1 /* 2 * Copyright (c) 2018, 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 "logging/logStream.hpp" 27 #include "memory/allocation.inline.hpp" 28 #include "runtime/jniHandles.inline.hpp" 29 #include "runtime/thread.inline.hpp" 30 #include "runtime/threadSMR.inline.hpp" 31 #include "runtime/vm_operations.hpp" 32 #include "services/threadService.hpp" 33 #include "utilities/copy.hpp" 34 #include "utilities/globalDefinitions.hpp" 35 #include "utilities/resourceHash.hpp" 36 #include "utilities/vmError.hpp" 37 38 Monitor* ThreadsSMRSupport::_delete_lock = 39 new Monitor(Monitor::special, "Thread_SMR_delete_lock", 40 false /* allow_vm_block */, 41 Monitor::_safepoint_check_never); 42 // The '_cnt', '_max' and '_times" fields are enabled via 43 // -XX:+EnableThreadSMRStatistics: 44 45 // # of parallel threads in _delete_lock->wait(). 46 // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit, 47 // but there is no nice 16-bit _FORMAT support. 48 uint ThreadsSMRSupport::_delete_lock_wait_cnt = 0; 49 50 // Max # of parallel threads in _delete_lock->wait(). 51 // Impl note: See _delete_lock_wait_cnt note. 52 uint ThreadsSMRSupport::_delete_lock_wait_max = 0; 53 54 // Flag to indicate when an _delete_lock->notify() is needed. 55 // Impl note: See _delete_lock_wait_cnt note. 56 volatile uint ThreadsSMRSupport::_delete_notify = 0; 57 58 // # of threads deleted over VM lifetime. 59 // Impl note: Atomically incremented over VM lifetime so use unsigned for more 60 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 61 // isn't available everywhere (or is it?). 62 volatile uint ThreadsSMRSupport::_deleted_thread_cnt = 0; 63 64 // Max time in millis to delete a thread. 65 // Impl note: 16-bit might be too small on an overloaded machine. Use 66 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a 67 // loop for correctness. 68 volatile uint ThreadsSMRSupport::_deleted_thread_time_max = 0; 69 70 // Cumulative time in millis to delete threads. 71 // Impl note: Atomically added to over VM lifetime so use unsigned for more 72 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 73 // isn't available everywhere (or is it?). 74 volatile uint ThreadsSMRSupport::_deleted_thread_times = 0; 75 76 ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = new ThreadsList(0); 77 78 // # of ThreadsLists allocated over VM lifetime. 79 // Impl note: We allocate a new ThreadsList for every thread create and 80 // every thread delete so we need a bigger type than the 81 // _deleted_thread_cnt field. 82 uint64_t ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1; 83 84 // # of ThreadsLists freed over VM lifetime. 85 // Impl note: See _java_thread_list_alloc_cnt note. 86 uint64_t ThreadsSMRSupport::_java_thread_list_free_cnt = 0; 87 88 // Max size ThreadsList allocated. 89 // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit. 90 uint ThreadsSMRSupport::_java_thread_list_max = 0; 91 92 // Max # of nested ThreadsLists for a thread. 93 // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be 94 // 16-bit, but there is no nice 16-bit _FORMAT support. 95 uint ThreadsSMRSupport::_nested_thread_list_max = 0; 96 97 // # of ThreadsListHandles deleted over VM lifetime. 98 // Impl note: Atomically incremented over VM lifetime so use unsigned for 99 // more range. There will be fewer ThreadsListHandles than threads so 100 // unsigned 32-bit should be fine. 101 volatile uint ThreadsSMRSupport::_tlh_cnt = 0; 102 103 // Max time in millis to delete a ThreadsListHandle. 104 // Impl note: 16-bit might be too small on an overloaded machine. Use 105 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a 106 // loop for correctness. 107 volatile uint ThreadsSMRSupport::_tlh_time_max = 0; 108 109 // Cumulative time in millis to delete ThreadsListHandles. 110 // Impl note: Atomically added to over VM lifetime so use unsigned for more 111 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 112 // isn't available everywhere (or is it?). 113 volatile uint ThreadsSMRSupport::_tlh_times = 0; 114 115 ThreadsList* ThreadsSMRSupport::_to_delete_list = NULL; 116 117 // # of parallel ThreadsLists on the to-delete list. 118 // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so 119 // this could be 16-bit, but there is no nice 16-bit _FORMAT support. 120 uint ThreadsSMRSupport::_to_delete_list_cnt = 0; 121 122 // Max # of parallel ThreadsLists on the to-delete list. 123 // Impl note: See _to_delete_list_cnt note. 124 uint ThreadsSMRSupport::_to_delete_list_max = 0; 125 126 127 // 'inline' functions first so the definitions are before first use: 128 129 inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) { 130 Atomic::add(add_value, &_deleted_thread_times); 131 } 132 133 inline void ThreadsSMRSupport::inc_deleted_thread_cnt() { 134 Atomic::inc(&_deleted_thread_cnt); 135 } 136 137 inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() { 138 _java_thread_list_alloc_cnt++; 139 } 140 141 inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) { 142 while (true) { 143 uint cur_value = _deleted_thread_time_max; 144 if (new_value <= cur_value) { 145 // No need to update max value so we're done. 146 break; 147 } 148 if (Atomic::cmpxchg(new_value, &_deleted_thread_time_max, cur_value) == cur_value) { 149 // Updated max value so we're done. Otherwise try it all again. 