1 /*
2 * Copyright (c) 1998, 2010, 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 "runtime/jniHandles.hpp"
29 #include "runtime/mutexLocker.hpp"
30 #ifdef TARGET_OS_FAMILY_linux
31 # include "thread_linux.inline.hpp"
32 #endif
33 #ifdef TARGET_OS_FAMILY_solaris
34 # include "thread_solaris.inline.hpp"
35 #endif
36 #ifdef TARGET_OS_FAMILY_windows
37 # include "thread_windows.inline.hpp"
38 #endif
39
40
41 JNIHandleBlock* JNIHandles::_global_handles = NULL;
42 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
43 oop JNIHandles::_deleted_handle = NULL;
44
45
46 jobject JNIHandles::make_local(oop obj) {
47 if (obj == NULL) {
48 return NULL; // ignore null handles
49 } else {
50 Thread* thread = Thread::current();
51 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
52 return thread->active_handles()->allocate_handle(obj);
53 }
54 }
55
56
57 // optimized versions
58
59 jobject JNIHandles::make_local(Thread* thread, oop obj) {
60 if (obj == NULL) {
61 return NULL; // ignore null handles
62 } else {
63 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
64 return thread->active_handles()->allocate_handle(obj);
65 }
66 }
67
68
69 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
70 if (obj == NULL) {
71 return NULL; // ignore null handles
72 } else {
73 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
74 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
75 return thread->active_handles()->allocate_handle(obj);
76 }
77 }
78
79
80 jobject JNIHandles::make_global(Handle obj) {
81 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
82 jobject res = NULL;
83 if (!obj.is_null()) {
84 // ignore null handles
85 MutexLocker ml(JNIGlobalHandle_lock);
86 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
87 res = _global_handles->allocate_handle(obj());
88 } else {
89 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
90 }
91
92 return res;
93 }
94
95
96 jobject JNIHandles::make_weak_global(Handle obj) {
97 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
98 jobject res = NULL;
99 if (!obj.is_null()) {
100 // ignore null handles
101 MutexLocker ml(JNIGlobalHandle_lock);
102 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
103 res = _weak_global_handles->allocate_handle(obj());
104 } else {
105 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
106 }
107 return res;
108 }
109
110 jmethodID JNIHandles::make_jmethod_id(methodHandle mh) {
111 return (jmethodID) make_weak_global(mh);
112 }
113
114
115
116 void JNIHandles::change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh) {
117 MutexLocker ml(JNIGlobalHandle_lock); // Is this necessary?
118 Handle obj = (Handle)mh;
119 oop* jobj = (oop*)jmid;
120 *jobj = obj();
121 }
122
123
124 void JNIHandles::destroy_global(jobject handle) {
125 if (handle != NULL) {
126 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
127 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
128 }
129 }
130
131
132 void JNIHandles::destroy_weak_global(jobject handle) {
133 if (handle != NULL) {
134 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
135 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
136 }
137 }
138
139 void JNIHandles::destroy_jmethod_id(jmethodID mid) {
140 destroy_weak_global((jobject)mid);
141 }
142
143
144 void JNIHandles::oops_do(OopClosure* f) {
145 f->do_oop(&_deleted_handle);
146 _global_handles->oops_do(f);
147 }
148
149
150 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
151 _weak_global_handles->weak_oops_do(is_alive, f);
152 }
153
154
155 void JNIHandles::initialize() {
156 _global_handles = JNIHandleBlock::allocate_block();
157 _weak_global_handles = JNIHandleBlock::allocate_block();
158 EXCEPTION_MARK;
159 // We will never reach the CATCH below since Exceptions::_throw will cause
160 // the VM to exit if an exception is thrown during initialization
161 klassOop k = SystemDictionary::Object_klass();
162 _deleted_handle = instanceKlass::cast(k)->allocate_permanent_instance(CATCH);
163 }
164
165
166 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
167 JNIHandleBlock* block = thread->active_handles();
168
169 // Look back past possible native calls to jni_PushLocalFrame.
170 while (block != NULL) {
171 if (block->chain_contains(handle)) {
172 return true;
173 }
174 block = block->pop_frame_link();
175 }
176 return false;
177 }
178
179
180 // Determine if the handle is somewhere in the current thread's stack.
