1 /*
2 * Copyright (c) 2017, 2020, 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/atomic.hpp"
29 #include "runtime/jniHandles.inline.hpp"
30 #include "runtime/orderAccess.hpp"
31 #include "runtime/sharedRuntime.hpp"
32 #include "runtime/thread.inline.hpp"
33 #include "runtime/threadSMR.inline.hpp"
34 #include "runtime/vmOperations.hpp"
35 #include "services/threadIdTable.hpp"
36 #include "services/threadService.hpp"
37 #include "utilities/copy.hpp"
38 #include "utilities/globalDefinitions.hpp"
39 #include "utilities/ostream.hpp"
40 #include "utilities/powerOfTwo.hpp"
41 #include "utilities/resourceHash.hpp"
42 #include "utilities/vmError.hpp"
43
44 // The '_cnt', '_max' and '_times" fields are enabled via
45 // -XX:+EnableThreadSMRStatistics:
46
47 // # of parallel threads in _delete_lock->wait().
48 // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit,
49 // but there is no nice 16-bit _FORMAT support.
50 uint ThreadsSMRSupport::_delete_lock_wait_cnt = 0;
51
52 // Max # of parallel threads in _delete_lock->wait().
53 // Impl note: See _delete_lock_wait_cnt note.
54 uint ThreadsSMRSupport::_delete_lock_wait_max = 0;
55
56 // Flag to indicate when an _delete_lock->notify() is needed.
57 // Impl note: See _delete_lock_wait_cnt note.
58 volatile uint ThreadsSMRSupport::_delete_notify = 0;
59
60 // # of threads deleted over VM lifetime.
61 // Impl note: Atomically incremented over VM lifetime so use unsigned for more
62 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
63 // isn't available everywhere (or is it?).
64 volatile uint ThreadsSMRSupport::_deleted_thread_cnt = 0;
65
66 // Max time in millis to delete a thread.
67 // Impl note: 16-bit might be too small on an overloaded machine. Use
68 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
69 // loop for correctness.
70 volatile uint ThreadsSMRSupport::_deleted_thread_time_max = 0;
71
72 // Cumulative time in millis to delete threads.
73 // Impl note: Atomically added to over VM lifetime so use unsigned for more
74 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
75 // isn't available everywhere (or is it?).
76 volatile uint ThreadsSMRSupport::_deleted_thread_times = 0;
77
78 // The bootstrap list is empty and cannot be freed.
79 ThreadsList ThreadsSMRSupport::_bootstrap_list = ThreadsList(0);
80
81 // This is the VM's current "threads list" and it contains all of
82 // the JavaThreads the VM considers to be alive at this moment in
83 // time. The other ThreadsList objects in the VM contain past
84 // snapshots of the "threads list". _java_thread_list is initially
85 // set to _bootstrap_list so that we can detect when we have a very
86 // early use of a ThreadsListHandle.
87 ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = &_bootstrap_list;
88
89 // # of ThreadsLists allocated over VM lifetime.
90 // Impl note: We allocate a new ThreadsList for every thread create and
91 // every thread delete so we need a bigger type than the
92 // _deleted_thread_cnt field.
93 uint64_t ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1;
94
95 // # of ThreadsLists freed over VM lifetime.
96 // Impl note: See _java_thread_list_alloc_cnt note.
97 uint64_t ThreadsSMRSupport::_java_thread_list_free_cnt = 0;
98
99 // Max size ThreadsList allocated.
100 // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit.
101 uint ThreadsSMRSupport::_java_thread_list_max = 0;
102
103 // Max # of nested ThreadsLists for a thread.
104 // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be
105 // 16-bit, but there is no nice 16-bit _FORMAT support.
106 uint ThreadsSMRSupport::_nested_thread_list_max = 0;
107
108 // # of ThreadsListHandles deleted over VM lifetime.
109 // Impl note: Atomically incremented over VM lifetime so use unsigned for
110 // more range. There will be fewer ThreadsListHandles than threads so
111 // unsigned 32-bit should be fine.
112 volatile uint ThreadsSMRSupport::_tlh_cnt = 0;
113
114 // Max time in millis to delete a ThreadsListHandle.
115 // Impl note: 16-bit might be too small on an overloaded machine. Use
116 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
117 // loop for correctness.
118 volatile uint ThreadsSMRSupport::_tlh_time_max = 0;
119
120 // Cumulative time in millis to delete ThreadsListHandles.
121 // Impl note: Atomically added to over VM lifetime so use unsigned for more
122 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
123 // isn't available everywhere (or is it?).
124 volatile uint ThreadsSMRSupport::_tlh_times = 0;
125
126 ThreadsList* ThreadsSMRSupport::_to_delete_list = NULL;
127
128 // # of parallel ThreadsLists on the to-delete list.
129 // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so
130 // this could be 16-bit, but there is no nice 16-bit _FORMAT support.
131 uint ThreadsSMRSupport::_to_delete_list_cnt = 0;
132
133 // Max # of parallel ThreadsLists on the to-delete list.
134 // Impl note: See _to_delete_list_cnt note.
135 uint ThreadsSMRSupport::_to_delete_list_max = 0;
136
137 // 'inline' functions first so the definitions are before first use:
138
139 inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) {
140 Atomic::add(&_deleted_thread_times, add_value);
141 }
142
143 inline void ThreadsSMRSupport::inc_deleted_thread_cnt() {
144 Atomic::inc(&_deleted_thread_cnt);
145 }
146
147 inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() {
148 _java_thread_list_alloc_cnt++;
149 }
150
151 inline bool ThreadsSMRSupport::is_bootstrap_list(ThreadsList* list) {
152 return list == &_bootstrap_list;
153 }
154
155 inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) {
156 while (true) {
157 uint cur_value = _deleted_thread_time_max;
158 if (new_value <= cur_value) {
159 // No need to update max value so we're done.
