1 /*
2 * Copyright (c) 2017, 2019, 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/sharedRuntime.hpp"
30 #include "runtime/thread.inline.hpp"
31 #include "runtime/threadSMR.inline.hpp"
32 #include "runtime/vmOperations.hpp"
33 #include "services/threadIdTable.hpp"
34 #include "services/threadService.hpp"
35 #include "utilities/copy.hpp"
36 #include "utilities/globalDefinitions.hpp"
37 #include "utilities/ostream.hpp"
38 #include "utilities/resourceHash.hpp"
39 #include "utilities/vmError.hpp"
40
41 // The '_cnt', '_max' and '_times" fields are enabled via
42 // -XX:+EnableThreadSMRStatistics:
43
44 // # of parallel threads in _delete_lock->wait().
45 // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit,
46 // but there is no nice 16-bit _FORMAT support.
47 uint ThreadsSMRSupport::_delete_lock_wait_cnt = 0;
48
49 // Max # of parallel threads in _delete_lock->wait().
50 // Impl note: See _delete_lock_wait_cnt note.
51 uint ThreadsSMRSupport::_delete_lock_wait_max = 0;
52
53 // Flag to indicate when an _delete_lock->notify() is needed.
54 // Impl note: See _delete_lock_wait_cnt note.
55 volatile uint ThreadsSMRSupport::_delete_notify = 0;
56
57 // # of threads deleted over VM lifetime.
58 // Impl note: Atomically incremented over VM lifetime so use unsigned for more
59 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
60 // isn't available everywhere (or is it?).
61 volatile uint ThreadsSMRSupport::_deleted_thread_cnt = 0;
62
63 // Max time in millis to delete a thread.
64 // Impl note: 16-bit might be too small on an overloaded machine. Use
65 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
66 // loop for correctness.
67 volatile uint ThreadsSMRSupport::_deleted_thread_time_max = 0;
68
69 // Cumulative time in millis to delete threads.
70 // Impl note: Atomically added to over VM lifetime so use unsigned for more
71 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
72 // isn't available everywhere (or is it?).
73 volatile uint ThreadsSMRSupport::_deleted_thread_times = 0;
74
75 // The bootstrap list is empty and cannot be freed.
76 ThreadsList ThreadsSMRSupport::_bootstrap_list = ThreadsList(0);
77
78 // This is the VM's current "threads list" and it contains all of
79 // the JavaThreads the VM considers to be alive at this moment in
80 // time. The other ThreadsList objects in the VM contain past
81 // snapshots of the "threads list". _java_thread_list is initially
82 // set to _bootstrap_list so that we can detect when we have a very
83 // early use of a ThreadsListHandle.
84 ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = &_bootstrap_list;
85
86 // # of ThreadsLists allocated over VM lifetime.
87 // Impl note: We allocate a new ThreadsList for every thread create and
88 // every thread delete so we need a bigger type than the
89 // _deleted_thread_cnt field.
90 uint64_t ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1;
91
92 // # of ThreadsLists freed over VM lifetime.
93 // Impl note: See _java_thread_list_alloc_cnt note.
94 uint64_t ThreadsSMRSupport::_java_thread_list_free_cnt = 0;
95
96 // Max size ThreadsList allocated.
97 // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit.
98 uint ThreadsSMRSupport::_java_thread_list_max = 0;
99
100 // Max # of nested ThreadsLists for a thread.
101 // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be
102 // 16-bit, but there is no nice 16-bit _FORMAT support.
103 uint ThreadsSMRSupport::_nested_thread_list_max = 0;
104
105 // # of ThreadsListHandles deleted over VM lifetime.
106 // Impl note: Atomically incremented over VM lifetime so use unsigned for
107 // more range. There will be fewer ThreadsListHandles than threads so
108 // unsigned 32-bit should be fine.
109 volatile uint ThreadsSMRSupport::_tlh_cnt = 0;
110
111 // Max time in millis to delete a ThreadsListHandle.
112 // Impl note: 16-bit might be too small on an overloaded machine. Use
113 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
114 // loop for correctness.
115 volatile uint ThreadsSMRSupport::_tlh_time_max = 0;
116
117 // Cumulative time in millis to delete ThreadsListHandles.
118 // Impl note: Atomically added to over VM lifetime so use unsigned for more
119 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
120 // isn't available everywhere (or is it?).
121 volatile uint ThreadsSMRSupport::_tlh_times = 0;
122
123 ThreadsList* ThreadsSMRSupport::_to_delete_list = NULL;
124
125 // # of parallel ThreadsLists on the to-delete list.
126 // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so
127 // this could be 16-bit, but there is no nice 16-bit _FORMAT support.
128 uint ThreadsSMRSupport::_to_delete_list_cnt = 0;
129
130 // Max # of parallel ThreadsLists on the to-delete list.
131 // Impl note: See _to_delete_list_cnt note.
132 uint ThreadsSMRSupport::_to_delete_list_max = 0;
133
134 // 'inline' functions first so the definitions are before first use:
135
136 inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) {
137 Atomic::add(add_value, &_deleted_thread_times);
138 }
139
140 inline void ThreadsSMRSupport::inc_deleted_thread_cnt() {
141 Atomic::inc(&_deleted_thread_cnt);
142 }
143
144 inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() {
145 _java_thread_list_alloc_cnt++;
146 }
147
148 inline bool ThreadsSMRSupport::is_bootstrap_list(ThreadsList* list) {
149 return list == &_bootstrap_list;
150 }
151
152 inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) {
153 while (true) {
154 uint cur_value = _deleted_thread_time_max;
155 if (new_value <= cur_value) {
156 // No need to update max value so we're done.
