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