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 "memory/iterator.hpp"
28 #include "oops/oop.inline.hpp"
29 #include "prims/jvmtiExport.hpp"
30 #include "runtime/jniHandles.hpp"
31 #include "runtime/mutexLocker.hpp"
32 #include "runtime/thread.inline.hpp"
33 #if INCLUDE_ALL_GCS
34 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
35 #endif
36
37 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
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 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 || (UseShenandoahGC && ShenandoahSATBBarrier))) {
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 void JNIHandles::destroy_weak_global(jobject handle) {
137 if (handle != NULL) {
138 jweak_ref(handle) = deleted_handle();
139 }
140 }
141
142
143 void JNIHandles::oops_do(OopClosure* f) {
144 f->do_oop(&_deleted_handle);
145 _global_handles->oops_do(f);
146 }
147
148
149 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
150 _weak_global_handles->weak_oops_do(is_alive, f);
151 }
152
153
154 void JNIHandles::weak_oops_do(OopClosure* f) {
155 AlwaysTrueClosure always_true;
156 weak_oops_do(&always_true, f);
157 }
158
159
160 void JNIHandles::initialize() {
161 _global_handles = JNIHandleBlock::allocate_block();
162 _weak_global_handles = JNIHandleBlock::allocate_block();
163 EXCEPTION_MARK;
164 // We will never reach the CATCH below since Exceptions::_throw will cause
165 // the VM to exit if an exception is thrown during initialization
166 Klass* k = SystemDictionary::Object_klass();
167 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
168 }
169
170
171 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
172 JNIHandleBlock* block = thread->active_handles();
173
174 // Look back past possible native calls to jni_PushLocalFrame.
175 while (block != NULL) {
176 if (block->chain_contains(handle)) {
177 return true;
178 }
179 block = block->pop_frame_link();
180 }
181 return false;
182 }
183
184
185 // Determine if the handle is somewhere in the current thread's stack.
186 // We easily can't isolate any particular stack frame the handle might
187 // come from, so we'll check the whole stack.
188
189 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
190 // If there is no java frame, then this must be top level code, such
191 // as the java command executable, in which case, this type of handle
192 // is not permitted.
193 return (thr->has_last_Java_frame() &&
194 (void*)obj < (void*)thr->stack_base() &&
195 (void*)obj >= (void*)thr->last_Java_sp());
196 }
197
198
199 bool JNIHandles::is_global_handle(jobject handle) {
200 return _global_handles->chain_contains(handle);
201 }
202
203
204 bool JNIHandles::is_weak_global_handle(jobject handle) {
205 return _weak_global_handles->chain_contains(handle);
206 }
207
208 long JNIHandles::global_handle_memory_usage() {
209 return _global_handles->memory_usage();
210 }
211
212 long JNIHandles::weak_global_handle_memory_usage() {
213 return _weak_global_handles->memory_usage();
214 }
215
216
217 class CountHandleClosure: public OopClosure {
218 private:
219 int _count;
220 public:
221 CountHandleClosure(): _count(0) {}
222 virtual void do_oop(oop* ooph) {
223 if (*ooph != JNIHandles::deleted_handle()) {
224 _count++;
225 }
226 }
227 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
228 int count() { return _count; }
229 };
230
231 // We assume this is called at a safepoint: no lock is needed.
232 void JNIHandles::print_on(outputStream* st) {
233 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
234 assert(_global_handles != NULL && _weak_global_handles != NULL,
235 "JNIHandles not initialized");
236
237 CountHandleClosure global_handle_count;
238 oops_do(&global_handle_count);
239 weak_oops_do(&global_handle_count);
240
241 st->print_cr("JNI global references: %d", global_handle_count.count());
242 st->cr();
243 st->flush();
244 }
245
246 class VerifyHandleClosure: public OopClosure {
247 public:
248 virtual void do_oop(oop* root) {
249 (*root)->verify();
250 }
251 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
252 };
253
254 void JNIHandles::verify() {
255 VerifyHandleClosure verify_handle;
256
257 oops_do(&verify_handle);
258 weak_oops_do(&verify_handle);
259 }
260
261
262
263 void jni_handles_init() {
264 JNIHandles::initialize();
265 }
266
267
268 int JNIHandleBlock::_blocks_allocated = 0;
269 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
270 #ifndef PRODUCT
271 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
272 #endif
273
274
275 void JNIHandleBlock::zap() {
276 // Zap block values
277 _top = 0;
278 for (int index = 0; index < block_size_in_oops; index++) {
279 _handles[index] = badJNIHandle;
280 }
281 }
282
283 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
284 assert(thread == NULL || thread == Thread::current(), "sanity check");
285 JNIHandleBlock* block;
286 // Check the thread-local free list for a block so we don't
287 // have to acquire a mutex.