181 // We easily can't isolate any particular stack frame the handle might
182 // come from, so we'll check the whole stack.
183
184 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
185 // If there is no java frame, then this must be top level code, such
186 // as the java command executable, in which case, this type of handle
187 // is not permitted.
188 return (thr->has_last_Java_frame() &&
189 (void*)obj < (void*)thr->stack_base() &&
190 (void*)obj >= (void*)thr->last_Java_sp());
191 }
192
193
194 bool JNIHandles::is_global_handle(jobject handle) {
195 return _global_handles->chain_contains(handle);
196 }
197
198
199 bool JNIHandles::is_weak_global_handle(jobject handle) {
200 return _weak_global_handles->chain_contains(handle);
201 }
202
203 long JNIHandles::global_handle_memory_usage() {
204 return _global_handles->memory_usage();
205 }
206
207 long JNIHandles::weak_global_handle_memory_usage() {
208 return _weak_global_handles->memory_usage();
209 }
210
211
212 class AlwaysAliveClosure: public BoolObjectClosure {
213 public:
214 bool do_object_b(oop obj) { return true; }
215 void do_object(oop obj) { assert(false, "Don't call"); }
216 };
217
218 class CountHandleClosure: public OopClosure {
219 private:
220 int _count;
221 public:
222 CountHandleClosure(): _count(0) {}
223 virtual void do_oop(oop* unused) {
224 _count++;
225 }
226 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
227 int count() { return _count; }
228 };
229
230 // We assume this is called at a safepoint: no lock is needed.
231 void JNIHandles::print_on(outputStream* st) {
232 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
233 assert(_global_handles != NULL && _weak_global_handles != NULL,
234 "JNIHandles not initialized");
235
236 CountHandleClosure global_handle_count;
237 AlwaysAliveClosure always_alive;
238 oops_do(&global_handle_count);
239 weak_oops_do(&always_alive, &global_handle_count);
240
241 st->print_cr("JNI global references: %d", global_handle_count.count());
242 st->cr();
243 st->flush();
244 }
245
246 class VerifyHandleClosure: public OopClosure {
247 public:
248 virtual void do_oop(oop* root) {
249 (*root)->verify();
250 }
251 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
252 };
253
254 void JNIHandles::verify() {
255 VerifyHandleClosure verify_handle;
256 AlwaysAliveClosure always_alive;
257
258 oops_do(&verify_handle);
259 weak_oops_do(&always_alive, &verify_handle);
260 }
261
262
263
264 void jni_handles_init() {
265 JNIHandles::initialize();
266 }
267
268
269 int JNIHandleBlock::_blocks_allocated = 0;
270 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
271 #ifndef PRODUCT
272 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
273 #endif
274
275
276 void JNIHandleBlock::zap() {
277 // Zap block values
278 _top = 0;
279 for (int index = 0; index < block_size_in_oops; index++) {
280 _handles[index] = badJNIHandle;
281 }
282 }
283
284 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
285 assert(thread == NULL || thread == Thread::current(), "sanity check");
286 JNIHandleBlock* block;
287 // Check the thread-local free list for a block so we don't
288 // have to acquire a mutex.
289 if (thread != NULL && thread->free_handle_block() != NULL) {
290 block = thread->free_handle_block();
291 thread->set_free_handle_block(block->_next);
292 }
293 else {
294 // locking with safepoint checking introduces a potential deadlock:
295 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
296 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
297 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
298 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
299 Mutex::_no_safepoint_check_flag);
300 if (_block_free_list == NULL) {
301 // Allocate new block
302 block = new JNIHandleBlock();
303 _blocks_allocated++;
304 if (TraceJNIHandleAllocation) {
305 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
306 block, _blocks_allocated);
307 }
308 if (ZapJNIHandleArea) block->zap();
309 #ifndef PRODUCT
310 // Link new block to list of all allocated blocks
311 block->_block_list_link = _block_list;
312 _block_list = block;
313 #endif
314 } else {
315 // Get block from free list
316 block = _block_free_list;
317 _block_free_list = _block_free_list->_next;
318 }
319 }
320 block->_top = 0;
321 block->_next = NULL;
322 block->_pop_frame_link = NULL;
323 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
324 debug_only(block->_last = NULL);
325 debug_only(block->_free_list = NULL);
326 debug_only(block->_allocate_before_rebuild = -1);
327 return block;
328 }
329
330
331 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
332 assert(thread == NULL || thread == Thread::current(), "sanity check");
333 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
334 // Put returned block at the beginning of the thread-local free list.
