1 /* 2 * Copyright (c) 2017, 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/ostream.hpp" 36 #include "utilities/resourceHash.hpp" 37 #include "utilities/vmError.hpp" 38 39 Monitor* ThreadsSMRSupport::_delete_lock = 40 new Monitor(Monitor::special, "Thread_SMR_delete_lock", 41 false /* allow_vm_block */, 42 Monitor::_safepoint_check_never); 43 // The '_cnt', '_max' and '_times" fields are enabled via 44 // -XX:+EnableThreadSMRStatistics: 45 46 // # of parallel threads in _delete_lock->wait(). 47 // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit, 48 // but there is no nice 16-bit _FORMAT support. 49 uint ThreadsSMRSupport::_delete_lock_wait_cnt = 0; 50 51 // Max # of parallel threads in _delete_lock->wait(). 52 // Impl note: See _delete_lock_wait_cnt note. 53 uint ThreadsSMRSupport::_delete_lock_wait_max = 0; 54 55 // Flag to indicate when an _delete_lock->notify() is needed. 56 // Impl note: See _delete_lock_wait_cnt note. 57 volatile uint ThreadsSMRSupport::_delete_notify = 0; 58 59 // # of threads deleted over VM lifetime. 60 // Impl note: Atomically incremented over VM lifetime so use unsigned for more 61 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 62 // isn't available everywhere (or is it?). 63 volatile uint ThreadsSMRSupport::_deleted_thread_cnt = 0; 64 65 // Max time in millis to delete a thread. 66 // Impl note: 16-bit might be too small on an overloaded machine. Use 67 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a 68 // loop for correctness. 69 volatile uint ThreadsSMRSupport::_deleted_thread_time_max = 0; 70 71 // Cumulative time in millis to delete threads. 72 // Impl note: Atomically added to over VM lifetime so use unsigned for more 73 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 74 // isn't available everywhere (or is it?). 75 volatile uint ThreadsSMRSupport::_deleted_thread_times = 0; 76 77 ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = new ThreadsList(0); 78 79 // # of ThreadsLists allocated over VM lifetime. 80 // Impl note: We allocate a new ThreadsList for every thread create and 81 // every thread delete so we need a bigger type than the 82 // _deleted_thread_cnt field. 83 uint64_t ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1; 84 85 // # of ThreadsLists freed over VM lifetime. 86 // Impl note: See _java_thread_list_alloc_cnt note. 87 uint64_t ThreadsSMRSupport::_java_thread_list_free_cnt = 0; 88 89 // Max size ThreadsList allocated. 90 // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit. 91 uint ThreadsSMRSupport::_java_thread_list_max = 0; 92 93 // Max # of nested ThreadsLists for a thread. 94 // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be 95 // 16-bit, but there is no nice 16-bit _FORMAT support. 96 uint ThreadsSMRSupport::_nested_thread_list_max = 0; 97 98 // # of ThreadsListHandles deleted over VM lifetime. 99 // Impl note: Atomically incremented over VM lifetime so use unsigned for 100 // more range. There will be fewer ThreadsListHandles than threads so 101 // unsigned 32-bit should be fine. 102 volatile uint ThreadsSMRSupport::_tlh_cnt = 0; 103 104 // Max time in millis to delete a ThreadsListHandle. 105 // Impl note: 16-bit might be too small on an overloaded machine. Use 106 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a 107 // loop for correctness. 108 volatile uint ThreadsSMRSupport::_tlh_time_max = 0; 109 110 // Cumulative time in millis to delete ThreadsListHandles. 111 // Impl note: Atomically added to over VM lifetime so use unsigned for more 112 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc 113 // isn't available everywhere (or is it?). 114 volatile uint ThreadsSMRSupport::_tlh_times = 0; 115 116 ThreadsList* ThreadsSMRSupport::_to_delete_list = NULL; 117 118 // # of parallel ThreadsLists on the to-delete list. 119 // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so 120 // this could be 16-bit, but there is no nice 16-bit _FORMAT support. 121 uint ThreadsSMRSupport::_to_delete_list_cnt = 0; 122 123 // Max # of parallel ThreadsLists on the to-delete list. 124 // Impl note: See _to_delete_list_cnt note. 125 uint ThreadsSMRSupport::_to_delete_list_max = 0; 126 127 128 // 'inline' functions first so the definitions are before first use: 129 130 inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) { 131 Atomic::add(add_value, &_deleted_thread_times); 132 } 133 134 inline void ThreadsSMRSupport::inc_deleted_thread_cnt() { 135 Atomic::inc(&_deleted_thread_cnt); 136 } 137 138 inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() { 139 _java_thread_list_alloc_cnt++; 140 } 141 142 inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) { 143 while (true) { 144 uint cur_value = _deleted_thread_time_max; 145 if (new_value <= cur_value) { 146 // No need to update max value so we're done. 147 break; 148 } 149 if (Atomic::cmpxchg(new_value, &_deleted_thread_time_max, cur_value) == cur_value) { 150 // Updated max value so we're done. Otherwise try it all again. 151 break; 152 } 153 } 154 } 155 156 inline void ThreadsSMRSupport::update_java_thread_list_max(uint new_value) { 157 if (new_value > _java_thread_list_max) { 158 _java_thread_list_max = new_value; 159 } 160 } 161 162 inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) { 163 return (ThreadsList*)Atomic::xchg(new_list, &_java_thread_list); 164 } 165 166 167 // Hash table of pointers found by a scan. Used for collecting hazard 168 // pointers (ThreadsList references). Also used for collecting JavaThreads 169 // that are indirectly referenced by hazard ptrs. An instance of this 170 // class only contains one type of pointer. 