157 break;
158 }
159 if (Atomic::cmpxchg(new_value, &_deleted_thread_time_max, cur_value) == cur_value) {
160 // Updated max value so we're done. Otherwise try it all again.
161 break;
162 }
163 }
164 }
165
166 inline void ThreadsSMRSupport::update_java_thread_list_max(uint new_value) {
167 if (new_value > _java_thread_list_max) {
168 _java_thread_list_max = new_value;
169 }
170 }
171
172 inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) {
173 return (ThreadsList*)Atomic::xchg(new_list, &_java_thread_list);
174 }
175
176 // Hash table of pointers found by a scan. Used for collecting hazard
177 // pointers (ThreadsList references). Also used for collecting JavaThreads
178 // that are indirectly referenced by hazard ptrs. An instance of this
179 // class only contains one type of pointer.
180 //
181 class ThreadScanHashtable : public CHeapObj<mtThread> {
182 private:
183 static bool ptr_equals(void * const& s1, void * const& s2) {
184 return s1 == s2;
185 }
186
187 static unsigned int ptr_hash(void * const& s1) {
188 // 2654435761 = 2^32 * Phi (golden ratio)
189 return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u);
190 }
191
192 int _table_size;
193 // ResourceHashtable SIZE is specified at compile time so our
194 // dynamic _table_size is unused for now; 1031 is the first prime
195 // after 1024.
196 typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash,
197 &ThreadScanHashtable::ptr_equals, 1031,
198 ResourceObj::C_HEAP, mtThread> PtrTable;
199 PtrTable * _ptrs;
200
201 public:
202 // ResourceHashtable is passed to various functions and populated in
203 // different places so we allocate it using C_HEAP to make it immune
204 // from any ResourceMarks that happen to be in the code paths.
205 ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}
206
207 ~ThreadScanHashtable() { delete _ptrs; }
208
209 bool has_entry(void *pointer) {
210 int *val_ptr = _ptrs->get(pointer);
211 return val_ptr != NULL && *val_ptr == 1;
212 }
213
214 void add_entry(void *pointer) {
215 _ptrs->put(pointer, 1);
216 }
217 };
218
219 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
220 // (ThreadsList references) into a hash table. This closure handles part 2
221 // of the dance - adding all the JavaThreads referenced by the hazard
222 // pointer (ThreadsList reference) to the hash table.
223 //
224 class AddThreadHazardPointerThreadClosure : public ThreadClosure {
225 private:
226 ThreadScanHashtable *_table;
227
228 public:
229 AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {}
230
231 virtual void do_thread(Thread *thread) {
232 if (!_table->has_entry((void*)thread)) {
233 // The same JavaThread might be on more than one ThreadsList or
234 // more than one thread might be using the same ThreadsList. In
235 // either case, we only need a single entry for a JavaThread.
236 _table->add_entry((void*)thread);
237 }
238 }
239 };
240
241 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
242 // (ThreadsList references) into a hash table. This closure handles part 1
243 // of the dance - hazard ptr chain walking and dispatch to another
244 // closure.
245 //
246 class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure {
247 private:
248 ThreadScanHashtable *_table;
249 public:
250 ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {}
251
252 virtual void do_thread(Thread *thread) {
253 assert_locked_or_safepoint(Threads_lock);
254
255 if (thread == NULL) return;
256
257 // This code races with ThreadsSMRSupport::acquire_stable_list() which
258 // is lock-free so we have to handle some special situations.
259 //
260 ThreadsList *current_list = NULL;
261 while (true) {
262 current_list = thread->get_threads_hazard_ptr();
263 // No hazard ptr so nothing more to do.
264 if (current_list == NULL) {
265 return;
266 }
267
268 // If the hazard ptr is verified as stable (since it is not tagged),
269 // then it is safe to use.
270 if (!Thread::is_hazard_ptr_tagged(current_list)) break;
271
272 // The hazard ptr is tagged as not yet verified as being stable
273 // so we are racing with acquire_stable_list(). This exchange
274 // attempts to invalidate the hazard ptr. If we win the race,
275 // then we can ignore this unstable hazard ptr and the other
276 // thread will retry the attempt to publish a stable hazard ptr.
277 // If we lose the race, then we retry our attempt to look at the
278 // hazard ptr.
279 if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return;
280 }
281
282 // The current JavaThread has a hazard ptr (ThreadsList reference)
283 // which might be _java_thread_list or it might be an older
284 // ThreadsList that has been removed but not freed. In either case,
285 // the hazard ptr is protecting all the JavaThreads on that
286 // ThreadsList.
287 AddThreadHazardPointerThreadClosure add_cl(_table);
288 current_list->threads_do(&add_cl);
289 }
290 };
291
292 // Closure to gather hazard ptrs (ThreadsList references) into a hash table.
293 //
294 class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure {
295 private:
296 ThreadScanHashtable *_table;
297 public:
298 ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {}
299
300 virtual void do_thread(Thread* thread) {
301 assert_locked_or_safepoint(Threads_lock);
302
303 if (thread == NULL) return;
304 ThreadsList *threads = thread->get_threads_hazard_ptr();
305 if (threads == NULL) {
306 return;
307 }
308 // In this closure we always ignore the tag that might mark this
309 // hazard ptr as not yet verified. If we happen to catch an
310 // unverified hazard ptr that is subsequently discarded (not
311 // published), then the only side effect is that we might keep a
312 // to-be-deleted ThreadsList alive a little longer.
