1 /* 2 * Copyright (c) 1998, 2017, 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 "logging/log.hpp" 28 #include "memory/iterator.hpp" 29 #include "oops/oop.inline.hpp" 30 #include "prims/jvmtiExport.hpp" 31 #include "runtime/jniHandles.hpp" 32 #include "runtime/mutexLocker.hpp" 33 #include "runtime/thread.inline.hpp" 34 #if INCLUDE_ALL_GCS 35 #include "gc/g1/g1SATBCardTableModRefBS.hpp" 36 #endif 37 38 JNIHandleBlock* JNIHandles::_global_handles = NULL; 39 JNIHandleBlock* JNIHandles::_weak_global_handles = NULL; 40 oop JNIHandles::_deleted_handle = NULL; 41 42 43 jobject JNIHandles::make_local(oop obj) { 44 if (obj == NULL) { 45 return NULL; // ignore null handles 46 } else { 47 Thread* thread = Thread::current(); 48 assert(Universe::heap()->is_in_reserved(obj), "sanity check"); 49 return thread->active_handles()->allocate_handle(obj); 50 } 51 } 52 53 54 // optimized versions 55 56 jobject JNIHandles::make_local(Thread* thread, oop obj) { 57 if (obj == NULL) { 58 return NULL; // ignore null handles 59 } else { 60 assert(Universe::heap()->is_in_reserved(obj), "sanity check"); 61 return thread->active_handles()->allocate_handle(obj); 62 } 63 } 64 65 66 jobject JNIHandles::make_local(JNIEnv* env, oop obj) { 67 if (obj == NULL) { 68 return NULL; // ignore null handles 69 } else { 70 JavaThread* thread = JavaThread::thread_from_jni_environment(env); 71 assert(Universe::heap()->is_in_reserved(obj), "sanity check"); 72 return thread->active_handles()->allocate_handle(obj); 73 } 74 } 75 76 77 jobject JNIHandles::make_global(Handle obj) { 78 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC"); 79 jobject res = NULL; 80 if (!obj.is_null()) { 81 // ignore null handles 82 MutexLocker ml(JNIGlobalHandle_lock); 83 assert(Universe::heap()->is_in_reserved(obj()), "sanity check"); 84 res = _global_handles->allocate_handle(obj()); 85 } else { 86 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops()); 87 } 88 89 return res; 90 } 91 92 93 jobject JNIHandles::make_weak_global(Handle obj) { 94 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC"); 95 jobject res = NULL; 96 if (!obj.is_null()) { 97 // ignore null handles 98 { 99 MutexLocker ml(JNIGlobalHandle_lock); 100 assert(Universe::heap()->is_in_reserved(obj()), "sanity check"); 101 res = _weak_global_handles->allocate_handle(obj()); 102 } 103 // Add weak tag. 104 assert(is_ptr_aligned(res, weak_tag_alignment), "invariant"); 105 char* tptr = reinterpret_cast<char*>(res) + weak_tag_value; 106 res = reinterpret_cast<jobject>(tptr); 107 } else { 108 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops()); 109 } 110 return res; 111 } 112 113 template<bool external_guard> 114 oop JNIHandles::resolve_jweak(jweak handle) { 115 assert(is_jweak(handle), "precondition"); 116 oop result = jweak_ref(handle); 117 result = guard_value<external_guard>(result); 118 #if INCLUDE_ALL_GCS 119 if (result != NULL && UseG1GC) { 120 G1SATBCardTableModRefBS::enqueue(result); 121 } 122 #endif // INCLUDE_ALL_GCS 123 return result; 124 } 125 126 template oop JNIHandles::resolve_jweak<true>(jweak); 127 template oop JNIHandles::resolve_jweak<false>(jweak); 128 129 void JNIHandles::destroy_global(jobject handle) { 130 if (handle != NULL) { 131 assert(is_global_handle(handle), "Invalid delete of global JNI handle"); 132 jobject_ref(handle) = deleted_handle(); 133 } 134 } 135 136 137 void JNIHandles::destroy_weak_global(jobject handle) { 138 if (handle != NULL) { 139 jweak_ref(handle) = deleted_handle(); 140 } 141 } 142 143 144 void JNIHandles::oops_do(OopClosure* f) { 145 f->do_oop(&_deleted_handle); 146 _global_handles->oops_do(f); 147 } 148 149 150 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) { 151 _weak_global_handles->weak_oops_do(is_alive, f); 152 } 153 154 155 void JNIHandles::weak_oops_do(OopClosure* f) { 156 AlwaysTrueClosure always_true; 157 weak_oops_do(&always_true, f); 158 } 159 160 161 void JNIHandles::initialize() { 162 _global_handles = JNIHandleBlock::allocate_block(); 163 _weak_global_handles = JNIHandleBlock::allocate_block(); 164 EXCEPTION_MARK; 165 // We will never reach the CATCH below since Exceptions::_throw will cause 166 // the VM to exit if an exception is thrown during initialization 167 Klass* k = SystemDictionary::Object_klass(); 168 _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH); 169 } 170 171 172 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) { 173 JNIHandleBlock* block = thread->active_handles(); 174 175 // Look back past possible native calls to jni_PushLocalFrame. 