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
36 JNIHandleBlock* JNIHandles::_global_handles = NULL;
37 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
38 oop JNIHandles::_deleted_handle = NULL;
39
40
41 jobject JNIHandles::make_local(oop obj) {
42 if (obj == NULL) {
43 return NULL; // ignore null handles
44 } else {
45 Thread* thread = Thread::current();
46 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
47 return thread->active_handles()->allocate_handle(obj);
48 }
49 }
50
51
52 // optimized versions
53
54 jobject JNIHandles::make_local(Thread* thread, oop obj) {
55 if (obj == NULL) {
56 return NULL; // ignore null handles
57 } else {
58 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
59 return thread->active_handles()->allocate_handle(obj);
60 }
61 }
62
63
64 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
65 if (obj == NULL) {
66 return NULL; // ignore null handles
67 } else {
68 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
69 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
70 return thread->active_handles()->allocate_handle(obj);
71 }
72 }
73
74
75 jobject JNIHandles::make_global(Handle obj) {
76 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
77 jobject res = NULL;
78 if (!obj.is_null()) {
79 // ignore null handles
80 MutexLocker ml(JNIGlobalHandle_lock);
81 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
82 res = _global_handles->allocate_handle(obj());
83 } else {
84 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
85 }
86
87 return res;
88 }
89
90
91 jobject JNIHandles::make_weak_global(Handle obj) {
92 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
93 jobject res = NULL;
94 if (!obj.is_null()) {
95 // ignore null handles
96 {
97 MutexLocker ml(JNIGlobalHandle_lock);
98 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
99 res = _weak_global_handles->allocate_handle(obj());
100 }
101 // Add weak tag.
102 assert(is_aligned(res, weak_tag_alignment), "invariant");
103 char* tptr = reinterpret_cast<char*>(res) + weak_tag_value;
104 res = reinterpret_cast<jobject>(tptr);
105 } else {
106 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
107 }
108 return res;
109 }
110
111 template<bool external_guard>
112 oop JNIHandles::resolve_jweak(jweak handle) {
113 assert(is_jweak(handle), "precondition");
114 oop result = jweak_ref(handle);
115 result = guard_value<external_guard>(result);
116 #if INCLUDE_ALL_GCS
117 oopDesc::bs()->keep_alive_barrier(result);
118 #endif
119 return result;
120 }
121
122 template oop JNIHandles::resolve_jweak<true>(jweak);
123 template oop JNIHandles::resolve_jweak<false>(jweak);
124
125 void JNIHandles::destroy_global(jobject handle) {
126 if (handle != NULL) {
127 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
128 jobject_ref(handle) = deleted_handle();
129 }
130 }
131
132
133 void JNIHandles::destroy_weak_global(jobject handle) {
134 if (handle != NULL) {
135 jweak_ref(handle) = deleted_handle();
136 }
137 }
138
139
140 void JNIHandles::oops_do(OopClosure* f) {
141 f->do_oop(&_deleted_handle);
142 _global_handles->oops_do(f);
143 }
144
145
146 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
147 _weak_global_handles->weak_oops_do(is_alive, f);
148 }
149
150
151 void JNIHandles::weak_oops_do(OopClosure* f) {
152 AlwaysTrueClosure always_true;
153 weak_oops_do(&always_true, f);
154 }
155
156
157 void JNIHandles::initialize() {
158 _global_handles = JNIHandleBlock::allocate_block();
159 _weak_global_handles = JNIHandleBlock::allocate_block();
160 EXCEPTION_MARK;
161 // We will never reach the CATCH below since Exceptions::_throw will cause
162 // the VM to exit if an exception is thrown during initialization
163 Klass* k = SystemDictionary::Object_klass();
164 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
165 }
166
167
168 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
169 JNIHandleBlock* block = thread->active_handles();
170
171 // Look back past possible native calls to jni_PushLocalFrame.