313 threads = Thread::untag_hazard_ptr(threads);
314 if (!_table->has_entry((void*)threads)) {
315 _table->add_entry((void*)threads);
316 }
317 }
318 };
319
320 // Closure to print JavaThreads that have a hazard ptr (ThreadsList
321 // reference) that contains an indirect reference to a specific JavaThread.
322 //
323 class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure {
324 private:
325 JavaThread *_thread;
326 public:
327 ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {}
328
329 virtual void do_thread(Thread *thread) {
330 assert_locked_or_safepoint(Threads_lock);
331
332 if (thread == NULL) return;
333 ThreadsList *current_list = thread->get_threads_hazard_ptr();
334 if (current_list == NULL) {
335 return;
336 }
337 // If the hazard ptr is unverified, then ignore it.
338 if (Thread::is_hazard_ptr_tagged(current_list)) return;
339
340 // The current JavaThread has a hazard ptr (ThreadsList reference)
341 // which might be _java_thread_list or it might be an older
342 // ThreadsList that has been removed but not freed. In either case,
343 // the hazard ptr is protecting all the JavaThreads on that
344 // ThreadsList, but we only care about matching a specific JavaThread.
345 JavaThreadIterator jti(current_list);
346 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) {
347 if (p == _thread) {
348 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));
349 break;
350 }
351 }
352 }
353 };
354
355 // Closure to determine if the specified JavaThread is found by
356 // threads_do().
357 //
358 class VerifyHazardPtrThreadClosure : public ThreadClosure {
359 private:
360 bool _found;
361 Thread *_self;
362
363 public:
364 VerifyHazardPtrThreadClosure(Thread *self) : _found(false), _self(self) {}
365
366 bool found() const { return _found; }
367
368 virtual void do_thread(Thread *thread) {
369 if (thread == _self) {
370 _found = true;
371 }
372 }
373 };
374
375
376 // Acquire a stable ThreadsList.
377 //
378 void SafeThreadsListPtr::acquire_stable_list() {
379 assert(_thread != NULL, "sanity check");
380 _needs_release = true;
381 _previous = _thread->_threads_list_ptr;
382 _thread->_threads_list_ptr = this;
383
384 if (_thread->get_threads_hazard_ptr() == NULL) {
385 // The typical case is first.
386 acquire_stable_list_fast_path();
387 return;
388 }
389
390 // The nested case is rare.
391 acquire_stable_list_nested_path();
392 }
393
394 // Fast path way to acquire a stable ThreadsList.
395 //
396 void SafeThreadsListPtr::acquire_stable_list_fast_path() {
397 assert(_thread != NULL, "sanity check");
398 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
399
400 ThreadsList* threads;
401
402 // Stable recording of a hazard ptr for SMR. This code does not use
403 // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr
404 // fields is racy relative to code that uses those fields with locks.
405 // OrderAccess and Atomic functions are used to deal with those races.
406 //
407 while (true) {
408 threads = ThreadsSMRSupport::get_java_thread_list();
409
410 // Publish a tagged hazard ptr to denote that the hazard ptr is not
411 // yet verified as being stable. Due to the fence after the hazard
412 // ptr write, it will be sequentially consistent w.r.t. the
413 // sequentially consistent writes of the ThreadsList, even on
414 // non-multiple copy atomic machines where stores can be observed
415 // in different order from different observer threads.
416 ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads);
417 _thread->set_threads_hazard_ptr(unverified_threads);
418
419 // If _smr_java_thread_list has changed, we have lost a race with
420 // Threads::add() or Threads::remove() and have to try again.
421 if (ThreadsSMRSupport::get_java_thread_list() != threads) {
422 continue;
423 }
424
425 // We try to remove the tag which will verify the hazard ptr as
426 // being stable. This exchange can race with a scanning thread
427 // which might invalidate the tagged hazard ptr to keep it from
428 // being followed to access JavaThread ptrs. If we lose the race,
429 // we simply retry. If we win the race, then the stable hazard
430 // ptr is officially published.
431 if (_thread->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) {
432 break;
433 }
434 }
435
436 // A stable hazard ptr has been published letting other threads know
437 // that the ThreadsList and the JavaThreads reachable from this list
438 // are protected and hence they should not be deleted until everyone
439 // agrees it is safe to do so.
440
441 _list = threads;
442
443 verify_hazard_ptr_scanned();
444 }
445
446 // Acquire a nested stable ThreadsList; this is rare so it uses
447 // reference counting.
448 //
449 void SafeThreadsListPtr::acquire_stable_list_nested_path() {
450 assert(_thread != NULL, "sanity check");
451 assert(_thread->get_threads_hazard_ptr() != NULL,
452 "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr");
453
454 // The thread already has a hazard ptr (ThreadsList ref) so we need
455 // to create a nested ThreadsListHandle with the current ThreadsList
456 // since it might be different than our current hazard ptr. To remedy
457 // the situation, the ThreadsList pointed to by the pre-existing
458 // stable hazard ptr is reference counted before the hazard ptr may
459 // be released and moved to a new ThreadsList. The old ThreadsList
460 // is remembered in the ThreadsListHandle.
