1 /*
2 * Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "logging/logStream.hpp"
27 #include "memory/allocation.inline.hpp"
28 #include "runtime/jniHandles.inline.hpp"
29 #include "runtime/thread.inline.hpp"
30 #include "runtime/threadSMR.inline.hpp"
31 #include "runtime/vm_operations.hpp"
32 #include "services/threadService.hpp"
33 #include "utilities/copy.hpp"
34 #include "utilities/globalDefinitions.hpp"
35 #include "utilities/ostream.hpp"
36 #include "utilities/resourceHash.hpp"
37 #include "utilities/vmError.hpp"
38
39 // The '_cnt', '_max' and '_times" fields are enabled via
40 // -XX:+EnableThreadSMRStatistics:
41
42 // # of parallel threads in _delete_lock->wait().
43 // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit,
44 // but there is no nice 16-bit _FORMAT support.
45 uint ThreadsSMRSupport::_delete_lock_wait_cnt = 0;
46
47 // Max # of parallel threads in _delete_lock->wait().
48 // Impl note: See _delete_lock_wait_cnt note.
49 uint ThreadsSMRSupport::_delete_lock_wait_max = 0;
50
51 // Flag to indicate when an _delete_lock->notify() is needed.
52 // Impl note: See _delete_lock_wait_cnt note.
53 volatile uint ThreadsSMRSupport::_delete_notify = 0;
54
55 // # of threads deleted over VM lifetime.
56 // Impl note: Atomically incremented over VM lifetime so use unsigned for more
57 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
58 // isn't available everywhere (or is it?).
59 volatile uint ThreadsSMRSupport::_deleted_thread_cnt = 0;
60
61 // Max time in millis to delete a thread.
62 // Impl note: 16-bit might be too small on an overloaded machine. Use
63 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
64 // loop for correctness.
65 volatile uint ThreadsSMRSupport::_deleted_thread_time_max = 0;
66
67 // Cumulative time in millis to delete threads.
68 // Impl note: Atomically added to over VM lifetime so use unsigned for more
69 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
70 // isn't available everywhere (or is it?).
71 volatile uint ThreadsSMRSupport::_deleted_thread_times = 0;
72
73 ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = new ThreadsList(0);
74
75 // # of ThreadsLists allocated over VM lifetime.
76 // Impl note: We allocate a new ThreadsList for every thread create and
77 // every thread delete so we need a bigger type than the
78 // _deleted_thread_cnt field.
79 uint64_t ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1;
80
81 // # of ThreadsLists freed over VM lifetime.
82 // Impl note: See _java_thread_list_alloc_cnt note.
83 uint64_t ThreadsSMRSupport::_java_thread_list_free_cnt = 0;
84
85 // Max size ThreadsList allocated.
86 // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit.
87 uint ThreadsSMRSupport::_java_thread_list_max = 0;
88
89 // Max # of nested ThreadsLists for a thread.
90 // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be
91 // 16-bit, but there is no nice 16-bit _FORMAT support.
92 uint ThreadsSMRSupport::_nested_thread_list_max = 0;
93
94 // # of ThreadsListHandles deleted over VM lifetime.
95 // Impl note: Atomically incremented over VM lifetime so use unsigned for
96 // more range. There will be fewer ThreadsListHandles than threads so
97 // unsigned 32-bit should be fine.
98 volatile uint ThreadsSMRSupport::_tlh_cnt = 0;
99
100 // Max time in millis to delete a ThreadsListHandle.
101 // Impl note: 16-bit might be too small on an overloaded machine. Use
102 // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
103 // loop for correctness.
104 volatile uint ThreadsSMRSupport::_tlh_time_max = 0;
105
106 // Cumulative time in millis to delete ThreadsListHandles.
107 // Impl note: Atomically added to over VM lifetime so use unsigned for more
108 // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
109 // isn't available everywhere (or is it?).
110 volatile uint ThreadsSMRSupport::_tlh_times = 0;
111
112 ThreadsList* ThreadsSMRSupport::_to_delete_list = NULL;
113
114 // # of parallel ThreadsLists on the to-delete list.
115 // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so
116 // this could be 16-bit, but there is no nice 16-bit _FORMAT support.
117 uint ThreadsSMRSupport::_to_delete_list_cnt = 0;
118
119 // Max # of parallel ThreadsLists on the to-delete list.
120 // Impl note: See _to_delete_list_cnt note.
121 uint ThreadsSMRSupport::_to_delete_list_max = 0;
122
123
124 // 'inline' functions first so the definitions are before first use:
125
126 inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) {
127 Atomic::add(add_value, &_deleted_thread_times);
128 }
129
130 inline void ThreadsSMRSupport::inc_deleted_thread_cnt() {
131 Atomic::inc(&_deleted_thread_cnt);
132 }
133
134 inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() {
135 _java_thread_list_alloc_cnt++;
136 }
137
138 inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) {
139 while (true) {
140 uint cur_value = _deleted_thread_time_max;
141 if (new_value <= cur_value) {
142 // No need to update max value so we're done.
143 break;
144 }
145 if (Atomic::cmpxchg(new_value, &_deleted_thread_time_max, cur_value) == cur_value) {
146 // Updated max value so we're done. Otherwise try it all again.
147 break;
148 }
149 }
150 }
151
152 inline void ThreadsSMRSupport::update_java_thread_list_max(uint new_value) {
153 if (new_value > _java_thread_list_max) {
154 _java_thread_list_max = new_value;
155 }
156 }
157
158 inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) {
159 return (ThreadsList*)Atomic::xchg(new_list, &_java_thread_list);
160 }
161
162
163 // Hash table of pointers found by a scan. Used for collecting hazard
164 // pointers (ThreadsList references). Also used for collecting JavaThreads
165 // that are indirectly referenced by hazard ptrs. An instance of this
166 // class only contains one type of pointer.