150 break; 151 } 152 } 153 } 154 155 inline void ThreadsSMRSupport::update_java_thread_list_max(uint new_value) { 156 if (new_value > _java_thread_list_max) { 157 _java_thread_list_max = new_value; 158 } 159 } 160 161 inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) { 162 return (ThreadsList*)Atomic::xchg(new_list, &_java_thread_list); 163 } 164 165 166 // Hash table of pointers found by a scan. Used for collecting hazard 167 // pointers (ThreadsList references). Also used for collecting JavaThreads 168 // that are indirectly referenced by hazard ptrs. An instance of this 169 // class only contains one type of pointer. 170 // 171 class ThreadScanHashtable : public CHeapObj<mtThread> { 172 private: 173 static bool ptr_equals(void * const& s1, void * const& s2) { 174 return s1 == s2; 175 } 176 177 static unsigned int ptr_hash(void * const& s1) { 178 // 2654435761 = 2^32 * Phi (golden ratio) 179 return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u); 180 } 181 182 int _table_size; 183 // ResourceHashtable SIZE is specified at compile time so our 184 // dynamic _table_size is unused for now; 1031 is the first prime 185 // after 1024. 186 typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash, 187 &ThreadScanHashtable::ptr_equals, 1031, 188 ResourceObj::C_HEAP, mtThread> PtrTable; 189 PtrTable * _ptrs; 190 191 public: 192 // ResourceHashtable is passed to various functions and populated in 193 // different places so we allocate it using C_HEAP to make it immune 194 // from any ResourceMarks that happen to be in the code paths. 195 ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {} 196 197 ~ThreadScanHashtable() { delete _ptrs; } 198 199 bool has_entry(void *pointer) { 200 int *val_ptr = _ptrs->get(pointer); 201 return val_ptr != NULL && *val_ptr == 1; 202 } 203 204 void add_entry(void *pointer) { 205 _ptrs->put(pointer, 1); 206 } 207 }; 208 209 // Closure to gather JavaThreads indirectly referenced by hazard ptrs 210 // (ThreadsList references) into a hash table. This closure handles part 2 211 // of the dance - adding all the JavaThreads referenced by the hazard 212 // pointer (ThreadsList reference) to the hash table. 213 // 214 class AddThreadHazardPointerThreadClosure : public ThreadClosure { 215 private: 216 ThreadScanHashtable *_table; 217 218 public: 219 AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {} 220 221 virtual void do_thread(Thread *thread) { 222 if (!_table->has_entry((void*)thread)) { 223 // The same JavaThread might be on more than one ThreadsList or 224 // more than one thread might be using the same ThreadsList. In 225 // either case, we only need a single entry for a JavaThread. 226 _table->add_entry((void*)thread); 227 } 228 } 229 }; 230 231 // Closure to gather JavaThreads indirectly referenced by hazard ptrs 232 // (ThreadsList references) into a hash table. This closure handles part 1 233 // of the dance - hazard ptr chain walking and dispatch to another 234 // closure. 235 // 236 class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure { 237 private: 238 ThreadScanHashtable *_table; 239 public: 240 ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {} 241 242 virtual void do_thread(Thread *thread) { 243 assert_locked_or_safepoint(Threads_lock); 244 245 if (thread == NULL) return; 246 247 // This code races with ThreadsSMRSupport::acquire_stable_list() which 248 // is lock-free so we have to handle some special situations. 249 // 250 ThreadsList *current_list = NULL; 251 while (true) { 252 current_list = thread->get_threads_hazard_ptr(); 253 // No hazard ptr so nothing more to do. 254 if (current_list == NULL) { 255 assert(thread->get_nested_threads_hazard_ptr() == NULL, 256 "cannot have a nested hazard ptr with a NULL regular hazard ptr"); 257 return; 258 } 259 260 // If the hazard ptr is verified as stable (since it is not tagged), 261 // then it is safe to use. 262 if (!Thread::is_hazard_ptr_tagged(current_list)) break; 263 264 // The hazard ptr is tagged as not yet verified as being stable 265 // so we are racing with acquire_stable_list(). This exchange 266 // attempts to invalidate the hazard ptr. If we win the race, 267 // then we can ignore this unstable hazard ptr and the other 268 // thread will retry the attempt to publish a stable hazard ptr. 269 // If we lose the race, then we retry our attempt to look at the 270 // hazard ptr. 271 if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return; 272 } 273 274 // The current JavaThread has a hazard ptr (ThreadsList reference) 275 // which might be _java_thread_list or it might be an older 276 // ThreadsList that has been removed but not freed. In either case, 277 // the hazard ptr is protecting all the JavaThreads on that 278 // ThreadsList. 279 AddThreadHazardPointerThreadClosure add_cl(_table); 280 current_list->threads_do(&add_cl); 281 282 // Any NestedThreadsLists are also protecting JavaThreads so 283 // gather those also; the ThreadsLists may be different. 284 for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); 285 node != NULL; node = node->next()) { 286 node->t_list()->threads_do(&add_cl); 287 } 288 } 289 }; 290 291 // Closure to gather hazard ptrs (ThreadsList references) into a hash table. 