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 "prims/jvmtiExport.hpp"
31 #include "runtime/jniHandles.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/thread.inline.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 void JNIHandles::destroy_global(jobject handle) {
131 if (handle != NULL) {
132 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
133 jobject_ref(handle) = deleted_handle();
134 }
135 }
136
137
138 void JNIHandles::destroy_weak_global(jobject handle) {
139 if (handle != NULL) {
140 jweak_ref(handle) = deleted_handle();
141 }
142 }
143
144
145 void JNIHandles::oops_do(OopClosure* f) {
146 f->do_oop(&_deleted_handle);
147 _global_handles->oops_do(f);
148 }
149
150
151 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
152 _weak_global_handles->weak_oops_do(is_alive, f);
153 }
154
155
156 void JNIHandles::weak_oops_do(OopClosure* f) {
157 AlwaysTrueClosure always_true;
158 weak_oops_do(&always_true, f);
159 }
160
161
162 void JNIHandles::initialize() {
163 _global_handles = JNIHandleBlock::allocate_block();
164 _weak_global_handles = JNIHandleBlock::allocate_block();
165 EXCEPTION_MARK;
166 // We will never reach the CATCH below since Exceptions::_throw will cause
167 // the VM to exit if an exception is thrown during initialization
168 Klass* k = SystemDictionary::Object_klass();
169 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
170 }
171
172
173 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
174 JNIHandleBlock* block = thread->active_handles();
175
176 // Look back past possible native calls to jni_PushLocalFrame.
177 while (block != NULL) {
178 if (block->chain_contains(handle)) {
179 return true;
180 }
181 block = block->pop_frame_link();
182 }
183 return false;
184 }
185
186
187 // Determine if the handle is somewhere in the current thread's stack.
188 // We easily can't isolate any particular stack frame the handle might
189 // come from, so we'll check the whole stack.
190
191 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
192 // If there is no java frame, then this must be top level code, such
193 // as the java command executable, in which case, this type of handle
194 // is not permitted.
195 return (thr->has_last_Java_frame() &&
196 (void*)obj < (void*)thr->stack_base() &&
197 (void*)obj >= (void*)thr->last_Java_sp());
198 }
199
200
201 bool JNIHandles::is_global_handle(jobject handle) {
202 return _global_handles->chain_contains(handle);
203 }
204
205
206 bool JNIHandles::is_weak_global_handle(jobject handle) {
207 return _weak_global_handles->chain_contains(handle);
208 }
209
210 long JNIHandles::global_handle_memory_usage() {
211 return _global_handles->memory_usage();
212 }
213
214 long JNIHandles::weak_global_handle_memory_usage() {
215 return _weak_global_handles->memory_usage();
216 }
217
218
219 class CountHandleClosure: public OopClosure {
220 private:
221 int _count;
222 public:
223 CountHandleClosure(): _count(0) {}
224 virtual void do_oop(oop* ooph) {
225 if (*ooph != JNIHandles::deleted_handle()) {
226 _count++;
227 }
228 }
229 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
230 int count() { return _count; }
231 };
232
233 // We assume this is called at a safepoint: no lock is needed.
234 void JNIHandles::print_on(outputStream* st) {
235 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
236 assert(_global_handles != NULL && _weak_global_handles != NULL,
237 "JNIHandles not initialized");
238
239 CountHandleClosure global_handle_count;
240 oops_do(&global_handle_count);
241 weak_oops_do(&global_handle_count);
242
243 st->print_cr("JNI global references: %d", global_handle_count.count());
244 st->cr();
245 st->flush();
246 }
247
248 class VerifyHandleClosure: public OopClosure {
249 public:
250 virtual void do_oop(oop* root) {
251 (*root)->verify();
252 }
253 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
254 };
255
256 void JNIHandles::verify() {
257 VerifyHandleClosure verify_handle;
258
259 oops_do(&verify_handle);
260 weak_oops_do(&verify_handle);
261 }
262
263
264
265 void jni_handles_init() {
266 JNIHandles::initialize();
267 }
268
269
270 int JNIHandleBlock::_blocks_allocated = 0;
271 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
272 #ifndef PRODUCT
273 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
274 #endif
275
276
277 void JNIHandleBlock::zap() {
278 // Zap block values
279 _top = 0;
280 for (int index = 0; index < block_size_in_oops; index++) {
281 _handles[index] = badJNIHandle;
282 }
283 }
284
285 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
286 assert(thread == NULL || thread == Thread::current(), "sanity check");
287 JNIHandleBlock* block;
288 // Check the thread-local free list for a block so we don't
289 // have to acquire a mutex.