335 // Note that if thread == NULL, we use it as an implicit argument that
336 // we _don't_ want the block to be kept on the free_handle_block.
337 // See for instance JavaThread::exit().
338 if (thread != NULL ) {
339 if (ZapJNIHandleArea) block->zap();
340 JNIHandleBlock* freelist = thread->free_handle_block();
341 block->_pop_frame_link = NULL;
342 thread->set_free_handle_block(block);
343
344 // Add original freelist to end of chain
345 if ( freelist != NULL ) {
346 while ( block->_next != NULL ) block = block->_next;
347 block->_next = freelist;
348 }
349 block = NULL;
350 }
351 if (block != NULL) {
352 // Return blocks to free list
353 // locking with safepoint checking introduces a potential deadlock:
354 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
355 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
356 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
357 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
358 Mutex::_no_safepoint_check_flag);
359 while (block != NULL) {
360 if (ZapJNIHandleArea) block->zap();
361 JNIHandleBlock* next = block->_next;
362 block->_next = _block_free_list;
363 _block_free_list = block;
364 block = next;
365 }
366 }
367 if (pop_frame_link != NULL) {
368 // As a sanity check we release blocks pointed to by the pop_frame_link.
369 // This should never happen (only if PopLocalFrame is not called the
370 // correct number of times).
371 release_block(pop_frame_link, thread);
372 }
373 }
374
375
376 void JNIHandleBlock::oops_do(OopClosure* f) {
377 JNIHandleBlock* current_chain = this;
378 // Iterate over chain of blocks, followed by chains linked through the
379 // pop frame links.
380 while (current_chain != NULL) {
381 for (JNIHandleBlock* current = current_chain; current != NULL;
382 current = current->_next) {
383 assert(current == current_chain || current->pop_frame_link() == NULL,
384 "only blocks first in chain should have pop frame link set");
385 for (int index = 0; index < current->_top; index++) {
386 oop* root = &(current->_handles)[index];
387 oop value = *root;
388 // traverse heap pointers only, not deleted handles or free list
389 // pointers
390 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
391 f->do_oop(root);
392 }
393 }
394 // the next handle block is valid only if current block is full
395 if (current->_top < block_size_in_oops) {
396 break;
397 }
398 }
399 current_chain = current_chain->pop_frame_link();
400 }
401 }
402
403
404 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
405 OopClosure* f) {
406 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
407 assert(current->pop_frame_link() == NULL,
408 "blocks holding weak global JNI handles should not have pop frame link set");
409 for (int index = 0; index < current->_top; index++) {
410 oop* root = &(current->_handles)[index];
411 oop value = *root;
412 // traverse heap pointers only, not deleted handles or free list pointers
413 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
414 if (is_alive->do_object_b(value)) {
415 // The weakly referenced object is alive, update pointer
416 f->do_oop(root);
417 } else {
418 // The weakly referenced object is not alive, clear the reference by storing NULL
419 if (TraceReferenceGC) {
420 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
421 }
422 *root = NULL;
423 }
424 }
425 }
426 // the next handle block is valid only if current block is full
427 if (current->_top < block_size_in_oops) {
428 break;
429 }
430 }
431 }
432
433
434 jobject JNIHandleBlock::allocate_handle(oop obj) {
435 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
436 if (_top == 0) {
437 // This is the first allocation or the initial block got zapped when
438 // entering a native function. If we have any following blocks they are
439 // not valid anymore.
