1 /*
2 * Copyright 1998-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any 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 jobject res = NULL;
70 if (!obj.is_null()) {
71 // ignore null handles
72 MutexLocker ml(JNIGlobalHandle_lock);
73 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
74 res = _global_handles->allocate_handle(obj());
75 } else {
76 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
77 }
78
79 return res;
80 }
81
82
83 jobject JNIHandles::make_weak_global(Handle obj) {
84 jobject res = NULL;
85 if (!obj.is_null()) {
86 // ignore null handles
87 MutexLocker ml(JNIGlobalHandle_lock);
88 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
89 res = _weak_global_handles->allocate_handle(obj());
90 } else {
91 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
92 }
93 return res;
94 }
95
96 jmethodID JNIHandles::make_jmethod_id(methodHandle mh) {
97 return (jmethodID) make_weak_global(mh);
98 }
99
100
101
102 void JNIHandles::change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh) {
103 MutexLocker ml(JNIGlobalHandle_lock); // Is this necessary?
104 Handle obj = (Handle)mh;
105 oop* jobj = (oop*)jmid;
106 *jobj = obj();
107 }
108
109
110 void JNIHandles::destroy_global(jobject handle) {
111 if (handle != NULL) {
112 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
113 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
114 }
115 }
116
117
118 void JNIHandles::destroy_weak_global(jobject handle) {
119 if (handle != NULL) {
120 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
121 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
122 }
123 }
124
125 void JNIHandles::destroy_jmethod_id(jmethodID mid) {
126 destroy_weak_global((jobject)mid);
127 }
128
129
130 void JNIHandles::oops_do(OopClosure* f) {
131 f->do_oop(&_deleted_handle);
132 _global_handles->oops_do(f);
133 }
134
135
136 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
137 _weak_global_handles->weak_oops_do(is_alive, f);
138 }
139
140
141 void JNIHandles::initialize() {
142 _global_handles = JNIHandleBlock::allocate_block();
143 _weak_global_handles = JNIHandleBlock::allocate_block();
144 EXCEPTION_MARK;
145 // We will never reach the CATCH below since Exceptions::_throw will cause
146 // the VM to exit if an exception is thrown during initialization
147 klassOop k = SystemDictionary::Object_klass();
148 _deleted_handle = instanceKlass::cast(k)->allocate_permanent_instance(CATCH);
149 }
150
151
152 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
153 JNIHandleBlock* block = thread->active_handles();
154
155 // Look back past possible native calls to jni_PushLocalFrame.
156 while (block != NULL) {
157 if (block->chain_contains(handle)) {
158 return true;
159 }
160 block = block->pop_frame_link();
161 }
162 return false;
163 }
164
165
166 // Determine if the handle is somewhere in the current thread's stack.
167 // We easily can't isolate any particular stack frame the handle might
168 // come from, so we'll check the whole stack.
169
170 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
171 // If there is no java frame, then this must be top level code, such
172 // as the java command executable, in which case, this type of handle
173 // is not permitted.
174 return (thr->has_last_Java_frame() &&
175 (void*)obj < (void*)thr->stack_base() &&
176 (void*)obj >= (void*)thr->last_Java_sp());
177 }
178
179
180 bool JNIHandles::is_global_handle(jobject handle) {
181 return _global_handles->chain_contains(handle);
182 }
183
184
185 bool JNIHandles::is_weak_global_handle(jobject handle) {
186 return _weak_global_handles->chain_contains(handle);
187 }
188
189 long JNIHandles::global_handle_memory_usage() {
190 return _global_handles->memory_usage();
191 }
192
193 long JNIHandles::weak_global_handle_memory_usage() {
194 return _weak_global_handles->memory_usage();
195 }
196
197
198 class AlwaysAliveClosure: public BoolObjectClosure {
199 public:
200 bool do_object_b(oop obj) { return true; }
201 void do_object(oop obj) { assert(false, "Don't call"); }
202 };
203
204 class CountHandleClosure: public OopClosure {
205 private:
206 int _count;
207 public:
208 CountHandleClosure(): _count(0) {}
209 virtual void do_oop(oop* unused) {
210 _count++;
211 }
212 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
213 int count() { return _count; }
214 };
215
216 // We assume this is called at a safepoint: no lock is needed.
217 void JNIHandles::print_on(outputStream* st) {
218 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
219 assert(_global_handles != NULL && _weak_global_handles != NULL,
220 "JNIHandles not initialized");
221
222 CountHandleClosure global_handle_count;
223 AlwaysAliveClosure always_alive;
224 oops_do(&global_handle_count);
225 weak_oops_do(&always_alive, &global_handle_count);
226
227 st->print_cr("JNI global references: %d", global_handle_count.count());
228 st->cr();
229 st->flush();
230 }
231
232 class VerifyHandleClosure: public OopClosure {
233 public:
234 virtual void do_oop(oop* root) {
235 (*root)->verify();
236 }
237 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
238 };
239
240 void JNIHandles::verify() {
241 VerifyHandleClosure verify_handle;
242 AlwaysAliveClosure always_alive;
243
244 oops_do(&verify_handle);
245 weak_oops_do(&always_alive, &verify_handle);
246 }
247
248
249
250 void jni_handles_init() {
251 JNIHandles::initialize();
252 }
253
254
255 int JNIHandleBlock::_blocks_allocated = 0;
256 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
257 #ifndef PRODUCT
258 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
259 #endif
260
261
262 void JNIHandleBlock::zap() {
263 // Zap block values
264 _top = 0;
265 for (int index = 0; index < block_size_in_oops; index++) {
266 _handles[index] = badJNIHandle;
267 }
268 }
269
270 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
271 assert(thread == NULL || thread == Thread::current(), "sanity check");
272 JNIHandleBlock* block;
273 // Check the thread-local free list for a block so we don't
274 // have to acquire a mutex.
