1 /*
2 * Copyright (c) 1998, 2016, 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
35 JNIHandleBlock* JNIHandles::_global_handles = NULL;
36 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
37 oop JNIHandles::_deleted_handle = NULL;
38
39
40 jobject JNIHandles::make_local(oop obj) {
41 if (obj == NULL) {
42 return NULL; // ignore null handles
43 } else {
44 Thread* thread = Thread::current();
45 assert(GC::gc()->heap()->is_in_reserved(obj), "sanity check");
46 return thread->active_handles()->allocate_handle(obj);
47 }
48 }
49
50
51 // optimized versions
52
53 jobject JNIHandles::make_local(Thread* thread, oop obj) {
54 if (obj == NULL) {
55 return NULL; // ignore null handles
56 } else {
57 assert(GC::gc()->heap()->is_in_reserved(obj), "sanity check");
58 return thread->active_handles()->allocate_handle(obj);
59 }
60 }
61
62
63 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
64 if (obj == NULL) {
65 return NULL; // ignore null handles
66 } else {
67 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
68 assert(GC::gc()->heap()->is_in_reserved(obj), "sanity check");
69 return thread->active_handles()->allocate_handle(obj);
70 }
71 }
72
73
74 jobject JNIHandles::make_global(Handle obj) {
75 assert(!GC::gc()->heap()->is_gc_active(), "can't extend the root set during GC");
76 jobject res = NULL;
77 if (!obj.is_null()) {
78 // ignore null handles
79 MutexLocker ml(JNIGlobalHandle_lock);
80 assert(GC::gc()->heap()->is_in_reserved(obj()), "sanity check");
81 res = _global_handles->allocate_handle(obj());
82 } else {
83 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
84 }
85
86 return res;
87 }
88
89
90 jobject JNIHandles::make_weak_global(Handle obj) {
91 assert(!GC::gc()->heap()->is_gc_active(), "can't extend the root set during GC");
92 jobject res = NULL;
93 if (!obj.is_null()) {
94 // ignore null handles
95 MutexLocker ml(JNIGlobalHandle_lock);
96 assert(GC::gc()->heap()->is_in_reserved(obj()), "sanity check");
97 res = _weak_global_handles->allocate_handle(obj());
98 } else {
99 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
100 }
101 return res;
102 }
103
104
105 void JNIHandles::destroy_global(jobject handle) {
106 if (handle != NULL) {
107 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
108 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
109 }
110 }
111
112
113 void JNIHandles::destroy_weak_global(jobject handle) {
114 if (handle != NULL) {
115 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
116 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
117 }
118 }
119
120
121 void JNIHandles::oops_do(OopClosure* f) {
122 f->do_oop(&_deleted_handle);
123 _global_handles->oops_do(f);
124 }
125
126
127 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
128 _weak_global_handles->weak_oops_do(is_alive, f);
129 }
130
131
132 void JNIHandles::weak_oops_do(OopClosure* f) {
133 AlwaysTrueClosure always_true;
134 weak_oops_do(&always_true, f);
135 }
136
137
138 void JNIHandles::initialize() {
139 _global_handles = JNIHandleBlock::allocate_block();
140 _weak_global_handles = JNIHandleBlock::allocate_block();
141 EXCEPTION_MARK;
142 // We will never reach the CATCH below since Exceptions::_throw will cause
143 // the VM to exit if an exception is thrown during initialization
144 Klass* k = SystemDictionary::Object_klass();
145 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
146 }
147
148
149 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
150 JNIHandleBlock* block = thread->active_handles();
151
152 // Look back past possible native calls to jni_PushLocalFrame.
153 while (block != NULL) {
154 if (block->chain_contains(handle)) {
155 return true;
156 }
157 block = block->pop_frame_link();
158 }
159 return false;
160 }
161
162
163 // Determine if the handle is somewhere in the current thread's stack.
164 // We easily can't isolate any particular stack frame the handle might
165 // come from, so we'll check the whole stack.
166
167 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
168 // If there is no java frame, then this must be top level code, such
169 // as the java command executable, in which case, this type of handle
170 // is not permitted.
