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 #ifdef TARGET_OS_FAMILY_bsd
41 # include "thread_bsd.inline.hpp"
42 #endif
43
44
45 JNIHandleBlock* JNIHandles::_global_handles = NULL;
46 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
47 oop JNIHandles::_deleted_handle = NULL;
48
49
50 jobject JNIHandles::make_local(oop obj) {
51 if (obj == NULL) {
52 return NULL; // ignore null handles
53 } else {
54 Thread* thread = Thread::current();
55 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
56 return thread->active_handles()->allocate_handle(obj);
57 }
58 }
59
60
61 // optimized versions
62
63 jobject JNIHandles::make_local(Thread* thread, oop obj) {
64 if (obj == NULL) {
65 return NULL; // ignore null handles
66 } else {
67 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
68 return thread->active_handles()->allocate_handle(obj);
69 }
70 }
71
72
73 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
74 if (obj == NULL) {
75 return NULL; // ignore null handles
76 } else {
77 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
78 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
79 return thread->active_handles()->allocate_handle(obj);
80 }
81 }
82
83
84 jobject JNIHandles::make_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 = _global_handles->allocate_handle(obj());
92 } else {
93 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
94 }
95
96 return res;
97 }
98
99
100 jobject JNIHandles::make_weak_global(Handle obj) {
101 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
102 jobject res = NULL;
103 if (!obj.is_null()) {
104 // ignore null handles
105 MutexLocker ml(JNIGlobalHandle_lock);
106 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
107 res = _weak_global_handles->allocate_handle(obj());
108 } else {
109 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
110 }
111 return res;
112 }
113
114 jmethodID JNIHandles::make_jmethod_id(methodHandle mh) {
115 return (jmethodID) make_weak_global(mh);
116 }
117
118
119
120 void JNIHandles::change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh) {
121 MutexLocker ml(JNIGlobalHandle_lock); // Is this necessary?
122 Handle obj = (Handle)mh;
123 oop* jobj = (oop*)jmid;
124 *jobj = obj();
125 }
126
127
128 void JNIHandles::destroy_global(jobject handle) {
129 if (handle != NULL) {
130 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
131 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
132 }
133 }
134
135
136 void JNIHandles::destroy_weak_global(jobject handle) {
137 if (handle != NULL) {
138 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
139 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
140 }
141 }
142
143 void JNIHandles::destroy_jmethod_id(jmethodID mid) {
144 destroy_weak_global((jobject)mid);
145 }
146
147
148 void JNIHandles::oops_do(OopClosure* f) {
149 f->do_oop(&_deleted_handle);
150 _global_handles->oops_do(f);
151 }
152
153
154 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
155 _weak_global_handles->weak_oops_do(is_alive, f);
156 }
157
158
159 void JNIHandles::initialize() {
160 _global_handles = JNIHandleBlock::allocate_block();
161 _weak_global_handles = JNIHandleBlock::allocate_block();
162 EXCEPTION_MARK;
163 // We will never reach the CATCH below since Exceptions::_throw will cause
164 // the VM to exit if an exception is thrown during initialization
165 klassOop k = SystemDictionary::Object_klass();
166 _deleted_handle = instanceKlass::cast(k)->allocate_permanent_instance(CATCH);
167 }
168
169
170 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
171 JNIHandleBlock* block = thread->active_handles();
172
173 // Look back past possible native calls to jni_PushLocalFrame.
174 while (block != NULL) {
175 if (block->chain_contains(handle)) {
176 return true;
177 }
178 block = block->pop_frame_link();
179 }
180 return false;
181 }
182
183
184 // Determine if the handle is somewhere in the current thread's stack.
185 // We easily can't isolate any particular stack frame the handle might
186 // come from, so we'll check the whole stack.
187
188 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
189 // If there is no java frame, then this must be top level code, such
190 // as the java command executable, in which case, this type of handle
191 // is not permitted.