292 // 293 class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure { 294 private: 295 ThreadScanHashtable *_table; 296 public: 297 ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {} 298 299 virtual void do_thread(Thread* thread) { 300 assert_locked_or_safepoint(Threads_lock); 301 302 if (thread == NULL) return; 303 ThreadsList *threads = thread->get_threads_hazard_ptr(); 304 if (threads == NULL) { 305 assert(thread->get_nested_threads_hazard_ptr() == NULL, 306 "cannot have a nested hazard ptr with a NULL regular hazard ptr"); 307 return; 308 } 309 // In this closure we always ignore the tag that might mark this 310 // hazard ptr as not yet verified. If we happen to catch an 311 // unverified hazard ptr that is subsequently discarded (not 312 // published), then the only side effect is that we might keep a 313 // to-be-deleted ThreadsList alive a little longer. 314 threads = Thread::untag_hazard_ptr(threads); 315 if (!_table->has_entry((void*)threads)) { 316 _table->add_entry((void*)threads); 317 } 318 319 // Any NestedThreadsLists are also protecting JavaThreads so 320 // gather those also; the ThreadsLists may be different. 321 for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); 322 node != NULL; node = node->next()) { 323 threads = node->t_list(); 324 if (!_table->has_entry((void*)threads)) { 325 _table->add_entry((void*)threads); 326 } 327 } 328 } 329 }; 330 331 // Closure to print JavaThreads that have a hazard ptr (ThreadsList 332 // reference) that contains an indirect reference to a specific JavaThread. 333 // 334 class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure { 335 private: 336 JavaThread *_thread; 337 public: 338 ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {} 339 340 virtual void do_thread(Thread *thread) { 341 assert_locked_or_safepoint(Threads_lock); 342 343 if (thread == NULL) return; 344 ThreadsList *current_list = thread->get_threads_hazard_ptr(); 345 if (current_list == NULL) { 346 assert(thread->get_nested_threads_hazard_ptr() == NULL, 347 "cannot have a nested hazard ptr with a NULL regular hazard ptr"); 348 return; 349 } 350 // If the hazard ptr is unverified, then ignore it. 351 if (Thread::is_hazard_ptr_tagged(current_list)) return; 352 353 // The current JavaThread has a hazard ptr (ThreadsList reference) 354 // which might be _java_thread_list or it might be an older 355 // ThreadsList that has been removed but not freed. In either case, 356 // the hazard ptr is protecting all the JavaThreads on that 357 // ThreadsList, but we only care about matching a specific JavaThread. 358 JavaThreadIterator jti(current_list); 359 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) { 360 if (p == _thread) { 361 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread)); 362 break; 363 } 364 } 365 366 // Any NestedThreadsLists are also protecting JavaThreads so 367 // check those also; the ThreadsLists may be different. 368 for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); 369 node != NULL; node = node->next()) { 370 JavaThreadIterator jti(node->t_list()); 371 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) { 372 if (p == _thread) { 373 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a nested hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread)); 374 return; 375 } 376 } 377 } 378 } 379 }; 380 381 382 // 'entries + 1' so we always have at least one entry. 383 ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), _next_list(NULL) { 384 *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL. 385 } 386 387 ThreadsList::~ThreadsList() { 388 FREE_C_HEAP_ARRAY(JavaThread*, _threads); 389 } 390 391 // Add a JavaThread to a ThreadsList. The returned ThreadsList is a 392 // new copy of the specified ThreadsList with the specified JavaThread 393 // appended to the end. 394 ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) { 395 const uint index = list->_length; 396 const uint new_length = index + 1; 397 const uint head_length = index; 398 ThreadsList *const new_list = new ThreadsList(new_length); 399 400 if (head_length > 0) { 401 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); 402 } 403 *(JavaThread**)(new_list->_threads + index) = java_thread; 404 405 return new_list; 406 } 407 408 int ThreadsList::find_index_of_JavaThread(JavaThread *target) { 409 if (target == NULL) { 410 return -1; 411 } 412 for (uint i = 0; i < length(); i++) { 413 if (target == thread_at(i)) { 414 return (int)i; 415 } 416 } 417 return -1; 418 } 419 420 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const { 421 for (uint i = 0; i < length(); i++) { 422 JavaThread* thread = thread_at(i); 423 oop tobj = thread->threadObj(); 424 // Ignore the thread if it hasn't run yet, has exited 425 // or is starting to exit. 426 if (tobj != NULL && !thread->is_exiting() && 427 java_tid == java_lang_Thread::thread_id(tobj)) { 428 // found a match 429 return thread; 430 } 431 } 432 return NULL; 433 } 434 435 bool ThreadsList::includes(const JavaThread * const p) const { 436 if (p == NULL) { 437 return false; 438 } 439 for (uint i = 0; i < length(); i++) { 440 if (thread_at(i) == p) { 441 return true; 442 } 443 } 444 return false; 445 } 446 447 // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a 448 // new copy of the specified ThreadsList with the specified JavaThread 449 // removed. 