1 /*
2 * Copyright (c) 1998, 2012, 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 #include "runtime/thread.inline.hpp"
32
33
34 JNIHandleBlock* JNIHandles::_global_handles = NULL;
35 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL;
36 oop JNIHandles::_deleted_handle = NULL;
37
38
39 jobject JNIHandles::make_local(oop obj) {
40 if (obj == NULL) {
41 return NULL; // ignore null handles
42 } else {
43 Thread* thread = Thread::current();
44 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
45 return thread->active_handles()->allocate_handle(obj);
46 }
47 }
48
49
50 // optimized versions
51
52 jobject JNIHandles::make_local(Thread* thread, oop obj) {
53 if (obj == NULL) {
54 return NULL; // ignore null handles
55 } else {
56 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
57 return thread->active_handles()->allocate_handle(obj);
58 }
59 }
60
61
62 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
63 if (obj == NULL) {
64 return NULL; // ignore null handles
65 } else {
66 JavaThread* thread = JavaThread::thread_from_jni_environment(env);
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_global(Handle obj) {
74 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
75 jobject res = NULL;
76 if (!obj.is_null()) {
77 // ignore null handles
78 MutexLocker ml(JNIGlobalHandle_lock);
79 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
80 res = _global_handles->allocate_handle(obj());
81 } else {
82 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
83 }
84
85 return res;
86 }
87
88
89 jobject JNIHandles::make_weak_global(Handle obj) {
90 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
91 jobject res = NULL;
92 if (!obj.is_null()) {
93 // ignore null handles
94 MutexLocker ml(JNIGlobalHandle_lock);
95 assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
96 res = _weak_global_handles->allocate_handle(obj());
97 } else {
98 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
99 }
100 return res;
101 }
102
103
104 void JNIHandles::destroy_global(jobject handle) {
105 if (handle != NULL) {
106 assert(is_global_handle(handle), "Invalid delete of global JNI handle");
107 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
108 }
109 }
110
111
112 void JNIHandles::destroy_weak_global(jobject handle) {
113 if (handle != NULL) {
114 assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
115 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
116 }
117 }
118
119
120 void JNIHandles::oops_do(OopClosure* f) {
121 f->do_oop(&_deleted_handle);
122 _global_handles->oops_do(f);
123 }
124
125
126 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
127 _weak_global_handles->weak_oops_do(is_alive, f);
128 }
129
130
131 void JNIHandles::initialize() {
132 _global_handles = JNIHandleBlock::allocate_block();
133 _weak_global_handles = JNIHandleBlock::allocate_block();
134 EXCEPTION_MARK;
135 // We will never reach the CATCH below since Exceptions::_throw will cause
136 // the VM to exit if an exception is thrown during initialization
137 Klass* k = SystemDictionary::Object_klass();
138 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
139 }
140
141
142 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
143 JNIHandleBlock* block = thread->active_handles();
144
145 // Look back past possible native calls to jni_PushLocalFrame.
146 while (block != NULL) {
147 if (block->chain_contains(handle)) {
148 return true;
149 }
150 block = block->pop_frame_link();
151 }
152 return false;
153 }
154
155
156 // Determine if the handle is somewhere in the current thread's stack.
157 // We easily can't isolate any particular stack frame the handle might
158 // come from, so we'll check the whole stack.
159
160 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
161 // If there is no java frame, then this must be top level code, such
162 // as the java command executable, in which case, this type of handle
163 // is not permitted.
164 return (thr->has_last_Java_frame() &&
165 (void*)obj < (void*)thr->stack_base() &&
166 (void*)obj >= (void*)thr->last_Java_sp());
167 }
168
169
170 bool JNIHandles::is_global_handle(jobject handle) {
171 return _global_handles->chain_contains(handle);
172 }
173
174
175 bool JNIHandles::is_weak_global_handle(jobject handle) {
176 return _weak_global_handles->chain_contains(handle);
177 }
178
179 long JNIHandles::global_handle_memory_usage() {
180 return _global_handles->memory_usage();
181 }
182
183 long JNIHandles::weak_global_handle_memory_usage() {
184 return _weak_global_handles->memory_usage();
185 }
186
187
188 class AlwaysAliveClosure: public BoolObjectClosure {
189 public:
190 bool do_object_b(oop obj) { return true; }
191 };
192
193 class CountHandleClosure: public OopClosure {
194 private:
195 int _count;
196 public:
197 CountHandleClosure(): _count(0) {}
198 virtual void do_oop(oop* unused) {
199 _count++;
200 }
201 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
202 int count() { return _count; }
203 };
204
205 // We assume this is called at a safepoint: no lock is needed.