461
462 ThreadsList* current_list = _previous->_list;
463 if (EnableThreadSMRStatistics) {
464 _thread->inc_nested_threads_hazard_ptr_cnt();
465 }
466 current_list->inc_nested_handle_cnt();
467 _previous->_has_ref_count = true; // promote SafeThreadsListPtr to be reference counted
468 _thread->_threads_hazard_ptr = NULL; // clear the hazard ptr so we can go through the fast path below
469
470 if (EnableThreadSMRStatistics && _thread->nested_threads_hazard_ptr_cnt() > ThreadsSMRSupport::_nested_thread_list_max) {
471 ThreadsSMRSupport::_nested_thread_list_max = _thread->nested_threads_hazard_ptr_cnt();
472 }
473
474 acquire_stable_list_fast_path();
475
476 verify_hazard_ptr_scanned();
477
478 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));
479 }
480
481 // Release a stable ThreadsList.
482 //
483 void SafeThreadsListPtr::release_stable_list() {
484 assert(_thread != NULL, "sanity check");
485 assert(_thread->_threads_list_ptr == this, "sanity check");
486 _thread->_threads_list_ptr = _previous;
487
488 if (_has_ref_count) {
489 // If a SafeThreadsListPtr has been promoted to use reference counting
490 // due to nesting of ThreadsListHandles, then the reference count must be
491 // decremented, at which point it may be freed. The forgotten value of
492 // the list no longer matters at this point and should already be NULL.
493 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
494 if (EnableThreadSMRStatistics) {
495 _thread->dec_nested_threads_hazard_ptr_cnt();
496 }
497 _list->dec_nested_handle_cnt();
498
499 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));
500 } else {
501 // The normal case: a leaf ThreadsListHandle. This merely requires setting
502 // the thread hazard ptr back to NULL.
503 assert(_thread->get_threads_hazard_ptr() != NULL, "sanity check");
504 _thread->set_threads_hazard_ptr(NULL);
505 }
506
507 // After releasing the hazard ptr, other threads may go ahead and
508 // free up some memory temporarily used by a ThreadsList snapshot.
509
510 // We use double-check locking to reduce traffic on the system
511 // wide Thread-SMR delete_lock.
512 if (ThreadsSMRSupport::delete_notify()) {
513 // An exiting thread might be waiting in smr_delete(); we need to
514 // check with delete_lock to be sure.
515 ThreadsSMRSupport::release_stable_list_wake_up(_has_ref_count);
516 }
517 }
518
519 // Verify that the stable hazard ptr used to safely keep threads
520 // alive is scanned by threads_do() which is a key piece of honoring
521 // the Thread-SMR protocol.
522 void SafeThreadsListPtr::verify_hazard_ptr_scanned() {
523 #ifdef ASSERT
524 assert(_list != NULL, "_list must not be NULL");
525
526 if (ThreadsSMRSupport::is_bootstrap_list(_list)) {
527 // We are early in VM bootstrapping so nothing to do here.
528 return;
529 }
530
531 if ( _thread == VM_Exit::shutdown_thread()) {
532 // The shutdown thread has removed itself from the Threads
533 // list and is safe to have a waiver from this check because
534 // VM_Exit::_shutdown_thread is not set until after the VMThread
535 // has started the final safepoint which holds the Threads_lock
536 // for the remainder of the VM's life.
537 return;
538 }
539
540 if (VMError::is_error_reported() &&
541 VMError::get_first_error_tid() == os::current_thread_id()) {
542 // If there is an error reported by this thread it may use ThreadsList even
543 // if it's unsafe.
544 return;
545 }
546
547 // The closure will attempt to verify that the calling thread can
548 // be found by threads_do() on the specified ThreadsList. If it
549 // is successful, then the specified ThreadsList was acquired as
550 // a stable hazard ptr by the calling thread in a way that honored
551 // the Thread-SMR protocol.
552 //
553 // If the calling thread cannot be found by threads_do() and if
554 // it is not the shutdown thread, then the calling thread is not
555 // honoring the Thread-SMR ptotocol. This means that the specified
556 // ThreadsList is not a stable hazard ptr and can be freed by
557 // another thread from the to-be-deleted list at any time.
558 //
559 VerifyHazardPtrThreadClosure cl(_thread);
560 ThreadsSMRSupport::threads_do(&cl, _list);
561
562 // If the calling thread is not honoring the Thread-SMR protocol,
563 // then we will either crash in threads_do() above because 'threads'
564 // was freed by another thread or we will fail the assert() below.
565 // In either case, we won't get past this point with a badly placed
566 // ThreadsListHandle.
567
568 assert(cl.found(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol.");
569 #endif
570 }
571
572 // 'entries + 1' so we always have at least one entry.
573 ThreadsList::ThreadsList(int entries) :
574 _length(entries),
575 _next_list(NULL),
576 _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)),
577 _nested_handle_cnt(0)
578 {
579 *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
580 }
581
582 ThreadsList::~ThreadsList() {
583 FREE_C_HEAP_ARRAY(JavaThread*, _threads);
584 }
585
586 // Add a JavaThread to a ThreadsList. The returned ThreadsList is a
587 // new copy of the specified ThreadsList with the specified JavaThread
588 // appended to the end.
589 ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) {
590 const uint index = list->_length;
591 const uint new_length = index + 1;
592 const uint head_length = index;
593 ThreadsList *const new_list = new ThreadsList(new_length);
594
595 if (head_length > 0) {
596 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
597 }
598 *(JavaThread**)(new_list->_threads + index) = java_thread;
599
600 return new_list;
601 }
602
603 void ThreadsList::dec_nested_handle_cnt() {
604 // The decrement only needs to be MO_ACQ_REL since the reference
605 // counter is volatile (and the hazard ptr is already NULL).
