1 /*
2 * Copyright (c) 1998, 2011, 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 #ifdef TARGET_OS_FAMILY_linux
32 # include "thread_linux.inline.hpp"
33 #endif
34 #ifdef TARGET_OS_FAMILY_solaris
35 # include "thread_solaris.inline.hpp"
36 #endif
37 #ifdef TARGET_OS_FAMILY_windows
38 # include "thread_windows.inline.hpp"
39 #endif
40
41
42 JNIHandleBlock* JNIHandles::_global_handles = NULL;
43 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
44 oop JNIHandles::_deleted_handle = NULL;
45
46
47 jobject JNIHandles::make_local(oop obj) {
48 if (obj == NULL) {
49 return NULL; // ignore null handles
50 } else {
51 Thread* thread = Thread::current();
52 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
53 return thread->active_handles()->allocate_handle(obj);
54 }
55 }
56
57
58 // optimized versions
59
60 jobject JNIHandles::make_local(Thread* thread, oop obj) {
61 if (obj == NULL) {
62 return NULL; // ignore null handles
63 } else {
64 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
65 return thread->active_handles()->allocate_handle(obj);
66 }
67 }
68
69
70 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
71 if (obj == NULL) {
72 return NULL; // ignore null handles
73 } else {
74 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
75 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
76 return thread->active_handles()->allocate_handle(obj);
77 }
78 }
79
80
81 jobject JNIHandles::make_global(Handle obj) {
82 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
83 jobject res = NULL;
84 if (!obj.is_null()) {
85 // ignore null handles
86 MutexLocker ml(JNIGlobalHandle_lock);
87 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
88 res = _global_handles->allocate_handle(obj());
89 } else {
90 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
91 }
92
93 return res;
94 }
95
96
97 jobject JNIHandles::make_weak_global(Handle obj) {
98 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
99 jobject res = NULL;
100 if (!obj.is_null()) {
101 // ignore null handles
102 MutexLocker ml(JNIGlobalHandle_lock);
103 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
104 res = _weak_global_handles->allocate_handle(obj());
105 } else {
106 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
107 }
108 return res;
109 }
110
111 jmethodID JNIHandles::make_jmethod_id(methodHandle mh) {
112 return (jmethodID) make_weak_global(mh);
113 }
114
115
116
117 void JNIHandles::change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh) {
118 MutexLocker ml(JNIGlobalHandle_lock); // Is this necessary?
119 Handle obj = (Handle)mh;
120 oop* jobj = (oop*)jmid;
121 *jobj = obj();
122 }
123
124
125 void JNIHandles::destroy_global(jobject handle) {
126 if (handle != NULL) {
127 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
128 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
129 }
130 }
131
132
133 void JNIHandles::destroy_weak_global(jobject handle) {
134 if (handle != NULL) {
135 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
136 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
137 }
138 }
139
140 void JNIHandles::destroy_jmethod_id(jmethodID mid) {
141 destroy_weak_global((jobject)mid);
142 }
143
144
145 void JNIHandles::oops_do(OopClosure* f) {
146 f->do_oop(&_deleted_handle);
147 _global_handles->oops_do(f);
148 }
149
150
151 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
152 _weak_global_handles->weak_oops_do(is_alive, f);
153 }
154
155
156 void JNIHandles::initialize() {
157 _global_handles = JNIHandleBlock::allocate_block();
158 _weak_global_handles = JNIHandleBlock::allocate_block();
159 EXCEPTION_MARK;
160 // We will never reach the CATCH below since Exceptions::_throw will cause
161 // the VM to exit if an exception is thrown during initialization
162 klassOop k = SystemDictionary::Object_klass();
163 _deleted_handle = instanceKlass::cast(k)->allocate_permanent_instance(CATCH);
164 }
165
166
167 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
168 JNIHandleBlock* block = thread->active_handles();
169
170 // Look back past possible native calls to jni_PushLocalFrame.
171 while (block != NULL) {
172 if (block->chain_contains(handle)) {
173 return true;
174 }
175 block = block->pop_frame_link();
176 }
177 return false;
178 }
179
180
181 // Determine if the handle is somewhere in the current thread's stack.