450 ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) { 451 assert(list->_length > 0, "sanity"); 452 453 uint i = (uint)list->find_index_of_JavaThread(java_thread); 454 assert(i < list->_length, "did not find JavaThread on the list"); 455 const uint index = i; 456 const uint new_length = list->_length - 1; 457 const uint head_length = index; 458 const uint tail_length = (new_length >= index) ? (new_length - index) : 0; 459 ThreadsList *const new_list = new ThreadsList(new_length); 460 461 if (head_length > 0) { 462 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); 463 } 464 if (tail_length > 0) { 465 Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length); 466 } 467 468 return new_list; 469 } 470 471 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(ThreadsSMRSupport::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) { 472 assert(self == Thread::current(), "sanity check"); 473 if (EnableThreadSMRStatistics) { 474 _timer.start(); 475 } 476 } 477 478 ThreadsListHandle::~ThreadsListHandle() { 479 ThreadsSMRSupport::release_stable_list(_self); 480 if (EnableThreadSMRStatistics) { 481 _timer.stop(); 482 uint millis = (uint)_timer.milliseconds(); 483 ThreadsSMRSupport::update_tlh_stats(millis); 484 } 485 } 486 487 // Convert an internal thread reference to a JavaThread found on the 488 // associated ThreadsList. This ThreadsListHandle "protects" the 489 // returned JavaThread *. 490 // 491 // If thread_oop_p is not NULL, then the caller wants to use the oop 492 // after this call so the oop is returned. On success, *jt_pp is set 493 // to the converted JavaThread * and true is returned. On error, 494 // returns false. 495 // 496 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread, 497 JavaThread ** jt_pp, 498 oop * thread_oop_p) { 499 assert(this->list() != NULL, "must have a ThreadsList"); 500 assert(jt_pp != NULL, "must have a return JavaThread pointer"); 501 // thread_oop_p is optional so no assert() 502 503 // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI 504 // allows a NULL thread parameter to signify "current thread" which 505 // allows us to avoid calling cv_external_thread_to_JavaThread(). 506 // The JVM_* interfaces have no such leeway. 507 508 oop thread_oop = JNIHandles::resolve_non_null(jthread); 509 // Looks like an oop at this point. 510 if (thread_oop_p != NULL) { 511 // Return the oop to the caller; the caller may still want 512 // the oop even if this function returns false. 513 *thread_oop_p = thread_oop; 514 } 515 516 JavaThread *java_thread = java_lang_Thread::thread(thread_oop); 517 if (java_thread == NULL) { 518 // The java.lang.Thread does not contain a JavaThread * so it has 519 // not yet run or it has died. 520 return false; 521 } 522 // Looks like a live JavaThread at this point. 523 524 if (java_thread != JavaThread::current()) { 525 // jthread is not for the current JavaThread so have to verify 526 // the JavaThread * against the ThreadsList. 527 if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) { 528 // Not on the JavaThreads list so it is not alive. 529 return false; 530 } 531 } 532 533 // Return a live JavaThread that is "protected" by the 534 // ThreadsListHandle in the caller. 535 *jt_pp = java_thread; 536 return true; 537 } 538 539 ThreadsListSetter::~ThreadsListSetter() { 540 if (_target_needs_release) { 541 // The hazard ptr in the target needs to be released. 542 ThreadsSMRSupport::release_stable_list(_target); 543 } 544 } 545 546 // Closure to determine if the specified JavaThread is found by 547 // threads_do(). 548 // 549 class VerifyHazardPointerThreadClosure : public ThreadClosure { 550 private: 551 bool _found; 552 Thread *_self; 553 554 public: 555 VerifyHazardPointerThreadClosure(Thread *self) : _found(false), _self(self) {} 556 557 bool found() const { return _found; } 558 559 virtual void do_thread(Thread *thread) { 560 if (thread == _self) { 561 _found = true; 562 } 563 } 564 }; 565 566 // Apply the closure to all threads in the system, with a snapshot of 567 // all JavaThreads provided by the list parameter. 568 void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) { 569 list->threads_do(tc); 570 Threads::non_java_threads_do(tc); 571 } 572 573 // Apply the closure to all threads in the system. 574 void ThreadsSMRSupport::threads_do(ThreadClosure *tc) { 575 threads_do(tc, _java_thread_list); 576 } 577 578 // Verify that the stable hazard pointer used to safely keep threads 579 // alive is scanned by threads_do() which is a key piece of honoring 580 // the Thread-SMR protocol. 581 void ThreadsSMRSupport::verify_hazard_pointer_scanned(Thread *self, ThreadsList *threads) { 582 #ifdef ASSERT 583 // The closure will attempt to verify that the calling thread can 584 // be found by threads_do() on the specified ThreadsList. If it 585 // is successful, then the specified ThreadsList was acquired as 586 // a stable hazard pointer by the calling thread in a way that 587 // honored the Thread-SMR protocol. 588 // 589 // If the calling thread cannot be found by threads_do() and if 590 // it is not the shutdown thread, then the calling thread is not 591 // honoring the Thread-SMR ptotocol. This means that the specified 592 // ThreadsList is not a stable hazard pointer and can be freed 593 // by another thread from the to-be-deleted list at any time. 594 // 595 // Note: The shutdown thread has removed itself from the Threads 596 // list and is safe to have a waiver from this check because 597 // VM_Exit::_shutdown_thread is not set until after the VMThread 598 // has started the final safepoint which holds the Threads_lock 599 // for the remainder of the VM's life. 600 // 601 VerifyHazardPointerThreadClosure cl(self); 602 threads_do(&cl, threads); 603 604 // If the calling thread is not honoring the Thread-SMR protocol, 605 // then we will either crash in threads_do() above because 'threads' 606 // was freed by another thread or we will fail the assert() below. 