440 for (JNIHandleBlock* current = _next; current != NULL;
441 current = current->_next) {
442 assert(current->_last == NULL, "only first block should have _last set");
443 assert(current->_free_list == NULL,
444 "only first block should have _free_list set");
445 current->_top = 0;
446 if (ZapJNIHandleArea) current->zap();
447 }
448 // Clear initial block
449 _free_list = NULL;
450 _allocate_before_rebuild = 0;
451 _last = this;
452 if (ZapJNIHandleArea) zap();
453 }
454
455 // Try last block
456 if (_last->_top < block_size_in_oops) {
457 oop* handle = &(_last->_handles)[_last->_top++];
458 *handle = obj;
459 return (jobject) handle;
460 }
461
462 // Try free list
463 if (_free_list != NULL) {
464 oop* handle = _free_list;
465 _free_list = (oop*) *_free_list;
466 *handle = obj;
467 return (jobject) handle;
468 }
469 // Check if unused block follow last
470 if (_last->_next != NULL) {
471 // update last and retry
472 _last = _last->_next;
473 return allocate_handle(obj);
474 }
475
476 // No space available, we have to rebuild free list or expand
477 if (_allocate_before_rebuild == 0) {
478 rebuild_free_list(); // updates _allocate_before_rebuild counter
479 } else {
480 // Append new block
481 Thread* thread = Thread::current();
482 Handle obj_handle(thread, obj);
483 // This can block, so we need to preserve obj accross call.
484 _last->_next = JNIHandleBlock::allocate_block(thread);
485 _last = _last->_next;
486 _allocate_before_rebuild--;
487 obj = obj_handle();
488 }
489 return allocate_handle(obj); // retry
490 }
491
492
493 void JNIHandleBlock::rebuild_free_list() {
494 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
495 int free = 0;
496 int blocks = 0;
497 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
498 for (int index = 0; index < current->_top; index++) {
499 oop* handle = &(current->_handles)[index];
500 if (*handle == JNIHandles::deleted_handle()) {
501 // this handle was cleared out by a delete call, reuse it
502 *handle = (oop) _free_list;
503 _free_list = handle;
504 free++;
505 }
506 }
507 // we should not rebuild free list if there are unused handles at the end
508 assert(current->_top == block_size_in_oops, "just checking");
509 blocks++;
510 }
511 // Heuristic: if more than half of the handles are free we rebuild next time
512 // as well, otherwise we append a corresponding number of new blocks before
513 // attempting a free list rebuild again.
514 int total = blocks * block_size_in_oops;
515 int extra = total - 2*free;
516 if (extra > 0) {
517 // Not as many free handles as we would like - compute number of new blocks to append
518 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
519 }
520 if (TraceJNIHandleAllocation) {
521 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
522 this, blocks, total-free, free, _allocate_before_rebuild);
523 }
524 }
525
526
527 bool JNIHandleBlock::contains(jobject handle) const {
528 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
529 }
530
531
532 bool JNIHandleBlock::chain_contains(jobject handle) const {
533 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
534 if (current->contains(handle)) {
535 return true;
536 }
537 }
538 return false;
539 }
540
541
542 int JNIHandleBlock::length() const {
543 int result = 1;
544 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
545 result++;
546 }
547 return result;
548 }
549
550 // This method is not thread-safe, i.e., must be called whule holding a lock on the
551 // structure.
552 long JNIHandleBlock::memory_usage() const {
553 return length() * sizeof(JNIHandleBlock);
554 }
555
556
557 #ifndef PRODUCT
558
559 bool JNIHandleBlock::any_contains(jobject handle) {
560 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
561 if (current->contains(handle)) {
562 return true;
563 }
564 }
565 return false;
566 }
567
568 void JNIHandleBlock::print_statistics() {
569 int used_blocks = 0;
570 int free_blocks = 0;
571 int used_handles = 0;
572 int free_handles = 0;
573 JNIHandleBlock* block = _block_list;
574 while (block != NULL) {
575 if (block->_top > 0) {
576 used_blocks++;
577 } else {
578 free_blocks++;
579 }
580 used_handles += block->_top;
581 free_handles += (block_size_in_oops - block->_top);
582 block = block->_block_list_link;
583 }
584 tty->print_cr("JNIHandleBlocks statistics");
585 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
586 tty->print_cr("- blocks in use: %d", used_blocks);
587 tty->print_cr("- blocks free: %d", free_blocks);
588 tty->print_cr("- handles in use: %d", used_handles);
589 tty->print_cr("- handles free: %d", free_handles);
590 }
591
592 #endif