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 #ifdef ZERO
177 (void*)obj >= (void*)thr->zero_stack()->sp()
178 #else
179 (void*)obj >= (void*)thr->last_Java_sp()
180 #endif // ZERO
181 );
182 }
183
184
185 bool JNIHandles::is_global_handle(jobject handle) {
186 return _global_handles->chain_contains(handle);
187 }
188
189
190 bool JNIHandles::is_weak_global_handle(jobject handle) {
191 return _weak_global_handles->chain_contains(handle);
192 }
193
194 long JNIHandles::global_handle_memory_usage() {
195 return _global_handles->memory_usage();
196 }
197
198 long JNIHandles::weak_global_handle_memory_usage() {
199 return _weak_global_handles->memory_usage();
200 }
201
202
203 class AlwaysAliveClosure: public BoolObjectClosure {
204 public:
205 bool do_object_b(oop obj) { return true; }
206 void do_object(oop obj) { assert(false, "Don't call"); }
207 };
208
209 class CountHandleClosure: public OopClosure {
210 private:
211 int _count;
212 public:
213 CountHandleClosure(): _count(0) {}
214 virtual void do_oop(oop* unused) {
215 _count++;
216 }
217 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
218 int count() { return _count; }
219 };
220
221 // We assume this is called at a safepoint: no lock is needed.
222 void JNIHandles::print_on(outputStream* st) {
223 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
224 assert(_global_handles != NULL && _weak_global_handles != NULL,
225 "JNIHandles not initialized");
226
227 CountHandleClosure global_handle_count;
228 AlwaysAliveClosure always_alive;
229 oops_do(&global_handle_count);
230 weak_oops_do(&always_alive, &global_handle_count);
231
232 st->print_cr("JNI global references: %d", global_handle_count.count());
233 st->cr();
234 st->flush();
235 }
236
237 class VerifyHandleClosure: public OopClosure {
238 public:
239 virtual void do_oop(oop* root) {
240 (*root)->verify();
241 }
242 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
243 };
244
245 void JNIHandles::verify() {
246 VerifyHandleClosure verify_handle;
247 AlwaysAliveClosure always_alive;
248
249 oops_do(&verify_handle);
250 weak_oops_do(&always_alive, &verify_handle);
251 }
252
253
254
255 void jni_handles_init() {
256 JNIHandles::initialize();
257 }
258
259
260 int JNIHandleBlock::_blocks_allocated = 0;
261 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
262 #ifndef PRODUCT
263 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
264 #endif
265
266
267 void JNIHandleBlock::zap() {
268 // Zap block values
269 _top = 0;
270 for (int index = 0; index < block_size_in_oops; index++) {
271 _handles[index] = badJNIHandle;
272 }
273 }
274
275 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
276 assert(thread == NULL || thread == Thread::current(), "sanity check");
277 JNIHandleBlock* block;
278 // Check the thread-local free list for a block so we don't
279 // have to acquire a mutex.
280 if (thread != NULL && thread->free_handle_block() != NULL) {
281 block = thread->free_handle_block();
282 thread->set_free_handle_block(block->_next);
283 }
284 else {
285 // locking with safepoint checking introduces a potential deadlock:
286 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
287 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
288 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
289 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
290 Mutex::_no_safepoint_check_flag);
291 if (_block_free_list == NULL) {
292 // Allocate new block
293 block = new JNIHandleBlock();
294 _blocks_allocated++;
295 if (TraceJNIHandleAllocation) {
296 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
297 block, _blocks_allocated);
298 }
299 if (ZapJNIHandleArea) block->zap();
300 #ifndef PRODUCT
301 // Link new block to list of all allocated blocks
302 block->_block_list_link = _block_list;
303 _block_list = block;
304 #endif
305 } else {
306 // Get block from free list
307 block = _block_free_list;
308 _block_free_list = _block_free_list->_next;
309 }
310 }
311 block->_top = 0;
312 block->_next = NULL;
313 block->_pop_frame_link = NULL;
314 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
315 debug_only(block->_last = NULL);
316 debug_only(block->_free_list = NULL);
317 debug_only(block->_allocate_before_rebuild = -1);
318 return block;
319 }
320
321
322 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
323 assert(thread == NULL || thread == Thread::current(), "sanity check");
324 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
325 // Put returned block at the beginning of the thread-local free list.