606 Atomic::dec(&_nested_handle_cnt);
607 }
608
609 int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
610 if (target == NULL) {
611 return -1;
612 }
613 for (uint i = 0; i < length(); i++) {
614 if (target == thread_at(i)) {
615 return (int)i;
616 }
617 }
618 return -1;
619 }
620
621 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
622 ThreadIdTable::lazy_initialize(this);
623 JavaThread* thread = ThreadIdTable::find_thread_by_tid(java_tid);
624 if (thread == NULL) {
625 // If the thread is not found in the table find it
626 // with a linear search and add to the table.
627 for (uint i = 0; i < length(); i++) {
628 thread = thread_at(i);
629 oop tobj = thread->threadObj();
630 // Ignore the thread if it hasn't run yet, has exited
631 // or is starting to exit.
632 if (tobj != NULL && java_tid == java_lang_Thread::thread_id(tobj)) {
633 MutexLocker ml(Threads_lock);
634 // Must be inside the lock to ensure that we don't add a thread to the table
635 // that has just passed the removal point in ThreadsSMRSupport::remove_thread()
636 if (!thread->is_exiting()) {
637 ThreadIdTable::add_thread(java_tid, thread);
638 return thread;
639 }
640 }
641 }
642 } else if (!thread->is_exiting()) {
643 return thread;
644 }
645 return NULL;
646 }
647
648 void ThreadsList::inc_nested_handle_cnt() {
649 // The increment needs to be MO_SEQ_CST so that the reference counter
650 // update is seen before the subsequent hazard ptr update.
651 Atomic::inc(&_nested_handle_cnt);
652 }
653
654 bool ThreadsList::includes(const JavaThread * const p) const {
655 if (p == NULL) {
656 return false;
657 }
658 for (uint i = 0; i < length(); i++) {
659 if (thread_at(i) == p) {
660 return true;
661 }
662 }
663 return false;
664 }
665
666 // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a
667 // new copy of the specified ThreadsList with the specified JavaThread
668 // removed.
669 ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) {
670 assert(list->_length > 0, "sanity");
671
672 uint i = (uint)list->find_index_of_JavaThread(java_thread);
673 assert(i < list->_length, "did not find JavaThread on the list");
674 const uint index = i;
675 const uint new_length = list->_length - 1;
676 const uint head_length = index;
677 const uint tail_length = (new_length >= index) ? (new_length - index) : 0;
678 ThreadsList *const new_list = new ThreadsList(new_length);
679
680 if (head_length > 0) {
681 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
682 }
683 if (tail_length > 0) {
684 Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length);
685 }
686
687 return new_list;
688 }
689
690 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list_ptr(self, /* acquire */ true) {
691 assert(self == Thread::current(), "sanity check");
692 if (EnableThreadSMRStatistics) {
693 _timer.start();
694 }
695 }
696
697 ThreadsListHandle::~ThreadsListHandle() {
698 if (EnableThreadSMRStatistics) {
699 _timer.stop();
700 uint millis = (uint)_timer.milliseconds();
701 ThreadsSMRSupport::update_tlh_stats(millis);
702 }
703 }
704
705 // Convert an internal thread reference to a JavaThread found on the
706 // associated ThreadsList. This ThreadsListHandle "protects" the
707 // returned JavaThread *.
708 //
709 // If thread_oop_p is not NULL, then the caller wants to use the oop
710 // after this call so the oop is returned. On success, *jt_pp is set
711 // to the converted JavaThread * and true is returned. On error,
712 // returns false.
713 //
714 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
715 JavaThread ** jt_pp,
716 oop * thread_oop_p) {
717 assert(this->list() != NULL, "must have a ThreadsList");
718 assert(jt_pp != NULL, "must have a return JavaThread pointer");
719 // thread_oop_p is optional so no assert()
720
721 // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI
722 // allows a NULL thread parameter to signify "current thread" which
723 // allows us to avoid calling cv_external_thread_to_JavaThread().
724 // The JVM_* interfaces have no such leeway.
725
726 oop thread_oop = JNIHandles::resolve_non_null(jthread);
727 // Looks like an oop at this point.
728 if (thread_oop_p != NULL) {
729 // Return the oop to the caller; the caller may still want
730 // the oop even if this function returns false.
731 *thread_oop_p = thread_oop;
732 }
733
734 JavaThread *java_thread = java_lang_Thread::thread(thread_oop);
735 if (java_thread == NULL) {
736 // The java.lang.Thread does not contain a JavaThread * so it has
737 // not yet run or it has died.
738 return false;
739 }
740 // Looks like a live JavaThread at this point.
741
742 if (java_thread != JavaThread::current()) {
743 // jthread is not for the current JavaThread so have to verify
744 // the JavaThread * against the ThreadsList.
745 if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) {
746 // Not on the JavaThreads list so it is not alive.
747 return false;
748 }
749 }
750
751 // Return a live JavaThread that is "protected" by the
752 // ThreadsListHandle in the caller.
753 *jt_pp = java_thread;
754 return true;
755 }
756
757 void ThreadsSMRSupport::add_thread(JavaThread *thread){
758 ThreadsList *new_list = ThreadsList::add_thread(get_java_thread_list(), thread);
759 if (EnableThreadSMRStatistics) {
760 inc_java_thread_list_alloc_cnt();
761 update_java_thread_list_max(new_list->length());
762 }
763 // Initial _java_thread_list will not generate a "Threads::add" mesg.