607 // In either case, we won't get past this point with a badly placed 608 // ThreadsListHandle. 609 610 assert(cl.found() || self == VM_Exit::shutdown_thread(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol."); 611 #endif 612 } 613 614 void ThreadsListSetter::set() { 615 assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set"); 616 (void) ThreadsSMRSupport::acquire_stable_list(_target, /* is_ThreadsListSetter */ true); 617 _target_needs_release = true; 618 } 619 620 // Acquire a stable ThreadsList. 621 // 622 ThreadsList *ThreadsSMRSupport::acquire_stable_list(Thread *self, bool is_ThreadsListSetter) { 623 assert(self != NULL, "sanity check"); 624 // acquire_stable_list_nested_path() will grab the Threads_lock 625 // so let's make sure the ThreadsListHandle is in a safe place. 626 // ThreadsListSetter cannot make this check on this code path. 627 debug_only(if (!is_ThreadsListSetter && StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);) 628 629 if (self->get_threads_hazard_ptr() == NULL) { 630 // The typical case is first. 631 return acquire_stable_list_fast_path(self); 632 } 633 634 // The nested case is rare. 635 return acquire_stable_list_nested_path(self); 636 } 637 638 // Fast path (and lock free) way to acquire a stable ThreadsList. 639 // 640 ThreadsList *ThreadsSMRSupport::acquire_stable_list_fast_path(Thread *self) { 641 assert(self != NULL, "sanity check"); 642 assert(self->get_threads_hazard_ptr() == NULL, "sanity check"); 643 assert(self->get_nested_threads_hazard_ptr() == NULL, 644 "cannot have a nested hazard ptr with a NULL regular hazard ptr"); 645 646 ThreadsList* threads; 647 648 // Stable recording of a hazard ptr for SMR. This code does not use 649 // locks so its use of the _java_thread_list & _threads_hazard_ptr 650 // fields is racy relative to code that uses those fields with locks. 651 // OrderAccess and Atomic functions are used to deal with those races. 652 // 653 while (true) { 654 threads = get_java_thread_list(); 655 656 // Publish a tagged hazard ptr to denote that the hazard ptr is not 657 // yet verified as being stable. Due to the fence after the hazard 658 // ptr write, it will be sequentially consistent w.r.t. the 659 // sequentially consistent writes of the ThreadsList, even on 660 // non-multiple copy atomic machines where stores can be observed 661 // in different order from different observer threads. 662 ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads); 663 self->set_threads_hazard_ptr(unverified_threads); 664 665 // If _java_thread_list has changed, we have lost a race with 666 // Threads::add() or Threads::remove() and have to try again. 667 if (get_java_thread_list() != threads) { 668 continue; 669 } 670 671 // We try to remove the tag which will verify the hazard ptr as 672 // being stable. This exchange can race with a scanning thread 673 // which might invalidate the tagged hazard ptr to keep it from 674 // being followed to access JavaThread ptrs. If we lose the race, 675 // we simply retry. If we win the race, then the stable hazard 676 // ptr is officially published. 677 if (self->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) { 678 break; 679 } 680 } 681 682 // A stable hazard ptr has been published letting other threads know 683 // that the ThreadsList and the JavaThreads reachable from this list 684 // are protected and hence they should not be deleted until everyone 685 // agrees it is safe to do so. 686 687 verify_hazard_pointer_scanned(self, threads); 688 689 return threads; 690 } 691 692 // Acquire a nested stable ThreadsList; this is rare so it uses 693 // Threads_lock. 694 // 695 ThreadsList *ThreadsSMRSupport::acquire_stable_list_nested_path(Thread *self) { 696 assert(self != NULL, "sanity check"); 697 assert(self->get_threads_hazard_ptr() != NULL, 698 "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr"); 699 700 // The thread already has a hazard ptr (ThreadsList ref) so we need 701 // to create a nested ThreadsListHandle with the current ThreadsList 702 // since it might be different than our current hazard ptr. The need 703 // for a nested ThreadsListHandle is rare so we do this while holding 704 // the Threads_lock so we don't race with the scanning code; the code 705 // is so much simpler this way. 706 707 NestedThreadsList* node; 708 { 709 // Only grab the Threads_lock if we don't already own it. 710 MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock); 711 node = new NestedThreadsList(get_java_thread_list()); 712 // We insert at the front of the list to match up with the delete 713 // in release_stable_list(). 