171 // 172 class ThreadScanHashtable : public CHeapObj<mtThread> { 173 private: 174 static bool ptr_equals(void * const& s1, void * const& s2) { 175 return s1 == s2; 176 } 177 178 static unsigned int ptr_hash(void * const& s1) { 179 // 2654435761 = 2^32 * Phi (golden ratio) 180 return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u); 181 } 182 183 int _table_size; 184 // ResourceHashtable SIZE is specified at compile time so our 185 // dynamic _table_size is unused for now; 1031 is the first prime 186 // after 1024. 187 typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash, 188 &ThreadScanHashtable::ptr_equals, 1031, 189 ResourceObj::C_HEAP, mtThread> PtrTable; 190 PtrTable * _ptrs; 191 192 public: 193 // ResourceHashtable is passed to various functions and populated in 194 // different places so we allocate it using C_HEAP to make it immune 195 // from any ResourceMarks that happen to be in the code paths. 196 ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {} 197 198 ~ThreadScanHashtable() { delete _ptrs; } 199 200 bool has_entry(void *pointer) { 201 int *val_ptr = _ptrs->get(pointer); 202 return val_ptr != NULL && *val_ptr == 1; 203 } 204 205 void add_entry(void *pointer) { 206 _ptrs->put(pointer, 1); 207 } 208 }; 209 210 // Closure to gather JavaThreads indirectly referenced by hazard ptrs 211 // (ThreadsList references) into a hash table. This closure handles part 2 212 // of the dance - adding all the JavaThreads referenced by the hazard 213 // pointer (ThreadsList reference) to the hash table. 214 // 215 class AddThreadHazardPointerThreadClosure : public ThreadClosure { 216 private: 217 ThreadScanHashtable *_table; 218 219 public: 220 AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {} 221 222 virtual void do_thread(Thread *thread) { 223 if (!_table->has_entry((void*)thread)) { 224 // The same JavaThread might be on more than one ThreadsList or 225 // more than one thread might be using the same ThreadsList. In 226 // either case, we only need a single entry for a JavaThread. 227 _table->add_entry((void*)thread); 228 } 229 } 230 }; 231 232 // Closure to gather JavaThreads indirectly referenced by hazard ptrs 233 // (ThreadsList references) into a hash table. This closure handles part 1 234 // of the dance - hazard ptr chain walking and dispatch to another 235 // closure. 236 // 237 class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure { 238 private: 239 ThreadScanHashtable *_table; 240 public: 241 ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {} 242 243 virtual void do_thread(Thread *thread) { 244 assert_locked_or_safepoint(Threads_lock); 245 246 if (thread == NULL) return; 247 248 // This code races with ThreadsSMRSupport::acquire_stable_list() which 249 // is lock-free so we have to handle some special situations. 250 // 251 ThreadsList *current_list = NULL; 252 while (true) { 253 current_list = thread->get_threads_hazard_ptr(); 254 // No hazard ptr so nothing more to do. 255 if (current_list == NULL) { 256 return; 257 } 258 259 // If the hazard ptr is verified as stable (since it is not tagged), 260 // then it is safe to use. 261 if (!Thread::is_hazard_ptr_tagged(current_list)) break; 262 263 // The hazard ptr is tagged as not yet verified as being stable 264 // so we are racing with acquire_stable_list(). This exchange 265 // attempts to invalidate the hazard ptr. If we win the race, 266 // then we can ignore this unstable hazard ptr and the other 267 // thread will retry the attempt to publish a stable hazard ptr. 268 // If we lose the race, then we retry our attempt to look at the 269 // hazard ptr. 270 if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return; 271 } 272 273 // The current JavaThread has a hazard ptr (ThreadsList reference) 274 // which might be _java_thread_list or it might be an older 275 // ThreadsList that has been removed but not freed. In either case, 276 // the hazard ptr is protecting all the JavaThreads on that 277 // ThreadsList. 278 AddThreadHazardPointerThreadClosure add_cl(_table); 279 current_list->threads_do(&add_cl); 280 } 281 }; 282 283 // Closure to gather hazard ptrs (ThreadsList references) into a hash table. 284 // 285 class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure { 286 private: 287 ThreadScanHashtable *_table; 288 public: 289 ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {} 290 291 virtual void do_thread(Thread* thread) { 292 assert_locked_or_safepoint(Threads_lock); 293 294 if (thread == NULL) return; 295 ThreadsList *threads = thread->get_threads_hazard_ptr(); 296 if (threads == NULL) { 297 return; 298 } 299 // In this closure we always ignore the tag that might mark this 300 // hazard ptr as not yet verified. If we happen to catch an 301 // unverified hazard ptr that is subsequently discarded (not 302 // published), then the only side effect is that we might keep a 303 // to-be-deleted ThreadsList alive a little longer. 304 threads = Thread::untag_hazard_ptr(threads); 305 if (!