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/access.inline.hpp"
32 #include "runtime/jniHandles.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "runtime/thread.inline.hpp"
35
36 JNIHandleBlock* JNIHandles::_global_handles = NULL;
37 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
38 oop JNIHandles::_deleted_handle = NULL;
39
40 oop JNIHandles::resolve_handle(jobject handle) {
41 oop* addr = oop_addr(handle);
42 if (is_jweak(handle)) {
43 return RootAccess<GC_ACCESS_ON_PHANTOM>::oop_load(addr);
44 } else {
45 return RootAccess<GC_ACCESS_ON_STRONG>::oop_load(addr);
46 }
47 }
48
49 jobject JNIHandles::make_local(oop obj) {
50 if (obj == NULL) {
51 return NULL; // ignore null handles
52 } else {
53 Thread* thread = Thread::current();
54 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
55 return thread->active_handles()->allocate_handle(obj);
56 }
57 }
58
59 // optimized versions
60
61 jobject JNIHandles::make_local(Thread* thread, oop obj) {
62 if (obj == NULL) {
63 return NULL; // ignore null handles
64 } else {
65 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
66 return thread->active_handles()->allocate_handle(obj);
67 }
68 }
69
70
71 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
72 if (obj == NULL) {
73 return NULL; // ignore null handles
74 } else {
75 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
76 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
77 return thread->active_handles()->allocate_handle(obj);
78 }
79 }
80
81
82 jobject JNIHandles::make_global(Handle obj) {
83 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
84 jobject res = NULL;
85 if (!obj.is_null()) {
86 // ignore null handles
87 MutexLocker ml(JNIGlobalHandle_lock);
88 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
89 res = _global_handles->allocate_handle(obj());
90 } else {
91 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
92 }
93
94 return res;
95 }
96
97
98 jobject JNIHandles::make_weak_global(Handle obj) {
99 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
100 jobject res = NULL;
101 if (!obj.is_null()) {
102 // ignore null handles
103 {
104 MutexLocker ml(JNIGlobalHandle_lock);
105 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
106 res = _weak_global_handles->allocate_handle(obj());
107 }
108 // Add weak tag.
109 assert(is_ptr_aligned(res, weak_tag_alignment), "invariant");
110 char* tptr = reinterpret_cast<char*>(res) + weak_tag_value;
111 res = reinterpret_cast<jobject>(tptr);
112 } else {
113 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
114 }
115 return res;
116 }
117
118 void JNIHandles::destroy_global(jobject handle) {
119 if (handle != NULL) {
120 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
121 *oop_addr(handle) = deleted_handle();
122 }
123 }
124
125
126 void JNIHandles::destroy_weak_global(jobject handle) {
127 if (handle != NULL) {
128 *oop_addr(handle) = deleted_handle();
129 }
130 }
131
132
133 void JNIHandles::oops_do(OopClosure* f) {
134 f->do_oop(&_deleted_handle);
135 _global_handles->oops_do(f);
136 }
137
138
139 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
140 _weak_global_handles->weak_oops_do(is_alive, f);
141 }
142
143
144 void JNIHandles::weak_oops_do(OopClosure* f) {
145 AlwaysTrueClosure always_true;
146 weak_oops_do(&always_true, f);
147 }
148
149
150 void JNIHandles::initialize() {
151 _global_handles = JNIHandleBlock::allocate_block();
152 _weak_global_handles = JNIHandleBlock::allocate_block();
153 EXCEPTION_MARK;
154 // We will never reach the CATCH below since Exceptions::_throw will cause
155 // the VM to exit if an exception is thrown during initialization
156 Klass* k = SystemDictionary::Object_klass();
157 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
158 }
159
160
161 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
162 JNIHandleBlock* block = thread->active_handles();
163
164 // Look back past possible native calls to jni_PushLocalFrame.
165 while (block != NULL) {
166 if (block->chain_contains(handle)) {
167 return true;
168 }
169 block = block->pop_frame_link();
170 }
171 return false;
172 }
173
174
175 // Determine if the handle is somewhere in the current thread's stack.
176 // We easily can't isolate any particular stack frame the handle might
177 // come from, so we'll check the whole stack.