171 return (thr->has_last_Java_frame() &&
172 (void*)obj < (void*)thr->stack_base() &&
173 (void*)obj >= (void*)thr->last_Java_sp());
174 }
175
176
177 bool JNIHandles::is_global_handle(jobject handle) {
178 return _global_handles->chain_contains(handle);
179 }
180
181
182 bool JNIHandles::is_weak_global_handle(jobject handle) {
183 return _weak_global_handles->chain_contains(handle);
184 }
185
186 long JNIHandles::global_handle_memory_usage() {
187 return _global_handles->memory_usage();
188 }
189
190 long JNIHandles::weak_global_handle_memory_usage() {
191 return _weak_global_handles->memory_usage();
192 }
193
194
195 class CountHandleClosure: public OopClosure {
196 private:
197 int _count;
198 public:
199 CountHandleClosure(): _count(0) {}
200 virtual void do_oop(oop* ooph) {
201 if (*ooph != JNIHandles::deleted_handle()) {
202 _count++;
203 }
204 }
205 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
206 int count() { return _count; }
207 };
208
209 // We assume this is called at a safepoint: no lock is needed.
210 void JNIHandles::print_on(outputStream* st) {
211 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
212 assert(_global_handles != NULL && _weak_global_handles != NULL,
213 "JNIHandles not initialized");
214
215 CountHandleClosure global_handle_count;
216 oops_do(&global_handle_count);
217 weak_oops_do(&global_handle_count);
218
219 st->print_cr("JNI global references: %d", global_handle_count.count());
220 st->cr();
221 st->flush();
222 }
223
224 class VerifyHandleClosure: public OopClosure {
225 public:
226 virtual void do_oop(oop* root) {
227 (*root)->verify();
228 }
229 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
230 };
231
232 void JNIHandles::verify() {
233 VerifyHandleClosure verify_handle;
234
235 oops_do(&verify_handle);
236 weak_oops_do(&verify_handle);
237 }
238
239
240
241 void jni_handles_init() {
242 JNIHandles::initialize();
243 }
244
245
246 int JNIHandleBlock::_blocks_allocated = 0;
247 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
248 #ifndef PRODUCT
249 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
250 #endif
251
252
253 void JNIHandleBlock::zap() {
254 // Zap block values
255 _top = 0;
256 for (int index = 0; index < block_size_in_oops; index++) {
257 _handles[index] = badJNIHandle;
258 }
259 }
260
261 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
262 assert(thread == NULL || thread == Thread::current(), "sanity check");
263 JNIHandleBlock* block;
264 // Check the thread-local free list for a block so we don't
265 // have to acquire a mutex.
266 if (thread != NULL && thread->free_handle_block() != NULL) {
267 block = thread->free_handle_block();
268 thread->set_free_handle_block(block->_next);
269 }
270 else {
271 // locking with safepoint checking introduces a potential deadlock:
272 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
273 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
274 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
275 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
276 Mutex::_no_safepoint_check_flag);
277 if (_block_free_list == NULL) {
278 // Allocate new block
279 block = new JNIHandleBlock();
280 _blocks_allocated++;
281 if (ZapJNIHandleArea) block->zap();
282 #ifndef PRODUCT
283 // Link new block to list of all allocated blocks
284 block->_block_list_link = _block_list;
285 _block_list = block;
286 #endif
287 } else {
288 // Get block from free list
289 block = _block_free_list;
290 _block_free_list = _block_free_list->_next;
291 }
292 }
293 block->_top = 0;
294 block->_next = NULL;
295 block->_pop_frame_link = NULL;
296 block->_planned_capacity = block_size_in_oops;
297 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
298 debug_only(block->_last = NULL);
299 debug_only(block->_free_list = NULL);
300 debug_only(block->_allocate_before_rebuild = -1);
301 return block;
302 }
303
304
305 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
306 assert(thread == NULL || thread == Thread::current(), "sanity check");
307 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
308 // Put returned block at the beginning of the thread-local free list.
309 // Note that if thread == NULL, we use it as an implicit argument that
310 // we _don't_ want the block to be kept on the free_handle_block.
311 // See for instance JavaThread::exit().