_table->has_entry((void*)threads)) { 306 _table->add_entry((void*)threads); 307 } 308 } 309 }; 310 311 // Closure to print JavaThreads that have a hazard ptr (ThreadsList 312 // reference) that contains an indirect reference to a specific JavaThread. 313 // 314 class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure { 315 private: 316 JavaThread *_thread; 317 public: 318 ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {} 319 320 virtual void do_thread(Thread *thread) { 321 assert_locked_or_safepoint(Threads_lock); 322 323 if (thread == NULL) return; 324 ThreadsList *current_list = thread->get_threads_hazard_ptr(); 325 if (current_list == NULL) { 326 return; 327 } 328 // If the hazard ptr is unverified, then ignore it. 329 if (Thread::is_hazard_ptr_tagged(current_list)) return; 330 331 // The current JavaThread has a hazard ptr (ThreadsList reference) 332 // which might be _java_thread_list or it might be an older 333 // ThreadsList that has been removed but not freed. In either case, 334 // the hazard ptr is protecting all the JavaThreads on that 335 // ThreadsList, but we only care about matching a specific JavaThread. 336 JavaThreadIterator jti(current_list); 337 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) { 338 if (p == _thread) { 339 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)); 340 break; 341 } 342 } 343 } 344 }; 345 346 // Closure to determine if the specified JavaThread is found by 347 // threads_do(). 348 // 349 class VerifyHazardPtrThreadClosure : public ThreadClosure { 350 private: 351 bool _found; 352 Thread *_self; 353 354 public: 355 VerifyHazardPtrThreadClosure(Thread *self) : _found(false), _self(self) {} 356 357 bool found() const { return _found; } 358 359 virtual void do_thread(Thread *thread) { 360 if (thread == _self) { 361 _found = true; 362 } 363 } 364 }; 365 366 367 // Acquire a stable ThreadsList. 368 // 369 void SafeThreadsListPtr::acquire_stable_list() { 370 assert(_thread != NULL, "sanity check"); 371 _needs_release = true; 372 _previous = _thread->_threads_list_ptr; 373 _thread->_threads_list_ptr = this; 374 375 if (_thread->get_threads_hazard_ptr() == NULL) { 376 // The typical case is first. 377 acquire_stable_list_fast_path(); 378 return; 379 } 380 381 // The nested case is rare. 382 acquire_stable_list_nested_path(); 383 } 384 385 // Fast path way to acquire a stable ThreadsList. 386 // 387 void SafeThreadsListPtr::acquire_stable_list_fast_path() { 388 assert(_thread != NULL, "sanity check"); 389 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check"); 390 391 ThreadsList* threads; 392 393 // Stable recording of a hazard ptr for SMR. This code does not use 394 // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr 395 // fields is racy relative to code that uses those fields with locks. 396 // OrderAccess and Atomic functions are used to deal with those races. 397 // 398 while (true) { 399 threads = ThreadsSMRSupport::get_java_thread_list(); 400 401 // Publish a tagged hazard ptr to denote that the hazard ptr is not 402 // yet verified as being stable. Due to the fence after the hazard 403 // ptr write, it will be sequentially consistent w.r.t. the 404 // sequentially consistent writes of the ThreadsList, even on 405 // non-multiple copy atomic machines where stores can be observed 406 // in different order from different observer threads. 407 ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads); 408 _thread->set_threads_hazard_ptr(unverified_threads); 409 410 // If _smr_java_thread_list has changed, we have lost a race with 411 // Threads::add() or Threads::remove() and have to try again. 412 if (ThreadsSMRSupport::get_java_thread_list() != threads) { 413 continue; 414 } 415 416 // We try to remove the tag which will verify the hazard ptr as 417 // being stable. This exchange can race with a scanning thread 418 // which might invalidate the tagged hazard ptr to keep it from 419 // being followed to access JavaThread ptrs. If we lose the race, 420 // we simply retry. If we win the race, then the stable hazard 421 // ptr is officially published. 422 if (_thread->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) { 423 break; 424 } 425 } 426 427 // A stable hazard ptr has been published letting other threads know 428 // that the ThreadsList and the JavaThreads reachable from this list 429 // are protected and hence they should not be deleted until everyone 430 // agrees it is safe to do so. 431 432 _list = threads; 433 434 verify_hazard_ptr_scanned(); 435 } 436 437 // Acquire a nested stable ThreadsList; this is rare so it uses 438 // reference counting. 439 // 440 void SafeThreadsListPtr::acquire_stable_list_nested_path() { 441 assert(_thread != NULL, "sanity check"); 442 assert(_thread->get_threads_hazard_ptr() != NULL, 443 "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr"); 444 445 // The thread already has a hazard ptr (ThreadsList ref) so we need 446 // to create a nested ThreadsListHandle with the current ThreadsList 447 // since it might be different than our current hazard ptr. To remedy 448 // the situation, the ThreadsList pointed to by the pre-existing 449 // stable hazard ptr is reference counted before the hazard ptr may 450 // be released and moved to a new ThreadsList. The old ThreadsList 451 // is remembered in the ThreadsListHandle. 