326 // Note that if thread == NULL, we use it as an implicit argument that
327 // we _don't_ want the block to be kept on the free_handle_block.
328 // See for instance JavaThread::exit().
329 if (thread != NULL ) {
330 if (ZapJNIHandleArea) block->zap();
331 JNIHandleBlock* freelist = thread->free_handle_block();
332 block->_pop_frame_link = NULL;
333 thread->set_free_handle_block(block);
334
335 // Add original freelist to end of chain
336 if ( freelist != NULL ) {
337 while ( block->_next != NULL ) block = block->_next;
338 block->_next = freelist;
339 }
340 block = NULL;
341 }
342 if (block != NULL) {
343 // Return blocks to free list
344 // locking with safepoint checking introduces a potential deadlock:
345 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
346 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
347 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
348 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
349 Mutex::_no_safepoint_check_flag);
350 while (block != NULL) {
351 if (ZapJNIHandleArea) block->zap();
352 JNIHandleBlock* next = block->_next;
353 block->_next = _block_free_list;
354 _block_free_list = block;
355 block = next;
356 }
357 }
358 if (pop_frame_link != NULL) {
359 // As a sanity check we release blocks pointed to by the pop_frame_link.
360 // This should never happen (only if PopLocalFrame is not called the
361 // correct number of times).
362 release_block(pop_frame_link, thread);
363 }
364 }
365
366
367 void JNIHandleBlock::oops_do(OopClosure* f) {
368 JNIHandleBlock* current_chain = this;
369 // Iterate over chain of blocks, followed by chains linked through the
370 // pop frame links.
371 while (current_chain != NULL) {
372 for (JNIHandleBlock* current = current_chain; current != NULL;
373 current = current->_next) {
374 assert(current == current_chain || current->pop_frame_link() == NULL,
375 "only blocks first in chain should have pop frame link set");
376 for (int index = 0; index < current->_top; index++) {
377 oop* root = &(current->_handles)[index];
378 oop value = *root;
379 // traverse heap pointers only, not deleted handles or free list
380 // pointers
381 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
382 f->do_oop(root);
383 }
384 }
385 // the next handle block is valid only if current block is full
386 if (current->_top < block_size_in_oops) {
387 break;
388 }
389 }
390 current_chain = current_chain->pop_frame_link();
391 }
392 }
393
394
395 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
396 OopClosure* f) {
397 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
398 assert(current->pop_frame_link() == NULL,
399 "blocks holding weak global JNI handles should not have pop frame link set");
400 for (int index = 0; index < current->_top; index++) {
401 oop* root = &(current->_handles)[index];
402 oop value = *root;
403 // traverse heap pointers only, not deleted handles or free list pointers
404 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
405 if (is_alive->do_object_b(value)) {
406 // The weakly referenced object is alive, update pointer
407 f->do_oop(root);
408 } else {
409 // The weakly referenced object is not alive, clear the reference by storing NULL
410 if (TraceReferenceGC) {
411 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
412 }
413 *root = NULL;
414 }
415 }
416 }
417 // the next handle block is valid only if current block is full
418 if (current->_top < block_size_in_oops) {
419 break;
420 }
421 }
422 }
423
424
425 jobject JNIHandleBlock::allocate_handle(oop obj) {
426 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
427 if (_top == 0) {
428 // This is the first allocation or the initial block got zapped when
429 // entering a native function. If we have any following blocks they are
430 // not valid anymore.
