1 /*
2 * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/systemDictionary.hpp"
27 #include "logging/log.hpp"
28 #include "memory/iterator.hpp"
29 #include "oops/oop.inline.hpp"
30 #include "runtime/jniHandles.hpp"
31 #include "runtime/mutexLocker.hpp"
32 #include "runtime/thread.inline.hpp"
33 #include "trace/traceMacros.hpp"
34 #include "utilities/align.hpp"
35 #if INCLUDE_ALL_GCS
36 #include "gc/g1/g1SATBCardTableModRefBS.hpp"
37 #endif
38
39 JNIHandleBlock* JNIHandles::_global_handles = NULL;
40 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
41 oop JNIHandles::_deleted_handle = NULL;
42
43
44 jobject JNIHandles::make_local(oop obj) {
45 if (obj == NULL) {
46 return NULL; // ignore null handles
47 } else {
48 Thread* thread = Thread::current();
49 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
50 assert(!current_thread_in_native(), "must not be in native");
51 return thread->active_handles()->allocate_handle(obj);
52 }
53 }
54
55
56 // optimized versions
57
58 jobject JNIHandles::make_local(Thread* thread, oop obj) {
59 if (obj == NULL) {
60 return NULL; // ignore null handles
61 } else {
62 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
63 assert(thread->is_Java_thread(), "not a Java thread");
64 assert(!current_thread_in_native(), "must not be in native");
65 return thread->active_handles()->allocate_handle(obj);
66 }
67 }
68
69
70 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
71 if (obj == NULL) {
72 return NULL; // ignore null handles
73 } else {
74 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
75 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
76 assert(!current_thread_in_native(), "must not be in native");
77 return thread->active_handles()->allocate_handle(obj);
78 }
79 }
80
81
82 jobject JNIHandles::make_global(Handle obj) {
83 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
84 assert(!current_thread_in_native(), "must not be in native");
85 jobject res = NULL;
86 if (!obj.is_null()) {
87 // ignore null handles
88 MutexLocker ml(JNIGlobalHandle_lock);
89 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
90 res = _global_handles->allocate_handle(obj());
91 } else {
92 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
93 }
94
95 return res;
96 }
97
98
99 jobject JNIHandles::make_weak_global(Handle obj) {
100 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
101 assert(!current_thread_in_native(), "must not be in native");
102 jobject res = NULL;
103 if (!obj.is_null()) {
104 // ignore null handles
105 {
106 MutexLocker ml(JNIGlobalHandle_lock);
107 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
108 res = _weak_global_handles->allocate_handle(obj());
109 }
110 // Add weak tag.
111 assert(is_aligned(res, weak_tag_alignment), "invariant");
112 char* tptr = reinterpret_cast<char*>(res) + weak_tag_value;
113 res = reinterpret_cast<jobject>(tptr);
114 } else {
115 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
116 }
117 return res;
118 }
119
120 template<bool external_guard>
121 oop JNIHandles::resolve_jweak(jweak handle) {
122 assert(is_jweak(handle), "precondition");
123 oop result = jweak_ref(handle);
124 result = guard_value<external_guard>(result);
125 #if INCLUDE_ALL_GCS
126 if (result != NULL && UseG1GC) {
127 G1SATBCardTableModRefBS::enqueue(result);
128 }
129 #endif // INCLUDE_ALL_GCS
130 return result;
131 }
132
133 template oop JNIHandles::resolve_jweak<true>(jweak);
134 template oop JNIHandles::resolve_jweak<false>(jweak);
135
136 bool JNIHandles::is_global_weak_cleared(jweak handle) {
137 assert(is_jweak(handle), "not a weak handle");
138 return guard_value<false>(jweak_ref(handle)) == NULL;
139 }
140
141 void JNIHandles::destroy_global(jobject handle) {
142 if (handle != NULL) {
143 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
144 jobject_ref(handle) = deleted_handle();
145 }
146 }
147
148
149 void JNIHandles::destroy_weak_global(jobject handle) {
150 if (handle != NULL) {
151 jweak_ref(handle) = deleted_handle();
152 }
153 }
154
155
156 void JNIHandles::oops_do(OopClosure* f) {
157 f->do_oop(&_deleted_handle);
158 _global_handles->oops_do(f);
159 }
160
161
162 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
163 _weak_global_handles->weak_oops_do(is_alive, f);
164 }
165
166
167 void JNIHandles::weak_oops_do(OopClosure* f) {
168 AlwaysTrueClosure always_true;
169 weak_oops_do(&always_true, f);
170 }
171
172
173 void JNIHandles::initialize() {
174 _global_handles = JNIHandleBlock::allocate_block();
175 _weak_global_handles = JNIHandleBlock::allocate_block();
176 EXCEPTION_MARK;
177 // We will never reach the CATCH below since Exceptions::_throw will cause
178 // the VM to exit if an exception is thrown during initialization
179 Klass* k = SystemDictionary::Object_klass();
180 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
181 }
182
183
184 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
185 JNIHandleBlock* block = thread->active_handles();
186
187 // Look back past possible native calls to jni_PushLocalFrame.