452 453 ThreadsList* current_list = _previous->_list; 454 if (EnableThreadSMRStatistics) { 455 _thread->inc_nested_threads_hazard_ptr_cnt(); 456 } 457 current_list->inc_nested_handle_cnt(); 458 _previous->_has_ref_count = true; // promote SafeThreadsListPtr to be reference counted 459 _thread->_threads_hazard_ptr = NULL; // clear the hazard ptr so we can go through the fast path below 460 461 if (EnableThreadSMRStatistics && _thread->nested_threads_hazard_ptr_cnt() > ThreadsSMRSupport::_nested_thread_list_max) { 462 ThreadsSMRSupport::_nested_thread_list_max = _thread->nested_threads_hazard_ptr_cnt(); 463 } 464 465 acquire_stable_list_fast_path(); 466 467 verify_hazard_ptr_scanned(); 468 469 log_debug(thread, smr)("tid=" UINTX_FORMAT ": SafeThreadsListPtr::acquire_stable_list: add nested list pointer to ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(_list)); 470 } 471 472 // Release a stable ThreadsList. 473 // 474 void SafeThreadsListPtr::release_stable_list() { 475 assert(_thread != NULL, "sanity check"); 476 assert(_thread->_threads_list_ptr == this, "sanity check"); 477 _thread->_threads_list_ptr = _previous; 478 479 if (_has_ref_count) { 480 // If a SafeThreadsListPtr has been promoted to use reference counting 481 // due to nesting of ThreadsListHandles, then the reference count must be 482 // decremented, at which point it may be freed. The forgotten value of 483 // the list no longer matters at this point and should already be NULL. 484 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check"); 485 if (EnableThreadSMRStatistics) { 486 _thread->dec_nested_threads_hazard_ptr_cnt(); 487 } 488 _list->dec_nested_handle_cnt(); 489 490 log_debug(thread, smr)("tid=" UINTX_FORMAT ": SafeThreadsListPtr::release_stable_list: delete nested list pointer to ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(_list)); 491 } else { 492 // The normal case: a leaf ThreadsListHandle. This merely requires setting 493 // the thread hazard ptr back to NULL. 494 assert(_thread->get_threads_hazard_ptr() != NULL, "sanity check"); 495 _thread->set_threads_hazard_ptr(NULL); 496 } 497 498 // After releasing the hazard ptr, other threads may go ahead and 499 // free up some memory temporarily used by a ThreadsList snapshot. 500 501 // We use double-check locking to reduce traffic on the system 502 // wide Thread-SMR delete_lock. 503 if (ThreadsSMRSupport::delete_notify()) { 504 // An exiting thread might be waiting in smr_delete(); we need to 505 // check with delete_lock to be sure. 506 ThreadsSMRSupport::release_stable_list_wake_up(_has_ref_count); 507 } 508 } 509 510 // Verify that the stable hazard ptr used to safely keep threads 511 // alive is scanned by threads_do() which is a key piece of honoring 512 // the Thread-SMR protocol. 513 void SafeThreadsListPtr::verify_hazard_ptr_scanned() { 514 #ifdef ASSERT 515 assert(_list != NULL, "_list must not be NULL"); 516 517 // The closure will attempt to verify that the calling thread can 518 // be found by threads_do() on the specified ThreadsList. If it 519 // is successful, then the specified ThreadsList was acquired as 520 // a stable hazard ptr by the calling thread in a way that honored 521 // the Thread-SMR protocol. 522 // 523 // If the calling thread cannot be found by threads_do() and if 524 // it is not the shutdown thread, then the calling thread is not 525 // honoring the Thread-SMR ptotocol. This means that the specified 526 // ThreadsList is not a stable hazard ptr and can be freed by 527 // another thread from the to-be-deleted list at any time. 528 // 529 // Note: The shutdown thread has removed itself from the Threads 530 // list and is safe to have a waiver from this check because 531 // VM_Exit::_shutdown_thread is not set until after the VMThread 532 // has started the final safepoint which holds the Threads_lock 533 // for the remainder of the VM's life. 534 // 535 VerifyHazardPtrThreadClosure cl(_thread); 536 ThreadsSMRSupport::threads_do(&cl, _list); 537 538 // If the calling thread is not honoring the Thread-SMR protocol, 539 // then we will either crash in threads_do() above because 'threads' 540 // was freed by another thread or we will fail the assert() below. 541 // In either case, we won't get past this point with a badly placed 542 // ThreadsListHandle. 543 544 assert(cl.found() || _thread == VM_Exit::shutdown_thread(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol."); 545 #endif 546 } 547 548 // 'entries + 1' so we always have at least one entry. 549 ThreadsList::ThreadsList(int entries) : 550 _length(entries), 551 _next_list(NULL), 552 _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), 553 _nested_handle_cnt(0) 554 { 555 *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL. 556 } 557 558 ThreadsList::~ThreadsList() { 559 FREE_C_HEAP_ARRAY(JavaThread*, _threads); 560 } 561 562 // Add a JavaThread to a ThreadsList. The returned ThreadsList is a 563 // new copy of the specified ThreadsList with the specified JavaThread 564 // appended to the end. 565 ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) { 566 const uint index = list->_length; 567 const uint new_length = index + 1; 568 const uint head_length = index; 569 ThreadsList *const new_list = new ThreadsList(new_length); 570 571 if (head_length > 0) { 572 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); 573 } 574 *(JavaThread**)(new_list->_threads + index) = java_thread; 575 576 return new_list; 577 } 578 579 void ThreadsList::dec_nested_handle_cnt() { 580 // The decrement needs to be MO_ACQ_REL. At the moment, the Atomic::dec 581 // backend on PPC does not yet conform to these requirements. Therefore 582 // the decrement is simulated with an Atomic::sub(1, &addr). 