178
179 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
180 // If there is no java frame, then this must be top level code, such
181 // as the java command executable, in which case, this type of handle
182 // is not permitted.
183 return (thr->has_last_Java_frame() &&
184 (void*)obj < (void*)thr->stack_base() &&
185 (void*)obj >= (void*)thr->last_Java_sp());
186 }
187
188
189 bool JNIHandles::is_global_handle(jobject handle) {
190 return _global_handles->chain_contains(handle);
191 }
192
193
194 bool JNIHandles::is_weak_global_handle(jobject handle) {
195 return _weak_global_handles->chain_contains(handle);
196 }
197
198 long JNIHandles::global_handle_memory_usage() {
199 return _global_handles->memory_usage();
200 }
201
202 long JNIHandles::weak_global_handle_memory_usage() {
203 return _weak_global_handles->memory_usage();
204 }
205
206
207 class CountHandleClosure: public OopClosure {
208 private:
209 int _count;
210 public:
211 CountHandleClosure(): _count(0) {}
212 virtual void do_oop(oop* ooph) {
213 if (*ooph != JNIHandles::deleted_handle()) {
214 _count++;
215 }
216 }
217 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
218 int count() { return _count; }
219 };
220
221 // We assume this is called at a safepoint: no lock is needed.
222 void JNIHandles::print_on(outputStream* st) {
223 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
224 assert(_global_handles != NULL && _weak_global_handles != NULL,
225 "JNIHandles not initialized");
226
227 CountHandleClosure global_handle_count;
228 oops_do(&global_handle_count);
229 weak_oops_do(&global_handle_count);
230
231 st->print_cr("JNI global references: %d", global_handle_count.count());
232 st->cr();
233 st->flush();
234 }
235
236 class VerifyHandleClosure: public OopClosure {
237 public:
238 virtual void do_oop(oop* root) {
239 (*root)->verify();
240 }
241 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
242 };
243
244 void JNIHandles::verify() {
245 VerifyHandleClosure verify_handle;
246
247 oops_do(&verify_handle);
248 weak_oops_do(&verify_handle);
249 }
250
251
252
253 void jni_handles_init() {
254 JNIHandles::initialize();
255 }
256
257
258 int JNIHandleBlock::_blocks_allocated = 0;
259 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
260 #ifndef PRODUCT
261 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
262 #endif
263
264
265 void JNIHandleBlock::zap() {
266 // Zap block values
267 _top = 0;
268 for (int index = 0; index < block_size_in_oops; index++) {
269 _handles[index] = badJNIHandle;
270 }
271 }
272
273 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
274 assert(thread == NULL || thread == Thread::current(), "sanity check");
275 JNIHandleBlock* block;
276 // Check the thread-local free list for a block so we don't
277 // have to acquire a mutex.
278 if (thread != NULL && thread->free_handle_block() != NULL) {
279 block = thread->free_handle_block();
280 thread->set_free_handle_block(block->_next);
281 }
282 else {
283 // locking with safepoint checking introduces a potential deadlock:
284 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
285 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
286 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
287 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
288 Mutex::_no_safepoint_check_flag);
289 if (_block_free_list == NULL) {
290 // Allocate new block
291 block = new JNIHandleBlock();
292 _blocks_allocated++;
293 if (ZapJNIHandleArea) block->zap();
294 #ifndef PRODUCT
295 // Link new block to list of all allocated blocks
296 block->_block_list_link = _block_list;
297 _block_list = block;
298 #endif
299 } else {
300 // Get block from free list
301 block = _block_free_list;
302 _block_free_list = _block_free_list->_next;
303 }
304 }
305 block->_top = 0;
306 block->_next = NULL;
307 block->_pop_frame_link = NULL;
308 block->_planned_capacity = block_size_in_oops;
309 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
310 debug_only(block->_last = NULL);
311 debug_only(block->_free_list = NULL);
312 debug_only(block->_allocate_before_rebuild = -1);
313 return block;
314 }
315
316
317 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
318 assert(thread == NULL || thread == Thread::current(), "sanity check");
319 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
320 // Put returned block at the beginning of the thread-local free list.
321 // Note that if thread == NULL, we use it as an implicit argument that
322 // we _don't_ want the block to be kept on the free_handle_block.