290 if (thread != NULL && thread->free_handle_block() != NULL) {
291 block = thread->free_handle_block();
292 thread->set_free_handle_block(block->_next);
293 }
294 else {
295 // locking with safepoint checking introduces a potential deadlock:
296 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
297 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
298 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
299 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
300 Mutex::_no_safepoint_check_flag);
301 if (_block_free_list == NULL) {
302 // Allocate new block
303 block = new JNIHandleBlock();
304 _blocks_allocated++;
305 if (ZapJNIHandleArea) block->zap();
306 #ifndef PRODUCT
307 // Link new block to list of all allocated blocks
308 block->_block_list_link = _block_list;
309 _block_list = block;
310 #endif
311 } else {
312 // Get block from free list
313 block = _block_free_list;
314 _block_free_list = _block_free_list->_next;
315 }
316 }
317 block->_top = 0;
318 block->_next = NULL;
319 block->_pop_frame_link = NULL;
320 block->_planned_capacity = block_size_in_oops;
321 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
322 debug_only(block->_last = NULL);
323 debug_only(block->_free_list = NULL);
324 debug_only(block->_allocate_before_rebuild = -1);
325 return block;
326 }
327
328
329 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
330 assert(thread == NULL || thread == Thread::current(), "sanity check");
331 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
332 // Put returned block at the beginning of the thread-local free list.
333 // Note that if thread == NULL, we use it as an implicit argument that
334 // we _don't_ want the block to be kept on the free_handle_block.
335 // See for instance JavaThread::exit().
336 if (thread != NULL ) {
337 if (ZapJNIHandleArea) block->zap();
338 JNIHandleBlock* freelist = thread->free_handle_block();
339 block->_pop_frame_link = NULL;
340 thread->set_free_handle_block(block);
341
342 // Add original freelist to end of chain
343 if ( freelist != NULL ) {
344 while ( block->_next != NULL ) block = block->_next;
345 block->_next = freelist;
346 }
347 block = NULL;
348 }
349 if (block != NULL) {
350 // Return blocks to free list
351 // locking with safepoint checking introduces a potential deadlock:
352 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
353 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
354 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
355 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
356 Mutex::_no_safepoint_check_flag);
357 while (block != NULL) {
358 if (ZapJNIHandleArea) block->zap();
359 JNIHandleBlock* next = block->_next;
360 block->_next = _block_free_list;
361 _block_free_list = block;
362 block = next;
363 }
364 }
365 if (pop_frame_link != NULL) {
366 // As a sanity check we release blocks pointed to by the pop_frame_link.
367 // This should never happen (only if PopLocalFrame is not called the
368 // correct number of times).
369 release_block(pop_frame_link, thread);
370 }
371 }
372
373
374 void JNIHandleBlock::oops_do(OopClosure* f) {
375 JNIHandleBlock* current_chain = this;
376 // Iterate over chain of blocks, followed by chains linked through the
377 // pop frame links.
378 while (current_chain != NULL) {
379 for (JNIHandleBlock* current = current_chain; current != NULL;
380 current = current->_next) {
381 assert(current == current_chain || current->pop_frame_link() == NULL,
382 "only blocks first in chain should have pop frame link set");
383 for (int index = 0; index < current->_top; index++) {
384 oop* root = &(current->_handles)[index];
385 oop value = *root;
386 // traverse heap pointers only, not deleted handles or free list
387 // pointers
388 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
389 f->do_oop(root);
390 }
391 }
392 // the next handle block is valid only if current block is full
393 if (current->_top < block_size_in_oops) {
394 break;
395 }
396 }
397 current_chain = current_chain->pop_frame_link();
398 }
399 }
400
401
402 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
403 OopClosure* f) {
404 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
405 assert(current->pop_frame_link() == NULL,
406 "blocks holding weak global JNI handles should not have pop frame link set");
407 for (int index = 0; index < current->_top; index++) {
408 oop* root = &(current->_handles)[index];
409 oop value = *root;
410 // traverse heap pointers only, not deleted handles or free list pointers
411 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
412 if (is_alive->do_object_b(value)) {
413 // The weakly referenced object is alive, update pointer
414 f->do_oop(root);
415 } else {
416 // The weakly referenced object is not alive, clear the reference by storing NULL
417 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
418 *root = NULL;
419 }
420 }
421 }
422 // the next handle block is valid only if current block is full
423 if (current->_top < block_size_in_oops) {
424 break;
425 }
426 }
427
428 /*
429 * JVMTI data structures may also contain weak oops. The iteration of them
430 * is placed here so that we don't need to add it to each of the collectors.
431 */
432 JvmtiExport::weak_oops_do(is_alive, f);
433 }
434
435
436 jobject JNIHandleBlock::allocate_handle(oop obj) {
437 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
438 if (_top == 0) {
439 // This is the first allocation or the initial block got zapped when
440 // entering a native function. If we have any following blocks they are
441 // not valid anymore.
442 for (JNIHandleBlock* current = _next; current != NULL;
443 current = current->_next) {
444 assert(current->_last == NULL, "only first block should have _last set");
445 assert(current->_free_list == NULL,
446 "only first block should have _free_list set");
447 if (current->_top == 0) {
448 // All blocks after the first clear trailing block are already cleared.
