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 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 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
302 debug_only(block->_last = NULL);
303 debug_only(block->_free_list = NULL);
304 debug_only(block->_allocate_before_rebuild = -1);
305 return block;
306 }
307
308
309 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
310 assert(thread == NULL || thread == Thread::current(), "sanity check");
311 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
312 // Put returned block at the beginning of the thread-local free list.
313 // Note that if thread == NULL, we use it as an implicit argument that
314 // we _don't_ want the block to be kept on the free_handle_block.
315 // See for instance JavaThread::exit().
316 if (thread != NULL ) {
317 if (ZapJNIHandleArea) block->zap();
318 JNIHandleBlock* freelist = thread->free_handle_block();
319 block->_pop_frame_link = NULL;
320 thread->set_free_handle_block(block);
321
322 // Add original freelist to end of chain
323 if ( freelist != NULL ) {
324 while ( block->_next != NULL ) block = block->_next;
325 block->_next = freelist;
326 }
327 block = NULL;
328 }
329 if (block != NULL) {
330 // Return blocks to free list
331 // locking with safepoint checking introduces a potential deadlock:
332 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
333 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
334 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
335 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
336 Mutex::_no_safepoint_check_flag);
337 while (block != NULL) {
338 if (ZapJNIHandleArea) block->zap();
339 JNIHandleBlock* next = block->_next;
340 block->_next = _block_free_list;
341 _block_free_list = block;
342 block = next;
343 }
344 }
345 if (pop_frame_link != NULL) {
346 // As a sanity check we release blocks pointed to by the pop_frame_link.
347 // This should never happen (only if PopLocalFrame is not called the
348 // correct number of times).
349 release_block(pop_frame_link, thread);
350 }
351 }
352
353
354 void JNIHandleBlock::oops_do(OopClosure* f) {
355 JNIHandleBlock* current_chain = this;
356 // Iterate over chain of blocks, followed by chains linked through the
357 // pop frame links.
358 while (current_chain != NULL) {
359 for (JNIHandleBlock* current = current_chain; current != NULL;
360 current = current->_next) {
361 assert(current == current_chain || current->pop_frame_link() == NULL,
362 "only blocks first in chain should have pop frame link set");
363 for (int index = 0; index < current->_top; index++) {
364 oop* root = &(current->_handles)[index];
365 oop value = *root;
366 // traverse heap pointers only, not deleted handles or free list
367 // pointers
368 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
369 f->do_oop(root);
370 }
371 }
372 // the next handle block is valid only if current block is full
373 if (current->_top < block_size_in_oops) {
374 break;
375 }
376 }
377 current_chain = current_chain->pop_frame_link();
378 }
379 }
380
381
382 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
383 OopClosure* f) {
384 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
385 assert(current->pop_frame_link() == NULL,
386 "blocks holding weak global JNI handles should not have pop frame link set");
387 for (int index = 0; index < current->_top; index++) {
388 oop* root = &(current->_handles)[index];
389 oop value = *root;
390 // traverse heap pointers only, not deleted handles or free list pointers
391 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
392 if (is_alive->do_object_b(value)) {
393 // The weakly referenced object is alive, update pointer
394 f->do_oop(root);
395 } else {
396 // The weakly referenced object is not alive, clear the reference by storing NULL
397 if (TraceReferenceGC) {
398 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
399 }
400 *root = NULL;
401 }
402 }
403 }
404 // the next handle block is valid only if current block is full
405 if (current->_top < block_size_in_oops) {
406 break;
407 }
408 }
409
410 /*
411 * JVMTI data structures may also contain weak oops. The iteration of them
412 * is placed here so that we don't need to add it to each of the collectors.
413 */
414 JvmtiExport::weak_oops_do(is_alive, f);
415 }
416
417
418 jobject JNIHandleBlock::allocate_handle(oop obj) {
419 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
420 if (_top == 0) {
421 // This is the first allocation or the initial block got zapped when
422 // entering a native function. If we have any following blocks they are
423 // not valid anymore.