192 return (thr->has_last_Java_frame() &&
193 (void*)obj < (void*)thr->stack_base() &&
194 (void*)obj >= (void*)thr->last_Java_sp());
195 }
196
197
198 bool JNIHandles::is_global_handle(jobject handle) {
199 return _global_handles->chain_contains(handle);
200 }
201
202
203 bool JNIHandles::is_weak_global_handle(jobject handle) {
204 return _weak_global_handles->chain_contains(handle);
205 }
206
207 long JNIHandles::global_handle_memory_usage() {
208 return _global_handles->memory_usage();
209 }
210
211 long JNIHandles::weak_global_handle_memory_usage() {
212 return _weak_global_handles->memory_usage();
213 }
214
215
216 class AlwaysAliveClosure: public BoolObjectClosure {
217 public:
218 bool do_object_b(oop obj) { return true; }
219 void do_object(oop obj) { assert(false, "Don't call"); }
220 };
221
222 class CountHandleClosure: public OopClosure {
223 private:
224 int _count;
225 public:
226 CountHandleClosure(): _count(0) {}
227 virtual void do_oop(oop* unused) {
228 _count++;
229 }
230 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
231 int count() { return _count; }
232 };
233
234 // We assume this is called at a safepoint: no lock is needed.
235 void JNIHandles::print_on(outputStream* st) {
236 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
237 assert(_global_handles != NULL && _weak_global_handles != NULL,
238 "JNIHandles not initialized");
239
240 CountHandleClosure global_handle_count;
241 AlwaysAliveClosure always_alive;
242 oops_do(&global_handle_count);
243 weak_oops_do(&always_alive, &global_handle_count);
244
245 st->print_cr("JNI global references: %d", global_handle_count.count());
246 st->cr();
247 st->flush();
248 }
249
250 class VerifyHandleClosure: public OopClosure {
251 public:
252 virtual void do_oop(oop* root) {
253 (*root)->verify();
254 }
255 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
256 };
257
258 void JNIHandles::verify() {
259 VerifyHandleClosure verify_handle;
260 AlwaysAliveClosure always_alive;
261
262 oops_do(&verify_handle);
263 weak_oops_do(&always_alive, &verify_handle);
264 }
265
266
267
268 void jni_handles_init() {
269 JNIHandles::initialize();
270 }
271
272
273 int JNIHandleBlock::_blocks_allocated = 0;
274 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
275 #ifndef PRODUCT
276 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
277 #endif
278
279
280 void JNIHandleBlock::zap() {
281 // Zap block values
282 _top = 0;
283 for (int index = 0; index < block_size_in_oops; index++) {
284 _handles[index] = badJNIHandle;
285 }
286 }
287
288 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
289 assert(thread == NULL || thread == Thread::current(), "sanity check");
290 JNIHandleBlock* block;
291 // Check the thread-local free list for a block so we don't
292 // have to acquire a mutex.
293 if (thread != NULL && thread->free_handle_block() != NULL) {
294 block = thread->free_handle_block();
295 thread->set_free_handle_block(block->_next);
296 }
297 else {
298 // locking with safepoint checking introduces a potential deadlock:
299 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
300 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
301 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
302 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
303 Mutex::_no_safepoint_check_flag);
304 if (_block_free_list == NULL) {
305 // Allocate new block
306 block = new JNIHandleBlock();
307 _blocks_allocated++;
308 if (TraceJNIHandleAllocation) {
309 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
310 block, _blocks_allocated);
311 }
312 if (ZapJNIHandleArea) block->zap();
313 #ifndef PRODUCT
314 // Link new block to list of all allocated blocks
315 block->_block_list_link = _block_list;
316 _block_list = block;
317 #endif
318 } else {
319 // Get block from free list
320 block = _block_free_list;
321 _block_free_list = _block_free_list->_next;
322 }
323 }
324 block->_top = 0;
325 block->_next = NULL;
326 block->_pop_frame_link = NULL;
327 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
328 debug_only(block->_last = NULL);
329 debug_only(block->_free_list = NULL);
330 debug_only(block->_allocate_before_rebuild = -1);
331 return block;
332 }
333
334
335 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
336 assert(thread == NULL || thread == Thread::current(), "sanity check");
337 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
338 // Put returned block at the beginning of the thread-local free list.