275 if (thread != NULL && thread->free_handle_block() != NULL) {
276 block = thread->free_handle_block();
277 thread->set_free_handle_block(block->_next);
278 }
279 else {
280 // locking with safepoint checking introduces a potential deadlock:
281 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
282 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
283 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
284 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
285 Mutex::_no_safepoint_check_flag);
286 if (_block_free_list == NULL) {
287 // Allocate new block
288 block = new JNIHandleBlock();
289 _blocks_allocated++;
290 if (TraceJNIHandleAllocation) {
291 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
292 block, _blocks_allocated);
293 }
294 if (ZapJNIHandleArea) block->zap();
295 #ifndef PRODUCT
296 // Link new block to list of all allocated blocks
297 block->_block_list_link = _block_list;
298 _block_list = block;
299 #endif
300 } else {
301 // Get block from free list
302 block = _block_free_list;
303 _block_free_list = _block_free_list->_next;
304 }
305 }
306 block->_top = 0;
307 block->_next = NULL;
308 block->_pop_frame_link = NULL;
309 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
310 debug_only(block->_last = NULL);
311 debug_only(block->_free_list = NULL);
312 debug_only(block->_allocate_before_rebuild = -1);
313 return block;
314 }
315
316
317 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
318 assert(thread == NULL || thread == Thread::current(), "sanity check");
319 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
320 // Put returned block at the beginning of the thread-local free list.
321 // Note that if thread == NULL, we use it as an implicit argument that
322 // we _don't_ want the block to be kept on the free_handle_block.
323 // See for instance JavaThread::exit().
324 if (thread != NULL ) {
325 if (ZapJNIHandleArea) block->zap();
326 JNIHandleBlock* freelist = thread->free_handle_block();
327 block->_pop_frame_link = NULL;
328 thread->set_free_handle_block(block);
329
330 // Add original freelist to end of chain
331 if ( freelist != NULL ) {
332 while ( block->_next != NULL ) block = block->_next;
333 block->_next = freelist;
334 }
335 block = NULL;
336 }
337 if (block != NULL) {
338 // Return blocks to free list
339 // locking with safepoint checking introduces a potential deadlock:
340 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
341 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
342 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
343 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
344 Mutex::_no_safepoint_check_flag);
345 while (block != NULL) {
346 if (ZapJNIHandleArea) block->zap();
347 JNIHandleBlock* next = block->_next;
348 block->_next = _block_free_list;
349 _block_free_list = block;
350 block = next;
351 }
352 }
353 if (pop_frame_link != NULL) {
354 // As a sanity check we release blocks pointed to by the pop_frame_link.
355 // This should never happen (only if PopLocalFrame is not called the
356 // correct number of times).
357 release_block(pop_frame_link, thread);
358 }
359 }
360
361
362 void JNIHandleBlock::oops_do(OopClosure* f) {
363 JNIHandleBlock* current_chain = this;
364 // Iterate over chain of blocks, followed by chains linked through the
365 // pop frame links.
366 while (current_chain != NULL) {
367 for (JNIHandleBlock* current = current_chain; current != NULL;
368 current = current->_next) {
369 assert(current == current_chain || current->pop_frame_link() == NULL,
370 "only blocks first in chain should have pop frame link set");
371 for (int index = 0; index < current->_top; index++) {
372 oop* root = &(current->_handles)[index];
373 oop value = *root;
374 // traverse heap pointers only, not deleted handles or free list
375 // pointers
376 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
377 f->do_oop(root);
378 }
379 }
380 // the next handle block is valid only if current block is full
381 if (current->_top < block_size_in_oops) {
382 break;
383 }
384 }
385 current_chain = current_chain->pop_frame_link();
386 }
387 }
388
389
390 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
391 OopClosure* f) {
392 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
393 assert(current->pop_frame_link() == NULL,
394 "blocks holding weak global JNI handles should not have pop frame link set");
395 for (int index = 0; index < current->_top; index++) {
396 oop* root = &(current->_handles)[index];
397 oop value = *root;
398 // traverse heap pointers only, not deleted handles or free list pointers
399 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
400 if (is_alive->do_object_b(value)) {
401 // The weakly referenced object is alive, update pointer
402 f->do_oop(root);
403 } else {
404 // The weakly referenced object is not alive, clear the reference by storing NULL
405 if (TraceReferenceGC) {
406 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
407 }
408 *root = NULL;
409 }
410 }
411 }
412 // the next handle block is valid only if current block is full
413 if (current->_top < block_size_in_oops) {
414 break;
415 }
416 }
417 }
418
419
420 jobject JNIHandleBlock::allocate_handle(oop obj) {
421 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
422 if (_top == 0) {
423 // This is the first allocation or the initial block got zapped when
424 // entering a native function. If we have any following blocks they are
425 // not valid anymore.
