1 /*
2 * Copyright (c) 1998, 2014, 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 JNIHandleBlock* JNIHandles::_global_handles = NULL;
34 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
35 oop JNIHandles::_deleted_handle = NULL;
36
37
38 jobject JNIHandles::make_local(oop obj) {
39 if (obj == NULL) {
40 return NULL; // ignore null handles
41 } else {
42 Thread* thread = Thread::current();
43 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
44 return thread->active_handles()->allocate_handle(obj);
45 }
46 }
47
48
49 // optimized versions
50
51 jobject JNIHandles::make_local(Thread* thread, oop obj) {
52 if (obj == NULL) {
53 return NULL; // ignore null handles
54 } else {
55 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
56 return thread->active_handles()->allocate_handle(obj);
57 }
58 }
59
60
61 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
62 if (obj == NULL) {
63 return NULL; // ignore null handles
64 } else {
65 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
66 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
67 return thread->active_handles()->allocate_handle(obj);
68 }
69 }
70
71
72 jobject JNIHandles::make_global(Handle obj) {
73 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
74 jobject res = NULL;
75 if (!obj.is_null()) {
76 // ignore null handles
77 MutexLocker ml(JNIGlobalHandle_lock);
78 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
79 res = _global_handles->allocate_handle(obj());
80 } else {
81 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
82 }
83
84 return res;
85 }
86
87
88 jobject JNIHandles::make_weak_global(Handle obj) {
89 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
90 jobject res = NULL;
91 if (!obj.is_null()) {
92 // ignore null handles
93 MutexLocker ml(JNIGlobalHandle_lock);
94 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
95 res = _weak_global_handles->allocate_handle(obj());
96 } else {
97 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
98 }
99 return res;
100 }
101
102
103 void JNIHandles::destroy_global(jobject handle) {
104 if (handle != NULL) {
105 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
106 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
107 }
108 }
109
110
111 void JNIHandles::destroy_weak_global(jobject handle) {
112 if (handle != NULL) {
113 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
114 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
115 }
116 }
117
118
119 void JNIHandles::oops_do(OopClosure* f) {
120 f->do_oop(&_deleted_handle);
121 _global_handles->oops_do(f);
122 }
123
124
125 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
126 _weak_global_handles->weak_oops_do(is_alive, f);
127 }
128
129
130 void JNIHandles::initialize() {
131 _global_handles = JNIHandleBlock::allocate_block();
132 _weak_global_handles = JNIHandleBlock::allocate_block();
133 EXCEPTION_MARK;
134 // We will never reach the CATCH below since Exceptions::_throw will cause
135 // the VM to exit if an exception is thrown during initialization
136 Klass* k = SystemDictionary::Object_klass();
137 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
138 }
139
140
141 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
142 JNIHandleBlock* block = thread->active_handles();
143
144 // Look back past possible native calls to jni_PushLocalFrame.
145 while (block != NULL) {
146 if (block->chain_contains(handle)) {
147 return true;
148 }
149 block = block->pop_frame_link();
150 }
151 return false;
152 }
153
154
155 // Determine if the handle is somewhere in the current thread's stack.
156 // We easily can't isolate any particular stack frame the handle might
157 // come from, so we'll check the whole stack.
158
159 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
160 // If there is no java frame, then this must be top level code, such
161 // as the java command executable, in which case, this type of handle
162 // is not permitted.
163 return (thr->has_last_Java_frame() &&
164 (void*)obj < (void*)thr->stack_base() &&
165 (void*)obj >= (void*)thr->last_Java_sp());
166 }
167
168
169 bool JNIHandles::is_global_handle(jobject handle) {
170 return _global_handles->chain_contains(handle);
171 }
172
173
174 bool JNIHandles::is_weak_global_handle(jobject handle) {
175 return _weak_global_handles->chain_contains(handle);
176 }
177
178 long JNIHandles::global_handle_memory_usage() {
179 return _global_handles->memory_usage();
180 }
181
182 long JNIHandles::weak_global_handle_memory_usage() {
183 return _weak_global_handles->memory_usage();
184 }
185
186
187 class AlwaysAliveClosure: public BoolObjectClosure {
188 public:
189 bool do_object_b(oop obj) { return true; }
190 };
191
192 class CountHandleClosure: public OopClosure {
193 private:
194 int _count;
195 public:
196 CountHandleClosure(): _count(0) {}
197 virtual void do_oop(oop* ooph) {
198 if (*ooph != JNIHandles::deleted_handle()) {
199 _count++;
200 }
201 }
202 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
203 int count() { return _count; }
204 };
205
206 // We assume this is called at a safepoint: no lock is needed.
