1 /*
2 * Copyright (c) 1998, 2019, 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 "oops/oop.inline.hpp"
28 #include "prims/jvmtiExport.hpp"
29 #include "runtime/jniHandles.hpp"
30 #include "runtime/mutexLocker.hpp"
31 #include "runtime/thread.inline.hpp"
32
33 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
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(Universe::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(Universe::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(Universe::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(!Universe::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(Universe::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(!Universe::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(Universe::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::initialize() {
133 _global_handles = JNIHandleBlock::allocate_block();
134 _weak_global_handles = JNIHandleBlock::allocate_block();
135 EXCEPTION_MARK;
136 // We will never reach the CATCH below since Exceptions::_throw will cause
137 // the VM to exit if an exception is thrown during initialization
138 Klass* k = SystemDictionary::Object_klass();
139 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
140 }
141
142
143 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
144 JNIHandleBlock* block = thread->active_handles();
145
146 // Look back past possible native calls to jni_PushLocalFrame.
147 while (block != NULL) {
148 if (block->chain_contains(handle)) {
149 return true;
150 }
151 block = block->pop_frame_link();
152 }
153 return false;
154 }
155
156
157 // Determine if the handle is somewhere in the current thread's stack.
158 // We easily can't isolate any particular stack frame the handle might
159 // come from, so we'll check the whole stack.
160
161 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
162 // If there is no java frame, then this must be top level code, such
163 // as the java command executable, in which case, this type of handle
164 // is not permitted.
165 return (thr->has_last_Java_frame() &&
166 (void*)obj < (void*)thr->stack_base() &&
167 (void*)obj >= (void*)thr->last_Java_sp());
168 }
169
170
171 bool JNIHandles::is_global_handle(jobject handle) {
172 return _global_handles->chain_contains(handle);
173 }
174
175
176 bool JNIHandles::is_weak_global_handle(jobject handle) {
177 return _weak_global_handles->chain_contains(handle);
178 }
179
180 long JNIHandles::global_handle_memory_usage() {
181 return _global_handles->memory_usage();
182 }
183
184 long JNIHandles::weak_global_handle_memory_usage() {
185 return _weak_global_handles->memory_usage();
186 }
187
188
189 class AlwaysAliveClosure: public BoolObjectClosure {
190 public:
191 bool do_object_b(oop obj) { return true; }
192 };
193
194 class CountHandleClosure: public OopClosure {
195 private:
196 int _count;
197 public:
198 CountHandleClosure(): _count(0) {}
199 virtual void do_oop(oop* ooph) {
200 if (*ooph != JNIHandles::deleted_handle()) {
201 _count++;
202 }
203 }
204 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
205 int count() { return _count; }
206 };
207
208 // We assume this is called at a safepoint: no lock is needed.
209 void JNIHandles::print_on(outputStream* st) {
210 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
211 assert(_global_handles != NULL && _weak_global_handles != NULL,
212 "JNIHandles not initialized");
213
214 CountHandleClosure global_handle_count;
215 AlwaysAliveClosure always_alive;
216 oops_do(&global_handle_count);
217 weak_oops_do(&always_alive, &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 AlwaysAliveClosure always_alive;
235
236 oops_do(&verify_handle);
237 weak_oops_do(&always_alive, &verify_handle);
238 }
239
240
241
242 void jni_handles_init() {
243 JNIHandles::initialize();
244 }
245
246
247 int JNIHandleBlock::_blocks_allocated = 0;
248 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
249 #ifndef PRODUCT
250 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
251 #endif
252
253
254 void JNIHandleBlock::zap() {
255 // Zap block values
256 _top = 0;
257 for (int index = 0; index < block_size_in_oops; index++) {
258 _handles[index] = badJNIHandle;
259 }
260 }
261
262 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
263 assert(thread == NULL || thread == Thread::current(), "sanity check");
264 JNIHandleBlock* block;
265 // Check the thread-local free list for a block so we don't
266 // have to acquire a mutex.
