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