160 break;
161 }
162 if (Atomic::cmpxchg(&_deleted_thread_time_max, cur_value, new_value) == cur_value) {
163 // Updated max value so we're done. Otherwise try it all again.
164 break;
165 }
166 }
167 }
168
169 inline void ThreadsSMRSupport::update_java_thread_list_max(uint new_value) {
170 if (new_value > _java_thread_list_max) {
171 _java_thread_list_max = new_value;
172 }
173 }
174
175 inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) {
176 return (ThreadsList*)Atomic::xchg(&_java_thread_list, new_list);
177 }
178
179 // Hash table of pointers found by a scan. Used for collecting hazard
180 // pointers (ThreadsList references). Also used for collecting JavaThreads
181 // that are indirectly referenced by hazard ptrs. An instance of this
182 // class only contains one type of pointer.
183 //
184 class ThreadScanHashtable : public CHeapObj<mtThread> {
185 private:
186 static bool ptr_equals(void * const& s1, void * const& s2) {
187 return s1 == s2;
188 }
189
190 static unsigned int ptr_hash(void * const& s1) {
191 // 2654435761 = 2^32 * Phi (golden ratio)
192 return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u);
193 }
194
195 int _table_size;
196 // ResourceHashtable SIZE is specified at compile time so our
197 // dynamic _table_size is unused for now; 1031 is the first prime
198 // after 1024.
199 typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash,
200 &ThreadScanHashtable::ptr_equals, 1031,
201 ResourceObj::C_HEAP, mtThread> PtrTable;
202 PtrTable * _ptrs;
203
204 public:
205 // ResourceHashtable is passed to various functions and populated in
206 // different places so we allocate it using C_HEAP to make it immune
207 // from any ResourceMarks that happen to be in the code paths.
208 ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}
209
210 ~ThreadScanHashtable() { delete _ptrs; }
211
212 bool has_entry(void *pointer) {
213 int *val_ptr = _ptrs->get(pointer);
214 return val_ptr != NULL && *val_ptr == 1;
215 }
216
217 void add_entry(void *pointer) {
218 _ptrs->put(pointer, 1);
219 }
220 };
221
222 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
223 // (ThreadsList references) into a hash table. This closure handles part 2
224 // of the dance - adding all the JavaThreads referenced by the hazard
225 // pointer (ThreadsList reference) to the hash table.
226 //
227 class AddThreadHazardPointerThreadClosure : public ThreadClosure {
228 private:
229 ThreadScanHashtable *_table;
230
231 public:
232 AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {}
233
234 virtual void do_thread(Thread *thread) {
235 if (!_table->has_entry((void*)thread)) {
236 // The same JavaThread might be on more than one ThreadsList or
237 // more than one thread might be using the same ThreadsList. In
238 // either case, we only need a single entry for a JavaThread.
239 _table->add_entry((void*)thread);
240 }
241 }
242 };
243
244 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
245 // (ThreadsList references) into a hash table. This closure handles part 1
246 // of the dance - hazard ptr chain walking and dispatch to another
247 // closure.
248 //
249 class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure {
250 private:
251 ThreadScanHashtable *_table;
252 public:
253 ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {}
254
255 virtual void do_thread(Thread *thread) {
256 assert_locked_or_safepoint(Threads_lock);
257
258 if (thread == NULL) return;
259
260 // This code races with ThreadsSMRSupport::acquire_stable_list() which
261 // is lock-free so we have to handle some special situations.
262 //
263 ThreadsList *current_list = NULL;
264 while (true) {
265 current_list = thread->get_threads_hazard_ptr();
266 // No hazard ptr so nothing more to do.
267 if (current_list == NULL) {
268 return;
269 }
270
271 // If the hazard ptr is verified as stable (since it is not tagged),
272 // then it is safe to use.
273 if (!Thread::is_hazard_ptr_tagged(current_list)) break;
274
275 // The hazard ptr is tagged as not yet verified as being stable
276 // so we are racing with acquire_stable_list(). This exchange
277 // attempts to invalidate the hazard ptr. If we win the race,
278 // then we can ignore this unstable hazard ptr and the other
279 // thread will retry the attempt to publish a stable hazard ptr.
280 // If we lose the race, then we retry our attempt to look at the
281 // hazard ptr.
282 if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return;
283 }
284
285 // The current JavaThread has a hazard ptr (ThreadsList reference)
286 // which might be _java_thread_list or it might be an older
287 // ThreadsList that has been removed but not freed. In either case,
288 // the hazard ptr is protecting all the JavaThreads on that
289 // ThreadsList.
290 AddThreadHazardPointerThreadClosure add_cl(_table);
291 current_list->threads_do(&add_cl);
292 }
293 };
294
295 // Closure to gather hazard ptrs (ThreadsList references) into a hash table.