267 if (thread != NULL && thread->free_handle_block() != NULL) {
268 block = thread->free_handle_block();
269 thread->set_free_handle_block(block->_next);
270 }
271 else {
272 // locking with safepoint checking introduces a potential deadlock:
273 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
274 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
275 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
276 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
277 Mutex::_no_safepoint_check_flag);
278 if (_block_free_list == NULL) {
279 // Allocate new block
280 block = new JNIHandleBlock();
281 _blocks_allocated++;
282 if (TraceJNIHandleAllocation) {
283 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
284 block, _blocks_allocated);
285 }
286 if (ZapJNIHandleArea) block->zap();
287 #ifndef PRODUCT
288 // Link new block to list of all allocated blocks
289 block->_block_list_link = _block_list;
290 _block_list = block;
291 #endif
292 } else {
293 // Get block from free list
294 block = _block_free_list;
295 _block_free_list = _block_free_list->_next;
296 }
297 }
298 block->_top = 0;
299 block->_next = NULL;
300 block->_pop_frame_link = NULL;
301 block->_planned_capacity = block_size_in_oops;
302 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
303 debug_only(block->_last = NULL);
304 debug_only(block->_free_list = NULL);
305 debug_only(block->_allocate_before_rebuild = -1);
306 return block;
307 }
308
309
310 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
311 assert(thread == NULL || thread == Thread::current(), "sanity check");
312 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
313 // Put returned block at the beginning of the thread-local free list.
314 // Note that if thread == NULL, we use it as an implicit argument that
315 // we _don't_ want the block to be kept on the free_handle_block.
316 // See for instance JavaThread::exit().
317 if (thread != NULL ) {
318 if (ZapJNIHandleArea) block->zap();
319 JNIHandleBlock* freelist = thread->free_handle_block();
320 block->_pop_frame_link = NULL;
321 thread->set_free_handle_block(block);
322
323 // Add original freelist to end of chain
324 if ( freelist != NULL ) {
325 while ( block->_next != NULL ) block = block->_next;
326 block->_next = freelist;
327 }
328 block = NULL;
329 }
330 if (block != NULL) {
331 // Return blocks to free list
332 // locking with safepoint checking introduces a potential deadlock:
333 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
334 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
335 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
336 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
337 Mutex::_no_safepoint_check_flag);
338 while (block != NULL) {
339 if (ZapJNIHandleArea) block->zap();
340 JNIHandleBlock* next = block->_next;
341 block->_next = _block_free_list;
342 _block_free_list = block;
343 block = next;
344 }
345 }
346 if (pop_frame_link != NULL) {
347 // As a sanity check we release blocks pointed to by the pop_frame_link.
348 // This should never happen (only if PopLocalFrame is not called the
349 // correct number of times).
350 release_block(pop_frame_link, thread);
351 }
352 }
353
354
355 void JNIHandleBlock::oops_do(OopClosure* f) {
356 JNIHandleBlock* current_chain = this;
357 // Iterate over chain of blocks, followed by chains linked through the
358 // pop frame links.
359 while (current_chain != NULL) {
360 for (JNIHandleBlock* current = current_chain; current != NULL;
361 current = current->_next) {
362 assert(current == current_chain || current->pop_frame_link() == NULL,
363 "only blocks first in chain should have pop frame link set");
364 for (int index = 0; index < current->_top; index++) {
365 oop* root = &(current->_handles)[index];
366 oop value = *root;
367 // traverse heap pointers only, not deleted handles or free list
368 // pointers
369 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
370 f->do_oop(root);
371 }
372 }
373 // the next handle block is valid only if current block is full
374 if (current->_top < block_size_in_oops) {
375 break;
376 }
377 }
378 current_chain = current_chain->pop_frame_link();
379 }
380 }
381
382
383 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
384 OopClosure* f) {
385 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
386 assert(current->pop_frame_link() == NULL,
387 "blocks holding weak global JNI handles should not have pop frame link set");
388 for (int index = 0; index < current->_top; index++) {
389 oop* root = &(current->_handles)[index];
390 oop value = *root;
391 // traverse heap pointers only, not deleted handles or free list pointers
392 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
393 if (is_alive->do_object_b(value)) {
394 // The weakly referenced object is alive, update pointer
395 f->do_oop(root);
396 } else {
397 // The weakly referenced object is not alive, clear the reference by storing NULL
398 if (TraceReferenceGC) {
399 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
400 }
401 *root = NULL;
402 }
403 }
404 }
405 // the next handle block is valid only if current block is full
406 if (current->_top < block_size_in_oops) {
407 break;
408 }
409 }
410
411 /*
412 * JVMTI data structures may also contain weak oops. The iteration of them
413 * is placed here so that we don't need to add it to each of the collectors.