182 // We easily can't isolate any particular stack frame the handle might
183 // come from, so we'll check the whole stack.
184
185 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
186 // If there is no java frame, then this must be top level code, such
187 // as the java command executable, in which case, this type of handle
188 // is not permitted.
189 return (thr->has_last_Java_frame() &&
190 (void*)obj < (void*)thr->stack_base() &&
191 (void*)obj >= (void*)thr->last_Java_sp());
192 }
193
194
195 bool JNIHandles::is_global_handle(jobject handle) {
196 return _global_handles->chain_contains(handle);
197 }
198
199
200 bool JNIHandles::is_weak_global_handle(jobject handle) {
201 return _weak_global_handles->chain_contains(handle);
202 }
203
204 long JNIHandles::global_handle_memory_usage() {
205 return _global_handles->memory_usage();
206 }
207
208 long JNIHandles::weak_global_handle_memory_usage() {
209 return _weak_global_handles->memory_usage();
210 }
211
212
213 class AlwaysAliveClosure: public BoolObjectClosure {
214 public:
215 bool do_object_b(oop obj) { return true; }
216 void do_object(oop obj) { assert(false, "Don't call"); }
217 };
218
219 class CountHandleClosure: public OopClosure {
220 private:
221 int _count;
222 public:
223 CountHandleClosure(): _count(0) {}
224 virtual void do_oop(oop* unused) {
225 _count++;
226 }
227 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
228 int count() { return _count; }
229 };
230
231 // We assume this is called at a safepoint: no lock is needed.
232 void JNIHandles::print_on(outputStream* st) {
233 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
234 assert(_global_handles != NULL && _weak_global_handles != NULL,
235 "JNIHandles not initialized");
236
237 CountHandleClosure global_handle_count;
238 AlwaysAliveClosure always_alive;
239 oops_do(&global_handle_count);
240 weak_oops_do(&always_alive, &global_handle_count);
241
242 st->print_cr("JNI global references: %d", global_handle_count.count());
243 st->cr();
244 st->flush();
245 }
246
247 class VerifyHandleClosure: public OopClosure {
248 public:
249 virtual void do_oop(oop* root) {
250 (*root)->verify();
251 }
252 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
253 };
254
255 void JNIHandles::verify() {
256 VerifyHandleClosure verify_handle;
257 AlwaysAliveClosure always_alive;
258
259 oops_do(&verify_handle);
260 weak_oops_do(&always_alive, &verify_handle);
261 }
262
263
264
265 void jni_handles_init() {
266 JNIHandles::initialize();
267 }
268
269
270 int JNIHandleBlock::_blocks_allocated = 0;
271 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
272 #ifndef PRODUCT
273 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
274 #endif
275
276
277 void JNIHandleBlock::zap() {
278 // Zap block values
279 _top = 0;
280 for (int index = 0; index < block_size_in_oops; index++) {
281 _handles[index] = badJNIHandle;
282 }
283 }
284
285 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
286 assert(thread == NULL || thread == Thread::current(), "sanity check");
287 JNIHandleBlock* block;
288 // Check the thread-local free list for a block so we don't
289 // have to acquire a mutex.
290 if (thread != NULL && thread->free_handle_block() != NULL) {
291 block = thread->free_handle_block();
292 thread->set_free_handle_block(block->_next);
293 }
294 else {
295 // locking with safepoint checking introduces a potential deadlock:
296 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
297 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
298 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
299 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
300 Mutex::_no_safepoint_check_flag);
301 if (_block_free_list == NULL) {
302 // Allocate new block
303 block = new JNIHandleBlock();
304 _blocks_allocated++;
305 if (TraceJNIHandleAllocation) {
306 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
307 block, _blocks_allocated);
308 }
309 if (ZapJNIHandleArea) block->zap();
310 #ifndef PRODUCT
311 // Link new block to list of all allocated blocks
312 block->_block_list_link = _block_list;
313 _block_list = block;
314 #endif
315 } else {
316 // Get block from free list
317 block = _block_free_list;
318 _block_free_list = _block_free_list->_next;
319 }
320 }
321 block->_top = 0;
322 block->_next = NULL;
323 block->_pop_frame_link = NULL;
324 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
325 debug_only(block->_last = NULL);
326 debug_only(block->_free_list = NULL);
327 debug_only(block->_allocate_before_rebuild = -1);
328 return block;
329 }
330
331
332 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
333 assert(thread == NULL || thread == Thread::current(), "sanity check");
334 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
335 // Put returned block at the beginning of the thread-local free list.