431 for (JNIHandleBlock* current = _next; current != NULL;
432 current = current->_next) {
433 assert(current->_last == NULL, "only first block should have _last set");
434 assert(current->_free_list == NULL,
435 "only first block should have _free_list set");
436 current->_top = 0;
437 if (ZapJNIHandleArea) current->zap();
438 }
439 // Clear initial block
440 _free_list = NULL;
441 _allocate_before_rebuild = 0;
442 _last = this;
443 if (ZapJNIHandleArea) zap();
444 }
445
446 // Try last block
447 if (_last->_top < block_size_in_oops) {
448 oop* handle = &(_last->_handles)[_last->_top++];
449 *handle = obj;
450 return (jobject) handle;
451 }
452
453 // Try free list
454 if (_free_list != NULL) {
455 oop* handle = _free_list;
456 _free_list = (oop*) *_free_list;
457 *handle = obj;
458 return (jobject) handle;
459 }
460 // Check if unused block follow last
461 if (_last->_next != NULL) {
462 // update last and retry
463 _last = _last->_next;
464 return allocate_handle(obj);
465 }
466
467 // No space available, we have to rebuild free list or expand
468 if (_allocate_before_rebuild == 0) {
469 rebuild_free_list(); // updates _allocate_before_rebuild counter
470 } else {
471 // Append new block
472 Thread* thread = Thread::current();
473 Handle obj_handle(thread, obj);
474 // This can block, so we need to preserve obj accross call.
475 _last->_next = JNIHandleBlock::allocate_block(thread);
476 _last = _last->_next;
477 _allocate_before_rebuild--;
478 obj = obj_handle();
479 }
480 return allocate_handle(obj); // retry
481 }
482
483
484 void JNIHandleBlock::rebuild_free_list() {
485 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
486 int free = 0;
487 int blocks = 0;
488 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
489 for (int index = 0; index < current->_top; index++) {
490 oop* handle = &(current->_handles)[index];
491 if (*handle == JNIHandles::deleted_handle()) {
492 // this handle was cleared out by a delete call, reuse it
493 *handle = (oop) _free_list;
494 _free_list = handle;
495 free++;
496 }
497 }
498 // we should not rebuild free list if there are unused handles at the end
499 assert(current->_top == block_size_in_oops, "just checking");
500 blocks++;
501 }
502 // Heuristic: if more than half of the handles are free we rebuild next time
503 // as well, otherwise we append a corresponding number of new blocks before
504 // attempting a free list rebuild again.
505 int total = blocks * block_size_in_oops;
506 int extra = total - 2*free;
507 if (extra > 0) {
508 // Not as many free handles as we would like - compute number of new blocks to append
509 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
510 }
511 if (TraceJNIHandleAllocation) {
512 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
513 this, blocks, total-free, free, _allocate_before_rebuild);
514 }
515 }
516
517
518 bool JNIHandleBlock::contains(jobject handle) const {
519 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
520 }
521
522
523 bool JNIHandleBlock::chain_contains(jobject handle) const {
524 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
525 if (current->contains(handle)) {
526 return true;
527 }
528 }
529 return false;
530 }
531
532
533 int JNIHandleBlock::length() const {
534 int result = 1;
535 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
536 result++;
537 }
538 return result;
539 }
540
541 // This method is not thread-safe, i.e., must be called whule holding a lock on the
542 // structure.
543 long JNIHandleBlock::memory_usage() const {
544 return length() * sizeof(JNIHandleBlock);
545 }
546
547
548 #ifndef PRODUCT
549
550 bool JNIHandleBlock::any_contains(jobject handle) {
551 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
552 if (current->contains(handle)) {
553 return true;
554 }
555 }
556 return false;
557 }
558
559 void JNIHandleBlock::print_statistics() {
560 int used_blocks = 0;
561 int free_blocks = 0;
562 int used_handles = 0;
563 int free_handles = 0;
564 JNIHandleBlock* block = _block_list;
565 while (block != NULL) {
566 if (block->_top > 0) {
567 used_blocks++;
568 } else {
569 free_blocks++;
570 }
571 used_handles += block->_top;
572 free_handles += (block_size_in_oops - block->_top);
573 block = block->_block_list_link;
574 }
575 tty->print_cr("JNIHandleBlocks statistics");
576 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
577 tty->print_cr("- blocks in use: %d", used_blocks);
578 tty->print_cr("- blocks free: %d", free_blocks);
579 tty->print_cr("- handles in use: %d", used_handles);
580 tty->print_cr("- handles free: %d", free_handles);
581 }
582
583 #endif