583 // Without this MO_ACQ_REL Atomic::dec simulation, the nested SMR mechanism 584 // is not generally safe to use. 585 Atomic::sub(1, &_nested_handle_cnt); 586 } 587 588 int ThreadsList::find_index_of_JavaThread(JavaThread *target) { 589 if (target == NULL) { 590 return -1; 591 } 592 for (uint i = 0; i < length(); i++) { 593 if (target == thread_at(i)) { 594 return (int)i; 595 } 596 } 597 return -1; 598 } 599 600 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const { 601 for (uint i = 0; i < length(); i++) { 602 JavaThread* thread = thread_at(i); 603 oop tobj = thread->threadObj(); 604 // Ignore the thread if it hasn't run yet, has exited 605 // or is starting to exit. 606 if (tobj != NULL && !thread->is_exiting() && 607 java_tid == java_lang_Thread::thread_id(tobj)) { 608 // found a match 609 return thread; 610 } 611 } 612 return NULL; 613 } 614 615 void ThreadsList::inc_nested_handle_cnt() { 616 // The increment needs to be MO_SEQ_CST. At the moment, the Atomic::inc 617 // backend on PPC does not yet conform to these requirements. Therefore 618 // the increment is simulated with a load phi; cas phi + 1; loop. 619 // Without this MO_SEQ_CST Atomic::inc simulation, the nested SMR mechanism 620 // is not generally safe to use. 621 intx sample = OrderAccess::load_acquire(&_nested_handle_cnt); 622 for (;;) { 623 if (Atomic::cmpxchg(sample + 1, &_nested_handle_cnt, sample) == sample) { 624 return; 625 } else { 626 sample = OrderAccess::load_acquire(&_nested_handle_cnt); 627 } 628 } 629 } 630 631 bool ThreadsList::includes(const JavaThread * const p) const { 632 if (p == NULL) { 633 return false; 634 } 635 for (uint i = 0; i < length(); i++) { 636 if (thread_at(i) == p) { 637 return true; 638 } 639 } 640 return false; 641 } 642 643 // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a 644 // new copy of the specified ThreadsList with the specified JavaThread 645 // removed. 646 ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) { 647 assert(list->_length > 0, "sanity"); 648 649 uint i = (uint)list->find_index_of_JavaThread(java_thread); 650 assert(i < list->_length, "did not find JavaThread on the list"); 651 const uint index = i; 652 const uint new_length = list->_length - 1; 653 const uint head_length = index; 654 const uint tail_length = (new_length >= index) ? (new_length - index) : 0; 655 ThreadsList *const new_list = new ThreadsList(new_length); 656 657 if (head_length > 0) { 658 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); 659 } 660 if (tail_length > 0) { 661 Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length); 662 } 663 664 return new_list; 665 } 666 667 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list_ptr(self, /* acquire */ true) { 668 assert(self == Thread::current(), "sanity check"); 669 if (EnableThreadSMRStatistics) { 670 _timer.start(); 671 } 672 } 673 674 ThreadsListHandle::~ThreadsListHandle() { 675 if (EnableThreadSMRStatistics) { 676 _timer.stop(); 677 uint millis = (uint)_timer.milliseconds(); 678 ThreadsSMRSupport::update_tlh_stats(millis); 679 } 680 } 681 682 // Convert an internal thread reference to a JavaThread found on the 683 // associated ThreadsList. This ThreadsListHandle "protects" the 684 // returned JavaThread *. 685 // 686 // If thread_oop_p is not NULL, then the caller wants to use the oop 687 // after this call so the oop is returned. On success, *jt_pp is set 688 // to the converted JavaThread * and true is returned. On error, 689 // returns false. 690 // 691 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread, 692 JavaThread ** jt_pp, 693 oop * thread_oop_p) { 694 assert(this->list() != NULL, "must have a ThreadsList"); 695 assert(jt_pp != NULL, "must have a return JavaThread pointer"); 696 // thread_oop_p is optional so no assert() 697 698 // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI 699 // allows a NULL thread parameter to signify "current thread" which 700 // allows us to avoid calling cv_external_thread_to_JavaThread(). 701 // The JVM_* interfaces have no such leeway. 702 703 oop thread_oop = JNIHandles::resolve_non_null(jthread); 704 // Looks like an oop at this point. 705 if (thread_oop_p != NULL) { 706 // Return the oop to the caller; the caller may still want 707 // the oop even if this function returns false. 708 *thread_oop_p = thread_oop; 709 } 710 711 JavaThread *java_thread = java_lang_Thread::thread(thread_oop); 712 if (java_thread == NULL) { 713 // The java.lang.Thread does not contain a JavaThread * so it has 714 // not yet run or it has died. 715 return false; 716 } 717 // Looks like a live JavaThread at this point. 718 719 if (java_thread != JavaThread::current()) { 720 // jthread is not for the current JavaThread so have to verify 721 // the JavaThread * against the ThreadsList. 722 if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) { 723 // Not on the JavaThreads list so it is not alive. 724 return false; 725 } 726 } 727 728 // Return a live JavaThread that is "protected" by the 729 // ThreadsListHandle in the caller. 