172 while (block != NULL) {
173 if (block->chain_contains(handle)) {
174 return true;
175 }
176 block = block->pop_frame_link();
177 }
178 return false;
179 }
180
181
182 // Determine if the handle is somewhere in the current thread's stack.
183 // We easily can't isolate any particular stack frame the handle might
184 // come from, so we'll check the whole stack.
185
186 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
187 // If there is no java frame, then this must be top level code, such
188 // as the java command executable, in which case, this type of handle
189 // is not permitted.
190 return (thr->has_last_Java_frame() &&
191 (void*)obj < (void*)thr->stack_base() &&
192 (void*)obj >= (void*)thr->last_Java_sp());
193 }
194
195
196 bool JNIHandles::is_global_handle(jobject handle) {
197 return _global_handles->chain_contains(handle);
198 }
199
200
201 bool JNIHandles::is_weak_global_handle(jobject handle) {
202 return _weak_global_handles->chain_contains(handle);
203 }
204
205 long JNIHandles::global_handle_memory_usage() {
206 return _global_handles->memory_usage();
207 }
208
209 long JNIHandles::weak_global_handle_memory_usage() {
210 return _weak_global_handles->memory_usage();
211 }
212
213
214 class CountHandleClosure: public OopClosure {
215 private:
216 int _count;
217 public:
218 CountHandleClosure(): _count(0) {}
219 virtual void do_oop(oop* ooph) {
220 if (! oopDesc::equals(*ooph, JNIHandles::deleted_handle())) {
221 _count++;
222 }
223 }
224 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
225 int count() { return _count; }
226 };
227
228 // We assume this is called at a safepoint: no lock is needed.
229 void JNIHandles::print_on(outputStream* st) {
230 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
231 assert(_global_handles != NULL && _weak_global_handles != NULL,
232 "JNIHandles not initialized");
233
234 CountHandleClosure global_handle_count;
235 oops_do(&global_handle_count);
236 weak_oops_do(&global_handle_count);
237
238 st->print_cr("JNI global references: %d", global_handle_count.count());
239 st->cr();
240 st->flush();
241 }
242
243 class VerifyHandleClosure: public OopClosure {
244 public:
245 virtual void do_oop(oop* root) {
246 (*root)->verify();
247 }
248 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
249 };
250
251 void JNIHandles::verify() {
252 VerifyHandleClosure verify_handle;
253
254 oops_do(&verify_handle);
255 weak_oops_do(&verify_handle);
256 }
257
258
259
260 void jni_handles_init() {
261 JNIHandles::initialize();
262 }
263
264
265 int JNIHandleBlock::_blocks_allocated = 0;
266 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
267 #ifndef PRODUCT
268 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
269 #endif
270
271
272 void JNIHandleBlock::zap() {
273 // Zap block values
274 _top = 0;
275 for (int index = 0; index < block_size_in_oops; index++) {
276 _handles[index] = badJNIHandle;
277 }
278 }
279
280 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
281 assert(thread == NULL || thread == Thread::current(), "sanity check");
282 JNIHandleBlock* block;
283 // Check the thread-local free list for a block so we don't
284 // have to acquire a mutex.
285 if (thread != NULL && thread->free_handle_block() != NULL) {
286 block = thread->free_handle_block();
287 thread->set_free_handle_block(block->_next);
288 }
289 else {
290 // locking with safepoint checking introduces a potential deadlock:
291 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
292 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
293 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
294 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
295 Mutex::_no_safepoint_check_flag);
296 if (_block_free_list == NULL) {
297 // Allocate new block
298 block = new JNIHandleBlock();
299 _blocks_allocated++;
300 if (ZapJNIHandleArea) block->zap();
301 #ifndef PRODUCT
302 // Link new block to list of all allocated blocks
303 block->_block_list_link = _block_list;
304 _block_list = block;
305 #endif
306 } else {
307 // Get block from free list
308 block = _block_free_list;
309 _block_free_list = _block_free_list->_next;
310 }
311 }
312 block->_top = 0;
313 block->_next = NULL;
314 block->_pop_frame_link = NULL;
315 block->_planned_capacity = block_size_in_oops;
316 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
317 debug_only(block->_last = NULL);
318 debug_only(block->_free_list = NULL);
319 debug_only(block->_allocate_before_rebuild = -1);
320 return block;
321 }
322
323
324 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
325 assert(thread == NULL || thread == Thread::current(), "sanity check");
326 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
327 // Put returned block at the beginning of the thread-local free list.