206 void JNIHandles::print_on(outputStream* st) {
207 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
208 assert(_global_handles != NULL && _weak_global_handles != NULL,
209 "JNIHandles not initialized");
210
211 CountHandleClosure global_handle_count;
212 AlwaysAliveClosure always_alive;
213 oops_do(&global_handle_count);
214 weak_oops_do(&always_alive, &global_handle_count);
215
216 st->print_cr("JNI global references: %d", global_handle_count.count());
217 st->cr();
218 st->flush();
219 }
220
221 class VerifyHandleClosure: public OopClosure {
222 public:
223 virtual void do_oop(oop* root) {
224 (*root)->verify();
225 }
226 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
227 };
228
229 void JNIHandles::verify() {
230 VerifyHandleClosure verify_handle;
231 AlwaysAliveClosure always_alive;
232
233 oops_do(&verify_handle);
234 weak_oops_do(&always_alive, &verify_handle);
235 }
236
237
238
239 void jni_handles_init() {
240 JNIHandles::initialize();
241 }
242
243
244 int JNIHandleBlock::_blocks_allocated = 0;
245 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL;
246 #ifndef PRODUCT
247 JNIHandleBlock* JNIHandleBlock::_block_list = NULL;
248 #endif
249
250
251 void JNIHandleBlock::zap() {
252 // Zap block values
253 _top = 0;
254 for (int index = 0; index < block_size_in_oops; index++) {
255 _handles[index] = badJNIHandle;
256 }
257 }
258
259 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) {
260 assert(thread == NULL || thread == Thread::current(), "sanity check");
261 JNIHandleBlock* block;
262 // Check the thread-local free list for a block so we don't
263 // have to acquire a mutex.
264 if (thread != NULL && thread->free_handle_block() != NULL) {
265 block = thread->free_handle_block();
266 thread->set_free_handle_block(block->_next);
267 }
268 else {
269 // locking with safepoint checking introduces a potential deadlock:
270 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
271 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
272 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
273 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
274 Mutex::_no_safepoint_check_flag);
275 if (_block_free_list == NULL) {
276 // Allocate new block
277 block = new JNIHandleBlock();
278 _blocks_allocated++;
279 if (TraceJNIHandleAllocation) {
280 tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
281 block, _blocks_allocated);
282 }
283 if (ZapJNIHandleArea) block->zap();
284 #ifndef PRODUCT
285 // Link new block to list of all allocated blocks
286 block->_block_list_link = _block_list;
287 _block_list = block;
288 #endif
289 } else {
290 // Get block from free list
291 block = _block_free_list;
292 _block_free_list = _block_free_list->_next;
293 }
294 }
295 block->_top = 0;
296 block->_next = NULL;
297 block->_pop_frame_link = NULL;
298 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
299 debug_only(block->_last = NULL);
300 debug_only(block->_free_list = NULL);
301 debug_only(block->_allocate_before_rebuild = -1);
302 return block;
303 }
304
305
306 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
307 assert(thread == NULL || thread == Thread::current(), "sanity check");
308 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
309 // Put returned block at the beginning of the thread-local free list.
310 // Note that if thread == NULL, we use it as an implicit argument that
311 // we _don't_ want the block to be kept on the free_handle_block.
312 // See for instance JavaThread::exit().