188 while (block != NULL) {
189 if (block->chain_contains(handle)) {
190 return true;
191 }
192 block = block->pop_frame_link();
193 }
194 return false;
195 }
196
197
198 // Determine if the handle is somewhere in the current thread's stack.
199 // We easily can't isolate any particular stack frame the handle might
200 // come from, so we'll check the whole stack.
201
202 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
203 // If there is no java frame, then this must be top level code, such
204 // as the java command executable, in which case, this type of handle
205 // is not permitted.
206 return (thr->has_last_Java_frame() &&
207 (void*)obj < (void*)thr->stack_base() &&
208 (void*)obj >= (void*)thr->last_Java_sp());
209 }
210
211
212 bool JNIHandles::is_global_handle(jobject handle) {
213 return _global_handles->chain_contains(handle);
214 }
215
216
217 bool JNIHandles::is_weak_global_handle(jobject handle) {
218 return _weak_global_handles->chain_contains(handle);
219 }
220
221 long JNIHandles::global_handle_memory_usage() {
222 return _global_handles->memory_usage();
223 }
224
225 long JNIHandles::weak_global_handle_memory_usage() {
226 return _weak_global_handles->memory_usage();
227 }
228
229
230 class CountHandleClosure: public OopClosure {
231 private:
232 int _count;
233 public:
234 CountHandleClosure(): _count(0) {}
235 virtual void do_oop(oop* ooph) {
236 if (*ooph != JNIHandles::deleted_handle()) {
237 _count++;
238 }
239 }
240 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
241 int count() { return _count; }
242 };
243
244 // We assume this is called at a safepoint: no lock is needed.
245 void JNIHandles::print_on(outputStream* st) {
246 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
247 assert(_global_handles != NULL && _weak_global_handles != NULL,
248 "JNIHandles not initialized");
249
250 CountHandleClosure global_handle_count;
251 oops_do(&global_handle_count);
252 weak_oops_do(&global_handle_count);
253
254 st->print_cr("JNI global references: %d", global_handle_count.count());
255 st->cr();
256 st->flush();
257 }
258
259 class VerifyHandleClosure: public OopClosure {
260 public:
261 virtual void do_oop(oop* root) {
262 (*root)->verify();
263 }
264 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
265 };
266
267 void JNIHandles::verify() {
268 VerifyHandleClosure verify_handle;
269
270 oops_do(&verify_handle);
271 weak_oops_do(&verify_handle);
272 }
273
274 // This method is implemented here to avoid circular includes between
275 // jniHandles.hpp and thread.hpp.
276 bool JNIHandles::current_thread_in_native() {
277 Thread* thread = Thread::current();
278 return (thread->is_Java_thread() &&
279 JavaThread::current()->thread_state() == _thread_in_native);
280 }
281
282
283 void jni_handles_init() {
284 JNIHandles::initialize();
285 }
286
287
288 int JNIHandleBlock::_blocks_allocated = 0;
289 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
290 #ifndef PRODUCT
291 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
292 #endif
293
294
295 #ifdef ASSERT
296 void JNIHandleBlock::zap() {
297 // Zap block values
298 _top = 0;
299 for (int index = 0; index < block_size_in_oops; index++) {
300 _handles[index] = NULL;
301 }
302 }
303 #endif // ASSERT
304
305 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
306 assert(thread == NULL || thread == Thread::current(), "sanity check");
307 JNIHandleBlock* block;
308 // Check the thread-local free list for a block so we don't
309 // have to acquire a mutex.