328 // Note that if thread == NULL, we use it as an implicit argument that
329 // we _don't_ want the block to be kept on the free_handle_block.
330 // See for instance JavaThread::exit().
331 if (thread != NULL ) {
332 if (ZapJNIHandleArea) block->zap();
333 JNIHandleBlock* freelist = thread->free_handle_block();
334 block->_pop_frame_link = NULL;
335 thread->set_free_handle_block(block);
336
337 // Add original freelist to end of chain
338 if ( freelist != NULL ) {
339 while ( block->_next != NULL ) block = block->_next;
340 block->_next = freelist;
341 }
342 block = NULL;
343 }
344 if (block != NULL) {
345 // Return blocks to free list
346 // locking with safepoint checking introduces a potential deadlock:
347 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
348 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
349 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
350 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
351 Mutex::_no_safepoint_check_flag);
352 while (block != NULL) {
353 if (ZapJNIHandleArea) block->zap();
354 JNIHandleBlock* next = block->_next;
355 block->_next = _block_free_list;
356 _block_free_list = block;
357 block = next;
358 }
359 }
360 if (pop_frame_link != NULL) {
361 // As a sanity check we release blocks pointed to by the pop_frame_link.
362 // This should never happen (only if PopLocalFrame is not called the
363 // correct number of times).
364 release_block(pop_frame_link, thread);
365 }
366 }
367
368
369 void JNIHandleBlock::oops_do(OopClosure* f) {
370 JNIHandleBlock* current_chain = this;
371 // Iterate over chain of blocks, followed by chains linked through the
372 // pop frame links.
373 while (current_chain != NULL) {
374 for (JNIHandleBlock* current = current_chain; current != NULL;
375 current = current->_next) {
376 assert(current == current_chain || current->pop_frame_link() == NULL,
377 "only blocks first in chain should have pop frame link set");
378 for (int index = 0; index < current->_top; index++) {
379 oop* root = &(current->_handles)[index];
380 oop value = *root;
381 // traverse heap pointers only, not deleted handles or free list
382 // pointers
383 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
384 f->do_oop(root);
385 }
386 }
387 // the next handle block is valid only if current block is full
388 if (current->_top < block_size_in_oops) {
389 break;
390 }
391 }
392 current_chain = current_chain->pop_frame_link();
393 }
394 }
395
396
397 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
398 OopClosure* f) {
399 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
400 assert(current->pop_frame_link() == NULL,
401 "blocks holding weak global JNI handles should not have pop frame link set");
402 for (int index = 0; index < current->_top; index++) {
403 oop* root = &(current->_handles)[index];
404 oop value = *root;
405 // traverse heap pointers only, not deleted handles or free list pointers
406 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
407 if (is_alive->do_object_b(value)) {
408 // The weakly referenced object is alive, update pointer
409 f->do_oop(root);
410 } else {
411 // The weakly referenced object is not alive, clear the reference by storing NULL
412 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
413 *root = NULL;
414 }
415 }
416 }
417 // the next handle block is valid only if current block is full
418 if (current->_top < block_size_in_oops) {
419 break;
420 }
421 }
422
423 /*
424 * JVMTI data structures may also contain weak oops. The iteration of them
425 * is placed here so that we don't need to add it to each of the collectors.
426 */
427 JvmtiExport::weak_oops_do(is_alive, f);
428 }
429
430
431 jobject JNIHandleBlock::allocate_handle(oop obj) {
432 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
433 if (_top == 0) {
434 // This is the first allocation or the initial block got zapped when
435 // entering a native function. If we have any following blocks they are
436 // not valid anymore.