313 if (thread != NULL ) {
314 if (ZapJNIHandleArea) block->zap();
315 JNIHandleBlock* freelist = thread->free_handle_block();
316 block->_pop_frame_link = NULL;
317 thread->set_free_handle_block(block);
318
319 // Add original freelist to end of chain
320 if ( freelist != NULL ) {
321 while ( block->_next != NULL ) block = block->_next;
322 block->_next = freelist;
323 }
324 block = NULL;
325 }
326 if (block != NULL) {
327 // Return blocks to free list
328 // locking with safepoint checking introduces a potential deadlock:
329 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
330 // - another would hold Threads_lock (jni_AttachCurrentThread) and then
331 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
332 MutexLockerEx ml(JNIHandleBlockFreeList_lock,
333 Mutex::_no_safepoint_check_flag);
334 while (block != NULL) {
335 if (ZapJNIHandleArea) block->zap();
336 JNIHandleBlock* next = block->_next;
337 block->_next = _block_free_list;
338 _block_free_list = block;
339 block = next;
340 }
341 }
342 if (pop_frame_link != NULL) {
343 // As a sanity check we release blocks pointed to by the pop_frame_link.
344 // This should never happen (only if PopLocalFrame is not called the
345 // correct number of times).
346 release_block(pop_frame_link, thread);
347 }
348 }
349
350
351 void JNIHandleBlock::oops_do(OopClosure* f) {
352 JNIHandleBlock* current_chain = this;
353 // Iterate over chain of blocks, followed by chains linked through the
354 // pop frame links.
355 while (current_chain != NULL) {
356 for (JNIHandleBlock* current = current_chain; current != NULL;
357 current = current->_next) {
358 assert(current == current_chain || current->pop_frame_link() == NULL,
359 "only blocks first in chain should have pop frame link set");
360 for (int index = 0; index < current->_top; index++) {
361 oop* root = &(current->_handles)[index];
362 oop value = *root;
363 // traverse heap pointers only, not deleted handles or free list
364 // pointers
365 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
366 f->do_oop(root);
367 }
368 }
369 // the next handle block is valid only if current block is full
370 if (current->_top < block_size_in_oops) {
371 break;
372 }
373 }
374 current_chain = current_chain->pop_frame_link();
375 }
376 }
377
378
379 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
380 OopClosure* f) {
381 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
382 assert(current->pop_frame_link() == NULL,
383 "blocks holding weak global JNI handles should not have pop frame link set");
384 for (int index = 0; index < current->_top; index++) {
385 oop* root = &(current->_handles)[index];
386 oop value = *root;
387 // traverse heap pointers only, not deleted handles or free list pointers
388 if (value != NULL && Universe::heap()->is_in_reserved(value)) {
389 if (is_alive->do_object_b(value)) {
390 // The weakly referenced object is alive, update pointer
391 f->do_oop(root);
392 } else {
393 // The weakly referenced object is not alive, clear the reference by storing NULL
394 if (TraceReferenceGC) {
395 tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
396 }
397 *root = NULL;
398 }
399 }
400 }
401 // the next handle block is valid only if current block is full
402 if (current->_top < block_size_in_oops) {
403 break;
404 }
405 }
406
407 /*
408 * JVMTI data structures may also contain weak oops. The iteration of them
409 * is placed here so that we don't need to add it to each of the collectors.
410 */
411 JvmtiExport::weak_oops_do(is_alive, f);
412 }
413
414
415 jobject JNIHandleBlock::allocate_handle(oop obj) {
416 assert(Universe::heap()->is_in_reserved(obj), "sanity check");
417 if (_top == 0) {
418 // This is the first allocation or the initial block got zapped when
419 // entering a native function. If we have any following blocks they are
420 // not valid anymore.