296 //
297 class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure {
298 private:
299 ThreadScanHashtable *_table;
300 public:
301 ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {}
302
303 virtual void do_thread(Thread* thread) {
304 assert_locked_or_safepoint(Threads_lock);
305
306 if (thread == NULL) return;
307 ThreadsList *threads = thread->get_threads_hazard_ptr();
308 if (threads == NULL) {
309 return;
310 }
311 // In this closure we always ignore the tag that might mark this
312 // hazard ptr as not yet verified. If we happen to catch an
313 // unverified hazard ptr that is subsequently discarded (not
314 // published), then the only side effect is that we might keep a
315 // to-be-deleted ThreadsList alive a little longer.
316 threads = Thread::untag_hazard_ptr(threads);
317 if (!_table->has_entry((void*)threads)) {
318 _table->add_entry((void*)threads);
319 }
320 }
321 };
322
323 // Closure to print JavaThreads that have a hazard ptr (ThreadsList
324 // reference) that contains an indirect reference to a specific JavaThread.
325 //
326 class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure {
327 private:
328 JavaThread *_thread;
329 public:
330 ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {}
331
332 virtual void do_thread(Thread *thread) {
333 assert_locked_or_safepoint(Threads_lock);
334
335 if (thread == NULL) return;
336 ThreadsList *current_list = thread->get_threads_hazard_ptr();
337 if (current_list == NULL) {
338 return;
339 }
340 // If the hazard ptr is unverified, then ignore it.
341 if (Thread::is_hazard_ptr_tagged(current_list)) return;
342
343 // The current JavaThread has a hazard ptr (ThreadsList reference)
344 // which might be _java_thread_list or it might be an older
345 // ThreadsList that has been removed but not freed. In either case,
346 // the hazard ptr is protecting all the JavaThreads on that
347 // ThreadsList, but we only care about matching a specific JavaThread.
348 JavaThreadIterator jti(current_list);
349 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) {
350 if (p == _thread) {
351 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));
352 break;
353 }
354 }
355 }
356 };
357
358 // Closure to determine if the specified JavaThread is found by
359 // threads_do().
360 //
361 class VerifyHazardPtrThreadClosure : public ThreadClosure {
362 private:
363 bool _found;
364 Thread *_self;
365
366 public:
367 VerifyHazardPtrThreadClosure(Thread *self) : _found(false), _self(self) {}
368
369 bool found() const { return _found; }
370
371 virtual void do_thread(Thread *thread) {
372 if (thread == _self) {
373 _found = true;
374 }
375 }
376 };
377
378
379 // Acquire a stable ThreadsList.
380 //
381 void SafeThreadsListPtr::acquire_stable_list() {
382 assert(_thread != NULL, "sanity check");
383 _needs_release = true;
384 _previous = _thread->_threads_list_ptr;
385 _thread->_threads_list_ptr = this;
386
387 if (_thread->get_threads_hazard_ptr() == NULL) {
388 // The typical case is first.
389 acquire_stable_list_fast_path();
390 return;
391 }
392
393 // The nested case is rare.
394 acquire_stable_list_nested_path();
395 }
396
397 // Fast path way to acquire a stable ThreadsList.
398 //
399 void SafeThreadsListPtr::acquire_stable_list_fast_path() {
400 assert(_thread != NULL, "sanity check");
401 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
402
403 ThreadsList* threads;
404
405 // Stable recording of a hazard ptr for SMR. This code does not use
406 // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr
407 // fields is racy relative to code that uses those fields with locks.
408 // OrderAccess and Atomic functions are used to deal with those races.
409 //
410 while (true) {
411 threads = ThreadsSMRSupport::get_java_thread_list();
412
413 // Publish a tagged hazard ptr to denote that the hazard ptr is not
414 // yet verified as being stable. Due to the fence after the hazard
415 // ptr write, it will be sequentially consistent w.r.t. the
416 // sequentially consistent writes of the ThreadsList, even on
417 // non-multiple copy atomic machines where stores can be observed
418 // in different order from different observer threads.
419 ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads);
420 _thread->set_threads_hazard_ptr(unverified_threads);
421
422 // If _smr_java_thread_list has changed, we have lost a race with
423 // Threads::add() or Threads::remove() and have to try again.
424 if (ThreadsSMRSupport::get_java_thread_list() != threads) {
425 continue;
426 }
427
428 // We try to remove the tag which will verify the hazard ptr as
429 // being stable. This exchange can race with a scanning thread
430 // which might invalidate the tagged hazard ptr to keep it from
431 // being followed to access JavaThread ptrs. If we lose the race,
432 // we simply retry. If we win the race, then the stable hazard
433 // ptr is officially published.
434 if (_thread->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) {
435 break;
436 }
437 }
438
439 // A stable hazard ptr has been published letting other threads know
440 // that the ThreadsList and the JavaThreads reachable from this list
441 // are protected and hence they should not be deleted until everyone
442 // agrees it is safe to do so.
443
444 _list = threads;
445
446 verify_hazard_ptr_scanned();
447 }
448
449 // Acquire a nested stable ThreadsList; this is rare so it uses
450 // reference counting.
451 //
452 void SafeThreadsListPtr::acquire_stable_list_nested_path() {
453 assert(_thread != NULL, "sanity check");
454 assert(_thread->get_threads_hazard_ptr() != NULL,
455 "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr");
456
457 // The thread already has a hazard ptr (ThreadsList ref) so we need
458 // to create a nested ThreadsListHandle with the current ThreadsList
459 // since it might be different than our current hazard ptr. To remedy
460 // the situation, the ThreadsList pointed to by the pre-existing
461 // stable hazard ptr is reference counted before the hazard ptr may
462 // be released and moved to a new ThreadsList. The old ThreadsList
463 // is remembered in the ThreadsListHandle.