288 if (thread != NULL && thread->free_handle_block() != NULL) {
289 block = thread->free_handle_block();
290 thread->set_free_handle_block(block->_next);
291 }
292 else {
293 // locking with safepoint checking introduces a potential deadlock:
294 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
295 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
296 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
297 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
298 Mutex::_no_safepoint_check_flag);
299 if (_block_free_list == NULL) {
300 // Allocate new block
301 block = new JNIHandleBlock();
302 _blocks_allocated++;
303 if (TraceJNIHandleAllocation) {
304 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
305 block, _blocks_allocated);
306 }
307 if (ZapJNIHandleArea) block->zap();
308 #ifndef PRODUCT
309 // Link new block to list of all allocated blocks
310 block->_block_list_link = _block_list;
311 _block_list = block;
312 #endif
313 } else {
314 // Get block from free list
315 block = _block_free_list;
316 _block_free_list = _block_free_list->_next;
317 }
318 }
319 block->_top = 0;
320 block->_next = NULL;
321 block->_pop_frame_link = NULL;
322 block->_planned_capacity = block_size_in_oops;
323 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
324 debug_only(block->_last = NULL);
325 debug_only(block->_free_list = NULL);
326 debug_only(block->_allocate_before_rebuild = -1);
327 return block;
328 }
329
330
331 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
332 assert(thread == NULL || thread == Thread::current(), "sanity check");
333 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
334 // Put returned block at the beginning of the thread-local free list.
335 // Note that if thread == NULL, we use it as an implicit argument that
336 // we _don't_ want the block to be kept on the free_handle_block.
337 // See for instance JavaThread::exit().
338 if (thread != NULL ) {
339 if (ZapJNIHandleArea) block->zap();
340 JNIHandleBlock* freelist = thread->free_handle_block();
341 block->_pop_frame_link = NULL;
342 thread->set_free_handle_block(block);
343
344 // Add original freelist to end of chain
345 if ( freelist != NULL ) {
346 while ( block->_next != NULL ) block = block->_next;
347 block->_next = freelist;
348 }
349 block = NULL;
350 }
351 if (block != NULL) {
352 // Return blocks to free list
353 // locking with safepoint checking introduces a potential deadlock:
354 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
355 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
356 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
357 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
358 Mutex::_no_safepoint_check_flag);
359 while (block != NULL) {
360 if (ZapJNIHandleArea) block->zap();
361 JNIHandleBlock* next = block->_next;
362 block->_next = _block_free_list;
363 _block_free_list = block;
364 block = next;
365 }
366 }
367 if (pop_frame_link != NULL) {
368 // As a sanity check we release blocks pointed to by the pop_frame_link.
369 // This should never happen (only if PopLocalFrame is not called the
370 // correct number of times).
371 release_block(pop_frame_link, thread);
372 }
373 }
374
375
376 void JNIHandleBlock::oops_do(OopClosure* f) {
377 JNIHandleBlock* current_chain = this;
378 // Iterate over chain of blocks, followed by chains linked through the
379 // pop frame links.
380 while (current_chain != NULL) {
381 for (JNIHandleBlock* current = current_chain; current != NULL;
382 current = current->_next) {
383 assert(current == current_chain || current->pop_frame_link() == NULL,
384 "only blocks first in chain should have pop frame link set");
385 for (int index = 0; index < current->_top; index++) {
386 oop* root = &(current->_handles)[index];
387 oop value = *root;
388 // traverse heap pointers only, not deleted handles or free list
389 // pointers
390 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
391 f->do_oop(root);
392 }
393 }
394 // the next handle block is valid only if current block is full
395 if (current->_top < block_size_in_oops) {
396 break;
397 }
398 }
399 current_chain = current_chain->pop_frame_link();
400 }
401 }
402
403
404 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
405 OopClosure* f) {
406 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
407 assert(current->pop_frame_link() == NULL,
408 "blocks holding weak global JNI handles should not have pop frame link set");
409 for (int index = 0; index < current->_top; index++) {
410 oop* root = &(current->_handles)[index];
411 oop value = *root;
412 // traverse heap pointers only, not deleted handles or free list pointers
413 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
414 if (is_alive->do_object_b(value)) {
415 // The weakly referenced object is alive, update pointer
416 f->do_oop(root);
417 } else {
418 // The weakly referenced object is not alive, clear the reference by storing NULL
419 if (TraceReferenceGC) {
420 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
421 }
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 * JVMTI data structures may also contain weak oops. The iteration of them
434 * is placed here so that we don't need to add it to each of the collectors.
435 */
436 JvmtiExport::weak_oops_do(is_alive, f);
437 }
438
439
440 jobject JNIHandleBlock::allocate_handle(oop obj) {
441 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
442 if (_top == 0) {
443 // This is the first allocation or the initial block got zapped when
444 // entering a native function. If we have any following blocks they are
445 // not valid anymore.