426 for (JNIHandleBlock* current = _next; current != NULL;
427 current = current->_next) {
428 assert(current->_last == NULL, "only first block should have _last set");
429 assert(current->_free_list == NULL,
430 "only first block should have _free_list set");
431 current->_top = 0;
432 if (ZapJNIHandleArea) current->zap();
433 }
434 // Clear initial block
435 _free_list = NULL;
436 _allocate_before_rebuild = 0;
437 _last = this;
438 if (ZapJNIHandleArea) zap();
439 }
440
441 // Try last block
442 if (_last->_top < block_size_in_oops) {
443 oop* handle = &(_last->_handles)[_last->_top++];
444 *handle = obj;
445 return (jobject) handle;
446 }
447
448 // Try free list
449 if (_free_list != NULL) {
450 oop* handle = _free_list;
451 _free_list = (oop*) *_free_list;
452 *handle = obj;
453 return (jobject) handle;
454 }
455 // Check if unused block follow last
456 if (_last->_next != NULL) {
457 // update last and retry
458 _last = _last->_next;
459 return allocate_handle(obj);
460 }
461
462 // No space available, we have to rebuild free list or expand
463 if (_allocate_before_rebuild == 0) {
464 rebuild_free_list(); // updates _allocate_before_rebuild counter
465 } else {
466 // Append new block
467 Thread* thread = Thread::current();
468 Handle obj_handle(thread, obj);
469 // This can block, so we need to preserve obj accross call.
470 _last->_next = JNIHandleBlock::allocate_block(thread);
471 _last = _last->_next;
472 _allocate_before_rebuild--;
473 obj = obj_handle();
474 }
475 return allocate_handle(obj); // retry
476 }
477
478
479 void JNIHandleBlock::rebuild_free_list() {
480 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
481 int free = 0;
482 int blocks = 0;
483 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
484 for (int index = 0; index < current->_top; index++) {
485 oop* handle = &(current->_handles)[index];
486 if (*handle == JNIHandles::deleted_handle()) {
487 // this handle was cleared out by a delete call, reuse it
488 *handle = (oop) _free_list;
489 _free_list = handle;
490 free++;
491 }
492 }
493 // we should not rebuild free list if there are unused handles at the end
494 assert(current->_top == block_size_in_oops, "just checking");
495 blocks++;
496 }
497 // Heuristic: if more than half of the handles are free we rebuild next time
498 // as well, otherwise we append a corresponding number of new blocks before
499 // attempting a free list rebuild again.
500 int total = blocks * block_size_in_oops;
501 int extra = total - 2*free;
502 if (extra > 0) {
503 // Not as many free handles as we would like - compute number of new blocks to append
504 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
505 }
506 if (TraceJNIHandleAllocation) {
507 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
508 this, blocks, total-free, free, _allocate_before_rebuild);
509 }
510 }
511
512
513 bool JNIHandleBlock::contains(jobject handle) const {
514 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
515 }
516
517
518 bool JNIHandleBlock::chain_contains(jobject handle) const {
519 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
520 if (current->contains(handle)) {
521 return true;
522 }
523 }
524 return false;
525 }
526
527
528 int JNIHandleBlock::length() const {
529 int result = 1;
530 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
531 result++;
532 }
533 return result;
534 }
535
536 // This method is not thread-safe, i.e., must be called whule holding a lock on the
537 // structure.
538 long JNIHandleBlock::memory_usage() const {
539 return length() * sizeof(JNIHandleBlock);
540 }
541
542
543 #ifndef PRODUCT
544
545 bool JNIHandleBlock::any_contains(jobject handle) {
546 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
547 if (current->contains(handle)) {
548 return true;
549 }
550 }
551 return false;
552 }
553
554 void JNIHandleBlock::print_statistics() {
555 int used_blocks = 0;
556 int free_blocks = 0;
557 int used_handles = 0;
558 int free_handles = 0;
559 JNIHandleBlock* block = _block_list;
560 while (block != NULL) {
561 if (block->_top > 0) {
562 used_blocks++;
563 } else {
564 free_blocks++;
565 }
566 used_handles += block->_top;
567 free_handles += (block_size_in_oops - block->_top);
568 block = block->_block_list_link;
569 }
570 tty->print_cr("JNIHandleBlocks statistics");
571 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
572 tty->print_cr("- blocks in use: %d", used_blocks);
573 tty->print_cr("- blocks free: %d", free_blocks);
574 tty->print_cr("- handles in use: %d", used_handles);
575 tty->print_cr("- handles free: %d", free_handles);
576 }
577
578 #endif