464
465 ThreadsList* current_list = _previous->_list;
466 if (EnableThreadSMRStatistics) {
467 _thread->inc_nested_threads_hazard_ptr_cnt();
468 }
469 current_list->inc_nested_handle_cnt();
470 _previous->_has_ref_count = true; // promote SafeThreadsListPtr to be reference counted
471 _thread->_threads_hazard_ptr = NULL; // clear the hazard ptr so we can go through the fast path below
472
473 if (EnableThreadSMRStatistics && _thread->nested_threads_hazard_ptr_cnt() > ThreadsSMRSupport::_nested_thread_list_max) {
474 ThreadsSMRSupport::_nested_thread_list_max = _thread->nested_threads_hazard_ptr_cnt();
475 }
476
477 acquire_stable_list_fast_path();
478
479 verify_hazard_ptr_scanned();
480
481 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));
482 }
483
484 // Release a stable ThreadsList.
485 //
486 void SafeThreadsListPtr::release_stable_list() {
487 assert(_thread != NULL, "sanity check");
488 assert(_thread->_threads_list_ptr == this, "sanity check");
489 _thread->_threads_list_ptr = _previous;
490
491 if (_has_ref_count) {
492 // If a SafeThreadsListPtr has been promoted to use reference counting
493 // due to nesting of ThreadsListHandles, then the reference count must be
494 // decremented, at which point it may be freed. The forgotten value of
495 // the list no longer matters at this point and should already be NULL.
496 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
497 if (EnableThreadSMRStatistics) {
498 _thread->dec_nested_threads_hazard_ptr_cnt();
499 }
500 _list->dec_nested_handle_cnt();
501
502 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));
503 } else {
504 // The normal case: a leaf ThreadsListHandle. This merely requires setting
505 // the thread hazard ptr back to NULL.
506 assert(_thread->get_threads_hazard_ptr() != NULL, "sanity check");
507 _thread->set_threads_hazard_ptr(NULL);
508 }
509
510 // After releasing the hazard ptr, other threads may go ahead and
511 // free up some memory temporarily used by a ThreadsList snapshot.
512
513 // We use double-check locking to reduce traffic on the system
514 // wide Thread-SMR delete_lock.
515 if (ThreadsSMRSupport::delete_notify()) {
516 // An exiting thread might be waiting in smr_delete(); we need to
517 // check with delete_lock to be sure.
518 ThreadsSMRSupport::release_stable_list_wake_up(_has_ref_count);
519 }
520 }
521
522 // Verify that the stable hazard ptr used to safely keep threads
523 // alive is scanned by threads_do() which is a key piece of honoring
524 // the Thread-SMR protocol.
525 void SafeThreadsListPtr::verify_hazard_ptr_scanned() {
526 #ifdef ASSERT
527 assert(_list != NULL, "_list must not be NULL");
528
529 if (ThreadsSMRSupport::is_bootstrap_list(_list)) {
530 // We are early in VM bootstrapping so nothing to do here.
531 return;
532 }
533
534 if ( _thread == VM_Exit::shutdown_thread()) {
535 // The shutdown thread has removed itself from the Threads
536 // list and is safe to have a waiver from this check because
537 // VM_Exit::_shutdown_thread is not set until after the VMThread
538 // has started the final safepoint which holds the Threads_lock
539 // for the remainder of the VM's life.
540 return;
541 }
542
543 if (VMError::is_error_reported() &&
544 VMError::get_first_error_tid() == os::current_thread_id()) {
545 // If there is an error reported by this thread it may use ThreadsList even
546 // if it's unsafe.
547 return;
548 }
549
550 // The closure will attempt to verify that the calling thread can
551 // be found by threads_do() on the specified ThreadsList. If it
552 // is successful, then the specified ThreadsList was acquired as
553 // a stable hazard ptr by the calling thread in a way that honored
554 // the Thread-SMR protocol.
555 //
556 // If the calling thread cannot be found by threads_do() and if
557 // it is not the shutdown thread, then the calling thread is not
558 // honoring the Thread-SMR ptotocol. This means that the specified
559 // ThreadsList is not a stable hazard ptr and can be freed by
560 // another thread from the to-be-deleted list at any time.
561 //
562 VerifyHazardPtrThreadClosure cl(_thread);
563 ThreadsSMRSupport::threads_do(&cl, _list);
564
565 // If the calling thread is not honoring the Thread-SMR protocol,
566 // then we will either crash in threads_do() above because 'threads'
567 // was freed by another thread or we will fail the assert() below.
568 // In either case, we won't get past this point with a badly placed
569 // ThreadsListHandle.
570
571 assert(cl.found(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol.");
572 #endif
573 }
574
575 // 'entries + 1' so we always have at least one entry.
576 ThreadsList::ThreadsList(int entries) :
577 _length(entries),
578 _next_list(NULL),
579 _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)),
580 _nested_handle_cnt(0)
581 {
582 *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
583 }
584
585 ThreadsList::~ThreadsList() {
586 FREE_C_HEAP_ARRAY(JavaThread*, _threads);
587 }
588
589 // Add a JavaThread to a ThreadsList. The returned ThreadsList is a
590 // new copy of the specified ThreadsList with the specified JavaThread
591 // appended to the end.
