1 /*
2 * Copyright (c) 1998, 2008, 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 "incls/_precompiled.incl"
26 # include "incls/_jniHandles.cpp.incl"
27
28
29 JNIHandleBlock* JNIHandles::_global_handles = NULL;
30 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
31 oop JNIHandles::_deleted_handle = NULL;
32
33
34 jobject JNIHandles::make_local(oop obj) {
35 if (obj == NULL) {
36 return NULL; // ignore null handles
37 } else {
38 Thread* thread = Thread::current();
39 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
40 return thread->active_handles()->allocate_handle(obj);
41 }
42 }
43
44
45 // optimized versions
46
47 jobject JNIHandles::make_local(Thread* thread, oop obj) {
48 if (obj == NULL) {
49 return NULL; // ignore null handles
50 } else {
51 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
52 return thread->active_handles()->allocate_handle(obj);
53 }
54 }
55
56
57 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
58 if (obj == NULL) {
59 return NULL; // ignore null handles
60 } else {
61 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
62 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
63 return thread->active_handles()->allocate_handle(obj);
64 }
65 }
66
67
68 jobject JNIHandles::make_global(Handle obj) {
69 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
70 jobject res = NULL;
71 if (!obj.is_null()) {
72 // ignore null handles
73 MutexLocker ml(JNIGlobalHandle_lock);
74 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
75 res = _global_handles->allocate_handle(obj());
76 } else {
77 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
78 }
79
80 return res;
81 }
82
83
84 jobject JNIHandles::make_weak_global(Handle obj) {
85 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
86 jobject res = NULL;
87 if (!obj.is_null()) {
88 // ignore null handles
89 MutexLocker ml(JNIGlobalHandle_lock);
90 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
91 res = _weak_global_handles->allocate_handle(obj());
92 } else {
93 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
94 }
95 return res;
96 }
97
98 jmethodID JNIHandles::make_jmethod_id(methodHandle mh) {
99 return (jmethodID) make_weak_global(mh);
100 }
101
102
103
104 void JNIHandles::change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh) {
105 MutexLocker ml(JNIGlobalHandle_lock); // Is this necessary?
106 Handle obj = (Handle)mh;
107 oop* jobj = (oop*)jmid;
108 *jobj = obj();
109 }
110
111
112 void JNIHandles::destroy_global(jobject handle) {
113 if (handle != NULL) {
114 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
115 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
116 }
117 }
118
119
120 void JNIHandles::destroy_weak_global(jobject handle) {
121 if (handle != NULL) {
122 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
123 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
124 }
125 }
126
127 void JNIHandles::destroy_jmethod_id(jmethodID mid) {
128 destroy_weak_global((jobject)mid);
129 }
130
131
132 void JNIHandles::oops_do(OopClosure* f) {
133 f->do_oop(&_deleted_handle);
134 _global_handles->oops_do(f);
135 }
136
137
138 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
139 _weak_global_handles->weak_oops_do(is_alive, f);
140 }
141
142
143 void JNIHandles::initialize() {
144 _global_handles = JNIHandleBlock::allocate_block();
145 _weak_global_handles = JNIHandleBlock::allocate_block();
146 EXCEPTION_MARK;
147 // We will never reach the CATCH below since Exceptions::_throw will cause
148 // the VM to exit if an exception is thrown during initialization
149 klassOop k = SystemDictionary::Object_klass();
150 _deleted_handle = instanceKlass::cast(k)->allocate_permanent_instance(CATCH);
151 }
152
153
154 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
155 JNIHandleBlock* block = thread->active_handles();
156
157 // Look back past possible native calls to jni_PushLocalFrame.
158 while (block != NULL) {
159 if (block->chain_contains(handle)) {
160 return true;
161 }
162 block = block->pop_frame_link();
163 }
164 return false;
165 }
166
167
168 // Determine if the handle is somewhere in the current thread's stack.
169 // We easily can't isolate any particular stack frame the handle might
170 // come from, so we'll check the whole stack.
171
172 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
173 // If there is no java frame, then this must be top level code, such
174 // as the java command executable, in which case, this type of handle
175 // is not permitted.