336 // Note that if thread == NULL, we use it as an implicit argument that
337 // we _don't_ want the block to be kept on the free_handle_block.
338 // See for instance JavaThread::exit().
339 if (thread != NULL ) {
340 if (ZapJNIHandleArea) block->zap();
341 JNIHandleBlock* freelist = thread->free_handle_block();
342 block->_pop_frame_link = NULL;
343 thread->set_free_handle_block(block);
344
345 // Add original freelist to end of chain
346 if ( freelist != NULL ) {
347 while ( block->_next != NULL ) block = block->_next;
348 block->_next = freelist;
349 }
350 block = NULL;
351 }
352 if (block != NULL) {
353 // Return blocks to free list
354 // locking with safepoint checking introduces a potential deadlock:
355 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
356 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
357 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
358 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
359 Mutex::_no_safepoint_check_flag);
360 while (block != NULL) {
361 if (ZapJNIHandleArea) block->zap();
362 JNIHandleBlock* next = block->_next;
363 block->_next = _block_free_list;
364 _block_free_list = block;
365 block = next;
366 }
367 }
368 if (pop_frame_link != NULL) {
369 // As a sanity check we release blocks pointed to by the pop_frame_link.
370 // This should never happen (only if PopLocalFrame is not called the
371 // correct number of times).
372 release_block(pop_frame_link, thread);
373 }
374 }
375
376
377 void JNIHandleBlock::oops_do(OopClosure* f) {
378 JNIHandleBlock* current_chain = this;
379 // Iterate over chain of blocks, followed by chains linked through the
380 // pop frame links.
381 while (current_chain != NULL) {
382 for (JNIHandleBlock* current = current_chain; current != NULL;
383 current = current->_next) {
384 assert(current == current_chain || current->pop_frame_link() == NULL,
385 "only blocks first in chain should 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
390 // pointers
391 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
392 f->do_oop(root);
393 }
394 }
395 // the next handle block is valid only if current block is full
396 if (current->_top < block_size_in_oops) {
397 break;
398 }
399 }
400 current_chain = current_chain->pop_frame_link();
401 }
402 }
403
404
405 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
406 OopClosure* f) {
407 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
408 assert(current->pop_frame_link() == NULL,
409 "blocks holding weak global JNI handles should not have pop frame link set");
410 for (int index = 0; index < current->_top; index++) {
411 oop* root = &(current->_handles)[index];
412 oop value = *root;
413 // traverse heap pointers only, not deleted handles or free list pointers
414 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
415 if (is_alive->do_object_b(value)) {
416 // The weakly referenced object is alive, update pointer
417 f->do_oop(root);
418 } else {
419 // The weakly referenced object is not alive, clear the reference by storing NULL
420 if (TraceReferenceGC) {
421 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
422 }
423 *root = NULL;
424 }
425 }
426 }
427 // the next handle block is valid only if current block is full
428 if (current->_top < block_size_in_oops) {
429 break;
430 }
431 }
432
433 /*
434 * JVMTI data structures may also contain weak oops. The iteration of them
435 * is placed here so that we don't need to add it to each of the collectors.
436 */
437 JvmtiExport::weak_oops_do(is_alive, f);
438 }
439
440
441 jobject JNIHandleBlock::allocate_handle(oop obj) {
442 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
443 if (_top == 0) {
444 // This is the first allocation or the initial block got zapped when
445 // entering a native function. If we have any following blocks they are
446 // not valid anymore.