592 ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) {
593 const uint index = list->_length;
594 const uint new_length = index + 1;
595 const uint head_length = index;
596 ThreadsList *const new_list = new ThreadsList(new_length);
597
598 if (head_length > 0) {
599 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
600 }
601 *(JavaThread**)(new_list->_threads + index) = java_thread;
602
603 return new_list;
604 }
605
606 void ThreadsList::dec_nested_handle_cnt() {
607 Atomic::dec(&_nested_handle_cnt);
608 }
609
610 int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
611 if (target == NULL) {
612 return -1;
613 }
614 for (uint i = 0; i < length(); i++) {
615 if (target == thread_at(i)) {
616 return (int)i;
617 }
618 }
619 return -1;
620 }
621
622 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
623 ThreadIdTable::lazy_initialize(this);
624 JavaThread* thread = ThreadIdTable::find_thread_by_tid(java_tid);
625 if (thread == NULL) {
626 // If the thread is not found in the table find it
627 // with a linear search and add to the table.
628 for (uint i = 0; i < length(); i++) {
629 thread = thread_at(i);
630 oop tobj = thread->threadObj();
631 // Ignore the thread if it hasn't run yet, has exited
632 // or is starting to exit.
633 if (tobj != NULL && java_tid == java_lang_Thread::thread_id(tobj)) {
634 MutexLocker ml(Threads_lock);
635 // Must be inside the lock to ensure that we don't add a thread to the table
636 // that has just passed the removal point in ThreadsSMRSupport::remove_thread()
637 if (!thread->is_exiting()) {
638 ThreadIdTable::add_thread(java_tid, thread);
639 return thread;
640 }
641 }
642 }
643 } else if (!thread->is_exiting()) {
644 return thread;
645 }
646 return NULL;
647 }
648
649 void ThreadsList::inc_nested_handle_cnt() {
650 Atomic::inc(&_nested_handle_cnt);
651 }
652
653 bool ThreadsList::includes(const JavaThread * const p) const {
654 if (p == NULL) {
655 return false;
656 }
657 for (uint i = 0; i < length(); i++) {
658 if (thread_at(i) == p) {
659 return true;
660 }
661 }
662 return false;
663 }
664
665 // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a
666 // new copy of the specified ThreadsList with the specified JavaThread
667 // removed.
668 ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) {
669 assert(list->_length > 0, "sanity");
670
671 uint i = (uint)list->find_index_of_JavaThread(java_thread);
672 assert(i < list->_length, "did not find JavaThread on the list");
673 const uint index = i;
674 const uint new_length = list->_length - 1;
675 const uint head_length = index;
676 const uint tail_length = (new_length >= index) ? (new_length - index) : 0;
677 ThreadsList *const new_list = new ThreadsList(new_length);
678
679 if (head_length > 0) {
680 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
681 }
682 if (tail_length > 0) {
683 Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length);
684 }
685
686 return new_list;
687 }
688
689 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list_ptr(self, /* acquire */ true) {
690 assert(self == Thread::current(), "sanity check");
691 if (EnableThreadSMRStatistics) {
692 _timer.start();
693 }
694 }
695
696 ThreadsListHandle::~ThreadsListHandle() {
697 if (EnableThreadSMRStatistics) {
698 _timer.stop();
699 uint millis = (uint)_timer.milliseconds();
700 ThreadsSMRSupport::update_tlh_stats(millis);
701 }
702 }
703
704 // Convert an internal thread reference to a JavaThread found on the
705 // associated ThreadsList. This ThreadsListHandle "protects" the
706 // returned JavaThread *.
707 //
708 // If thread_oop_p is not NULL, then the caller wants to use the oop
709 // after this call so the oop is returned. On success, *jt_pp is set
710 // to the converted JavaThread * and true is returned. On error,
711 // returns false.
712 //
713 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
714 JavaThread ** jt_pp,
715 oop * thread_oop_p) {
716 assert(this->list() != NULL, "must have a ThreadsList");
717 assert(jt_pp != NULL, "must have a return JavaThread pointer");
718 // thread_oop_p is optional so no assert()
719
720 // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI
721 // allows a NULL thread parameter to signify "current thread" which
722 // allows us to avoid calling cv_external_thread_to_JavaThread().
723 // The JVM_* interfaces have no such leeway.
724
725 oop thread_oop = JNIHandles::resolve_non_null(jthread);
726 // Looks like an oop at this point.
727 if (thread_oop_p != NULL) {
728 // Return the oop to the caller; the caller may still want
729 // the oop even if this function returns false.
730 *thread_oop_p = thread_oop;
731 }
732
733 JavaThread *java_thread = java_lang_Thread::thread(thread_oop);
734 if (java_thread == NULL) {
735 // The java.lang.Thread does not contain a JavaThread * so it has
736 // not yet run or it has died.
737 return false;
738 }
739 // Looks like a live JavaThread at this point.
740
741 if (java_thread != JavaThread::current()) {
742 // jthread is not for the current JavaThread so have to verify
743 // the JavaThread * against the ThreadsList.
744 if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) {
745 // Not on the JavaThreads list so it is not alive.
746 return false;
747 }
748 }
749
750 // Return a live JavaThread that is "protected" by the
751 // ThreadsListHandle in the caller.
752 *jt_pp = java_thread;
753 return true;
754 }
755
756 void ThreadsSMRSupport::add_thread(JavaThread *thread){
757 ThreadsList *new_list = ThreadsList::add_thread(get_java_thread_list(), thread);
758 if (EnableThreadSMRStatistics) {
759 inc_java_thread_list_alloc_cnt();
760 update_java_thread_list_max(new_list->length());
761 }
762 // Initial _java_thread_list will not generate a "Threads::add" mesg.