312 if (thread != NULL ) {
313 if (ZapJNIHandleArea) block->zap();
314 JNIHandleBlock* freelist = thread->free_handle_block();
315 block->_pop_frame_link = NULL;
316 thread->set_free_handle_block(block);
317
318 // Add original freelist to end of chain
319 if ( freelist != NULL ) {
320 while ( block->_next != NULL ) block = block->_next;
321 block->_next = freelist;
322 }
323 block = NULL;
324 }
325 if (block != NULL) {
326 // Return blocks to free list
327 // locking with safepoint checking introduces a potential deadlock:
328 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
329 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
330 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
331 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
332 Mutex::_no_safepoint_check_flag);
333 while (block != NULL) {
334 if (ZapJNIHandleArea) block->zap();
335 JNIHandleBlock* next = block->_next;
336 block->_next = _block_free_list;
337 _block_free_list = block;
338 block = next;
339 }
340 }
341 if (pop_frame_link != NULL) {
342 // As a sanity check we release blocks pointed to by the pop_frame_link.
343 // This should never happen (only if PopLocalFrame is not called the
344 // correct number of times).
345 release_block(pop_frame_link, thread);
346 }
347 }
348
349
350 void JNIHandleBlock::oops_do(OopClosure* f) {
351 JNIHandleBlock* current_chain = this;
352 // Iterate over chain of blocks, followed by chains linked through the
353 // pop frame links.
354 while (current_chain != NULL) {
355 for (JNIHandleBlock* current = current_chain; current != NULL;
356 current = current->_next) {
357 assert(current == current_chain || current->pop_frame_link() == NULL,
358 "only blocks first in chain should have pop frame link set");
359 for (int index = 0; index < current->_top; index++) {
360 oop* root = &(current->_handles)[index];
361 oop value = *root;
362 // traverse heap pointers only, not deleted handles or free list
363 // pointers
364 if (value != NULL && GC::gc()->heap()->is_in_reserved(value)) {
365 f->do_oop(root);
366 }
367 }
368 // the next handle block is valid only if current block is full
369 if (current->_top < block_size_in_oops) {
370 break;
371 }
372 }
373 current_chain = current_chain->pop_frame_link();
374 }
375 }
376
377
378 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
379 OopClosure* f) {
380 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
381 assert(current->pop_frame_link() == NULL,
382 "blocks holding weak global JNI handles should not 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 pointers
387 if (value != NULL && GC::gc()->heap()->is_in_reserved(value)) {
388 if (is_alive->do_object_b(value)) {
389 // The weakly referenced object is alive, update pointer
390 f->do_oop(root);
391 } else {
392 // The weakly referenced object is not alive, clear the reference by storing NULL
393 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
394 *root = NULL;
395 }
396 }
397 }
398 // the next handle block is valid only if current block is full
399 if (current->_top < block_size_in_oops) {
400 break;
401 }
402 }
403
404 /*
405 * JVMTI data structures may also contain weak oops. The iteration of them
406 * is placed here so that we don't need to add it to each of the collectors.
407 */
408 JvmtiExport::weak_oops_do(is_alive, f);
409 }
410
411
412 jobject JNIHandleBlock::allocate_handle(oop obj) {
413 assert(GC::gc()->heap()->is_in_reserved(obj), "sanity check");
414 if (_top == 0) {
415 // This is the first allocation or the initial block got zapped when
416 // entering a native function. If we have any following blocks they are
417 // not valid anymore.
418 for (JNIHandleBlock* current = _next; current != NULL;
419 current = current->_next) {
420 assert(current->_last == NULL, "only first block should have _last set");
421 assert(current->_free_list == NULL,
422 "only first block should have _free_list set");
423 current->_top = 0;
424 if (ZapJNIHandleArea) current->zap();
425 }
426 // Clear initial block
427 _free_list = NULL;
428 _allocate_before_rebuild = 0;
429 _last = this;
430 if (ZapJNIHandleArea) zap();
431 }
432
433 // Try last block
434 if (_last->_top < block_size_in_oops) {
435 oop* handle = &(_last->_handles)[_last->_top++];
436 *handle = obj;
437 return (jobject) handle;
438 }
439
440 // Try free list
441 if (_free_list != NULL) {
442 oop* handle = _free_list;
443 _free_list = (oop*) *_free_list;
444 *handle = obj;
445 return (jobject) handle;
446 }
447 // Check if unused block follow last
448 if (_last->_next != NULL) {
449 // update last and retry
450 _last = _last->_next;
451 return allocate_handle(obj);
452 }
453
454 // No space available, we have to rebuild free list or expand
455 if (_allocate_before_rebuild == 0) {
456 rebuild_free_list(); // updates _allocate_before_rebuild counter
457 } else {
458 // Append new block
459 Thread* thread = Thread::current();
460 Handle obj_handle(thread, obj);
461 // This can block, so we need to preserve obj across call.