207 void JNIHandles::print_on(outputStream* st) {
208 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
209 assert(_global_handles != NULL && _weak_global_handles != NULL,
210 "JNIHandles not initialized");
211
212 CountHandleClosure global_handle_count;
213 AlwaysAliveClosure always_alive;
214 oops_do(&global_handle_count);
215 weak_oops_do(&always_alive, &global_handle_count);
216
217 st->print_cr("JNI global references: %d", global_handle_count.count());
218 st->cr();
219 st->flush();
220 }
221
222 class VerifyHandleClosure: public OopClosure {
223 public:
224 virtual void do_oop(oop* root) {
225 (*root)->verify();
226 }
227 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
228 };
229
230 void JNIHandles::verify() {
231 VerifyHandleClosure verify_handle;
232 AlwaysAliveClosure always_alive;
233
234 oops_do(&verify_handle);
235 weak_oops_do(&always_alive, &verify_handle);
236 }
237
238
239
240 void jni_handles_init() {
241 JNIHandles::initialize();
242 }
243
244
245 int JNIHandleBlock::_blocks_allocated = 0;
246 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
247 #ifndef PRODUCT
248 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
249 #endif
250
251
252 void JNIHandleBlock::zap() {
253 // Zap block values
254 _top = 0;
255 for (int index = 0; index < block_size_in_oops; index++) {
256 _handles[index] = badJNIHandle;
257 }
258 }
259
260 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
261 assert(thread == NULL || thread == Thread::current(), "sanity check");
262 JNIHandleBlock* block;
263 // Check the thread-local free list for a block so we don't
264 // have to acquire a mutex.
265 if (thread != NULL && thread->free_handle_block() != NULL) {
266 block = thread->free_handle_block();
267 thread->set_free_handle_block(block->_next);
268 }
269 else {
270 // locking with safepoint checking introduces a potential deadlock:
271 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
272 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
273 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
274 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
275 Mutex::_no_safepoint_check_flag);
276 if (_block_free_list == NULL) {
277 // Allocate new block
278 block = new JNIHandleBlock();
279 _blocks_allocated++;
280 if (TraceJNIHandleAllocation) {
281 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
282 p2i(block), _blocks_allocated);
283 }
284 if (ZapJNIHandleArea) block->zap();
285 #ifndef PRODUCT
286 // Link new block to list of all allocated blocks
287 block->_block_list_link = _block_list;
288 _block_list = block;
289 #endif
290 } else {
291 // Get block from free list
292 block = _block_free_list;
293 _block_free_list = _block_free_list->_next;
294 }
295 }
296 block->_top = 0;
297 block->_next = NULL;
298 block->_pop_frame_link = NULL;
299 block->_planned_capacity = block_size_in_oops;
300 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
301 debug_only(block->_last = NULL);
302 debug_only(block->_free_list = NULL);
303 debug_only(block->_allocate_before_rebuild = -1);
304 return block;
305 }
306
307
308 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
309 assert(thread == NULL || thread == Thread::current(), "sanity check");
310 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
311 // Put returned block at the beginning of the thread-local free list.
312 // Note that if thread == NULL, we use it as an implicit argument that
313 // we _don't_ want the block to be kept on the free_handle_block.
314 // See for instance JavaThread::exit().