763 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
764
765 ThreadsList *old_list = xchg_java_thread_list(new_list);
766 free_list(old_list);
767 if (ThreadIdTable::is_initialized()) {
768 jlong tid = SharedRuntime::get_java_tid(thread);
769 ThreadIdTable::add_thread(tid, thread);
770 }
771 }
772
773 // set_delete_notify() and clear_delete_notify() are called
774 // under the protection of the delete_lock, but we also use an
775 // Atomic operation to ensure the memory update is seen earlier than
776 // when the delete_lock is dropped.
777 //
778 void ThreadsSMRSupport::clear_delete_notify() {
779 Atomic::dec(&_delete_notify);
780 }
781
782 bool ThreadsSMRSupport::delete_notify() {
783 // Use load_acquire() in order to see any updates to _delete_notify
784 // earlier than when delete_lock is grabbed.
785 return (Atomic::load_acquire(&_delete_notify) != 0);
786 }
787
788 // Safely free a ThreadsList after a Threads::add() or Threads::remove().
789 // The specified ThreadsList may not get deleted during this call if it
790 // is still in-use (referenced by a hazard ptr). Other ThreadsLists
791 // in the chain may get deleted by this call if they are no longer in-use.
792 void ThreadsSMRSupport::free_list(ThreadsList* threads) {
793 assert_locked_or_safepoint(Threads_lock);
794
795 if (is_bootstrap_list(threads)) {
796 // The bootstrap list cannot be freed and is empty so
797 // it does not need to be scanned. Nothing to do here.
798 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));
799 return;
800 }
801
802 threads->set_next_list(_to_delete_list);
803 _to_delete_list = threads;
804 if (EnableThreadSMRStatistics) {
805 _to_delete_list_cnt++;
806 if (_to_delete_list_cnt > _to_delete_list_max) {
807 _to_delete_list_max = _to_delete_list_cnt;
808 }
809 }
810
811 // Hash table size should be first power of two higher than twice the length of the ThreadsList
812 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
813 hash_table_size = round_up_power_of_2(hash_table_size);
814
815 // Gather a hash table of the current hazard ptrs:
816 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
817 ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
818 threads_do(&scan_cl);
819 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
820 // nested reference counters
821
822 // Walk through the linked list of pending freeable ThreadsLists
823 // and free the ones that are not referenced from hazard ptrs.
824 ThreadsList* current = _to_delete_list;
825 ThreadsList* prev = NULL;
826 ThreadsList* next = NULL;
827 bool threads_is_freed = false;
828 while (current != NULL) {
829 next = current->next_list();
830 if (!scan_table->has_entry((void*)current) && current->_nested_handle_cnt == 0) {
831 // This ThreadsList is not referenced by a hazard ptr.
832 if (prev != NULL) {
833 prev->set_next_list(next);
834 }
835 if (_to_delete_list == current) {
836 _to_delete_list = next;
837 }
838
839 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current));
840 if (current == threads) threads_is_freed = true;
841 delete current;
842 if (EnableThreadSMRStatistics) {
843 _java_thread_list_free_cnt++;
844 _to_delete_list_cnt--;
845 }
846 } else {
847 prev = current;
848 }
849 current = next;
850 }
851
852 if (!threads_is_freed) {
853 // Only report "is not freed" on the original call to
854 // free_list() for this ThreadsList.
855 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads));
856 }
857
858 delete scan_table;
859 }
860
861 // Return true if the specified JavaThread is protected by a hazard
862 // pointer (ThreadsList reference). Otherwise, returns false.
863 //
864 bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) {
865 assert_locked_or_safepoint(Threads_lock);
866
867 // Hash table size should be first power of two higher than twice
868 // the length of the Threads list.
869 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
870 hash_table_size = round_up_power_of_2(hash_table_size);
871
872 // Gather a hash table of the JavaThreads indirectly referenced by
873 // hazard ptrs.
874 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
875 ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table);
876 threads_do(&scan_cl);
877 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
878 // nested reference counters
879
880 // Walk through the linked list of pending freeable ThreadsLists
881 // and include the ones that are currently in use by a nested
882 // ThreadsListHandle in the search set.
883 ThreadsList* current = _to_delete_list;
884 while (current != NULL) {
885 if (current->_nested_handle_cnt != 0) {
886 // 'current' is in use by a nested ThreadsListHandle so the hazard
887 // ptr is protecting all the JavaThreads on that ThreadsList.
888 AddThreadHazardPointerThreadClosure add_cl(scan_table);
889 current->threads_do(&add_cl);
890 }
891 current = current->next_list();
892 }
893
894 bool thread_is_protected = false;
895 if (scan_table->has_entry((void*)thread)) {
896 thread_is_protected = true;
897 }
898 delete scan_table;
899 return thread_is_protected;
900 }
901
902 // Wake up portion of the release stable ThreadsList protocol;
903 // uses the delete_lock().
904 //
905 void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) {
906 const char* log_str = is_nested ? "nested hazard ptr" : "regular hazard ptr";
907
908 // Note: delete_lock is held in smr_delete() for the entire
909 // hazard ptr search so that we do not lose this notify() if
910 // the exiting thread has to wait. That code path also holds
911 // Threads_lock (which was grabbed before delete_lock) so that
912 // threads_do() can be called. This means the system can't start a
913 // safepoint which means this thread can't take too long to get to
914 // a safepoint because of being blocked on delete_lock.