323 // See for instance JavaThread::exit().
324 if (thread != NULL ) {
325 if (ZapJNIHandleArea) block->zap();
326 JNIHandleBlock* freelist = thread->free_handle_block();
327 block->_pop_frame_link = NULL;
328 thread->set_free_handle_block(block);
329
330 // Add original freelist to end of chain
331 if ( freelist != NULL ) {
332 while ( block->_next != NULL ) block = block->_next;
333 block->_next = freelist;
334 }
335 block = NULL;
336 }
337 if (block != NULL) {
338 // Return blocks to free list
339 // locking with safepoint checking introduces a potential deadlock:
340 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
341 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
342 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
343 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
344 Mutex::_no_safepoint_check_flag);
345 while (block != NULL) {
346 if (ZapJNIHandleArea) block->zap();
347 JNIHandleBlock* next = block->_next;
348 block->_next = _block_free_list;
349 _block_free_list = block;
350 block = next;
351 }
352 }
353 if (pop_frame_link != NULL) {
354 // As a sanity check we release blocks pointed to by the pop_frame_link.
355 // This should never happen (only if PopLocalFrame is not called the
356 // correct number of times).
357 release_block(pop_frame_link, thread);
358 }
359 }
360
361
362 void JNIHandleBlock::oops_do(OopClosure* f) {
363 JNIHandleBlock* current_chain = this;
364 // Iterate over chain of blocks, followed by chains linked through the
365 // pop frame links.
366 while (current_chain != NULL) {
367 for (JNIHandleBlock* current = current_chain; current != NULL;
368 current = current->_next) {
369 assert(current == current_chain || current->pop_frame_link() == NULL,
370 "only blocks first in chain should have pop frame link set");
371 for (int index = 0; index < current->_top; index++) {
372 oop* root = &(current->_handles)[index];
373 oop value = *root;
374 // traverse heap pointers only, not deleted handles or free list
375 // pointers
376 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
377 f->do_oop(root);
378 }
379 }
380 // the next handle block is valid only if current block is full
381 if (current->_top < block_size_in_oops) {
382 break;
383 }
384 }
385 current_chain = current_chain->pop_frame_link();
386 }
387 }
388
389
390 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
391 OopClosure* f) {
392 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
393 assert(current->pop_frame_link() == NULL,
394 "blocks holding weak global JNI handles should not have pop frame link set");
395 for (int index = 0; index < current->_top; index++) {
396 oop* root = &(current->_handles)[index];
397 oop value = *root;
398 // traverse heap pointers only, not deleted handles or free list pointers
399 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
400 if (is_alive->do_object_b(value)) {
401 // The weakly referenced object is alive, update pointer
402 f->do_oop(root);
403 } else {
404 // The weakly referenced object is not alive, clear the reference by storing NULL
405 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
406 *root = NULL;
407 }
408 }
409 }
410 // the next handle block is valid only if current block is full
411 if (current->_top < block_size_in_oops) {
412 break;
413 }
414 }
415
416 /*
417 * JVMTI data structures may also contain weak oops. The iteration of them
418 * is placed here so that we don't need to add it to each of the collectors.
419 */
420 JvmtiExport::weak_oops_do(is_alive, f);
421 }
422
423
424 jobject JNIHandleBlock::allocate_handle(oop obj) {
425 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
426 if (_top == 0) {
427 // This is the first allocation or the initial block got zapped when
428 // entering a native function. If we have any following blocks they are
429 // not valid anymore.