176 while (block != NULL) { 177 if (block->chain_contains(handle)) { 178 return true; 179 } 180 block = block->pop_frame_link(); 181 } 182 return false; 183 } 184 185 186 // Determine if the handle is somewhere in the current thread's stack. 187 // We easily can't isolate any particular stack frame the handle might 188 // come from, so we'll check the whole stack. 189 190 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) { 191 // If there is no java frame, then this must be top level code, such 192 // as the java command executable, in which case, this type of handle 193 // is not permitted. 194 return (thr->has_last_Java_frame() && 195 (void*)obj < (void*)thr->stack_base() && 196 (void*)obj >= (void*)thr->last_Java_sp()); 197 } 198 199 200 bool JNIHandles::is_global_handle(jobject handle) { 201 return _global_handles->chain_contains(handle); 202 } 203 204 205 bool JNIHandles::is_weak_global_handle(jobject handle) { 206 return _weak_global_handles->chain_contains(handle); 207 } 208 209 long JNIHandles::global_handle_memory_usage() { 210 return _global_handles->memory_usage(); 211 } 212 213 long JNIHandles::weak_global_handle_memory_usage() { 214 return _weak_global_handles->memory_usage(); 215 } 216 217 218 class CountHandleClosure: public OopClosure { 219 private: 220 int _count; 221 public: 222 CountHandleClosure(): _count(0) {} 223 virtual void do_oop(oop* ooph) { 224 if (*ooph != JNIHandles::deleted_handle()) { 225 _count++; 226 } 227 } 228 virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); } 229 int count() { return _count; } 230 }; 231 232 // We assume this is called at a safepoint: no lock is needed. 233 void JNIHandles::print_on(outputStream* st) { 234 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 235 assert(_global_handles != NULL && _weak_global_handles != NULL, 236 "JNIHandles not initialized"); 237 238 CountHandleClosure global_handle_count; 239 oops_do(&global_handle_count); 240 weak_oops_do(&global_handle_count); 241 242 st->print_cr("JNI global references: %d", global_handle_count.count()); 243 st->cr(); 244 st->flush(); 245 } 246 247 class VerifyHandleClosure: public OopClosure { 248 public: 249 virtual void do_oop(oop* root) { 250 (*root)->verify(); 251 } 252 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); } 253 }; 254 255 void JNIHandles::verify() { 256 VerifyHandleClosure verify_handle; 257 258 oops_do(&verify_handle); 259 weak_oops_do(&verify_handle); 260 } 261 262 263 264 void jni_handles_init() { 265 JNIHandles::initialize(); 266 } 267 268 269 int JNIHandleBlock::_blocks_allocated = 0; 270 JNIHandleBlock* JNIHandleBlock::_block_free_list = NULL; 271 #ifndef PRODUCT 272 JNIHandleBlock* JNIHandleBlock::_block_list = NULL; 273 #endif 274 275 276 void JNIHandleBlock::zap() { 277 // Zap block values 278 _top = 0; 279 for (int index = 0; index < block_size_in_oops; index++) { 280 _handles[index] = badJNIHandle; 281 } 282 } 283 284 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread) { 285 assert(thread == NULL || thread == Thread::current(), "sanity check"); 286 JNIHandleBlock* block; 287 // Check the thread-local free list for a block so we don't 288 // have to acquire a mutex. 289 if (thread != NULL && thread->free_handle_block() != NULL) { 290 block = thread->free_handle_block(); 291 thread->set_free_handle_block(block->_next); 292 } 293 else { 294 // locking with safepoint checking introduces a potential deadlock: 295 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock 296 // - another would hold Threads_lock (jni_AttachCurrentThread) and then 297 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block) 298 MutexLockerEx ml(JNIHandleBlockFreeList_lock, 299 Mutex::_no_safepoint_check_flag); 300 if (_block_free_list == NULL) { 301 // Allocate new block 302 block = new JNIHandleBlock(); 303 _blocks_allocated++; 304 if (ZapJNIHandleArea) block->zap(); 305 #ifndef PRODUCT 306 // Link new block to list of all allocated blocks 307 block->_block_list_link = _block_list; 308 _block_list = block; 309 #endif 310 } else { 311 // Get block from free list 312 block = _block_free_list; 313 _block_free_list = _block_free_list->_next; 314 } 315 } 316 block->_top = 0; 317 block->_next = NULL; 318 block->_pop_frame_link = NULL; 319 block->_planned_capacity = block_size_in_oops; 320 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle 321 debug_only(block->_last = NULL); 322 debug_only(block->_free_list = NULL); 323 debug_only(block->_allocate_before_rebuild = -1); 324 return block; 325 } 326 327 328 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) { 329 assert(thread == NULL || thread == Thread::current(), "sanity check"); 330 JNIHandleBlock* pop_frame_link = block->pop_frame_link(); 331 // Put returned block at the beginning of the thread-local free list. 332 // Note that if thread == NULL, we use it as an implicit argument that 333 // we _don't_ want the block to be kept on the free_handle_block. 