447 for (JNIHandleBlock* current = _next; current != NULL;
448 current = current->_next) {
449 assert(current->_last == NULL, "only first block should have _last set");
450 assert(current->_free_list == NULL,
451 "only first block should have _free_list set");
452 current->_top = 0;
453 if (ZapJNIHandleArea) current->zap();
454 }
455 // Clear initial block
456 _free_list = NULL;
457 _allocate_before_rebuild = 0;
458 _last = this;
459 if (ZapJNIHandleArea) zap();
460 }
461
462 // Try last block
463 if (_last->_top < block_size_in_oops) {
464 oop* handle = &(_last->_handles)[_last->_top++];
465 *handle = obj;
466 return (jobject) handle;
467 }
468
469 // Try free list
470 if (_free_list != NULL) {
471 oop* handle = _free_list;
472 _free_list = (oop*) *_free_list;
473 *handle = obj;
474 return (jobject) handle;
475 }
476 // Check if unused block follow last
477 if (_last->_next != NULL) {
478 // update last and retry
479 _last = _last->_next;
480 return allocate_handle(obj);
481 }
482
483 // No space available, we have to rebuild free list or expand
484 if (_allocate_before_rebuild == 0) {
485 rebuild_free_list(); // updates _allocate_before_rebuild counter
486 } else {
487 // Append new block
488 Thread* thread = Thread::current();
489 Handle obj_handle(thread, obj);
490 // This can block, so we need to preserve obj accross call.
491 _last->_next = JNIHandleBlock::allocate_block(thread);
492 _last = _last->_next;
493 _allocate_before_rebuild--;
494 obj = obj_handle();
495 }
496 return allocate_handle(obj); // retry
497 }
498
499
500 void JNIHandleBlock::rebuild_free_list() {
501 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
502 int free = 0;
503 int blocks = 0;
504 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
505 for (int index = 0; index < current->_top; index++) {
506 oop* handle = &(current->_handles)[index];
507 if (*handle == JNIHandles::deleted_handle()) {
508 // this handle was cleared out by a delete call, reuse it
509 *handle = (oop) _free_list;
510 _free_list = handle;
511 free++;
512 }
513 }
514 // we should not rebuild free list if there are unused handles at the end
515 assert(current->_top == block_size_in_oops, "just checking");
516 blocks++;
517 }
518 // Heuristic: if more than half of the handles are free we rebuild next time
519 // as well, otherwise we append a corresponding number of new blocks before
520 // attempting a free list rebuild again.
521 int total = blocks * block_size_in_oops;
522 int extra = total - 2*free;
523 if (extra > 0) {
524 // Not as many free handles as we would like - compute number of new blocks to append
525 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
526 }
527 if (TraceJNIHandleAllocation) {
528 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
529 this, blocks, total-free, free, _allocate_before_rebuild);
530 }
531 }
532
533
534 bool JNIHandleBlock::contains(jobject handle) const {
535 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
536 }
537
538
539 bool JNIHandleBlock::chain_contains(jobject handle) const {
540 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
541 if (current->contains(handle)) {
542 return true;
543 }
544 }
545 return false;
546 }
547
548
549 int JNIHandleBlock::length() const {
550 int result = 1;
551 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
552 result++;
553 }
554 return result;
555 }
556
557 // This method is not thread-safe, i.e., must be called whule holding a lock on the
558 // structure.
559 long JNIHandleBlock::memory_usage() const {
560 return length() * sizeof(JNIHandleBlock);
561 }
562
563
564 #ifndef PRODUCT
565
566 bool JNIHandleBlock::any_contains(jobject handle) {
567 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
568 if (current->contains(handle)) {
569 return true;
570 }
571 }
572 return false;
573 }
574
575 void JNIHandleBlock::print_statistics() {
576 int used_blocks = 0;
577 int free_blocks = 0;
578 int used_handles = 0;
579 int free_handles = 0;
580 JNIHandleBlock* block = _block_list;
581 while (block != NULL) {
582 if (block->_top > 0) {
583 used_blocks++;
584 } else {
585 free_blocks++;
586 }
587 used_handles += block->_top;
588 free_handles += (block_size_in_oops - block->_top);
589 block = block->_block_list_link;
590 }
591 tty->print_cr("JNIHandleBlocks statistics");
592 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
593 tty->print_cr("- blocks in use: %d", used_blocks);
594 tty->print_cr("- blocks free: %d", free_blocks);
595 tty->print_cr("- handles in use: %d", used_handles);
596 tty->print_cr("- handles free: %d", free_handles);
597 }
598
599 #endif