714 node->set_next(self->get_nested_threads_hazard_ptr()); 715 self->set_nested_threads_hazard_ptr(node); 716 if (EnableThreadSMRStatistics) { 717 self->inc_nested_threads_hazard_ptr_cnt(); 718 if (self->nested_threads_hazard_ptr_cnt() > _nested_thread_list_max) { 719 _nested_thread_list_max = self->nested_threads_hazard_ptr_cnt(); 720 } 721 } 722 } 723 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::acquire_stable_list: add NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list())); 724 725 verify_hazard_pointer_scanned(self, node->t_list()); 726 727 return node->t_list(); 728 } 729 730 void ThreadsSMRSupport::add_thread(JavaThread *thread){ 731 ThreadsList *new_list = ThreadsList::add_thread(ThreadsSMRSupport::get_java_thread_list(), thread); 732 if (EnableThreadSMRStatistics) { 733 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt(); 734 ThreadsSMRSupport::update_java_thread_list_max(new_list->length()); 735 } 736 // Initial _java_thread_list will not generate a "Threads::add" mesg. 737 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list)); 738 739 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list); 740 ThreadsSMRSupport::free_list(old_list); 741 } 742 743 // set_delete_notify() and clear_delete_notify() are called 744 // under the protection of the delete_lock, but we also use an 745 // Atomic operation to ensure the memory update is seen earlier than 746 // when the delete_lock is dropped. 747 // 748 void ThreadsSMRSupport::clear_delete_notify() { 749 Atomic::dec(&_delete_notify); 750 } 751 752 bool ThreadsSMRSupport::delete_notify() { 753 // Use load_acquire() in order to see any updates to _delete_notify 754 // earlier than when delete_lock is grabbed. 755 return (OrderAccess::load_acquire(&_delete_notify) != 0); 756 } 757 758 // Safely free a ThreadsList after a Threads::add() or Threads::remove(). 759 // The specified ThreadsList may not get deleted during this call if it 760 // is still in-use (referenced by a hazard ptr). Other ThreadsLists 761 // in the chain may get deleted by this call if they are no longer in-use. 762 void ThreadsSMRSupport::free_list(ThreadsList* threads) { 763 assert_locked_or_safepoint(Threads_lock); 764 765 threads->set_next_list(_to_delete_list); 766 _to_delete_list = threads; 767 if (EnableThreadSMRStatistics) { 768 _to_delete_list_cnt++; 769 if (_to_delete_list_cnt > _to_delete_list_max) { 770 _to_delete_list_max = _to_delete_list_cnt; 771 } 772 } 773 774 // Hash table size should be first power of two higher than twice the length of the ThreadsList 775 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1; 776 hash_table_size--; 777 hash_table_size |= hash_table_size >> 1; 778 hash_table_size |= hash_table_size >> 2; 779 hash_table_size |= hash_table_size >> 4; 780 hash_table_size |= hash_table_size >> 8; 781 hash_table_size |= hash_table_size >> 16; 782 hash_table_size++; 783 784 // Gather a hash table of the current hazard ptrs: 785 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); 786 ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table); 787 threads_do(&scan_cl); 788 789 // Walk through the linked list of pending freeable ThreadsLists 790 // and free the ones that are not referenced from hazard ptrs. 791 ThreadsList* current = _to_delete_list; 792 ThreadsList* prev = NULL; 793 ThreadsList* next = NULL; 794 bool threads_is_freed = false; 795 while (current != NULL) { 796 next = current->next_list(); 797 if (!scan_table->has_entry((void*)current)) { 798 // This ThreadsList is not referenced by a hazard ptr. 799 if (prev != NULL) { 800 prev->set_next_list(next); 801 } 802 if (_to_delete_list == current) { 803 _to_delete_list = next; 804 } 805 806 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current)); 807 if (current == threads) threads_is_freed = true; 808 delete current; 809 if (EnableThreadSMRStatistics) { 810 _java_thread_list_free_cnt++; 811 _to_delete_list_cnt--; 812 } 813 } else { 814 prev = current; 815 } 816 current = next; 817 } 818 819 if (!threads_is_freed) { 820 // Only report "is not freed" on the original call to 821 // free_list() for this ThreadsList. 822 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads)); 823 } 824 825 delete scan_table; 826 } 827 828 // Return true if the specified JavaThread is protected by a hazard 829 // pointer (ThreadsList reference). Otherwise, returns false. 830 // 831 bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) { 832 assert_locked_or_safepoint(Threads_lock); 833 834 // Hash table size should be first power of two higher than twice 835 // the length of the Threads list. 836 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1; 837 hash_table_size--; 838 hash_table_size |= hash_table_size >> 1; 839 hash_table_size |= hash_table_size >> 2; 840 hash_table_size |= hash_table_size >> 4; 841 hash_table_size |= hash_table_size >> 8; 842 hash_table_size |= hash_table_size >> 16; 843 hash_table_size++; 844 845 // Gather a hash table of the JavaThreads indirectly referenced by 846 // hazard ptrs. 847 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); 848 ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table); 849 threads_do(&scan_cl); 850 851 bool thread_is_protected = false; 852 if (scan_table->has_entry((void*)thread)) { 853 thread_is_protected = true; 854 } 855 delete scan_table; 856 return thread_is_protected; 857 } 858 859 // Release a stable ThreadsList. 860 // 861 void ThreadsSMRSupport::release_stable_list(Thread *self) { 862 assert(self != NULL, "sanity check"); 863 // release_stable_list_nested_path() will grab the Threads_lock 864 // so let's make sure the ThreadsListHandle is in a safe place. 