424 for (JNIHandleBlock* current = _next; current != NULL;
425 current = current->_next) {
426 assert(current->_last == NULL, "only first block should have _last set");
427 assert(current->_free_list == NULL,
428 "only first block should have _free_list set");
429 current->_top = 0;
430 if (ZapJNIHandleArea) current->zap();
431 }
432 // Clear initial block
433 _free_list = NULL;
434 _allocate_before_rebuild = 0;
435 _last = this;
436 if (ZapJNIHandleArea) zap();
437 }
438
439 // Try last block
440 if (_last->_top < block_size_in_oops) {
441 oop* handle = &(_last->_handles)[_last->_top++];
442 *handle = obj;
443 return (jobject) handle;
444 }
445
446 // Try free list
447 if (_free_list != NULL) {
448 oop* handle = _free_list;
449 _free_list = (oop*) *_free_list;
450 *handle = obj;
451 return (jobject) handle;
452 }
453 // Check if unused block follow last
454 if (_last->_next != NULL) {
455 // update last and retry
456 _last = _last->_next;
457 return allocate_handle(obj);
458 }
459
460 // No space available, we have to rebuild free list or expand
461 if (_allocate_before_rebuild == 0) {
462 rebuild_free_list(); // updates _allocate_before_rebuild counter
463 } else {
464 // Append new block
465 Thread* thread = Thread::current();
466 Handle obj_handle(thread, obj);
467 // This can block, so we need to preserve obj across call.
468 _last->_next = JNIHandleBlock::allocate_block(thread);
469 _last = _last->_next;
470 _allocate_before_rebuild--;
471 obj = obj_handle();
472 }
473 return allocate_handle(obj); // retry
474 }
475
476
477 void JNIHandleBlock::rebuild_free_list() {
478 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
479 int free = 0;
480 int blocks = 0;
481 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
482 for (int index = 0; index < current->_top; index++) {
483 oop* handle = &(current->_handles)[index];
484 if (*handle == JNIHandles::deleted_handle()) {
485 // this handle was cleared out by a delete call, reuse it
486 *handle = (oop) _free_list;
487 _free_list = handle;
488 free++;
489 }
490 }
491 // we should not rebuild free list if there are unused handles at the end
492 assert(current->_top == block_size_in_oops, "just checking");
493 blocks++;
494 }
495 // Heuristic: if more than half of the handles are free we rebuild next time
496 // as well, otherwise we append a corresponding number of new blocks before
497 // attempting a free list rebuild again.
498 int total = blocks * block_size_in_oops;
499 int extra = total - 2*free;
500 if (extra > 0) {
501 // Not as many free handles as we would like - compute number of new blocks to append
502 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
503 }
504 if (TraceJNIHandleAllocation) {
505 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
506 this, blocks, total-free, free, _allocate_before_rebuild);
507 }
508 }
509
510
511 bool JNIHandleBlock::contains(jobject handle) const {
512 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
513 }
514
515
516 bool JNIHandleBlock::chain_contains(jobject handle) const {
517 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
518 if (current->contains(handle)) {
519 return true;
520 }
521 }
522 return false;
523 }
524
525
526 int JNIHandleBlock::length() const {
527 int result = 1;
528 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
529 result++;
530 }
531 return result;
532 }
533
534 // This method is not thread-safe, i.e., must be called while holding a lock on the
535 // structure.
536 long JNIHandleBlock::memory_usage() const {
537 return length() * sizeof(JNIHandleBlock);
538 }
539
540
541 #ifndef PRODUCT
542
543 bool JNIHandleBlock::any_contains(jobject handle) {
544 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
545 if (current->contains(handle)) {
546 return true;
547 }
548 }
549 return false;
550 }
551
552 void JNIHandleBlock::print_statistics() {
553 int used_blocks = 0;
554 int free_blocks = 0;
555 int used_handles = 0;
556 int free_handles = 0;
557 JNIHandleBlock* block = _block_list;
558 while (block != NULL) {
559 if (block->_top > 0) {
560 used_blocks++;
561 } else {
562 free_blocks++;
563 }
564 used_handles += block->_top;
565 free_handles += (block_size_in_oops - block->_top);
566 block = block->_block_list_link;
567 }
568 tty->print_cr("JNIHandleBlocks statistics");
569 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
570 tty->print_cr("- blocks in use: %d", used_blocks);
571 tty->print_cr("- blocks free: %d", free_blocks);
572 tty->print_cr("- handles in use: %d", used_handles);
573 tty->print_cr("- handles free: %d", free_handles);
574 }
575
576 #endif