730 *jt_pp = java_thread; 731 return true; 732 } 733 734 void ThreadsSMRSupport::add_thread(JavaThread *thread){ 735 ThreadsList *new_list = ThreadsList::add_thread(get_java_thread_list(), thread); 736 if (EnableThreadSMRStatistics) { 737 inc_java_thread_list_alloc_cnt(); 738 update_java_thread_list_max(new_list->length()); 739 } 740 // Initial _java_thread_list will not generate a "Threads::add" mesg. 741 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list)); 742 743 ThreadsList *old_list = xchg_java_thread_list(new_list); 744 free_list(old_list); 745 } 746 747 // set_delete_notify() and clear_delete_notify() are called 748 // under the protection of the delete_lock, but we also use an 749 // Atomic operation to ensure the memory update is seen earlier than 750 // when the delete_lock is dropped. 751 // 752 void ThreadsSMRSupport::clear_delete_notify() { 753 Atomic::dec(&_delete_notify); 754 } 755 756 bool ThreadsSMRSupport::delete_notify() { 757 // Use load_acquire() in order to see any updates to _delete_notify 758 // earlier than when delete_lock is grabbed. 759 return (OrderAccess::load_acquire(&_delete_notify) != 0); 760 } 761 762 // Safely free a ThreadsList after a Threads::add() or Threads::remove(). 763 // The specified ThreadsList may not get deleted during this call if it 764 // is still in-use (referenced by a hazard ptr). Other ThreadsLists 765 // in the chain may get deleted by this call if they are no longer in-use. 766 void ThreadsSMRSupport::free_list(ThreadsList* threads) { 767 assert_locked_or_safepoint(Threads_lock); 768 769 threads->set_next_list(_to_delete_list); 770 _to_delete_list = threads; 771 if (EnableThreadSMRStatistics) { 772 _to_delete_list_cnt++; 773 if (_to_delete_list_cnt > _to_delete_list_max) { 774 _to_delete_list_max = _to_delete_list_cnt; 775 } 776 } 777 778 // Hash table size should be first power of two higher than twice the length of the ThreadsList 779 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1; 780 hash_table_size--; 781 hash_table_size |= hash_table_size >> 1; 782 hash_table_size |= hash_table_size >> 2; 783 hash_table_size |= hash_table_size >> 4; 784 hash_table_size |= hash_table_size >> 8; 785 hash_table_size |= hash_table_size >> 16; 786 hash_table_size++; 787 788 // Gather a hash table of the current hazard ptrs: 789 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); 790 ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table); 791 threads_do(&scan_cl); 792 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of 793 // nested reference counters 794 795 // Walk through the linked list of pending freeable ThreadsLists 796 // and free the ones that are not referenced from hazard ptrs. 797 ThreadsList* current = _to_delete_list; 798 ThreadsList* prev = NULL; 799 ThreadsList* next = NULL; 800 bool threads_is_freed = false; 801 while (current != NULL) { 802 next = current->next_list(); 803 if (!scan_table->has_entry((void*)current) && current->_nested_handle_cnt == 0) { 804 // This ThreadsList is not referenced by a hazard ptr. 805 if (prev != NULL) { 806 prev->set_next_list(next); 807 } 808 if (_to_delete_list == current) { 809 _to_delete_list = next; 810 } 811 812 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current)); 813 if (current == threads) threads_is_freed = true; 814 delete current; 815 if (EnableThreadSMRStatistics) { 816 _java_thread_list_free_cnt++; 817 _to_delete_list_cnt--; 818 } 819 } else { 820 prev = current; 821 } 822 current = next; 823 } 824 825 if (!threads_is_freed) { 826 // Only report "is not freed" on the original call to 827 // free_list() for this ThreadsList. 828 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads)); 829 } 830 831 delete scan_table; 832 } 833 834 // Return true if the specified JavaThread is protected by a hazard 835 // pointer (ThreadsList reference). Otherwise, returns false. 836 // 837 bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) { 838 assert_locked_or_safepoint(Threads_lock); 839 840 // Hash table size should be first power of two higher than twice 841 // the length of the Threads list. 842 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1; 843 hash_table_size--; 844 hash_table_size |= hash_table_size >> 1; 845 hash_table_size |= hash_table_size >> 2; 846 hash_table_size |= hash_table_size >> 4; 847 hash_table_size |= hash_table_size >> 8; 848 hash_table_size |= hash_table_size >> 16; 849 hash_table_size++; 850 851 // Gather a hash table of the JavaThreads indirectly referenced by 852 // hazard ptrs. 853 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); 854 ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table); 855 threads_do(&scan_cl); 856 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of 857 // nested reference counters 858 859 // Walk through the linked list of pending freeable ThreadsLists 860 // and include the ones that are currently in use by a nested 861 // ThreadsListHandle in the search set. 862 ThreadsList* current = _to_delete_list; 863 while (current != NULL) { 864 if (current->_nested_handle_cnt != 0) { 865 // 'current' is in use by a nested ThreadsListHandle so the hazard 866 // ptr is protecting all the JavaThreads on that ThreadsList. 