865 debug_only(if (StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);) 866 867 if (self->get_nested_threads_hazard_ptr() == NULL) { 868 // The typical case is first. 869 release_stable_list_fast_path(self); 870 return; 871 } 872 873 // The nested case is rare. 874 release_stable_list_nested_path(self); 875 } 876 877 // Fast path way to release a stable ThreadsList. The release portion 878 // is lock-free, but the wake up portion is not. 879 // 880 void ThreadsSMRSupport::release_stable_list_fast_path(Thread *self) { 881 assert(self != NULL, "sanity check"); 882 assert(self->get_threads_hazard_ptr() != NULL, "sanity check"); 883 assert(self->get_nested_threads_hazard_ptr() == NULL, 884 "cannot have a nested hazard ptr when releasing a regular hazard ptr"); 885 886 // After releasing the hazard ptr, other threads may go ahead and 887 // free up some memory temporarily used by a ThreadsList snapshot. 888 self->set_threads_hazard_ptr(NULL); 889 890 // We use double-check locking to reduce traffic on the system 891 // wide Thread-SMR delete_lock. 892 if (ThreadsSMRSupport::delete_notify()) { 893 // An exiting thread might be waiting in smr_delete(); we need to 894 // check with delete_lock to be sure. 895 release_stable_list_wake_up((char *) "regular hazard ptr"); 896 } 897 } 898 899 // Release a nested stable ThreadsList; this is rare so it uses 900 // Threads_lock. 901 // 902 void ThreadsSMRSupport::release_stable_list_nested_path(Thread *self) { 903 assert(self != NULL, "sanity check"); 904 assert(self->get_nested_threads_hazard_ptr() != NULL, "sanity check"); 905 assert(self->get_threads_hazard_ptr() != NULL, 906 "must have a regular hazard ptr to have nested hazard ptrs"); 907 908 // We have a nested ThreadsListHandle so we have to release it first. 909 // The need for a nested ThreadsListHandle is rare so we do this while 910 // holding the Threads_lock so we don't race with the scanning code; 911 // the code is so much simpler this way. 912 913 NestedThreadsList *node; 914 { 915 // Only grab the Threads_lock if we don't already own it. 916 MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock); 917 // We remove from the front of the list to match up with the insert 918 // in acquire_stable_list(). 919 node = self->get_nested_threads_hazard_ptr(); 920 self->set_nested_threads_hazard_ptr(node->next()); 921 if (EnableThreadSMRStatistics) { 922 self->dec_nested_threads_hazard_ptr_cnt(); 923 } 924 } 925 926 // An exiting thread might be waiting in smr_delete(); we need to 927 // check with delete_lock to be sure. 928 release_stable_list_wake_up((char *) "nested hazard ptr"); 929 930 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list: delete NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list())); 931 932 delete node; 933 } 934 935 // Wake up portion of the release stable ThreadsList protocol; 936 // uses the delete_lock(). 937 // 938 void ThreadsSMRSupport::release_stable_list_wake_up(char *log_str) { 939 assert(log_str != NULL, "sanity check"); 940 941 // Note: delete_lock is held in smr_delete() for the entire 942 // hazard ptr search so that we do not lose this notify() if 943 // the exiting thread has to wait. That code path also holds 944 // Threads_lock (which was grabbed before delete_lock) so that 945 // threads_do() can be called. This means the system can't start a 946 // safepoint which means this thread can't take too long to get to 947 // a safepoint because of being blocked on delete_lock. 948 // 949 MonitorLockerEx ml(ThreadsSMRSupport::delete_lock(), Monitor::_no_safepoint_check_flag); 950 if (ThreadsSMRSupport::delete_notify()) { 951 // Notify any exiting JavaThreads that are waiting in smr_delete() 952 // that we've released a ThreadsList. 953 ml.notify_all(); 954 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str); 955 } 956 } 957 958 void ThreadsSMRSupport::remove_thread(JavaThread *thread) { 959 ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_java_thread_list(), thread); 960 if (EnableThreadSMRStatistics) { 961 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt(); 962 // This list is smaller so no need to check for a "longest" update. 963 } 964 965 // Final _java_thread_list will not generate a "Threads::remove" mesg. 966 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list)); 967 968 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list); 969 ThreadsSMRSupport::free_list(old_list); 970 } 971 972 // See note for clear_delete_notify(). 973 // 974 void ThreadsSMRSupport::set_delete_notify() { 975 Atomic::inc(&_delete_notify); 976 } 977 978 // Safely delete a JavaThread when it is no longer in use by a 979 // ThreadsListHandle. 980 // 981 void ThreadsSMRSupport::smr_delete(JavaThread *thread) { 982 assert(!Threads_lock->owned_by_self(), "sanity"); 983 984 bool has_logged_once = false; 985 elapsedTimer timer; 986 if (EnableThreadSMRStatistics) { 987 timer.start(); 988 } 989 990 while (true) { 991 { 992 // No safepoint check because this JavaThread is not on the 993 // Threads list. 994 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag); 995 // Cannot use a MonitorLockerEx helper here because we have 996 // to drop the Threads_lock first if we wait. 997 ThreadsSMRSupport::delete_lock()->lock_without_safepoint_check(); 998 // Set the delete_notify flag after we grab delete_lock 999 // and before we scan hazard ptrs because we're doing 1000 // double-check locking in release_stable_list(). 