414 */
415 JvmtiExport::weak_oops_do(is_alive, f);
416 TRACE_WEAK_OOPS_DO(is_alive, f);
417 }
418
419
420 jobject JNIHandleBlock::allocate_handle(oop obj) {
421 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
422 if (_top == 0) {
423 // This is the first allocation or the initial block got zapped when
424 // entering a native function. If we have any following blocks they are
425 // not valid anymore.
426 for (JNIHandleBlock* current = _next; current != NULL;
427 current = current->_next) {
428 assert(current->_last == NULL, "only first block should have _last set");
429 assert(current->_free_list == NULL,
430 "only first block should have _free_list set");
431 current->_top = 0;
432 if (ZapJNIHandleArea) current->zap();
433 }
434 // Clear initial block
435 _free_list = NULL;
436 _allocate_before_rebuild = 0;
437 _last = this;
438 if (ZapJNIHandleArea) zap();
439 }
440
441 // Try last block
442 if (_last->_top < block_size_in_oops) {
443 oop* handle = &(_last->_handles)[_last->_top++];
444 *handle = obj;
445 return (jobject) handle;
446 }
447
448 // Try free list
449 if (_free_list != NULL) {
450 oop* handle = _free_list;
451 _free_list = (oop*) *_free_list;
452 *handle = obj;
453 return (jobject) handle;
454 }
455 // Check if unused block follow last
456 if (_last->_next != NULL) {
457 // update last and retry
458 _last = _last->_next;
459 return allocate_handle(obj);
460 }
461
462 // No space available, we have to rebuild free list or expand
463 if (_allocate_before_rebuild == 0) {
464 rebuild_free_list(); // updates _allocate_before_rebuild counter
465 } else {
466 // Append new block
467 Thread* thread = Thread::current();
468 Handle obj_handle(thread, obj);
469 // This can block, so we need to preserve obj accross call.
470 _last->_next = JNIHandleBlock::allocate_block(thread);
471 _last = _last->_next;
472 _allocate_before_rebuild--;
473 obj = obj_handle();
474 }
475 return allocate_handle(obj); // retry
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 if (TraceJNIHandleAllocation) {
507 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
508 this, blocks, total-free, free, _allocate_before_rebuild);
509 }
510 }
511
512
513 bool JNIHandleBlock::contains(jobject handle) const {
514 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
515 }
516
517
518 bool JNIHandleBlock::chain_contains(jobject handle) const {
519 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
520 if (current->contains(handle)) {
521 return true;
522 }
523 }
524 return false;
525 }
526
527
528 int JNIHandleBlock::length() const {
529 int result = 1;
530 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
531 result++;
532 }
533 return result;
534 }
535
536 const size_t JNIHandleBlock::get_number_of_live_handles() {
537 CountHandleClosure counter;
538 oops_do(&counter);
539 return counter.count();
540 }
541
542 // This method is not thread-safe, i.e., must be called whule holding a lock on the
543 // structure.
544 long JNIHandleBlock::memory_usage() const {
545 return length() * sizeof(JNIHandleBlock);
546 }
547
548
549 #ifndef PRODUCT
550
551 bool JNIHandleBlock::any_contains(jobject handle) {
552 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
553 if (current->contains(handle)) {
554 return true;
555 }
556 }
557 return false;
558 }
559
560 void JNIHandleBlock::print_statistics() {
561 int used_blocks = 0;
562 int free_blocks = 0;
563 int used_handles = 0;
564 int free_handles = 0;
565 JNIHandleBlock* block = _block_list;
566 while (block != NULL) {
567 if (block->_top > 0) {
568 used_blocks++;
569 } else {
570 free_blocks++;
571 }
572 used_handles += block->_top;
573 free_handles += (block_size_in_oops - block->_top);
574 block = block->_block_list_link;
575 }
576 tty->print_cr("JNIHandleBlocks statistics");
577 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
578 tty->print_cr("- blocks in use: %d", used_blocks);
579 tty->print_cr("- blocks free: %d", free_blocks);
580 tty->print_cr("- handles in use: %d", used_handles);
581 tty->print_cr("- handles free: %d", free_handles);
582 }
583
584 #endif