310 if (thread != NULL && thread->free_handle_block() != NULL) {
311 block = thread->free_handle_block();
312 thread->set_free_handle_block(block->_next);
313 }
314 else {
315 // locking with safepoint checking introduces a potential deadlock:
316 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
317 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
318 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
319 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
320 Mutex::_no_safepoint_check_flag);
321 if (_block_free_list == NULL) {
322 // Allocate new block
323 block = new JNIHandleBlock();
324 _blocks_allocated++;
325 block->zap();
326 #ifndef PRODUCT
327 // Link new block to list of all allocated blocks
328 block->_block_list_link = _block_list;
329 _block_list = block;
330 #endif
331 } else {
332 // Get block from free list
333 block = _block_free_list;
334 _block_free_list = _block_free_list->_next;
335 }
336 }
337 block->_top = 0;
338 block->_next = NULL;
339 block->_pop_frame_link = NULL;
340 block->_planned_capacity = block_size_in_oops;
341 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
342 debug_only(block->_last = NULL);
343 debug_only(block->_free_list = NULL);
344 debug_only(block->_allocate_before_rebuild = -1);
345 return block;
346 }
347
348
349 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
350 assert(thread == NULL || thread == Thread::current(), "sanity check");
351 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
352 // Put returned block at the beginning of the thread-local free list.
353 // Note that if thread == NULL, we use it as an implicit argument that
354 // we _don't_ want the block to be kept on the free_handle_block.
355 // See for instance JavaThread::exit().
356 if (thread != NULL ) {
357 block->zap();
358 JNIHandleBlock* freelist = thread->free_handle_block();
359 block->_pop_frame_link = NULL;
360 thread->set_free_handle_block(block);
361
362 // Add original freelist to end of chain
363 if ( freelist != NULL ) {
364 while ( block->_next != NULL ) block = block->_next;
365 block->_next = freelist;
366 }
367 block = NULL;
368 }
369 if (block != NULL) {
370 // Return blocks to free list
371 // locking with safepoint checking introduces a potential deadlock:
372 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
373 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
374 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
375 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
376 Mutex::_no_safepoint_check_flag);
377 while (block != NULL) {
378 block->zap();
379 JNIHandleBlock* next = block->_next;
380 block->_next = _block_free_list;
381 _block_free_list = block;
382 block = next;
383 }
384 }
385 if (pop_frame_link != NULL) {
386 // As a sanity check we release blocks pointed to by the pop_frame_link.
387 // This should never happen (only if PopLocalFrame is not called the
388 // correct number of times).
389 release_block(pop_frame_link, thread);
390 }
391 }
392
393
394 void JNIHandleBlock::oops_do(OopClosure* f) {
395 JNIHandleBlock* current_chain = this;
396 // Iterate over chain of blocks, followed by chains linked through the
397 // pop frame links.
398 while (current_chain != NULL) {
399 for (JNIHandleBlock* current = current_chain; current != NULL;
400 current = current->_next) {
401 assert(current == current_chain || current->pop_frame_link() == NULL,
402 "only blocks first in chain should have pop frame link set");
403 for (int index = 0; index < current->_top; index++) {
404 oop* root = &(current->_handles)[index];
405 oop value = *root;
406 // traverse heap pointers only, not deleted handles or free list
407 // pointers
408 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
409 f->do_oop(root);
410 }
411 }
412 // the next handle block is valid only if current block is full
413 if (current->_top < block_size_in_oops) {
414 break;
415 }
416 }
417 current_chain = current_chain->pop_frame_link();
418 }
419 }
420
421
422 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
423 OopClosure* f) {
424 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
425 assert(current->pop_frame_link() == NULL,
426 "blocks holding weak global JNI handles should not have pop frame link set");
427 for (int index = 0; index < current->_top; index++) {
428 oop* root = &(current->_handles)[index];
429 oop value = *root;
430 // traverse heap pointers only, not deleted handles or free list pointers
431 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
432 if (is_alive->do_object_b(value)) {
433 // The weakly referenced object is alive, update pointer
434 f->do_oop(root);
435 } else {
436 // The weakly referenced object is not alive, clear the reference by storing NULL
437 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
438 *root = NULL;
439 }
440 }
441 }
442 // the next handle block is valid only if current block is full
443 if (current->_top < block_size_in_oops) {
444 break;
445 }
446 }
447 }
448
449
450 jobject JNIHandleBlock::allocate_handle(oop obj) {
451 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
452 if (_top == 0) {
453 // This is the first allocation or the initial block got zapped when
454 // entering a native function. If we have any following blocks they are
455 // not valid anymore.
456 for (JNIHandleBlock* current = _next; current != NULL;
457 current = current->_next) {
458 assert(current->_last == NULL, "only first block should have _last set");
459 assert(current->_free_list == NULL,
460 "only first block should have _free_list set");
461 if (current->_top == 0) {
462 // All blocks after the first clear trailing block are already cleared.