1001 ThreadsSMRSupport::set_delete_notify(); 1002 1003 if (!is_a_protected_JavaThread(thread)) { 1004 // This is the common case. 1005 ThreadsSMRSupport::clear_delete_notify(); 1006 ThreadsSMRSupport::delete_lock()->unlock(); 1007 break; 1008 } 1009 if (!has_logged_once) { 1010 has_logged_once = true; 1011 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread)); 1012 if (log_is_enabled(Debug, os, thread)) { 1013 ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread); 1014 threads_do(&scan_cl); 1015 } 1016 } 1017 } // We have to drop the Threads_lock to wait or delete the thread 1018 1019 if (EnableThreadSMRStatistics) { 1020 _delete_lock_wait_cnt++; 1021 if (_delete_lock_wait_cnt > _delete_lock_wait_max) { 1022 _delete_lock_wait_max = _delete_lock_wait_cnt; 1023 } 1024 } 1025 // Wait for a release_stable_list() call before we check again. No 1026 // safepoint check, no timeout, and not as suspend equivalent flag 1027 // because this JavaThread is not on the Threads list. 1028 ThreadsSMRSupport::delete_lock()->wait(Mutex::_no_safepoint_check_flag, 0, 1029 !Mutex::_as_suspend_equivalent_flag); 1030 if (EnableThreadSMRStatistics) { 1031 _delete_lock_wait_cnt--; 1032 } 1033 1034 ThreadsSMRSupport::clear_delete_notify(); 1035 ThreadsSMRSupport::delete_lock()->unlock(); 1036 // Retry the whole scenario. 1037 } 1038 1039 if (ThreadLocalHandshakes) { 1040 // The thread is about to be deleted so cancel any handshake. 1041 thread->cancel_handshake(); 1042 } 1043 1044 delete thread; 1045 if (EnableThreadSMRStatistics) { 1046 timer.stop(); 1047 uint millis = (uint)timer.milliseconds(); 1048 ThreadsSMRSupport::inc_deleted_thread_cnt(); 1049 ThreadsSMRSupport::add_deleted_thread_times(millis); 1050 ThreadsSMRSupport::update_deleted_thread_time_max(millis); 1051 } 1052 1053 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread)); 1054 } 1055 1056 1057 // Debug, logging, and printing stuff at the end: 1058 1059 // Log Threads class SMR info. 1060 void ThreadsSMRSupport::log_statistics() { 1061 LogTarget(Info, thread, smr) log; 1062 if (log.is_enabled()) { 1063 LogStream out(log); 1064 print_info_on(&out); 1065 } 1066 } 1067 1068 // Print Threads class SMR info. 1069 void ThreadsSMRSupport::print_info_on(outputStream* st) { 1070 // Only grab the Threads_lock if we don't already own it 1071 // and if we are not reporting an error. 1072 MutexLockerEx ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock); 1073 1074 st->print_cr("Threads class SMR info:"); 1075 st->print_cr("_java_thread_list=" INTPTR_FORMAT ", length=%u, " 1076 "elements={", p2i(_java_thread_list), 1077 _java_thread_list->length()); 1078 print_info_elements_on(st, _java_thread_list); 1079 st->print_cr("}"); 1080 if (_to_delete_list != NULL) { 1081 st->print_cr("_to_delete_list=" INTPTR_FORMAT ", length=%u, " 1082 "elements={", p2i(_to_delete_list), 1083 _to_delete_list->length()); 1084 print_info_elements_on(st, _to_delete_list); 1085 st->print_cr("}"); 1086 for (ThreadsList *t_list = _to_delete_list->next_list(); 1087 t_list != NULL; t_list = t_list->next_list()) { 1088 st->print("next-> " INTPTR_FORMAT ", length=%u, " 1089 "elements={", p2i(t_list), t_list->length()); 1090 print_info_elements_on(st, t_list); 1091 st->print_cr("}"); 1092 } 1093 } 1094 if (!EnableThreadSMRStatistics) { 1095 return; 1096 } 1097 st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT "," 1098 "_java_thread_list_free_cnt=" UINT64_FORMAT "," 1099 "_java_thread_list_max=%u, " 1100 "_nested_thread_list_max=%u", 1101 _java_thread_list_alloc_cnt, 1102 _java_thread_list_free_cnt, 1103 _java_thread_list_max, 1104 _nested_thread_list_max); 1105 if (_tlh_cnt > 0) { 1106 st->print_cr("_tlh_cnt=%u" 1107 ", _tlh_times=%u" 1108 ", avg_tlh_time=%0.2f" 1109 ", _tlh_time_max=%u", 1110 _tlh_cnt, _tlh_times, 1111 ((double) _tlh_times / _tlh_cnt), 1112 _tlh_time_max); 1113 } 1114 if (_deleted_thread_cnt > 0) { 1115 st->print_cr("_deleted_thread_cnt=%u" 1116 ", _deleted_thread_times=%u" 1117 ", avg_deleted_thread_time=%0.2f" 1118 ", _deleted_thread_time_max=%u", 1119 _deleted_thread_cnt, _deleted_thread_times, 1120 ((double) _deleted_thread_times / _deleted_thread_cnt), 1121 _deleted_thread_time_max); 1122 } 1123 st->print_cr("_delete_lock_wait_cnt=%u, _delete_lock_wait_max=%u", 1124 _delete_lock_wait_cnt, _delete_lock_wait_max); 1125 st->print_cr("_to_delete_list_cnt=%u, _to_delete_list_max=%u", 1126 _to_delete_list_cnt, _to_delete_list_max); 1127 } 1128 1129 // Print ThreadsList elements (4 per line). 1130 void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_list) { 1131 uint cnt = 0; 1132 JavaThreadIterator jti(t_list); 1133 for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) { 1134 st->print(INTPTR_FORMAT, p2i(jt)); 1135 if (cnt < t_list->length() - 1) { 1136 // Separate with comma or comma-space except for the last one. 1137 if (((cnt + 1) % 4) == 0) { 1138 // Four INTPTR_FORMAT fit on an 80 column line so end the 1139 // current line with just a comma. 1140 st->print_cr(","); 1141 } else { 1142 // Not the last one on the current line so use comma-space: 1143 st->print(", "); 1144 } 1145 } else { 1146 // Last one so just end the current line. 1147 st->cr(); 1148 } 1149 cnt++; 1150 } 1151 }