430 for (JNIHandleBlock* current = _next; current != NULL;
431 current = current->_next) {
432 assert(current->_last == NULL, "only first block should have _last set");
433 assert(current->_free_list == NULL,
434 "only first block should have _free_list set");
435 current->_top = 0;
436 if (ZapJNIHandleArea) current->zap();
437 }
438 // Clear initial block
439 _free_list = NULL;
440 _allocate_before_rebuild = 0;
441 _last = this;
442 if (ZapJNIHandleArea) zap();
443 }
444
445 // Try last block
446 if (_last->_top < block_size_in_oops) {
447 oop* handle = &(_last->_handles)[_last->_top++];
448 *handle = obj;
449 return (jobject) handle;
450 }
451
452 // Try free list
453 if (_free_list != NULL) {
454 oop* handle = _free_list;
455 _free_list = (oop*) *_free_list;
456 *handle = obj;
457 return (jobject) handle;
458 }
459 // Check if unused block follow last
460 if (_last->_next != NULL) {
461 // update last and retry
462 _last = _last->_next;
463 return allocate_handle(obj);
464 }
465
466 // No space available, we have to rebuild free list or expand
467 if (_allocate_before_rebuild == 0) {
468 rebuild_free_list(); // updates _allocate_before_rebuild counter
469 } else {
470 // Append new block
471 Thread* thread = Thread::current();
472 Handle obj_handle(thread, obj);
473 // This can block, so we need to preserve obj across call.
474 _last->_next = JNIHandleBlock::allocate_block(thread);
475 _last = _last->_next;
476 _allocate_before_rebuild--;
477 obj = obj_handle();
478 }
479 return allocate_handle(obj); // retry
480 }
481
482 void JNIHandleBlock::release_handle(jobject h) {
483 if (h != NULL) {
484 assert(chain_contains(h), "does not contain the JNI handle");
485 // Mark the handle as deleted, allocate will reuse it
486 *((oop*)h) = JNIHandles::deleted_handle();
487 }
488 }
489
490
491 void JNIHandleBlock::rebuild_free_list() {
492 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
493 int free = 0;
494 int blocks = 0;
495 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
496 for (int index = 0; index < current->_top; index++) {
497 oop* handle = &(current->_handles)[index];
498 if (*handle == JNIHandles::deleted_handle()) {
499 // this handle was cleared out by a delete call, reuse it
500 *handle = (oop) _free_list;
501 _free_list = handle;
502 free++;
503 }
504 }
505 // we should not rebuild free list if there are unused handles at the end
506 assert(current->_top == block_size_in_oops, "just checking");
507 blocks++;
508 }
509 // Heuristic: if more than half of the handles are free we rebuild next time
510 // as well, otherwise we append a corresponding number of new blocks before
511 // attempting a free list rebuild again.
512 int total = blocks * block_size_in_oops;
513 int extra = total - 2*free;
514 if (extra > 0) {
515 // Not as many free handles as we would like - compute number of new blocks to append
516 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
517 }
518 }
519
520
521 bool JNIHandleBlock::contains(jobject handle) const {
522 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
523 }
524
525
526 bool JNIHandleBlock::chain_contains(jobject handle) const {
527 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
528 if (current->contains(handle)) {
529 return true;
530 }
531 }
532 return false;
533 }
534
535
536 int JNIHandleBlock::length() const {
537 int result = 1;
538 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
539 result++;
540 }
541 return result;
542 }
543
544 const size_t JNIHandleBlock::get_number_of_live_handles() {
545 CountHandleClosure counter;
546 oops_do(&counter);
547 return counter.count();
548 }
549
550 // This method is not thread-safe, i.e., must be called while holding a lock on the
551 // structure.
552 long JNIHandleBlock::memory_usage() const {
553 return length() * sizeof(JNIHandleBlock);
554 }
555
556
557 #ifndef PRODUCT
558
559 bool JNIHandleBlock::any_contains(jobject handle) {
560 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
561 if (current->contains(handle)) {
562 return true;
563 }
564 }
565 return false;
566 }
567
568 void JNIHandleBlock::print_statistics() {
569 int used_blocks = 0;
570 int free_blocks = 0;
571 int used_handles = 0;
572 int free_handles = 0;
573 JNIHandleBlock* block = _block_list;
574 while (block != NULL) {
575 if (block->_top > 0) {
576 used_blocks++;
577 } else {
578 free_blocks++;
579 }
580 used_handles += block->_top;
581 free_handles += (block_size_in_oops - block->_top);
582 block = block->_block_list_link;
583 }
584 tty->print_cr("JNIHandleBlocks statistics");
585 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
586 tty->print_cr("- blocks in use: %d", used_blocks);
587 tty->print_cr("- blocks free: %d", free_blocks);
588 tty->print_cr("- handles in use: %d", used_handles);
589 tty->print_cr("- handles free: %d", free_handles);
590 }
591
592 #endif