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