315 if (thread != NULL ) {
316 if (ZapJNIHandleArea) block->zap();
317 JNIHandleBlock* freelist = thread->free_handle_block();
318 block->_pop_frame_link = NULL;
319 thread->set_free_handle_block(block);
320
321 // Add original freelist to end of chain
322 if ( freelist != NULL ) {
323 while ( block->_next != NULL ) block = block->_next;
324 block->_next = freelist;
325 }
326 block = NULL;
327 }
328 if (block != NULL) {
329 // Return blocks to free list
330 // locking with safepoint checking introduces a potential deadlock:
331 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
332 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
333 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
334 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
335 Mutex::_no_safepoint_check_flag);
336 while (block != NULL) {
337 if (ZapJNIHandleArea) block->zap();
338 JNIHandleBlock* next = block->_next;
339 block->_next = _block_free_list;
340 _block_free_list = block;
341 block = next;
342 }
343 }
344 if (pop_frame_link != NULL) {
345 // As a sanity check we release blocks pointed to by the pop_frame_link.
346 // This should never happen (only if PopLocalFrame is not called the
347 // correct number of times).
348 release_block(pop_frame_link, thread);
349 }
350 }
351
352
353 void JNIHandleBlock::oops_do(OopClosure* f) {
354 JNIHandleBlock* current_chain = this;
355 // Iterate over chain of blocks, followed by chains linked through the
356 // pop frame links.
357 while (current_chain != NULL) {
358 for (JNIHandleBlock* current = current_chain; current != NULL;
359 current = current->_next) {
360 assert(current == current_chain || current->pop_frame_link() == NULL,
361 "only blocks first in chain should have pop frame link set");
362 for (int index = 0; index < current->_top; index++) {
363 oop* root = &(current->_handles)[index];
364 oop value = *root;
365 // traverse heap pointers only, not deleted handles or free list
366 // pointers
367 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
368 f->do_oop(root);
369 }
370 }
371 // the next handle block is valid only if current block is full
372 if (current->_top < block_size_in_oops) {
373 break;
374 }
375 }
376 current_chain = current_chain->pop_frame_link();
377 }
378 }
379
380
381 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
382 OopClosure* f) {
383 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
384 assert(current->pop_frame_link() == NULL,
385 "blocks holding weak global JNI handles should not have pop frame link set");
386 for (int index = 0; index < current->_top; index++) {
387 oop* root = &(current->_handles)[index];
388 oop value = *root;
389 // traverse heap pointers only, not deleted handles or free list pointers
390 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
391 if (is_alive->do_object_b(value)) {
392 // The weakly referenced object is alive, update pointer
393 f->do_oop(root);
394 } else {
395 // The weakly referenced object is not alive, clear the reference by storing NULL
396 if (TraceReferenceGC) {
397 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root));
398 }
399 *root = NULL;
400 }
401 }
402 }
403 // the next handle block is valid only if current block is full
404 if (current->_top < block_size_in_oops) {
405 break;
406 }
407 }
408
409 /*
410 * JVMTI data structures may also contain weak oops. The iteration of them
411 * is placed here so that we don't need to add it to each of the collectors.
412 */
413 JvmtiExport::weak_oops_do(is_alive, f);
414 }
415
416
417 jobject JNIHandleBlock::allocate_handle(oop obj) {
418 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
419 if (_top == 0) {
420 // This is the first allocation or the initial block got zapped when
421 // entering a native function. If we have any following blocks they are
422 // not valid anymore.
