + weak_tag_value;
118 res = reinterpret_cast<jobject>(tptr);
119 } else {
120 report_handle_allocation_failure(alloc_failmode, "weak global");
121 }
122 }
123 return res;
124 }
125
126 // Resolve some erroneous cases to NULL, rather than treating them as
127 // possibly unchecked errors. In particular, deleted handles are
128 // treated as NULL (though a deleted and later reallocated handle
129 // isn't detected).
130 oop JNIHandles::resolve_external_guard(jobject handle) {
131 oop result = NULL;
132 if (handle != NULL) {
133 result = resolve_impl<DECORATORS_NONE, true /* external_guard */>(handle);
134 }
135 return result;
136 }
137
138 bool JNIHandles::is_global_weak_cleared(jweak handle) {
139 assert(handle != NULL, "precondition");
140 assert(is_jweak(handle), "not a weak handle");
141 oop* oop_ptr = jweak_ptr(handle);
142 oop value = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(oop_ptr);
143 return value == NULL;
144 }
145
146 void JNIHandles::destroy_global(jobject handle) {
147 if (handle != NULL) {
148 assert(!is_jweak(handle), "wrong method for detroying jweak");
149 oop* oop_ptr = jobject_ptr(handle);
150 NativeAccess<>::oop_store(oop_ptr, (oop)NULL);
151 global_handles()->release(oop_ptr);
152 }
153 }
154
155
156 void JNIHandles::destroy_weak_global(jobject handle) {
157 if (handle != NULL) {
158 assert(is_jweak(handle), "JNI handle not jweak");
159 oop* oop_ptr = jweak_ptr(handle);
160 NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(oop_ptr, (oop)NULL);
161 weak_global_handles()->release(oop_ptr);
162 }
163 }
164
165
166 void JNIHandles::oops_do(OopClosure* f) {
167 global_handles()->oops_do(f);
168 }
169
170
171 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
172 weak_global_handles()->weak_oops_do(is_alive, f);
173 }
174
175
176 void JNIHandles::weak_oops_do(OopClosure* f) {
177 weak_global_handles()->weak_oops_do(f);
178 }
179
180 bool JNIHandles::is_global_storage(const OopStorage* storage) {
181 return _global_handles == storage;
182 }
183
184 inline bool is_storage_handle(const OopStorage* storage, const oop* ptr) {
185 return storage->allocation_status(ptr) == OopStorage::ALLOCATED_ENTRY;
186 }
187
188
189 jobjectRefType JNIHandles::handle_type(JavaThread* thread, jobject handle) {
190 assert(handle != NULL, "precondition");
191 jobjectRefType result = JNIInvalidRefType;
192 if (is_jweak(handle)) {
193 if (is_storage_handle(weak_global_handles(), jweak_ptr(handle))) {
194 result = JNIWeakGlobalRefType;
195 }
196 } else {
197 switch (global_handles()->allocation_status(jobject_ptr(handle))) {
198 case OopStorage::ALLOCATED_ENTRY:
199 result = JNIGlobalRefType;
200 break;
201
202 case OopStorage::UNALLOCATED_ENTRY:
203 break; // Invalid global handle
204
205 case OopStorage::INVALID_ENTRY:
206 // Not in global storage. Might be a local handle.
207 if (is_local_handle(thread, handle) || is_frame_handle(thread, handle)) {
208 result = JNILocalRefType;
209 }
210 break;
211
212 default:
213 ShouldNotReachHere();
214 }
215 }
216 return result;
217 }
218
219
220 bool JNIHandles::is_local_handle(JavaThread* thread, jobject handle) {
221 assert(handle != NULL, "precondition");
222 JNIHandleBlock* block = thread->active_handles();
223
224 // Look back past possible native calls to jni_PushLocalFrame.
225 while (block != NULL) {
226 if (block->chain_contains(handle)) {
227 return true;
228 }
229 block = block->pop_frame_link();
230 }
231 return false;
232 }
233
234
235 // Determine if the handle is somewhere in the current thread's stack.