446 for (JNIHandleBlock* current = _next; current != NULL;
447 current = current->_next) {
448 assert(current->_last == NULL, "only first block should have _last set");
449 assert(current->_free_list == NULL,
450 "only first block should have _free_list set");
451 current->_top = 0;
452 if (ZapJNIHandleArea) current->zap();
453 }
454 // Clear initial block
455 _free_list = NULL;
456 _allocate_before_rebuild = 0;
457 _last = this;
458 if (ZapJNIHandleArea) zap();
459 }
460
461 // Try last block
462 if (_last->_top < block_size_in_oops) {
463 oop* handle = &(_last->_handles)[_last->_top++];
464 *handle = obj;
465 return (jobject) handle;
466 }
467
468 // Try free list
469 if (_free_list != NULL) {
470 oop* handle = _free_list;
471 _free_list = (oop*) *_free_list;
472 *handle = obj;
473 return (jobject) handle;
474 }
475 // Check if unused block follow last
476 if (_last->_next != NULL) {
477 // update last and retry
478 _last = _last->_next;
479 return allocate_handle(obj);
480 }
481
482 // No space available, we have to rebuild free list or expand
483 if (_allocate_before_rebuild == 0) {
484 rebuild_free_list(); // updates _allocate_before_rebuild counter
485 } else {
486 // Append new block
487 Thread* thread = Thread::current();
488 Handle obj_handle(thread, obj);
489 // This can block, so we need to preserve obj accross call.
490 _last->_next = JNIHandleBlock::allocate_block(thread);
491 _last = _last->_next;
492 _allocate_before_rebuild--;
493 obj = obj_handle();
494 }
495 return allocate_handle(obj); // retry
496 }
497
498
499 void JNIHandleBlock::rebuild_free_list() {
500 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
501 int free = 0;
502 int blocks = 0;
503 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
504 for (int index = 0; index < current->_top; index++) {
505 oop* handle = &(current->_handles)[index];
506 if (*handle == JNIHandles::deleted_handle()) {
507 // this handle was cleared out by a delete call, reuse it
508 *handle = (oop) _free_list;
509 _free_list = handle;
510 free++;
511 }
512 }
513 // we should not rebuild free list if there are unused handles at the end
514 assert(current->_top == block_size_in_oops, "just checking");
515 blocks++;
516 }
517 // Heuristic: if more than half of the handles are free we rebuild next time
518 // as well, otherwise we append a corresponding number of new blocks before
519 // attempting a free list rebuild again.
520 int total = blocks * block_size_in_oops;
521 int extra = total - 2*free;
522 if (extra > 0) {
523 // Not as many free handles as we would like - compute number of new blocks to append
524 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
525 }
526 if (TraceJNIHandleAllocation) {
527 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
528 this, blocks, total-free, free, _allocate_before_rebuild);
529 }
530 }
531
532
533 bool JNIHandleBlock::contains(jobject handle) const {
534 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
535 }
536
537
538 bool JNIHandleBlock::chain_contains(jobject handle) const {
539 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
540 if (current->contains(handle)) {
541 return true;
542 }
543 }
544 return false;
545 }
546
547
548 int JNIHandleBlock::length() const {
549 int result = 1;
550 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
551 result++;
552 }
553 return result;
554 }
555
556 const size_t JNIHandleBlock::get_number_of_live_handles() {
557 CountHandleClosure counter;
558 oops_do(&counter);
559 return counter.count();
560 }
561
562 // This method is not thread-safe, i.e., must be called whule holding a lock on the
563 // structure.
564 long JNIHandleBlock::memory_usage() const {
565 return length() * sizeof(JNIHandleBlock);
566 }
567
568
569 #ifndef PRODUCT
570
571 bool JNIHandleBlock::any_contains(jobject handle) {
572 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
573 if (current->contains(handle)) {
574 return true;
575 }
576 }
577 return false;
578 }
579
580 void JNIHandleBlock::print_statistics() {
581 int used_blocks = 0;
582 int free_blocks = 0;
583 int used_handles = 0;
584 int free_handles = 0;
585 JNIHandleBlock* block = _block_list;
586 while (block != NULL) {
587 if (block->_top > 0) {
588 used_blocks++;
589 } else {
590 free_blocks++;
591 }
592 used_handles += block->_top;
593 free_handles += (block_size_in_oops - block->_top);
594 block = block->_block_list_link;
595 }
596 tty->print_cr("JNIHandleBlocks statistics");
597 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
598 tty->print_cr("- blocks in use: %d", used_blocks);
599 tty->print_cr("- blocks free: %d", free_blocks);
600 tty->print_cr("- handles in use: %d", used_handles);
601 tty->print_cr("- handles free: %d", free_handles);
602 }
603
604 #endif