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