236 // We easily can't isolate any particular stack frame the handle might
237 // come from, so we'll check the whole stack.
238
239 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject handle) {
240 assert(handle != NULL, "precondition");
241 // If there is no java frame, then this must be top level code, such
242 // as the java command executable, in which case, this type of handle
243 // is not permitted.
244 return (thr->has_last_Java_frame() &&
245 thr->is_in_stack_range_incl((address)handle, (address)thr->last_Java_sp()));
246 }
247
248
249 bool JNIHandles::is_global_handle(jobject handle) {
250 assert(handle != NULL, "precondition");
251 return !is_jweak(handle) && is_storage_handle(global_handles(), jobject_ptr(handle));
252 }
253
254
255 bool JNIHandles::is_weak_global_handle(jobject handle) {
256 assert(handle != NULL, "precondition");
257 return is_jweak(handle) && is_storage_handle(weak_global_handles(), jweak_ptr(handle));
258 }
259
260 size_t JNIHandles::global_handle_memory_usage() {
261 return global_handles()->total_memory_usage();
262 }
263
264 size_t JNIHandles::weak_global_handle_memory_usage() {
265 return weak_global_handles()->total_memory_usage();
266 }
267
268
269 // We assume this is called at a safepoint: no lock is needed.
270 void JNIHandles::print_on(outputStream* st) {
271 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
272
273 st->print_cr("JNI global refs: " SIZE_FORMAT ", weak refs: " SIZE_FORMAT,
274 global_handles()->allocation_count(),
275 weak_global_handles()->allocation_count());
276 st->cr();
277 st->flush();
278 }
279
280 void JNIHandles::print() { print_on(tty); }
281
282 class VerifyJNIHandles: public OopClosure {
283 public:
284 virtual void do_oop(oop* root) {
285 guarantee(oopDesc::is_oop_or_null(RawAccess<>::oop_load(root)), "Invalid oop");
286 }
287 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
288 };
289
290 void JNIHandles::verify() {
291 VerifyJNIHandles verify_handle;
292
293 oops_do(&verify_handle);
294 weak_oops_do(&verify_handle);
295 }
296
297 // This method is implemented here to avoid circular includes between
298 // jniHandles.hpp and thread.hpp.
299 bool JNIHandles::current_thread_in_native() {
300 Thread* thread = Thread::current();
301 return (thread->is_Java_thread() &&
302 JavaThread::cast(thread)->thread_state() == _thread_in_native);
303 }
304
305 int JNIHandleBlock::_blocks_allocated = 0;
306
307 static inline bool is_tagged_free_list(uintptr_t value) {
308 return (value & 1u) != 0;
309 }
310
311 static inline uintptr_t tag_free_list(uintptr_t value) {
312 return value | 1u;
313 }
314
315 static inline uintptr_t untag_free_list(uintptr_t value) {
316 return value & ~(uintptr_t)1u;
317 }
318
319 // There is a freelist of handles running through the JNIHandleBlock
320 // with a tagged next pointer, distinguishing these next pointers from
321 // oops. The freelist handling currently relies on the size of oops
322 // being the same as a native pointer. If this ever changes, then
323 // this freelist handling must change too.
324 STATIC_ASSERT(sizeof(oop) == sizeof(uintptr_t));
325
326 #ifdef ASSERT
327 void JNIHandleBlock::zap() {
328 // Zap block values
329 _top = 0;
330 for (int index = 0; index < block_size_in_oops; index++) {
331 // NOT using Access here; just bare clobbering to NULL, since the
332 // block no longer contains valid oops.
333 _handles[index] = 0;
334 }
335 }
336 #endif // ASSERT
337
338 JNIHandleBlock* JNIHandleBlock::allocate_block(JavaThread* thread, AllocFailType alloc_failmode) {
339 // The VM thread can allocate a handle block in behalf of another thread during a safepoint.