421 for (JNIHandleBlock* current = _next; current != NULL;
422 current = current->_next) {
423 assert(current->_last == NULL, "only first block should have _last set");
424 assert(current->_free_list == NULL,
425 "only first block should have _free_list set");
426 current->_top = 0;
427 if (ZapJNIHandleArea) current->zap();
428 }
429 // Clear initial block
430 _free_list = NULL;
431 _allocate_before_rebuild = 0;
432 _last = this;
433 if (ZapJNIHandleArea) zap();
434 }
435
436 // Try last block
437 if (_last->_top < block_size_in_oops) {
438 oop* handle = &(_last->_handles)[_last->_top++];
439 *handle = obj;
440 return (jobject) handle;
441 }
442
443 // Try free list
444 if (_free_list != NULL) {
445 oop* handle = _free_list;
446 _free_list = (oop*) *_free_list;
447 *handle = obj;
448 return (jobject) handle;
449 }
450 // Check if unused block follow last
451 if (_last->_next != NULL) {
452 // update last and retry
453 _last = _last->_next;
454 return allocate_handle(obj);
455 }
456
457 // No space available, we have to rebuild free list or expand
458 if (_allocate_before_rebuild == 0) {
459 rebuild_free_list(); // updates _allocate_before_rebuild counter
460 } else {
461 // Append new block
462 Thread* thread = Thread::current();
463 Handle obj_handle(thread, obj);
464 // This can block, so we need to preserve obj across call.
465 _last->_next = JNIHandleBlock::allocate_block(thread);
466 _last = _last->_next;
467 _allocate_before_rebuild--;
468 obj = obj_handle();
469 }
470 return allocate_handle(obj); // retry
471 }
472
473
474 void JNIHandleBlock::rebuild_free_list() {
475 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
476 int free = 0;
477 int blocks = 0;
478 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
479 for (int index = 0; index < current->_top; index++) {
480 oop* handle = &(current->_handles)[index];
481 if (*handle == JNIHandles::deleted_handle()) {
482 // this handle was cleared out by a delete call, reuse it
483 *handle = (oop) _free_list;
484 _free_list = handle;
485 free++;
486 }
487 }
488 // we should not rebuild free list if there are unused handles at the end
489 assert(current->_top == block_size_in_oops, "just checking");
490 blocks++;
491 }
492 // Heuristic: if more than half of the handles are free we rebuild next time
493 // as well, otherwise we append a corresponding number of new blocks before
494 // attempting a free list rebuild again.
495 int total = blocks * block_size_in_oops;
496 int extra = total - 2*free;
497 if (extra > 0) {
498 // Not as many free handles as we would like - compute number of new blocks to append
499 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
500 }
501 if (TraceJNIHandleAllocation) {
502 tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
503 this, blocks, total-free, free, _allocate_before_rebuild);
504 }
505 }
506
507
508 bool JNIHandleBlock::contains(jobject handle) const {
509 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
510 }
511
512
513 bool JNIHandleBlock::chain_contains(jobject handle) const {
514 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
515 if (current->contains(handle)) {
516 return true;
517 }
518 }
519 return false;
520 }
521
522
523 int JNIHandleBlock::length() const {
524 int result = 1;
525 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
526 result++;
527 }
528 return result;
529 }
530
531 // This method is not thread-safe, i.e., must be called while holding a lock on the
532 // structure.
533 long JNIHandleBlock::memory_usage() const {
534 return length() * sizeof(JNIHandleBlock);
535 }
536
537
538 #ifndef PRODUCT
539
540 bool JNIHandleBlock::any_contains(jobject handle) {
541 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
542 if (current->contains(handle)) {
543 return true;
544 }
545 }
546 return false;
547 }
548
549 void JNIHandleBlock::print_statistics() {
550 int used_blocks = 0;
551 int free_blocks = 0;
552 int used_handles = 0;
553 int free_handles = 0;
554 JNIHandleBlock* block = _block_list;
555 while (block != NULL) {
556 if (block->_top > 0) {
557 used_blocks++;
558 } else {
559 free_blocks++;
560 }
561 used_handles += block->_top;
562 free_handles += (block_size_in_oops - block->_top);
563 block = block->_block_list_link;
564 }
565 tty->print_cr("JNIHandleBlocks statistics");
566 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
567 tty->print_cr("- blocks in use: %d", used_blocks);
568 tty->print_cr("- blocks free: %d", free_blocks);
569 tty->print_cr("- handles in use: %d", used_handles);
570 tty->print_cr("- handles free: %d", free_handles);
571 }
572
573 #endif