339 // Note that if thread == NULL, we use it as an implicit argument that
340 // we _don't_ want the block to be kept on the free_handle_block.
341 // See for instance JavaThread::exit().
342 if (thread != NULL ) {
343 if (ZapJNIHandleArea) block->zap();
344 JNIHandleBlock* freelist = thread->free_handle_block();
345 block->_pop_frame_link = NULL;
346 thread->set_free_handle_block(block);
347
348 // Add original freelist to end of chain
349 if ( freelist != NULL ) {
350 while ( block->_next != NULL ) block = block->_next;
351 block->_next = freelist;
352 }
353 block = NULL;
354 }
355 if (block != NULL) {
356 // Return blocks to free list
357 // locking with safepoint checking introduces a potential deadlock:
358 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
359 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
360 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
361 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
362 Mutex::_no_safepoint_check_flag);
363 while (block != NULL) {
364 if (ZapJNIHandleArea) block->zap();
365 JNIHandleBlock* next = block->_next;
366 block->_next = _block_free_list;
367 _block_free_list = block;
368 block = next;
369 }
370 }
371 if (pop_frame_link != NULL) {
372 // As a sanity check we release blocks pointed to by the pop_frame_link.
373 // This should never happen (only if PopLocalFrame is not called the
374 // correct number of times).
375 release_block(pop_frame_link, thread);
376 }
377 }
378
379
380 void JNIHandleBlock::oops_do(OopClosure* f) {
381 JNIHandleBlock* current_chain = this;
382 // Iterate over chain of blocks, followed by chains linked through the
383 // pop frame links.
384 while (current_chain != NULL) {
385 for (JNIHandleBlock* current = current_chain; current != NULL;
386 current = current->_next) {
387 assert(current == current_chain || current->pop_frame_link() == NULL,
388 "only blocks first in chain should have pop frame link set");
389 for (int index = 0; index < current->_top; index++) {
390 oop* root = &(current->_handles)[index];
391 oop value = *root;
392 // traverse heap pointers only, not deleted handles or free list
393 // pointers
394 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
395 f->do_oop(root);
396 }
397 }
398 // the next handle block is valid only if current block is full
399 if (current->_top < block_size_in_oops) {
400 break;
401 }
402 }
403 current_chain = current_chain->pop_frame_link();
404 }
405 }
406
407
408 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
409 OopClosure* f) {
410 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
411 assert(current->pop_frame_link() == NULL,
412 "blocks holding weak global JNI handles should not have pop frame link set");
413 for (int index = 0; index < current->_top; index++) {
414 oop* root = &(current->_handles)[index];
415 oop value = *root;
416 // traverse heap pointers only, not deleted handles or free list pointers
417 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
418 if (is_alive->do_object_b(value)) {
419 // The weakly referenced object is alive, update pointer
420 f->do_oop(root);
421 } else {
422 // The weakly referenced object is not alive, clear the reference by storing NULL
423 if (TraceReferenceGC) {
424 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
425 }
426 *root = NULL;
427 }
428 }
429 }
430 // the next handle block is valid only if current block is full
431 if (current->_top < block_size_in_oops) {
432 break;
433 }
434 }
435
436 /*
437 * JVMTI data structures may also contain weak oops. The iteration of them
438 * is placed here so that we don't need to add it to each of the collectors.
439 */
440 JvmtiExport::weak_oops_do(is_alive, f);
441 }
442
443
444 jobject JNIHandleBlock::allocate_handle(oop obj) {
445 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
446 if (_top == 0) {
447 // This is the first allocation or the initial block got zapped when
448 // entering a native function. If we have any following blocks they are
449 // not valid anymore.