437 for (JNIHandleBlock* current = _next; current != NULL;
438 current = current->_next) {
439 assert(current->_last == NULL, "only first block should have _last set");
440 assert(current->_free_list == NULL,
441 "only first block should have _free_list set");
442 if (current->_top == 0) {
443 // All blocks after the first clear trailing block are already cleared.
444 #ifdef ASSERT
445 for (current = current->_next; current != NULL; current = current->_next) {
446 assert(current->_top == 0, "trailing blocks must already be cleared");
447 }
448 #endif
449 break;
450 }
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 across 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 void JNIHandleBlock::release_handle(jobject h) {
499 if (h != NULL) {
500 assert(chain_contains(h), "does not contain the JNI handle");
501 // Mark the handle as deleted, allocate will reuse it
502 *((oop*)h) = JNIHandles::deleted_handle();
503 }
504 }
505
506
507 void JNIHandleBlock::rebuild_free_list() {
508 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
509 int free = 0;
510 int blocks = 0;
511 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
512 for (int index = 0; index < current->_top; index++) {
513 oop* handle = &(current->_handles)[index];
514 if (oopDesc::equals(*handle, JNIHandles::deleted_handle())) {
515 // this handle was cleared out by a delete call, reuse it
516 *handle = (oop) _free_list;
517 _free_list = handle;
518 free++;
519 }
520 }
521 // we should not rebuild free list if there are unused handles at the end
522 assert(current->_top == block_size_in_oops, "just checking");
523 blocks++;
524 }
525 // Heuristic: if more than half of the handles are free we rebuild next time
526 // as well, otherwise we append a corresponding number of new blocks before
527 // attempting a free list rebuild again.
528 int total = blocks * block_size_in_oops;
529 int extra = total - 2*free;
530 if (extra > 0) {
531 // Not as many free handles as we would like - compute number of new blocks to append
532 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
533 }
534 }
535
536
537 bool JNIHandleBlock::contains(jobject handle) const {
538 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
539 }
540
541
542 bool JNIHandleBlock::chain_contains(jobject handle) const {
543 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
544 if (current->contains(handle)) {
545 return true;
546 }
547 }
548 return false;
549 }
550
551
552 int JNIHandleBlock::length() const {
553 int result = 1;
554 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
555 result++;
556 }
557 return result;
558 }
559
560 const size_t JNIHandleBlock::get_number_of_live_handles() {
561 CountHandleClosure counter;
562 oops_do(&counter);
563 return counter.count();
564 }
565
566 // This method is not thread-safe, i.e., must be called while holding a lock on the
567 // structure.
568 long JNIHandleBlock::memory_usage() const {
569 return length() * sizeof(JNIHandleBlock);
570 }
571
572
573 #ifndef PRODUCT
574
575 bool JNIHandleBlock::any_contains(jobject handle) {
576 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
577 if (current->contains(handle)) {
578 return true;
579 }
580 }
581 return false;
582 }
583
584 void JNIHandleBlock::print_statistics() {
585 int used_blocks = 0;
586 int free_blocks = 0;
587 int used_handles = 0;
588 int free_handles = 0;
589 JNIHandleBlock* block = _block_list;
590 while (block != NULL) {
591 if (block->_top > 0) {
592 used_blocks++;
593 } else {
594 free_blocks++;
595 }
596 used_handles += block->_top;
597 free_handles += (block_size_in_oops - block->_top);
598 block = block->_block_list_link;
599 }
600 tty->print_cr("JNIHandleBlocks statistics");
601 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
602 tty->print_cr("- blocks in use: %d", used_blocks);
603 tty->print_cr("- blocks free: %d", free_blocks);
604 tty->print_cr("- handles in use: %d", used_handles);
605 tty->print_cr("- handles free: %d", free_handles);
606 }
607
608 #endif