340 assert(thread == NULL || thread == Thread::current() || SafepointSynchronize::is_at_safepoint(),
341 "sanity check");
342 JNIHandleBlock* block;
343 // Check the thread-local free list for a block so we don't
344 // have to acquire a mutex.
345 if (thread != NULL && thread->free_handle_block() != NULL) {
346 block = thread->free_handle_block();
347 thread->set_free_handle_block(block->_next);
348 } else {
349 // Allocate new block
350 if (alloc_failmode == AllocFailStrategy::RETURN_NULL) {
351 block = new (std::nothrow) JNIHandleBlock();
352 if (block == NULL) {
353 return NULL;
354 }
355 } else {
356 block = new JNIHandleBlock();
357 }
358 Atomic::inc(&_blocks_allocated);
359 block->zap();
360 }
361 block->_top = 0;
362 block->_next = NULL;
363 block->_pop_frame_link = NULL;
364 block->_planned_capacity = block_size_in_oops;
365 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
366 debug_only(block->_last = NULL);
367 debug_only(block->_free_list = NULL);
368 debug_only(block->_allocate_before_rebuild = -1);
369 return block;
370 }
371
372
373 void JNIHandleBlock::release_block(JNIHandleBlock* block, JavaThread* thread) {
374 assert(thread == NULL || thread == Thread::current(), "sanity check");
375 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
376 // Put returned block at the beginning of the thread-local free list.
377 // Note that if thread == NULL, we use it as an implicit argument that
378 // we _don't_ want the block to be kept on the free_handle_block.
379 // See for instance JavaThread::exit().
380 if (thread != NULL ) {
381 block->zap();
382 JNIHandleBlock* freelist = thread->free_handle_block();
383 block->_pop_frame_link = NULL;
384 thread->set_free_handle_block(block);
385
386 // Add original freelist to end of chain
387 if ( freelist != NULL ) {
388 while ( block->_next != NULL ) block = block->_next;
389 block->_next = freelist;
390 }
391 block = NULL;
392 }
393 if (block != NULL) {
394 Atomic::dec(&_blocks_allocated);
395 delete block;
396 }
397 if (pop_frame_link != NULL) {
398 // As a sanity check we release blocks pointed to by the pop_frame_link.
399 // This should never happen (only if PopLocalFrame is not called the
400 // correct number of times).
401 release_block(pop_frame_link, thread);
402 }
403 }
404
405
406 void JNIHandleBlock::oops_do(OopClosure* f) {
407 JNIHandleBlock* current_chain = this;
408 // Iterate over chain of blocks, followed by chains linked through the
409 // pop frame links.
410 while (current_chain != NULL) {
411 for (JNIHandleBlock* current = current_chain; current != NULL;
412 current = current->_next) {
413 assert(current == current_chain || current->pop_frame_link() == NULL,
414 "only blocks first in chain should have pop frame link set");
415 for (int index = 0; index < current->_top; index++) {
416 uintptr_t* addr = &(current->_handles)[index];
417 uintptr_t value = *addr;
418 // traverse heap pointers only, not deleted handles or free list
419 // pointers
420 if (value != 0 && !is_tagged_free_list(value)) {
421 oop* root = (oop*)addr;
422 f->do_oop(root);
423 }
424 }
425 // the next handle block is valid only if current block is full
426 if (current->_top < block_size_in_oops) {
427 break;
428 }
429 }
430 current_chain = current_chain->pop_frame_link();
431 }
432 }
433
434
435 jobject JNIHandleBlock::allocate_handle(JavaThread* caller, oop obj, AllocFailType alloc_failmode) {
436 assert(Universe::heap()->is_in(obj), "sanity check");
437 if (_top == 0) {
438 // This is the first allocation or the initial block got zapped when
439 // entering a native function. If we have any following blocks they are
440 // not valid anymore.
441 for (JNIHandleBlock* current = _next; current != NULL;
442 current = current->_next) {
443 assert(current->_last == NULL, "only first block should have _last set");
444 assert(current->_free_list == NULL,
445 "only first block should have _free_list set");
446 if (current->_top == 0) {
447 // All blocks after the first clear trailing block are already cleared.