462 _last->_next = JNIHandleBlock::allocate_block(thread);
463 _last = _last->_next;
464 _allocate_before_rebuild--;
465 obj = obj_handle();
466 }
467 return allocate_handle(obj); // retry
468 }
469
470 void JNIHandleBlock::release_handle(jobject h) {
471 if (h != NULL) {
472 assert(chain_contains(h), "does not contain the JNI handle");
473 // Mark the handle as deleted, allocate will reuse it
474 *((oop*)h) = JNIHandles::deleted_handle();
475 }
476 }
477
478
479 void JNIHandleBlock::rebuild_free_list() {
480 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
481 int free = 0;
482 int blocks = 0;
483 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
484 for (int index = 0; index < current->_top; index++) {
485 oop* handle = &(current->_handles)[index];
486 if (*handle == JNIHandles::deleted_handle()) {
487 // this handle was cleared out by a delete call, reuse it
488 *handle = (oop) _free_list;
489 _free_list = handle;
490 free++;
491 }
492 }
493 // we should not rebuild free list if there are unused handles at the end
494 assert(current->_top == block_size_in_oops, "just checking");
495 blocks++;
496 }
497 // Heuristic: if more than half of the handles are free we rebuild next time
498 // as well, otherwise we append a corresponding number of new blocks before
499 // attempting a free list rebuild again.
500 int total = blocks * block_size_in_oops;
501 int extra = total - 2*free;
502 if (extra > 0) {
503 // Not as many free handles as we would like - compute number of new blocks to append
504 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
505 }
506 }
507
508
509 bool JNIHandleBlock::contains(jobject handle) const {
510 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
511 }
512
513
514 bool JNIHandleBlock::chain_contains(jobject handle) const {
515 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
516 if (current->contains(handle)) {
517 return true;
518 }
519 }
520 return false;
521 }
522
523
524 int JNIHandleBlock::length() const {
525 int result = 1;
526 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
527 result++;
528 }
529 return result;
530 }
531
532 const size_t JNIHandleBlock::get_number_of_live_handles() {
533 CountHandleClosure counter;
534 oops_do(&counter);
535 return counter.count();
536 }
537
538 // This method is not thread-safe, i.e., must be called while holding a lock on the
539 // structure.
540 long JNIHandleBlock::memory_usage() const {
541 return length() * sizeof(JNIHandleBlock);
542 }
543
544
545 #ifndef PRODUCT
546
547 bool JNIHandleBlock::any_contains(jobject handle) {
548 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
549 if (current->contains(handle)) {
550 return true;
551 }
552 }
553 return false;
554 }
555
556 void JNIHandleBlock::print_statistics() {
557 int used_blocks = 0;
558 int free_blocks = 0;
559 int used_handles = 0;
560 int free_handles = 0;
561 JNIHandleBlock* block = _block_list;
562 while (block != NULL) {
563 if (block->_top > 0) {
564 used_blocks++;
565 } else {
566 free_blocks++;
567 }
568 used_handles += block->_top;
569 free_handles += (block_size_in_oops - block->_top);
570 block = block->_block_list_link;
571 }
572 tty->print_cr("JNIHandleBlocks statistics");
573 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
574 tty->print_cr("- blocks in use: %d", used_blocks);
575 tty->print_cr("- blocks free: %d", free_blocks);
576 tty->print_cr("- handles in use: %d", used_handles);
577 tty->print_cr("- handles free: %d", free_handles);
578 }
579
580 #endif