915 //
916 MonitorLocker ml(ThreadsSMRSupport::delete_lock(), Monitor::_no_safepoint_check_flag);
917 if (ThreadsSMRSupport::delete_notify()) {
918 // Notify any exiting JavaThreads that are waiting in smr_delete()
919 // that we've released a ThreadsList.
920 ml.notify_all();
921 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str);
922 }
923 }
924
925 void ThreadsSMRSupport::remove_thread(JavaThread *thread) {
926 if (ThreadIdTable::is_initialized()) {
927 jlong tid = SharedRuntime::get_java_tid(thread);
928 ThreadIdTable::remove_thread(tid);
929 }
930 ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_java_thread_list(), thread);
931 if (EnableThreadSMRStatistics) {
932 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt();
933 // This list is smaller so no need to check for a "longest" update.
934 }
935
936 // Final _java_thread_list will not generate a "Threads::remove" mesg.
937 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
938
939 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list);
940 ThreadsSMRSupport::free_list(old_list);
941 }
942
943 // See note for clear_delete_notify().
944 //
945 void ThreadsSMRSupport::set_delete_notify() {
946 Atomic::inc(&_delete_notify);
947 }
948
949 // Safely delete a JavaThread when it is no longer in use by a
950 // ThreadsListHandle.
951 //
952 void ThreadsSMRSupport::smr_delete(JavaThread *thread) {
953 elapsedTimer timer;
954 if (EnableThreadSMRStatistics) {
955 timer.start();
956 }
957
958 wait_until_not_protected(thread);
959
960 delete thread;
961 if (EnableThreadSMRStatistics) {
962 timer.stop();
963 uint millis = (uint)timer.milliseconds();
964 ThreadsSMRSupport::inc_deleted_thread_cnt();
965 ThreadsSMRSupport::add_deleted_thread_times(millis);
966 ThreadsSMRSupport::update_deleted_thread_time_max(millis);
967 }
968
969 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread));
970 }
971
972 void ThreadsSMRSupport::wait_until_not_protected(JavaThread *thread) {
973 assert(!Threads_lock->owned_by_self(), "sanity");
974
975 bool has_logged_once = false;
976
977 while (true) {
978 {
979 // Will not make a safepoint check because this JavaThread
980 // is not on the current ThreadsList.
981 MutexLocker ml(Threads_lock);
982 // Cannot use a MonitorLocker helper here because we have
983 // to drop the Threads_lock first if we wait.
984 ThreadsSMRSupport::delete_lock()->lock_without_safepoint_check();
985 // Set the delete_notify flag after we grab delete_lock
986 // and before we scan hazard ptrs because we're doing
987 // double-check locking in release_stable_list().
988 ThreadsSMRSupport::set_delete_notify();
989
990 if (!is_a_protected_JavaThread(thread)) {
991 // This is the common case.
992 ThreadsSMRSupport::clear_delete_notify();
993 ThreadsSMRSupport::delete_lock()->unlock();
994 break;
995 }
996 if (!has_logged_once) {
997 has_logged_once = true;
998 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::wait_until_not_protected: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread));
999 if (log_is_enabled(Debug, os, thread)) {
1000 ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread);
1001 threads_do(&scan_cl);
1002 ThreadsList* current = _to_delete_list;
1003 while (current != NULL) {
1004 if (current->_nested_handle_cnt != 0 && current->includes(thread)) {
1005 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::wait_until_not_protected: found nested hazard pointer to thread=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread));
1006 }
1007 current = current->next_list();
1008 }
1009 }
1010 }
1011 } // We have to drop the Threads_lock to wait or delete the thread
1012
1013 if (EnableThreadSMRStatistics) {
1014 _delete_lock_wait_cnt++;
1015 if (_delete_lock_wait_cnt > _delete_lock_wait_max) {
1016 _delete_lock_wait_max = _delete_lock_wait_cnt;
1017 }
1018 }
1019 // Wait for a release_stable_list() call before we check again. No
1020 // safepoint check, no timeout, and not as suspend equivalent flag
1021 // because this JavaThread is not on the Threads list.
1022 ThreadsSMRSupport::delete_lock()->wait_without_safepoint_check();
1023 if (EnableThreadSMRStatistics) {
1024 _delete_lock_wait_cnt--;
1025 }
1026
1027 ThreadsSMRSupport::clear_delete_notify();
1028 ThreadsSMRSupport::delete_lock()->unlock();
1029 // Retry the whole scenario.
1030 }
1031 }
1032
1033 // Apply the closure to all threads in the system, with a snapshot of
1034 // all JavaThreads provided by the list parameter.
1035 void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) {
1036 list->threads_do(tc);
1037 Threads::non_java_threads_do(tc);
1038 }
1039
1040 // Apply the closure to all threads in the system.
1041 void ThreadsSMRSupport::threads_do(ThreadClosure *tc) {
1042 threads_do(tc, _java_thread_list);
1043 }
1044
1045
1046 // Debug, logging, and printing stuff at the end:
1047
1048 // Print SMR info for a SafeThreadsListPtr to a given output stream.
1049 void SafeThreadsListPtr::print_on(outputStream* st) {
1050 if (this == _thread->_threads_list_ptr) {
1051 // The top level hazard ptr.
1052 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1053 } else {
1054 // Nested hazard ptrs.
1055 st->print(", _nested_threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1056 }
1057 }
1058
1059 // Log Threads class SMR info.