764 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
765
766 ThreadsList *old_list = xchg_java_thread_list(new_list);
767 free_list(old_list);
768 if (ThreadIdTable::is_initialized()) {
769 jlong tid = SharedRuntime::get_java_tid(thread);
770 ThreadIdTable::add_thread(tid, thread);
771 }
772 }
773
774 // set_delete_notify() and clear_delete_notify() are called
775 // under the protection of the delete_lock, but we also use an
776 // Atomic operation to ensure the memory update is seen earlier than
777 // when the delete_lock is dropped.
778 //
779 void ThreadsSMRSupport::clear_delete_notify() {
780 Atomic::dec(&_delete_notify);
781 }
782
783 bool ThreadsSMRSupport::delete_notify() {
784 // Use load_acquire() in order to see any updates to _delete_notify
785 // earlier than when delete_lock is grabbed.
786 return (OrderAccess::load_acquire(&_delete_notify) != 0);
787 }
788
789 // Safely free a ThreadsList after a Threads::add() or Threads::remove().
790 // The specified ThreadsList may not get deleted during this call if it
791 // is still in-use (referenced by a hazard ptr). Other ThreadsLists
792 // in the chain may get deleted by this call if they are no longer in-use.
793 void ThreadsSMRSupport::free_list(ThreadsList* threads) {
794 assert_locked_or_safepoint(Threads_lock);
795
796 if (is_bootstrap_list(threads)) {
797 // The bootstrap list cannot be freed and is empty so
798 // it does not need to be scanned. Nothing to do here.
799 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: bootstrap ThreadsList=" INTPTR_FORMAT " is no longer in use.", os::current_thread_id(), p2i(threads));
800 return;
801 }
802
803 threads->set_next_list(_to_delete_list);
804 _to_delete_list = threads;
805 if (EnableThreadSMRStatistics) {
806 _to_delete_list_cnt++;
807 if (_to_delete_list_cnt > _to_delete_list_max) {
808 _to_delete_list_max = _to_delete_list_cnt;
809 }
810 }
811
812 // Hash table size should be first power of two higher than twice the length of the ThreadsList
813 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
814 hash_table_size--;
815 hash_table_size |= hash_table_size >> 1;
816 hash_table_size |= hash_table_size >> 2;
817 hash_table_size |= hash_table_size >> 4;
818 hash_table_size |= hash_table_size >> 8;
819 hash_table_size |= hash_table_size >> 16;
820 hash_table_size++;
821
822 // Gather a hash table of the current hazard ptrs:
823 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
824 ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
825 threads_do(&scan_cl);
826 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
827 // nested reference counters
828
829 // Walk through the linked list of pending freeable ThreadsLists
830 // and free the ones that are not referenced from hazard ptrs.
831 ThreadsList* current = _to_delete_list;
832 ThreadsList* prev = NULL;
833 ThreadsList* next = NULL;
834 bool threads_is_freed = false;
835 while (current != NULL) {
836 next = current->next_list();
837 if (!scan_table->has_entry((void*)current) && current->_nested_handle_cnt == 0) {
838 // This ThreadsList is not referenced by a hazard ptr.
839 if (prev != NULL) {
840 prev->set_next_list(next);
841 }
842 if (_to_delete_list == current) {
843 _to_delete_list = next;
844 }
845
846 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current));
847 if (current == threads) threads_is_freed = true;
848 delete current;
849 if (EnableThreadSMRStatistics) {
850 _java_thread_list_free_cnt++;
851 _to_delete_list_cnt--;
852 }
853 } else {
854 prev = current;
855 }
856 current = next;
857 }
858
859 if (!threads_is_freed) {
860 // Only report "is not freed" on the original call to
861 // free_list() for this ThreadsList.
862 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads));
863 }
864
865 delete scan_table;
866 }
867
868 // Return true if the specified JavaThread is protected by a hazard
869 // pointer (ThreadsList reference). Otherwise, returns false.
870 //
871 bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) {
872 assert_locked_or_safepoint(Threads_lock);
873
874 // Hash table size should be first power of two higher than twice
875 // the length of the Threads list.
876 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
877 hash_table_size--;
878 hash_table_size |= hash_table_size >> 1;
879 hash_table_size |= hash_table_size >> 2;
880 hash_table_size |= hash_table_size >> 4;
881 hash_table_size |= hash_table_size >> 8;
882 hash_table_size |= hash_table_size >> 16;
883 hash_table_size++;
884
885 // Gather a hash table of the JavaThreads indirectly referenced by
886 // hazard ptrs.
887 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
888 ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table);
889 threads_do(&scan_cl);
890 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
891 // nested reference counters
892
893 // Walk through the linked list of pending freeable ThreadsLists
894 // and include the ones that are currently in use by a nested
895 // ThreadsListHandle in the search set.
896 ThreadsList* current = _to_delete_list;
897 while (current != NULL) {
898 if (current->_nested_handle_cnt != 0) {
899 // 'current' is in use by a nested ThreadsListHandle so the hazard
900 // ptr is protecting all the JavaThreads on that ThreadsList.
901 AddThreadHazardPointerThreadClosure add_cl(scan_table);
902 current->threads_do(&add_cl);
903 }
904 current = current->next_list();
905 }
906
907 bool thread_is_protected = false;
908 if (scan_table->has_entry((void*)thread)) {
909 thread_is_protected = true;
910 }
911 delete scan_table;
912 return thread_is_protected;
913 }
914
915 // Wake up portion of the release stable ThreadsList protocol;
916 // uses the delete_lock().