449 #ifdef ASSERT
450 for ( ; current != NULL; current = current->_next) {
451 assert(current->_top == 0, "trailing blocks must already be cleared");
452 }
453 #endif
454 break;
455 }
456 current->_top = 0;
457 if (ZapJNIHandleArea) current->zap();
458 }
459 // Clear initial block
460 _free_list = NULL;
461 _allocate_before_rebuild = 0;
462 _last = this;
463 if (ZapJNIHandleArea) zap();
464 }
465
466 // Try last block
467 if (_last->_top < block_size_in_oops) {
468 oop* handle = &(_last->_handles)[_last->_top++];
469 *handle = obj;
470 return (jobject) handle;
471 }
472
473 // Try free list
474 if (_free_list != NULL) {
475 oop* handle = _free_list;
476 _free_list = (oop*) *_free_list;
477 *handle = obj;
478 return (jobject) handle;
479 }
480 // Check if unused block follow last
481 if (_last->_next != NULL) {
482 // update last and retry
483 _last = _last->_next;
484 return allocate_handle(obj);
485 }
486
487 // No space available, we have to rebuild free list or expand
488 if (_allocate_before_rebuild == 0) {
489 rebuild_free_list(); // updates _allocate_before_rebuild counter
490 } else {
491 // Append new block
492 Thread* thread = Thread::current();
493 Handle obj_handle(thread, obj);
494 // This can block, so we need to preserve obj across call.
495 _last->_next = JNIHandleBlock::allocate_block(thread);
496 _last = _last->_next;
497 _allocate_before_rebuild--;
498 obj = obj_handle();
499 }
500 return allocate_handle(obj); // retry
501 }
502
503 void JNIHandleBlock::release_handle(jobject h) {
504 if (h != NULL) {
505 assert(chain_contains(h), "does not contain the JNI handle");
506 // Mark the handle as deleted, allocate will reuse it
507 *((oop*)h) = JNIHandles::deleted_handle();
508 }
509 }
510
511
512 void JNIHandleBlock::rebuild_free_list() {
513 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
514 int free = 0;
515 int blocks = 0;
516 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
517 for (int index = 0; index < current->_top; index++) {
518 oop* handle = &(current->_handles)[index];
519 if (*handle == JNIHandles::deleted_handle()) {
520 // this handle was cleared out by a delete call, reuse it
521 *handle = (oop) _free_list;
522 _free_list = handle;
523 free++;
524 }
525 }
526 // we should not rebuild free list if there are unused handles at the end
527 assert(current->_top == block_size_in_oops, "just checking");
528 blocks++;
529 }
530 // Heuristic: if more than half of the handles are free we rebuild next time
531 // as well, otherwise we append a corresponding number of new blocks before
532 // attempting a free list rebuild again.
533 int total = blocks * block_size_in_oops;
534 int extra = total - 2*free;
535 if (extra > 0) {
536 // Not as many free handles as we would like - compute number of new blocks to append
537 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
538 }
539 }
540
541
542 bool JNIHandleBlock::contains(jobject handle) const {
543 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
544 }
545
546
547 bool JNIHandleBlock::chain_contains(jobject handle) const {
548 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
549 if (current->contains(handle)) {
550 return true;
551 }
552 }
553 return false;
554 }
555
556
557 int JNIHandleBlock::length() const {
558 int result = 1;
559 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
560 result++;
561 }
562 return result;
563 }
564
565 const size_t JNIHandleBlock::get_number_of_live_handles() {
566 CountHandleClosure counter;
567 oops_do(&counter);
568 return counter.count();
569 }
570
571 // This method is not thread-safe, i.e., must be called while holding a lock on the
572 // structure.
573 long JNIHandleBlock::memory_usage() const {
574 return length() * sizeof(JNIHandleBlock);
575 }
576
577
578 #ifndef PRODUCT
579
580 bool JNIHandleBlock::any_contains(jobject handle) {
581 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
582 if (current->contains(handle)) {
583 return true;
584 }
585 }
586 return false;
587 }
588
589 void JNIHandleBlock::print_statistics() {
590 int used_blocks = 0;
591 int free_blocks = 0;
592 int used_handles = 0;
593 int free_handles = 0;
594 JNIHandleBlock* block = _block_list;
595 while (block != NULL) {
596 if (block->_top > 0) {
597 used_blocks++;
598 } else {
599 free_blocks++;
600 }
601 used_handles += block->_top;
602 free_handles += (block_size_in_oops - block->_top);
603 block = block->_block_list_link;
604 }
605 tty->print_cr("JNIHandleBlocks statistics");
606 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
607 tty->print_cr("- blocks in use: %d", used_blocks);
608 tty->print_cr("- blocks free: %d", free_blocks);
609 tty->print_cr("- handles in use: %d", used_handles);
610 tty->print_cr("- handles free: %d", free_handles);
611 }
612
613 #endif