450 for (JNIHandleBlock* current = _next; current != NULL;
451 current = current->_next) {
452 assert(current->_last == NULL, "only first block should have _last set");
453 assert(current->_free_list == NULL,
454 "only first block should have _free_list set");
455 current->_top = 0;
456 if (ZapJNIHandleArea) current->zap();
457 }
458 // Clear initial block
459 _free_list = NULL;
460 _allocate_before_rebuild = 0;
461 _last = this;
462 if (ZapJNIHandleArea) zap();
463 }
464
465 // Try last block
466 if (_last->_top < block_size_in_oops) {
467 oop* handle = &(_last->_handles)[_last->_top++];
468 *handle = obj;
469 return (jobject) handle;
470 }
471
472 // Try free list
473 if (_free_list != NULL) {
474 oop* handle = _free_list;
475 _free_list = (oop*) *_free_list;
476 *handle = obj;
477 return (jobject) handle;
478 }
479 // Check if unused block follow last
480 if (_last->_next != NULL) {
481 // update last and retry
482 _last = _last->_next;
483 return allocate_handle(obj);
484 }
485
486 // No space available, we have to rebuild free list or expand
487 if (_allocate_before_rebuild == 0) {
488 rebuild_free_list(); // updates _allocate_before_rebuild counter
489 } else {
490 // Append new block
491 Thread* thread = Thread::current();
492 Handle obj_handle(thread, obj);
493 // This can block, so we need to preserve obj accross call.
494 _last->_next = JNIHandleBlock::allocate_block(thread);
495 _last = _last->_next;
496 _allocate_before_rebuild--;
497 obj = obj_handle();
498 }
499 return allocate_handle(obj); // retry
500 }
501
502
503 void JNIHandleBlock::rebuild_free_list() {
504 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
505 int free = 0;
506 int blocks = 0;
507 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
508 for (int index = 0; index < current->_top; index++) {
509 oop* handle = &(current->_handles)[index];
510 if (*handle == JNIHandles::deleted_handle()) {
511 // this handle was cleared out by a delete call, reuse it
512 *handle = (oop) _free_list;
513 _free_list = handle;
514 free++;
515 }
516 }
517 // we should not rebuild free list if there are unused handles at the end
518 assert(current->_top == block_size_in_oops, "just checking");
519 blocks++;
520 }
521 // Heuristic: if more than half of the handles are free we rebuild next time
522 // as well, otherwise we append a corresponding number of new blocks before
523 // attempting a free list rebuild again.
524 int total = blocks * block_size_in_oops;
525 int extra = total - 2*free;
526 if (extra > 0) {
527 // Not as many free handles as we would like - compute number of new blocks to append
528 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
529 }
530 if (TraceJNIHandleAllocation) {
531 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
532 this, blocks, total-free, free, _allocate_before_rebuild);
533 }
534 }
535
536
537 bool JNIHandleBlock::contains(jobject handle) const {
538 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
539 }
540
541
542 bool JNIHandleBlock::chain_contains(jobject handle) const {
543 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
544 if (current->contains(handle)) {
545 return true;
546 }
547 }
548 return false;
549 }
550
551
552 int JNIHandleBlock::length() const {
553 int result = 1;
554 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
555 result++;
556 }
557 return result;
558 }
559
560 // This method is not thread-safe, i.e., must be called whule holding a lock on the
561 // structure.
562 long JNIHandleBlock::memory_usage() const {
563 return length() * sizeof(JNIHandleBlock);
564 }
565
566
567 #ifndef PRODUCT
568
569 bool JNIHandleBlock::any_contains(jobject handle) {
570 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
571 if (current->contains(handle)) {
572 return true;
573 }
574 }
575 return false;
576 }
577
578 void JNIHandleBlock::print_statistics() {
579 int used_blocks = 0;
580 int free_blocks = 0;
581 int used_handles = 0;
582 int free_handles = 0;
583 JNIHandleBlock* block = _block_list;
584 while (block != NULL) {
585 if (block->_top > 0) {
586 used_blocks++;
587 } else {
588 free_blocks++;
589 }
590 used_handles += block->_top;
591 free_handles += (block_size_in_oops - block->_top);
592 block = block->_block_list_link;
593 }
594 tty->print_cr("JNIHandleBlocks statistics");
595 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
596 tty->print_cr("- blocks in use: %d", used_blocks);
597 tty->print_cr("- blocks free: %d", free_blocks);
598 tty->print_cr("- handles in use: %d", used_handles);
599 tty->print_cr("- handles free: %d", free_handles);
600 }
601
602 #endif