448 #ifdef ASSERT
449 for (current = current->_next; current != NULL; current = current->_next) {
450 assert(current->_top == 0, "trailing blocks must already be cleared");
451 }
452 #endif
453 break;
454 }
455 current->_top = 0;
456 current->zap();
457 }
458 // Clear initial block
459 _free_list = NULL;
460 _allocate_before_rebuild = 0;
461 _last = this;
462 zap();
463 }
464
465 // Try last block
466 if (_last->_top < block_size_in_oops) {
467 oop* handle = (oop*)&(_last->_handles)[_last->_top++];
468 NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, obj);
469 return (jobject) handle;
470 }
471
472 // Try free list
473 if (_free_list != NULL) {
474 oop* handle = (oop*)_free_list;
475 _free_list = (uintptr_t*) untag_free_list(*_free_list);
476 NativeAccess<IS_DEST_UNINITIALIZED>::oop_store(handle, obj);
477 return (jobject) handle;
478 }
479 // Check if unused block follow last
480 if (_last->_next != NULL) {
481 // update last and retry
482 _last = _last->_next;
483 return allocate_handle(caller, obj, alloc_failmode);
484 }
485
486 // No space available, we have to rebuild free list or expand
487 if (_allocate_before_rebuild == 0) {
488 rebuild_free_list(); // updates _allocate_before_rebuild counter
489 } else {
490 _last->_next = JNIHandleBlock::allocate_block(caller, alloc_failmode);
491 if (_last->_next == NULL) {
492 return NULL;
493 }
494 _last = _last->_next;
495 _allocate_before_rebuild--;
496 }
497 return allocate_handle(caller, obj, alloc_failmode); // retry
498 }
499
500 void JNIHandleBlock::rebuild_free_list() {
501 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
502 int free = 0;
503 int blocks = 0;
504 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
505 for (int index = 0; index < current->_top; index++) {
506 uintptr_t* handle = &(current->_handles)[index];
507 if (*handle == 0) {
508 // this handle was cleared out by a delete call, reuse it
509 *handle = _free_list == NULL ? 0 : tag_free_list((uintptr_t)_free_list);
510 _free_list = handle;
511 free++;
512 }
513 }
514 // we should not rebuild free list if there are unused handles at the end
515 assert(current->_top == block_size_in_oops, "just checking");
516 blocks++;
517 }
518 // Heuristic: if more than half of the handles are free we rebuild next time
519 // as well, otherwise we append a corresponding number of new blocks before
520 // attempting a free list rebuild again.
521 int total = blocks * block_size_in_oops;
522 int extra = total - 2*free;
523 if (extra > 0) {
524 // Not as many free handles as we would like - compute number of new blocks to append
525 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
526 }
527 }
528
529
530 bool JNIHandleBlock::contains(jobject handle) const {
531 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
532 }
533
534
535 bool JNIHandleBlock::chain_contains(jobject handle) const {
536 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
537 if (current->contains(handle)) {
538 return true;
539 }
540 }
541 return false;
542 }
543
544
545 size_t JNIHandleBlock::length() const {
546 size_t result = 1;
547 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
548 result++;
549 }
550 return result;
551 }
552
553 class CountJNIHandleClosure: public OopClosure {
554 private:
555 int _count;
556 public:
557 CountJNIHandleClosure(): _count(0) {}
558 virtual void do_oop(oop* ooph) { _count++; }
559 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
560 int count() { return _count; }
561 };
562
563 const size_t JNIHandleBlock::get_number_of_live_handles() {
564 CountJNIHandleClosure counter;
565 oops_do(&counter);
566 return counter.count();
567 }
568
569 // This method is not thread-safe, i.e., must be called while holding a lock on the
570 // structure.
571 size_t JNIHandleBlock::memory_usage() const {
572 return length() * sizeof(JNIHandleBlock);
573 }