867 AddThreadHazardPointerThreadClosure add_cl(scan_table); 868 current->threads_do(&add_cl); 869 } 870 current = current->next_list(); 871 } 872 873 bool thread_is_protected = false; 874 if (scan_table->has_entry((void*)thread)) { 875 thread_is_protected = true; 876 } 877 delete scan_table; 878 return thread_is_protected; 879 } 880 881 // Wake up portion of the release stable ThreadsList protocol; 882 // uses the delete_lock(). 883 // 884 void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) { 885 const char* log_str = is_nested ? "nested hazard ptr" : "regular hazard ptr"; 886 887 // Note: delete_lock is held in smr_delete() for the entire 888 // hazard ptr search so that we do not lose this notify() if 889 // the exiting thread has to wait. That code path also holds 890 // Threads_lock (which was grabbed before delete_lock) so that 891 // threads_do() can be called. This means the system can't start a 892 // safepoint which means this thread can't take too long to get to 893 // a safepoint because of being blocked on delete_lock. 894 // 895 MonitorLockerEx ml(ThreadsSMRSupport::delete_lock(), Monitor::_no_safepoint_check_flag); 896 if (ThreadsSMRSupport::delete_notify()) { 897 // Notify any exiting JavaThreads that are waiting in smr_delete() 898 // that we've released a ThreadsList. 899 ml.notify_all(); 900 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str); 901 } 902 } 903 904 void ThreadsSMRSupport::remove_thread(JavaThread *thread) { 905 ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_java_thread_list(), thread); 906 if (EnableThreadSMRStatistics) { 907 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt(); 908 // This list is smaller so no need to check for a "longest" update. 909 } 910 911 // Final _java_thread_list will not generate a "Threads::remove" mesg. 912 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list)); 913 914 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list); 915 ThreadsSMRSupport::free_list(old_list); 916 } 917 918 // See note for clear_delete_notify(). 919 // 920 void ThreadsSMRSupport::set_delete_notify() { 921 Atomic::inc(&_delete_notify); 922 } 923 924 // Safely delete a JavaThread when it is no longer in use by a 925 // ThreadsListHandle. 926 // 927 void ThreadsSMRSupport::smr_delete(JavaThread *thread) { 928 assert(!Threads_lock->owned_by_self(), "sanity"); 929 930 bool has_logged_once = false; 931 elapsedTimer timer; 932 if (EnableThreadSMRStatistics) { 933 timer.start(); 934 } 935 936 while (true) { 937 { 938 // No safepoint check because this JavaThread is not on the 939 // Threads list. 940 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag); 941 // Cannot use a MonitorLockerEx helper here because we have 942 // to drop the Threads_lock first if we wait. 943 ThreadsSMRSupport::delete_lock()->lock_without_safepoint_check(); 944 // Set the delete_notify flag after we grab delete_lock 945 // and before we scan hazard ptrs because we're doing 946 // double-check locking in release_stable_list(). 947 ThreadsSMRSupport::set_delete_notify(); 948 949 if (!is_a_protected_JavaThread(thread)) { 950 // This is the common case. 951 ThreadsSMRSupport::clear_delete_notify(); 952 ThreadsSMRSupport::delete_lock()->unlock(); 953 break; 954 } 955 if (!has_logged_once) { 956 has_logged_once = true; 957 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread)); 958 if (log_is_enabled(Debug, os, thread)) { 959 ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread); 960 threads_do(&scan_cl); 961 ThreadsList* current = _to_delete_list; 962 while (current != NULL) { 963 if (current->_nested_handle_cnt != 0 && current->includes(thread)) { 964 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: found nested hazard pointer to thread=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread)); 965 } 966 current = current->next_list(); 967 } 968 } 969 } 970 } // We have to drop the Threads_lock to wait or delete the thread 971 972 if (EnableThreadSMRStatistics) { 973 _delete_lock_wait_cnt++; 974 if (_delete_lock_wait_cnt > _delete_lock_wait_max) { 975 _delete_lock_wait_max = _delete_lock_wait_cnt; 976 } 977 } 978 // Wait for a release_stable_list() call before we check again. No 979 // safepoint check, no timeout, and not as suspend equivalent flag 980 // because this JavaThread is not on the Threads list. 981 ThreadsSMRSupport::delete_lock()->wait(Mutex::_no_safepoint_check_flag, 0, 982 !Mutex::_as_suspend_equivalent_flag); 983 if (EnableThreadSMRStatistics) { 984 _delete_lock_wait_cnt--; 985 } 986 987 ThreadsSMRSupport::clear_delete_notify(); 988 ThreadsSMRSupport::delete_lock()->unlock(); 989 // Retry the whole scenario. 990 } 991 992 delete thread; 993 if (EnableThreadSMRStatistics) { 994 timer.stop(); 995 uint millis = (uint)timer.milliseconds(); 996 ThreadsSMRSupport::inc_deleted_thread_cnt(); 997 ThreadsSMRSupport::add_deleted_thread_times(millis); 998 ThreadsSMRSupport::update_deleted_thread_time_max(millis); 999 } 1000 1001 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread)); 1002 } 1003 1004 // Apply the closure to all threads in the system, with a snapshot of 1005 // all JavaThreads provided by the list parameter. 1006 void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) { 1007 list->threads_do(tc); 1008 Threads::non_java_threads_do(tc); 1009 } 1010 1011 // Apply the closure to all threads in the system. 