334 // See for instance JavaThread::exit(). 335 if (thread != NULL ) { 336 if (ZapJNIHandleArea) block->zap(); 337 JNIHandleBlock* freelist = thread->free_handle_block(); 338 block->_pop_frame_link = NULL; 339 thread->set_free_handle_block(block); 340 341 // Add original freelist to end of chain 342 if ( freelist != NULL ) { 343 while ( block->_next != NULL ) block = block->_next; 344 block->_next = freelist; 345 } 346 block = NULL; 347 } 348 if (block != NULL) { 349 // Return blocks to free list 350 // locking with safepoint checking introduces a potential deadlock: 351 // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock 352 // - another would hold Threads_lock (jni_AttachCurrentThread) and then 353 // JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block) 354 MutexLockerEx ml(JNIHandleBlockFreeList_lock, 355 Mutex::_no_safepoint_check_flag); 356 while (block != NULL) { 357 if (ZapJNIHandleArea) block->zap(); 358 JNIHandleBlock* next = block->_next; 359 block->_next = _block_free_list; 360 _block_free_list = block; 361 block = next; 362 } 363 } 364 if (pop_frame_link != NULL) { 365 // As a sanity check we release blocks pointed to by the pop_frame_link. 366 // This should never happen (only if PopLocalFrame is not called the 367 // correct number of times). 368 release_block(pop_frame_link, thread); 369 } 370 } 371 372 373 void JNIHandleBlock::oops_do(OopClosure* f) { 374 JNIHandleBlock* current_chain = this; 375 // Iterate over chain of blocks, followed by chains linked through the 376 // pop frame links. 377 while (current_chain != NULL) { 378 for (JNIHandleBlock* current = current_chain; current != NULL; 379 current = current->_next) { 380 assert(current == current_chain || current->pop_frame_link() == NULL, 381 "only blocks first in chain should have pop frame link set"); 382 for (int index = 0; index < current->_top; index++) { 383 oop* root = &(current->_handles)[index]; 384 oop value = *root; 385 // traverse heap pointers only, not deleted handles or free list 386 // pointers 387 if (value != NULL && Universe::heap()->is_in_reserved(value)) { 388 f->do_oop(root); 389 } 390 } 391 // the next handle block is valid only if current block is full 392 if (current->_top < block_size_in_oops) { 393 break; 394 } 395 } 396 current_chain = current_chain->pop_frame_link(); 397 } 398 } 399 400 401 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive, 402 OopClosure* f) { 403 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) { 404 assert(current->pop_frame_link() == NULL, 405 "blocks holding weak global JNI handles should not have pop frame link set"); 406 for (int index = 0; index < current->_top; index++) { 407 oop* root = &(current->_handles)[index]; 408 oop value = *root; 409 // traverse heap pointers only, not deleted handles or free list pointers 410 if (value != NULL && Universe::heap()->is_in_reserved(value)) { 411 if (is_alive->do_object_b(value)) { 412 // The weakly referenced object is alive, update pointer 413 f->do_oop(root); 414 } else { 415 // The weakly referenced object is not alive, clear the reference by storing NULL 416 log_develop_trace(gc, ref)("Clearing JNI weak reference (" INTPTR_FORMAT ")", p2i(root)); 417 *root = NULL; 418 } 419 } 420 } 421 // the next handle block is valid only if current block is full 422 if (current->_top < block_size_in_oops) { 423 break; 424 } 425 } 426 427 /* 428 * JVMTI data structures may also contain weak oops. The iteration of them 429 * is placed here so that we don't need to add it to each of the collectors. 430 */ 431 JvmtiExport::weak_oops_do(is_alive, f); 432 } 433 434 435 jobject JNIHandleBlock::allocate_handle(oop obj) { 436 assert(Universe::heap()->is_in_reserved(obj), "sanity check"); 437 if (_top == 0) { 438 // This is the first allocation or the initial block got zapped when 439 // entering a native function. If we have any following blocks they are 440 // not valid anymore. 