917 //
918 void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) {
919 const char* log_str = is_nested ? "nested hazard ptr" : "regular hazard ptr";
920
921 // Note: delete_lock is held in smr_delete() for the entire
922 // hazard ptr search so that we do not lose this notify() if
923 // the exiting thread has to wait. That code path also holds
924 // Threads_lock (which was grabbed before delete_lock) so that
925 // threads_do() can be called. This means the system can't start a
926 // safepoint which means this thread can't take too long to get to
927 // a safepoint because of being blocked on delete_lock.
928 //
929 MonitorLocker ml(ThreadsSMRSupport::delete_lock(), Monitor::_no_safepoint_check_flag);
930 if (ThreadsSMRSupport::delete_notify()) {
931 // Notify any exiting JavaThreads that are waiting in smr_delete()
932 // that we've released a ThreadsList.
933 ml.notify_all();
934 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str);
935 }
936 }
937
938 void ThreadsSMRSupport::remove_thread(JavaThread *thread) {
939 if (ThreadIdTable::is_initialized()) {
940 jlong tid = SharedRuntime::get_java_tid(thread);
941 ThreadIdTable::remove_thread(tid);
942 }
943 ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_java_thread_list(), thread);
944 if (EnableThreadSMRStatistics) {
945 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt();
946 // This list is smaller so no need to check for a "longest" update.
947 }
948
949 // Final _java_thread_list will not generate a "Threads::remove" mesg.
950 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
951
952 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list);
953 ThreadsSMRSupport::free_list(old_list);
954 }
955
956 // See note for clear_delete_notify().
957 //
958 void ThreadsSMRSupport::set_delete_notify() {
959 Atomic::inc(&_delete_notify);
960 }
961
962 // Safely delete a JavaThread when it is no longer in use by a
963 // ThreadsListHandle.
964 //
965 void ThreadsSMRSupport::smr_delete(JavaThread *thread) {
966 assert(!Threads_lock->owned_by_self(), "sanity");
967
968 bool has_logged_once = false;
969 elapsedTimer timer;
970 if (EnableThreadSMRStatistics) {
971 timer.start();
972 }
973
974 while (true) {
975 {
976 // Will not make a safepoint check because this JavaThread
977 // is not on the current ThreadsList.
978 MutexLocker ml(Threads_lock);
979 // Cannot use a MonitorLocker helper here because we have
980 // to drop the Threads_lock first if we wait.
981 ThreadsSMRSupport::delete_lock()->lock_without_safepoint_check();
982 // Set the delete_notify flag after we grab delete_lock
983 // and before we scan hazard ptrs because we're doing
984 // double-check locking in release_stable_list().
985 ThreadsSMRSupport::set_delete_notify();
986
987 if (!is_a_protected_JavaThread(thread)) {
988 // This is the common case.
989 ThreadsSMRSupport::clear_delete_notify();
990 ThreadsSMRSupport::delete_lock()->unlock();
991 break;
992 }
993 if (!has_logged_once) {
994 has_logged_once = true;
995 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread));
996 if (log_is_enabled(Debug, os, thread)) {
997 ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread);
998 threads_do(&scan_cl);
999 ThreadsList* current = _to_delete_list;
1000 while (current != NULL) {
1001 if (current->_nested_handle_cnt != 0 && current->includes(thread)) {
1002 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: found nested hazard pointer to thread=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread));
1003 }
1004 current = current->next_list();
1005 }
1006 }
1007 }
1008 } // We have to drop the Threads_lock to wait or delete the thread
1009
1010 if (EnableThreadSMRStatistics) {
1011 _delete_lock_wait_cnt++;
1012 if (_delete_lock_wait_cnt > _delete_lock_wait_max) {
1013 _delete_lock_wait_max = _delete_lock_wait_cnt;
1014 }
1015 }
1016 // Wait for a release_stable_list() call before we check again. No
1017 // safepoint check, no timeout, and not as suspend equivalent flag
1018 // because this JavaThread is not on the Threads list.
1019 ThreadsSMRSupport::delete_lock()->wait_without_safepoint_check();
1020 if (EnableThreadSMRStatistics) {
1021 _delete_lock_wait_cnt--;
1022 }
1023
1024 ThreadsSMRSupport::clear_delete_notify();
1025 ThreadsSMRSupport::delete_lock()->unlock();
1026 // Retry the whole scenario.
1027 }
1028
1029 delete thread;
1030 if (EnableThreadSMRStatistics) {
1031 timer.stop();
1032 uint millis = (uint)timer.milliseconds();
1033 ThreadsSMRSupport::inc_deleted_thread_cnt();
1034 ThreadsSMRSupport::add_deleted_thread_times(millis);
1035 ThreadsSMRSupport::update_deleted_thread_time_max(millis);
1036 }
1037
1038 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread));
1039 }
1040
1041 // Apply the closure to all threads in the system, with a snapshot of
1042 // all JavaThreads provided by the list parameter.
1043 void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) {
1044 list->threads_do(tc);
1045 Threads::non_java_threads_do(tc);
1046 }
1047
1048 // Apply the closure to all threads in the system.
1049 void ThreadsSMRSupport::threads_do(ThreadClosure *tc) {
1050 threads_do(tc, _java_thread_list);
1051 }
1052
1053
1054 // Debug, logging, and printing stuff at the end:
1055
1056 // Print SMR info for a SafeThreadsListPtr to a given output stream.
1057 void SafeThreadsListPtr::print_on(outputStream* st) {
1058 if (this == _thread->_threads_list_ptr) {
1059 // The top level hazard ptr.
1060 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1061 } else {
1062 // Nested hazard ptrs.
1063 st->print(", _nested_threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1064 }
1065 }
1066
1067 // Log Threads class SMR info.