423 for (JNIHandleBlock* current = _next; current != NULL;
424 current = current->_next) {
425 assert(current->_last == NULL, "only first block should have _last set");
426 assert(current->_free_list == NULL,
427 "only first block should have _free_list set");
428 current->_top = 0;
429 if (ZapJNIHandleArea) current->zap();
430 }
431 // Clear initial block
432 _free_list = NULL;
433 _allocate_before_rebuild = 0;
434 _last = this;
435 if (ZapJNIHandleArea) zap();
436 }
437
438 // Try last block
439 if (_last->_top < block_size_in_oops) {
440 oop* handle = &(_last->_handles)[_last->_top++];
441 *handle = obj;
442 return (jobject) handle;
443 }
444
445 // Try free list
446 if (_free_list != NULL) {
447 oop* handle = _free_list;
448 _free_list = (oop*) *_free_list;
449 *handle = obj;
450 return (jobject) handle;
451 }
452 // Check if unused block follow last
453 if (_last->_next != NULL) {
454 // update last and retry
455 _last = _last->_next;
456 return allocate_handle(obj);
457 }
458
459 // No space available, we have to rebuild free list or expand
460 if (_allocate_before_rebuild == 0) {
461 rebuild_free_list(); // updates _allocate_before_rebuild counter
462 } else {
463 // Append new block
464 Thread* thread = Thread::current();
465 Handle obj_handle(thread, obj);
466 // This can block, so we need to preserve obj across call.
467 _last->_next = JNIHandleBlock::allocate_block(thread);
468 _last = _last->_next;
469 _allocate_before_rebuild--;
470 obj = obj_handle();
471 }
472 return allocate_handle(obj); // retry
473 }
474
475
476 void JNIHandleBlock::rebuild_free_list() {
477 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
478 int free = 0;
479 int blocks = 0;
480 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
481 for (int index = 0; index < current->_top; index++) {
482 oop* handle = &(current->_handles)[index];
483 if (*handle == JNIHandles::deleted_handle()) {
484 // this handle was cleared out by a delete call, reuse it
485 *handle = (oop) _free_list;
486 _free_list = handle;
487 free++;
488 }
489 }
490 // we should not rebuild free list if there are unused handles at the end
491 assert(current->_top == block_size_in_oops, "just checking");
492 blocks++;
493 }
494 // Heuristic: if more than half of the handles are free we rebuild next time
495 // as well, otherwise we append a corresponding number of new blocks before
496 // attempting a free list rebuild again.
497 int total = blocks * block_size_in_oops;
498 int extra = total - 2*free;
499 if (extra > 0) {
500 // Not as many free handles as we would like - compute number of new blocks to append
501 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
502 }
503 if (TraceJNIHandleAllocation) {
504 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
505 p2i(this), blocks, total-free, free, _allocate_before_rebuild);
506 }
507 }
508
509
510 bool JNIHandleBlock::contains(jobject handle) const {
511 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
512 }
513
514
515 bool JNIHandleBlock::chain_contains(jobject handle) const {
516 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
517 if (current->contains(handle)) {
518 return true;
519 }
520 }
521 return false;
522 }
523
524
525 int JNIHandleBlock::length() const {
526 int result = 1;
527 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
528 result++;
529 }
530 return result;
531 }
532
533 const size_t JNIHandleBlock::get_number_of_live_handles() {
534 CountHandleClosure counter;
535 oops_do(&counter);
536 return counter.count();
537 }
538
539 // This method is not thread-safe, i.e., must be called while holding a lock on the
540 // structure.
541 long JNIHandleBlock::memory_usage() const {
542 return length() * sizeof(JNIHandleBlock);
543 }
544
545
546 #ifndef PRODUCT
547
548 bool JNIHandleBlock::any_contains(jobject handle) {
549 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
550 if (current->contains(handle)) {
551 return true;
552 }
553 }
554 return false;
555 }
556
557 void JNIHandleBlock::print_statistics() {
558 int used_blocks = 0;
559 int free_blocks = 0;
560 int used_handles = 0;
561 int free_handles = 0;
562 JNIHandleBlock* block = _block_list;
563 while (block != NULL) {
564 if (block->_top > 0) {
565 used_blocks++;
566 } else {
567 free_blocks++;
568 }
569 used_handles += block->_top;
570 free_handles += (block_size_in_oops - block->_top);
571 block = block->_block_list_link;
572 }
573 tty->print_cr("JNIHandleBlocks statistics");
574 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
575 tty->print_cr("- blocks in use: %d", used_blocks);
576 tty->print_cr("- blocks free: %d", free_blocks);
577 tty->print_cr("- handles in use: %d", used_handles);
578 tty->print_cr("- handles free: %d", free_handles);
579 }
580
581 #endif