1060 void ThreadsSMRSupport::log_statistics() {
1061 LogTarget(Info, thread, smr) log;
1062 if (log.is_enabled()) {
1063 LogStream out(log);
1064 print_info_on(&out);
1065 }
1066 }
1067
1068 // Print SMR info for a thread to a given output stream.
1069 void ThreadsSMRSupport::print_info_on(const Thread* thread, outputStream* st) {
1070 if (thread->_threads_hazard_ptr != NULL) {
1071 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(thread->_threads_hazard_ptr));
1072 }
1073 if (EnableThreadSMRStatistics && thread->_threads_list_ptr != NULL) {
1074 // The count is only interesting if we have a _threads_list_ptr.
1075 st->print(", _nested_threads_hazard_ptr_cnt=%u", thread->_nested_threads_hazard_ptr_cnt);
1076 }
1077 if (SafepointSynchronize::is_at_safepoint() || Thread::current() == thread) {
1078 // It is only safe to walk the list if we're at a safepoint or the
1079 // calling thread is walking its own list.
1080 SafeThreadsListPtr* current = thread->_threads_list_ptr;
1081 if (current != NULL) {
1082 // Skip the top nesting level as it is always printed above.
1083 current = current->previous();
1084 }
1085 while (current != NULL) {
1086 current->print_on(st);
1087 current = current->previous();
1088 }
1089 }
1090 }
1091
1092 // Print Threads class SMR info.
1093 void ThreadsSMRSupport::print_info_on(outputStream* st) {
1094 // Only grab the Threads_lock if we don't already own it and if we
1095 // are not reporting an error.
1096 // Note: Not grabbing the Threads_lock during error reporting is
1097 // dangerous because the data structures we want to print can be
1098 // freed concurrently. However, grabbing the Threads_lock during
1099 // error reporting can be equally dangerous since this thread might
1100 // block during error reporting or a nested error could leave the
1101 // Threads_lock held. The classic no win scenario.
1102 //
1103 MutexLocker ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock);
1104
1105 st->print_cr("Threads class SMR info:");
1106 st->print_cr("_java_thread_list=" INTPTR_FORMAT ", length=%u, "
1107 "elements={", p2i(_java_thread_list),
1108 _java_thread_list->length());
1109 print_info_elements_on(st, _java_thread_list);
1110 st->print_cr("}");
1111 if (_to_delete_list != NULL) {
1112 st->print_cr("_to_delete_list=" INTPTR_FORMAT ", length=%u, "
1113 "elements={", p2i(_to_delete_list),
1114 _to_delete_list->length());
1115 print_info_elements_on(st, _to_delete_list);
1116 st->print_cr("}");
1117 for (ThreadsList *t_list = _to_delete_list->next_list();
1118 t_list != NULL; t_list = t_list->next_list()) {
1119 st->print("next-> " INTPTR_FORMAT ", length=%u, "
1120 "elements={", p2i(t_list), t_list->length());
1121 print_info_elements_on(st, t_list);
1122 st->print_cr("}");
1123 }
1124 }
1125 if (!EnableThreadSMRStatistics) {
1126 return;
1127 }
1128 st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ", "
1129 "_java_thread_list_free_cnt=" UINT64_FORMAT ", "
1130 "_java_thread_list_max=%u, "
1131 "_nested_thread_list_max=%u",
1132 _java_thread_list_alloc_cnt,
1133 _java_thread_list_free_cnt,
1134 _java_thread_list_max,
1135 _nested_thread_list_max);
1136 if (_tlh_cnt > 0) {
1137 st->print_cr("_tlh_cnt=%u"
1138 ", _tlh_times=%u"
1139 ", avg_tlh_time=%0.2f"
1140 ", _tlh_time_max=%u",
1141 _tlh_cnt, _tlh_times,
1142 ((double) _tlh_times / _tlh_cnt),
1143 _tlh_time_max);
1144 }
1145 if (_deleted_thread_cnt > 0) {
1146 st->print_cr("_deleted_thread_cnt=%u"
1147 ", _deleted_thread_times=%u"
1148 ", avg_deleted_thread_time=%0.2f"
1149 ", _deleted_thread_time_max=%u",
1150 _deleted_thread_cnt, _deleted_thread_times,
1151 ((double) _deleted_thread_times / _deleted_thread_cnt),
1152 _deleted_thread_time_max);
1153 }
1154 st->print_cr("_delete_lock_wait_cnt=%u, _delete_lock_wait_max=%u",
1155 _delete_lock_wait_cnt, _delete_lock_wait_max);
1156 st->print_cr("_to_delete_list_cnt=%u, _to_delete_list_max=%u",
1157 _to_delete_list_cnt, _to_delete_list_max);
1158 }
1159
1160 // Print ThreadsList elements (4 per line).
1161 void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_list) {
1162 uint cnt = 0;
1163 JavaThreadIterator jti(t_list);
1164 for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
1165 st->print(INTPTR_FORMAT, p2i(jt));
1166 if (cnt < t_list->length() - 1) {
1167 // Separate with comma or comma-space except for the last one.
1168 if (((cnt + 1) % 4) == 0) {
1169 // Four INTPTR_FORMAT fit on an 80 column line so end the
1170 // current line with just a comma.
1171 st->print_cr(",");
1172 } else {
1173 // Not the last one on the current line so use comma-space:
1174 st->print(", ");
1175 }
1176 } else {
1177 // Last one so just end the current line.
1178 st->cr();
1179 }
1180 cnt++;
1181 }
1182 }