1068 void ThreadsSMRSupport::log_statistics() {
1069 LogTarget(Info, thread, smr) log;
1070 if (log.is_enabled()) {
1071 LogStream out(log);
1072 print_info_on(&out);
1073 }
1074 }
1075
1076 // Print SMR info for a thread to a given output stream.
1077 void ThreadsSMRSupport::print_info_on(const Thread* thread, outputStream* st) {
1078 if (thread->_threads_hazard_ptr != NULL) {
1079 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(thread->_threads_hazard_ptr));
1080 }
1081 if (EnableThreadSMRStatistics && thread->_threads_list_ptr != NULL) {
1082 // The count is only interesting if we have a _threads_list_ptr.
1083 st->print(", _nested_threads_hazard_ptr_cnt=%u", thread->_nested_threads_hazard_ptr_cnt);
1084 }
1085 if (SafepointSynchronize::is_at_safepoint() || Thread::current() == thread) {
1086 // It is only safe to walk the list if we're at a safepoint or the
1087 // calling thread is walking its own list.
1088 SafeThreadsListPtr* current = thread->_threads_list_ptr;
1089 if (current != NULL) {
1090 // Skip the top nesting level as it is always printed above.
1091 current = current->previous();
1092 }
1093 while (current != NULL) {
1094 current->print_on(st);
1095 current = current->previous();
1096 }
1097 }
1098 }
1099
1100 // Print Threads class SMR info.
1101 void ThreadsSMRSupport::print_info_on(outputStream* st) {
1102 // Only grab the Threads_lock if we don't already own it and if we
1103 // are not reporting an error.
1104 // Note: Not grabbing the Threads_lock during error reporting is
1105 // dangerous because the data structures we want to print can be
1106 // freed concurrently. However, grabbing the Threads_lock during
1107 // error reporting can be equally dangerous since this thread might
1108 // block during error reporting or a nested error could leave the
1109 // Threads_lock held. The classic no win scenario.
1110 //
1111 MutexLocker ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock);
1112
1113 st->print_cr("Threads class SMR info:");
1114 st->print_cr("_java_thread_list=" INTPTR_FORMAT ", length=%u, "
1115 "elements={", p2i(_java_thread_list),
1116 _java_thread_list->length());
1117 print_info_elements_on(st, _java_thread_list);
1118 st->print_cr("}");
1119 if (_to_delete_list != NULL) {
1120 st->print_cr("_to_delete_list=" INTPTR_FORMAT ", length=%u, "
1121 "elements={", p2i(_to_delete_list),
1122 _to_delete_list->length());
1123 print_info_elements_on(st, _to_delete_list);
1124 st->print_cr("}");
1125 for (ThreadsList *t_list = _to_delete_list->next_list();
1126 t_list != NULL; t_list = t_list->next_list()) {
1127 st->print("next-> " INTPTR_FORMAT ", length=%u, "
1128 "elements={", p2i(t_list), t_list->length());
1129 print_info_elements_on(st, t_list);
1130 st->print_cr("}");
1131 }
1132 }
1133 if (!EnableThreadSMRStatistics) {
1134 return;
1135 }
1136 st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ", "
1137 "_java_thread_list_free_cnt=" UINT64_FORMAT ", "
1138 "_java_thread_list_max=%u, "
1139 "_nested_thread_list_max=%u",
1140 _java_thread_list_alloc_cnt,
1141 _java_thread_list_free_cnt,
1142 _java_thread_list_max,
1143 _nested_thread_list_max);
1144 if (_tlh_cnt > 0) {
1145 st->print_cr("_tlh_cnt=%u"
1146 ", _tlh_times=%u"
1147 ", avg_tlh_time=%0.2f"
1148 ", _tlh_time_max=%u",
1149 _tlh_cnt, _tlh_times,
1150 ((double) _tlh_times / _tlh_cnt),
1151 _tlh_time_max);
1152 }
1153 if (_deleted_thread_cnt > 0) {
1154 st->print_cr("_deleted_thread_cnt=%u"
1155 ", _deleted_thread_times=%u"
1156 ", avg_deleted_thread_time=%0.2f"
1157 ", _deleted_thread_time_max=%u",
1158 _deleted_thread_cnt, _deleted_thread_times,
1159 ((double) _deleted_thread_times / _deleted_thread_cnt),
1160 _deleted_thread_time_max);
1161 }
1162 st->print_cr("_delete_lock_wait_cnt=%u, _delete_lock_wait_max=%u",
1163 _delete_lock_wait_cnt, _delete_lock_wait_max);
1164 st->print_cr("_to_delete_list_cnt=%u, _to_delete_list_max=%u",
1165 _to_delete_list_cnt, _to_delete_list_max);
1166 }
1167
1168 // Print ThreadsList elements (4 per line).
1169 void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_list) {
1170 uint cnt = 0;
1171 JavaThreadIterator jti(t_list);
1172 for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
1173 st->print(INTPTR_FORMAT, p2i(jt));
1174 if (cnt < t_list->length() - 1) {
1175 // Separate with comma or comma-space except for the last one.
1176 if (((cnt + 1) % 4) == 0) {
1177 // Four INTPTR_FORMAT fit on an 80 column line so end the
1178 // current line with just a comma.
1179 st->print_cr(",");
1180 } else {
1181 // Not the last one on the current line so use comma-space:
1182 st->print(", ");
1183 }
1184 } else {
1185 // Last one so just end the current line.
1186 st->cr();
1187 }
1188 cnt++;
1189 }
1190 }