463 #ifdef ASSERT
464 for (current = current->_next; current != NULL; current = current->_next) {
465 assert(current->_top == 0, "trailing blocks must already be cleared");
466 }
467 #endif
468 break;
469 }
470 current->_top = 0;
471 current->zap();
472 }
473 // Clear initial block
474 _free_list = NULL;
475 _allocate_before_rebuild = 0;
476 _last = this;
477 zap();
478 }
479
480 // Try last block
481 if (_last->_top < block_size_in_oops) {
482 oop* handle = &(_last->_handles)[_last->_top++];
483 *handle = obj;
484 return (jobject) handle;
485 }
486
487 // Try free list
488 if (_free_list != NULL) {
489 oop* handle = _free_list;
490 _free_list = (oop*) *_free_list;
491 *handle = obj;
492 return (jobject) handle;
493 }
494 // Check if unused block follow last
495 if (_last->_next != NULL) {
496 // update last and retry
497 _last = _last->_next;
498 return allocate_handle(obj);
499 }
500
501 // No space available, we have to rebuild free list or expand
502 if (_allocate_before_rebuild == 0) {
503 rebuild_free_list(); // updates _allocate_before_rebuild counter
504 } else {
505 // Append new block
506 Thread* thread = Thread::current();
507 Handle obj_handle(thread, obj);
508 // This can block, so we need to preserve obj across call.
509 _last->_next = JNIHandleBlock::allocate_block(thread);
510 _last = _last->_next;
511 _allocate_before_rebuild--;
512 obj = obj_handle();
513 }
514 return allocate_handle(obj); // retry
515 }
516
517 void JNIHandleBlock::release_handle(jobject h) {
518 if (h != NULL) {
519 assert(chain_contains(h), "does not contain the JNI handle");
520 // Mark the handle as deleted, allocate will reuse it
521 *((oop*)h) = JNIHandles::deleted_handle();
522 }
523 }
524
525
526 void JNIHandleBlock::rebuild_free_list() {
527 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
528 int free = 0;
529 int blocks = 0;
530 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
531 for (int index = 0; index < current->_top; index++) {
532 oop* handle = &(current->_handles)[index];
533 if (*handle == JNIHandles::deleted_handle()) {
534 // this handle was cleared out by a delete call, reuse it
535 *handle = (oop) _free_list;
536 _free_list = handle;
537 free++;
538 }
539 }
540 // we should not rebuild free list if there are unused handles at the end
541 assert(current->_top == block_size_in_oops, "just checking");
542 blocks++;
543 }
544 // Heuristic: if more than half of the handles are free we rebuild next time
545 // as well, otherwise we append a corresponding number of new blocks before
546 // attempting a free list rebuild again.
547 int total = blocks * block_size_in_oops;
548 int extra = total - 2*free;
549 if (extra > 0) {
550 // Not as many free handles as we would like - compute number of new blocks to append
551 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
552 }
553 }
554
555
556 bool JNIHandleBlock::contains(jobject handle) const {
557 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
558 }
559
560
561 bool JNIHandleBlock::chain_contains(jobject handle) const {
562 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
563 if (current->contains(handle)) {
564 return true;
565 }
566 }
567 return false;
568 }
569
570
571 int JNIHandleBlock::length() const {
572 int result = 1;
573 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
574 result++;
575 }
576 return result;
577 }
578
579 const size_t JNIHandleBlock::get_number_of_live_handles() {
580 CountHandleClosure counter;
581 oops_do(&counter);
582 return counter.count();
583 }
584
585 // This method is not thread-safe, i.e., must be called while holding a lock on the
586 // structure.
587 long JNIHandleBlock::memory_usage() const {
588 return length() * sizeof(JNIHandleBlock);
589 }
590
591
592 #ifndef PRODUCT
593
594 bool JNIHandleBlock::any_contains(jobject handle) {
595 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
596 if (current->contains(handle)) {
597 return true;
598 }
599 }
600 return false;
601 }
602
603 void JNIHandleBlock::print_statistics() {
604 int used_blocks = 0;
605 int free_blocks = 0;
606 int used_handles = 0;
607 int free_handles = 0;
608 JNIHandleBlock* block = _block_list;
609 while (block != NULL) {
610 if (block->_top > 0) {
611 used_blocks++;
612 } else {
613 free_blocks++;
614 }
615 used_handles += block->_top;
616 free_handles += (block_size_in_oops - block->_top);
617 block = block->_block_list_link;
618 }
619 tty->print_cr("JNIHandleBlocks statistics");
620 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
621 tty->print_cr("- blocks in use: %d", used_blocks);
622 tty->print_cr("- blocks free: %d", free_blocks);
623 tty->print_cr("- handles in use: %d", used_handles);
624 tty->print_cr("- handles free: %d", free_handles);
625 }
626
627 #endif