176 return (thr->has_last_Java_frame() &&
177 (void*)obj < (void*)thr->stack_base() &&
178 (void*)obj >= (void*)thr->last_Java_sp());
179 }
180
181
182 bool JNIHandles::is_global_handle(jobject handle) {
183 return _global_handles->chain_contains(handle);
184 }
185
186
187 bool JNIHandles::is_weak_global_handle(jobject handle) {
188 return _weak_global_handles->chain_contains(handle);
189 }
190
191 long JNIHandles::global_handle_memory_usage() {
192 return _global_handles->memory_usage();
193 }
194
195 long JNIHandles::weak_global_handle_memory_usage() {
196 return _weak_global_handles->memory_usage();
197 }
198
199
200 class AlwaysAliveClosure: public BoolObjectClosure {
201 public:
202 bool do_object_b(oop obj) { return true; }
203 void do_object(oop obj) { assert(false, "Don't call"); }
204 };
205
206 class CountHandleClosure: public OopClosure {
207 private:
208 int _count;
209 public:
210 CountHandleClosure(): _count(0) {}
211 virtual void do_oop(oop* unused) {
212 _count++;
213 }
214 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
215 int count() { return _count; }
216 };
217
218 // We assume this is called at a safepoint: no lock is needed.
219 void JNIHandles::print_on(outputStream* st) {
220 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
221 assert(_global_handles != NULL && _weak_global_handles != NULL,
222 "JNIHandles not initialized");
223
224 CountHandleClosure global_handle_count;
225 AlwaysAliveClosure always_alive;
226 oops_do(&global_handle_count);
227 weak_oops_do(&always_alive, &global_handle_count);
228
229 st->print_cr("JNI global references: %d", global_handle_count.count());
230 st->cr();
231 st->flush();
232 }
233
234 class VerifyHandleClosure: public OopClosure {
235 public:
236 virtual void do_oop(oop* root) {
237 (*root)->verify();
238 }
239 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
240 };
241
242 void JNIHandles::verify() {
243 VerifyHandleClosure verify_handle;
244 AlwaysAliveClosure always_alive;
245
246 oops_do(&verify_handle);
247 weak_oops_do(&always_alive, &verify_handle);
248 }
249
250
251
252 void jni_handles_init() {
253 JNIHandles::initialize();
254 }
255
256
257 int JNIHandleBlock::_blocks_allocated = 0;
258 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
259 #ifndef PRODUCT
260 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
261 #endif
262
263
264 void JNIHandleBlock::zap() {
265 // Zap block values
266 _top = 0;
267 for (int index = 0; index < block_size_in_oops; index++) {
268 _handles[index] = badJNIHandle;
269 }
270 }
271
272 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
273 assert(thread == NULL || thread == Thread::current(), "sanity check");
274 JNIHandleBlock* block;
275 // Check the thread-local free list for a block so we don't
276 // have to acquire a mutex.
277 if (thread != NULL && thread->free_handle_block() != NULL) {
278 block = thread->free_handle_block();
279 thread->set_free_handle_block(block->_next);
280 }
281 else {
282 // locking with safepoint checking introduces a potential deadlock:
283 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
284 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
285 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
286 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
287 Mutex::_no_safepoint_check_flag);
288 if (_block_free_list == NULL) {
289 // Allocate new block
290 block = new JNIHandleBlock();
291 _blocks_allocated++;
292 if (TraceJNIHandleAllocation) {
293 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
294 block, _blocks_allocated);
295 }
296 if (ZapJNIHandleArea) block->zap();
297 #ifndef PRODUCT
298 // Link new block to list of all allocated blocks
299 block->_block_list_link = _block_list;
300 _block_list = block;
301 #endif
302 } else {
303 // Get block from free list
304 block = _block_free_list;
305 _block_free_list = _block_free_list->_next;
306 }
307 }
308 block->_top = 0;
309 block->_next = NULL;
310 block->_pop_frame_link = NULL;
311 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
312 debug_only(block->_last = NULL);
313 debug_only(block->_free_list = NULL);
314 debug_only(block->_allocate_before_rebuild = -1);
315 return block;
316 }
317
318
319 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
320 assert(thread == NULL || thread == Thread::current(), "sanity check");
321 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
322 // Put returned block at the beginning of the thread-local free list.