1012 void ThreadsSMRSupport::threads_do(ThreadClosure *tc) { 1013 threads_do(tc, _java_thread_list); 1014 } 1015 1016 1017 // Debug, logging, and printing stuff at the end: 1018 1019 // Print SMR info for a SafeThreadsListPtr to a given output stream. 1020 void SafeThreadsListPtr::print_on(outputStream* st) { 1021 if (this == _thread->_threads_list_ptr) { 1022 // The top level hazard ptr. 1023 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list)); 1024 } else { 1025 // Nested hazard ptrs. 1026 st->print(", _nested_threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list)); 1027 } 1028 } 1029 1030 // Log Threads class SMR info. 1031 void ThreadsSMRSupport::log_statistics() { 1032 LogTarget(Info, thread, smr) log; 1033 if (log.is_enabled()) { 1034 LogStream out(log); 1035 print_info_on(&out); 1036 } 1037 } 1038 1039 // Print SMR info for a thread to a given output stream. 1040 void ThreadsSMRSupport::print_info_on(const Thread* thread, outputStream* st) { 1041 if (thread->_threads_hazard_ptr != NULL) { 1042 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(thread->_threads_hazard_ptr)); 1043 } 1044 if (EnableThreadSMRStatistics && thread->_threads_list_ptr != NULL) { 1045 // The count is only interesting if we have a _threads_list_ptr. 1046 st->print(", _nested_threads_hazard_ptr_cnt=%u", thread->_nested_threads_hazard_ptr_cnt); 1047 } 1048 if (SafepointSynchronize::is_at_safepoint() || Thread::current() == thread) { 1049 // It is only safe to walk the list if we're at a safepoint or the 1050 // calling thread is walking its own list. 1051 SafeThreadsListPtr* current = thread->_threads_list_ptr; 1052 if (current != NULL) { 1053 // Skip the top nesting level as it is always printed above. 1054 current = current->previous(); 1055 } 1056 while (current != NULL) { 1057 current->print_on(st); 1058 current = current->previous(); 1059 } 1060 } 1061 } 1062 1063 // Print Threads class SMR info. 1064 void ThreadsSMRSupport::print_info_on(outputStream* st) { 1065 // Only grab the Threads_lock if we don't already own it and if we 1066 // are not reporting an error. 1067 // Note: Not grabbing the Threads_lock during error reporting is 1068 // dangerous because the data structures we want to print can be 1069 // freed concurrently. However, grabbing the Threads_lock during 1070 // error reporting can be equally dangerous since this thread might 1071 // block during error reporting or a nested error could leave the 1072 // Threads_lock held. The classic no win scenario. 1073 // 1074 MutexLockerEx ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock); 1075 1076 st->print_cr("Threads class SMR info:"); 1077 st->print_cr("_java_thread_list=" INTPTR_FORMAT ", length=%u, " 1078 "elements={", p2i(_java_thread_list), 1079 _java_thread_list->length()); 1080 print_info_elements_on(st, _java_thread_list); 1081 st->print_cr("}"); 1082 if (_to_delete_list != NULL) { 1083 st->print_cr("_to_delete_list=" INTPTR_FORMAT ", length=%u, " 1084 "elements={", p2i(_to_delete_list), 1085 _to_delete_list->length()); 1086 print_info_elements_on(st, _to_delete_list); 1087 st->print_cr("}"); 1088 for (ThreadsList *t_list = _to_delete_list->next_list(); 1089 t_list != NULL; t_list = t_list->next_list()) { 1090 st->print("next-> " INTPTR_FORMAT ", length=%u, " 1091 "elements={", p2i(t_list), t_list->length()); 1092 print_info_elements_on(st, t_list); 1093 st->print_cr("}"); 1094 } 1095 } 1096 if (!EnableThreadSMRStatistics) { 1097 return; 1098 } 1099 st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ", " 1100 "_java_thread_list_free_cnt=" UINT64_FORMAT ", " 1101 "_java_thread_list_max=%u, " 1102 "_nested_thread_list_max=%u", 1103 _java_thread_list_alloc_cnt, 1104 _java_thread_list_free_cnt, 1105 _java_thread_list_max, 1106 _nested_thread_list_max); 1107 if (_tlh_cnt > 0) { 1108 st->print_cr("_tlh_cnt=%u" 1109 ", _tlh_times=%u" 1110 ", avg_tlh_time=%0.2f" 1111 ", _tlh_time_max=%u", 1112 _tlh_cnt, _tlh_times, 1113 ((double) _tlh_times / _tlh_cnt), 1114 _tlh_time_max); 1115 } 1116 if (_deleted_thread_cnt > 0) { 1117 st->print_cr("_deleted_thread_cnt=%u" 1118 ", _deleted_thread_times=%u" 1119 ", avg_deleted_thread_time=%0.2f" 1120 ", _deleted_thread_time_max=%u", 1121 _deleted_thread_cnt, _deleted_thread_times, 1122 ((double) _deleted_thread_times / _deleted_thread_cnt), 1123 _deleted_thread_time_max); 1124 } 1125 st->print_cr("_delete_lock_wait_cnt=%u, _delete_lock_wait_max=%u", 1126 _delete_lock_wait_cnt, _delete_lock_wait_max); 1127 st->print_cr("_to_delete_list_cnt=%u, _to_delete_list_max=%u", 1128 _to_delete_list_cnt, _to_delete_list_max); 1129 } 1130 1131 // Print ThreadsList elements (4 per line). 1132 void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_list) { 1133 uint cnt = 0; 1134 JavaThreadIterator jti(t_list); 1135 for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) { 1136 st->print(INTPTR_FORMAT, p2i(jt)); 1137 if (cnt < t_list->length() - 1) { 1138 // Separate with comma or comma-space except for the last one. 1139 if (((cnt + 1) % 4) == 0) { 1140 // Four INTPTR_FORMAT fit on an 80 column line so end the 1141 // current line with just a comma. 1142 st->print_cr(","); 1143 } else { 1144 // Not the last one on the current line so use comma-space: 1145 st->print(", "); 1146 } 1147 } else { 1148 // Last one so just end the current line. 1149 st->cr(); 1150 } 1151 cnt++; 1152 } 1153 }