441 for (JNIHandleBlock* current = _next; current != NULL; 442 current = current->_next) { 443 assert(current->_last == NULL, "only first block should have _last set"); 444 assert(current->_free_list == NULL, 445 "only first block should have _free_list set"); 446 current->_top = 0; 447 if (ZapJNIHandleArea) current->zap(); 448 } 449 // Clear initial block 450 _free_list = NULL; 451 _allocate_before_rebuild = 0; 452 _last = this; 453 if (ZapJNIHandleArea) zap(); 454 } 455 456 // Try last block 457 if (_last->_top < block_size_in_oops) { 458 oop* handle = &(_last->_handles)[_last->_top++]; 459 *handle = obj; 460 return (jobject) handle; 461 } 462 463 // Try free list 464 if (_free_list != NULL) { 465 oop* handle = _free_list; 466 _free_list = (oop*) *_free_list; 467 *handle = obj; 468 return (jobject) handle; 469 } 470 // Check if unused block follow last 471 if (_last->_next != NULL) { 472 // update last and retry 473 _last = _last->_next; 474 return allocate_handle(obj); 475 } 476 477 // No space available, we have to rebuild free list or expand 478 if (_allocate_before_rebuild == 0) { 479 rebuild_free_list(); // updates _allocate_before_rebuild counter 480 } else { 481 // Append new block 482 Thread* thread = Thread::current(); 483 Handle obj_handle(thread, obj); 484 // This can block, so we need to preserve obj across call. 485 _last->_next = JNIHandleBlock::allocate_block(thread); 486 _last = _last->_next; 487 _allocate_before_rebuild--; 488 obj = obj_handle(); 489 } 490 return allocate_handle(obj); // retry 491 } 492 493 void JNIHandleBlock::release_handle(jobject h) { 494 if (h != NULL) { 495 assert(chain_contains(h), "does not contain the JNI handle"); 496 // Mark the handle as deleted, allocate will reuse it 497 *((oop*)h) = JNIHandles::deleted_handle(); 498 } 499 } 500 501 502 void JNIHandleBlock::rebuild_free_list() { 503 assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking"); 504 int free = 0; 505 int blocks = 0; 506 for (JNIHandleBlock* current = this; current != NULL; current = current->_next) { 507 for (int index = 0; index < current->_top; index++) { 508 oop* handle = &(current->_handles)[index]; 509 if (*handle == JNIHandles::deleted_handle()) { 510 // this handle was cleared out by a delete call, reuse it 511 *handle = (oop) _free_list; 512 _free_list = handle; 513 free++; 514 } 515 } 516 // we should not rebuild free list if there are unused handles at the end 517 assert(current->_top == block_size_in_oops, "just checking"); 518 blocks++; 519 } 520 // Heuristic: if more than half of the handles are free we rebuild next time 521 // as well, otherwise we append a corresponding number of new blocks before 522 // attempting a free list rebuild again. 523 int total = blocks * block_size_in_oops; 524 int extra = total - 2*free; 525 if (extra > 0) { 526 // Not as many free handles as we would like - compute number of new blocks to append 527 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops; 528 } 529 } 530 531 532 bool JNIHandleBlock::contains(jobject handle) const { 533 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]); 534 } 535 536 537 bool JNIHandleBlock::chain_contains(jobject handle) const { 538 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) { 539 if (current->contains(handle)) { 540 return true; 541 } 542 } 543 return false; 544 } 545 546 547 int JNIHandleBlock::length() const { 548 int result = 1; 549 for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) { 550 result++; 551 } 552 return result; 553 } 554 555 const size_t JNIHandleBlock::get_number_of_live_handles() { 556 CountHandleClosure counter; 557 oops_do(&counter); 558 return counter.count(); 559 } 560 561 // This method is not thread-safe, i.e., must be called while holding a lock on the 562 // structure. 563 long JNIHandleBlock::memory_usage() const { 564 return length() * sizeof(JNIHandleBlock); 565 } 566 567 568 #ifndef PRODUCT 569 570 bool JNIHandleBlock::any_contains(jobject handle) { 571 for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) { 572 if (current->contains(handle)) { 573 return true; 574 } 575 } 576 return false; 577 } 578 579 void JNIHandleBlock::print_statistics() { 580 int used_blocks = 0; 581 int free_blocks = 0; 582 int used_handles = 0; 583 int free_handles = 0; 584 JNIHandleBlock* block = _block_list; 585 while (block != NULL) { 586 if (block->_top > 0) { 587 used_blocks++; 588 } else { 589 free_blocks++; 590 } 591 used_handles += block->_top; 592 free_handles += (block_size_in_oops - block->_top); 593 block = block->_block_list_link; 594 } 595 tty->print_cr("JNIHandleBlocks statistics"); 596 tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks); 597 tty->print_cr("- blocks in use: %d", used_blocks); 598 tty->print_cr("- blocks free: %d", free_blocks); 599 tty->print_cr("- handles in use: %d", used_handles); 600 tty->print_cr("- handles free: %d", free_handles); 601 } 602 603 #endif