323 // Note that if thread == NULL, we use it as an implicit argument that
324 // we _don't_ want the block to be kept on the free_handle_block.
325 // See for instance JavaThread::exit().
326 if (thread != NULL ) {
327 if (ZapJNIHandleArea) block->zap();
328 JNIHandleBlock* freelist = thread->free_handle_block();
329 block->_pop_frame_link = NULL;
330 thread->set_free_handle_block(block);
331
332 // Add original freelist to end of chain
333 if ( freelist != NULL ) {
334 while ( block->_next != NULL ) block = block->_next;
335 block->_next = freelist;
336 }
337 block = NULL;
338 }
339 if (block != NULL) {
340 // Return blocks to free list
341 // locking with safepoint checking introduces a potential deadlock:
342 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
343 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
344 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
345 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
346 Mutex::_no_safepoint_check_flag);
347 while (block != NULL) {
348 if (ZapJNIHandleArea) block->zap();
349 JNIHandleBlock* next = block->_next;
350 block->_next = _block_free_list;
351 _block_free_list = block;
352 block = next;
353 }
354 }
355 if (pop_frame_link != NULL) {
356 // As a sanity check we release blocks pointed to by the pop_frame_link.
357 // This should never happen (only if PopLocalFrame is not called the
358 // correct number of times).
359 release_block(pop_frame_link, thread);
360 }
361 }
362
363
364 void JNIHandleBlock::oops_do(OopClosure* f) {
365 JNIHandleBlock* current_chain = this;
366 // Iterate over chain of blocks, followed by chains linked through the
367 // pop frame links.
368 while (current_chain != NULL) {
369 for (JNIHandleBlock* current = current_chain; current != NULL;
370 current = current->_next) {
371 assert(current == current_chain || current->pop_frame_link() == NULL,
372 "only blocks first in chain should have pop frame link set");
373 for (int index = 0; index < current->_top; index++) {
374 oop* root = &(current->_handles)[index];
375 oop value = *root;
376 // traverse heap pointers only, not deleted handles or free list
377 // pointers
378 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
379 f->do_oop(root);
380 }
381 }
382 // the next handle block is valid only if current block is full
383 if (current->_top < block_size_in_oops) {
384 break;
385 }
386 }
387 current_chain = current_chain->pop_frame_link();
388 }
389 }
390
391
392 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
393 OopClosure* f) {
394 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
395 assert(current->pop_frame_link() == NULL,
396 "blocks holding weak global JNI handles should not have pop frame link set");
397 for (int index = 0; index < current->_top; index++) {
398 oop* root = &(current->_handles)[index];
399 oop value = *root;
400 // traverse heap pointers only, not deleted handles or free list pointers
401 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
402 if (is_alive->do_object_b(value)) {
403 // The weakly referenced object is alive, update pointer
404 f->do_oop(root);
405 } else {
406 // The weakly referenced object is not alive, clear the reference by storing NULL
407 if (TraceReferenceGC) {
408 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
409 }
410 *root = NULL;
411 }
412 }
413 }
414 // the next handle block is valid only if current block is full
415 if (current->_top < block_size_in_oops) {
416 break;
417 }
418 }
419 }
420
421
422 jobject JNIHandleBlock::allocate_handle(oop obj) {
423 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
424 if (_top == 0) {
425 // This is the first allocation or the initial block got zapped when
426 // entering a native function. If we have any following blocks they are
427 // not valid anymore.
428 for (JNIHandleBlock* current = _next; current != NULL;
429 current = current->_next) {
430 assert(current->_last == NULL, "only first block should have _last set");
431 assert(current->_free_list == NULL,
432 "only first block should have _free_list set");
433 current->_top = 0;
434 if (ZapJNIHandleArea) current->zap();
435 }
436 // Clear initial block
437 _free_list = NULL;
438 _allocate_before_rebuild = 0;
439 _last = this;
440 if (ZapJNIHandleArea) zap();
441 }
442
443 // Try last block
444 if (_last->_top < block_size_in_oops) {
445 oop* handle = &(_last->_handles)[_last->_top++];
446 *handle = obj;
447 return (jobject) handle;
448 }
449
450 // Try free list
451 if (_free_list != NULL) {
452 oop* handle = _free_list;
453 _free_list = (oop*) *_free_list;
454 *handle = obj;
455 return (jobject) handle;
456 }
457 // Check if unused block follow last
458 if (_last->_next != NULL) {
459 // update last and retry
460 _last = _last->_next;
461 return allocate_handle(obj);
462 }
463
464 // No space available, we have to rebuild free list or expand
465 if (_allocate_before_rebuild == 0) {
466 rebuild_free_list(); // updates _allocate_before_rebuild counter
467 } else {
468 // Append new block
469 Thread* thread = Thread::current();
470 Handle obj_handle(thread, obj);
471 // This can block, so we need to preserve obj accross call.
472 _last->_next = JNIHandleBlock::allocate_block(thread);
473 _last = _last->_next;
474 _allocate_before_rebuild--;
475 obj = obj_handle();
476 }
477 return allocate_handle(obj); // retry
478 }
479
480
481 void JNIHandleBlock::rebuild_free_list() {
482 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
483 int free = 0;
484 int blocks = 0;
485 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
486 for (int index = 0; index < current->_top; index++) {
487 oop* handle = &(current->_handles)[index];
488 if (*handle == JNIHandles::deleted_handle()) {
489 // this handle was cleared out by a delete call, reuse it
490 *handle = (oop) _free_list;
491 _free_list = handle;
492 free++;
493 }
494 }
495 // we should not rebuild free list if there are unused handles at the end
496 assert(current->_top == block_size_in_oops, "just checking");
497 blocks++;
498 }
499 // Heuristic: if more than half of the handles are free we rebuild next time
500 // as well, otherwise we append a corresponding number of new blocks before
501 // attempting a free list rebuild again.
502 int total = blocks * block_size_in_oops;
503 int extra = total - 2*free;
504 if (extra > 0) {
505 // Not as many free handles as we would like - compute number of new blocks to append
506 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
507 }
508 if (TraceJNIHandleAllocation) {
509 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
510 this, blocks, total-free, free, _allocate_before_rebuild);
511 }
512 }
513
514
515 bool JNIHandleBlock::contains(jobject handle) const {
516 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
517 }
518
519
520 bool JNIHandleBlock::chain_contains(jobject handle) const {
521 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
522 if (current->contains(handle)) {
523 return true;
524 }
525 }
526 return false;
527 }
528
529
530 int JNIHandleBlock::length() const {
531 int result = 1;
532 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
533 result++;
534 }
535 return result;
536 }
537
538 // This method is not thread-safe, i.e., must be called whule holding a lock on the
539 // structure.
540 long JNIHandleBlock::memory_usage() const {
541 return length() * sizeof(JNIHandleBlock);
542 }
543
544
545 #ifndef PRODUCT
546
547 bool JNIHandleBlock::any_contains(jobject handle) {
548 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
549 if (current->contains(handle)) {
550 return true;
551 }
552 }
553 return false;
554 }
555
556 void JNIHandleBlock::print_statistics() {
557 int used_blocks = 0;
558 int free_blocks = 0;
559 int used_handles = 0;
560 int free_handles = 0;
561 JNIHandleBlock* block = _block_list;
562 while (block != NULL) {
563 if (block->_top > 0) {
564 used_blocks++;
565 } else {
566 free_blocks++;
567 }
568 used_handles += block->_top;
569 free_handles += (block_size_in_oops - block->_top);
570 block = block->_block_list_link;
571 }
572 tty->print_cr("JNIHandleBlocks statistics");
573 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
574 tty->print_cr("- blocks in use: %d", used_blocks);
575 tty->print_cr("- blocks free: %d", free_blocks);
576 tty->print_cr("- handles in use: %d", used_handles);
577 tty->print_cr("- handles free: %d", free_handles);
578 }
579
580 #endif