167 //
168 class ThreadScanHashtable : public CHeapObj<mtThread> {
169 private:
170 static bool ptr_equals(void * const& s1, void * const& s2) {
171 return s1 == s2;
172 }
173
174 static unsigned int ptr_hash(void * const& s1) {
175 // 2654435761 = 2^32 * Phi (golden ratio)
176 return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u);
177 }
178
179 int _table_size;
180 // ResourceHashtable SIZE is specified at compile time so our
181 // dynamic _table_size is unused for now; 1031 is the first prime
182 // after 1024.
183 typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash,
184 &ThreadScanHashtable::ptr_equals, 1031,
185 ResourceObj::C_HEAP, mtThread> PtrTable;
186 PtrTable * _ptrs;
187
188 public:
189 // ResourceHashtable is passed to various functions and populated in
190 // different places so we allocate it using C_HEAP to make it immune
191 // from any ResourceMarks that happen to be in the code paths.
192 ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}
193
194 ~ThreadScanHashtable() { delete _ptrs; }
195
196 bool has_entry(void *pointer) {
197 int *val_ptr = _ptrs->get(pointer);
198 return val_ptr != NULL && *val_ptr == 1;
199 }
200
201 void add_entry(void *pointer) {
202 _ptrs->put(pointer, 1);
203 }
204 };
205
206 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
207 // (ThreadsList references) into a hash table. This closure handles part 2
208 // of the dance - adding all the JavaThreads referenced by the hazard
209 // pointer (ThreadsList reference) to the hash table.
210 //
211 class AddThreadHazardPointerThreadClosure : public ThreadClosure {
212 private:
213 ThreadScanHashtable *_table;
214
215 public:
216 AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {}
217
218 virtual void do_thread(Thread *thread) {
219 if (!_table->has_entry((void*)thread)) {
220 // The same JavaThread might be on more than one ThreadsList or
221 // more than one thread might be using the same ThreadsList. In
222 // either case, we only need a single entry for a JavaThread.
223 _table->add_entry((void*)thread);
224 }
225 }
226 };
227
228 // Closure to gather JavaThreads indirectly referenced by hazard ptrs
229 // (ThreadsList references) into a hash table. This closure handles part 1
230 // of the dance - hazard ptr chain walking and dispatch to another
231 // closure.
232 //
233 class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure {
234 private:
235 ThreadScanHashtable *_table;
236 public:
237 ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {}
238
239 virtual void do_thread(Thread *thread) {
240 assert_locked_or_safepoint(Threads_lock);
241
242 if (thread == NULL) return;
243
244 // This code races with ThreadsSMRSupport::acquire_stable_list() which
245 // is lock-free so we have to handle some special situations.
246 //
247 ThreadsList *current_list = NULL;
248 while (true) {
249 current_list = thread->get_threads_hazard_ptr();
250 // No hazard ptr so nothing more to do.
251 if (current_list == NULL) {
252 return;
253 }
254
255 // If the hazard ptr is verified as stable (since it is not tagged),
256 // then it is safe to use.
257 if (!Thread::is_hazard_ptr_tagged(current_list)) break;
258
259 // The hazard ptr is tagged as not yet verified as being stable
260 // so we are racing with acquire_stable_list(). This exchange
261 // attempts to invalidate the hazard ptr. If we win the race,
262 // then we can ignore this unstable hazard ptr and the other
263 // thread will retry the attempt to publish a stable hazard ptr.
264 // If we lose the race, then we retry our attempt to look at the
265 // hazard ptr.
266 if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return;
267 }
268
269 // The current JavaThread has a hazard ptr (ThreadsList reference)
270 // which might be _java_thread_list or it might be an older
271 // ThreadsList that has been removed but not freed. In either case,
272 // the hazard ptr is protecting all the JavaThreads on that
273 // ThreadsList.
274 AddThreadHazardPointerThreadClosure add_cl(_table);
275 current_list->threads_do(&add_cl);
276 }
277 };
278
279 // Closure to gather hazard ptrs (ThreadsList references) into a hash table.
280 //
281 class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure {
282 private:
283 ThreadScanHashtable *_table;
284 public:
285 ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {}
286
287 virtual void do_thread(Thread* thread) {
288 assert_locked_or_safepoint(Threads_lock);
289
290 if (thread == NULL) return;
291 ThreadsList *threads = thread->get_threads_hazard_ptr();
292 if (threads == NULL) {
293 return;
294 }
295 // In this closure we always ignore the tag that might mark this
296 // hazard ptr as not yet verified. If we happen to catch an
297 // unverified hazard ptr that is subsequently discarded (not
298 // published), then the only side effect is that we might keep a
299 // to-be-deleted ThreadsList alive a little longer.
300 threads = Thread::untag_hazard_ptr(threads);
301 if (!_table->has_entry((void*)threads)) {
302 _table->add_entry((void*)threads);
303 }
304 }
305 };
306
307 // Closure to print JavaThreads that have a hazard ptr (ThreadsList
308 // reference) that contains an indirect reference to a specific JavaThread.
309 //
310 class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure {
311 private:
312 JavaThread *_thread;
313 public:
314 ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {}
315
316 virtual void do_thread(Thread *thread) {
317 assert_locked_or_safepoint(Threads_lock);
318
319 if (thread == NULL) return;
320 ThreadsList *current_list = thread->get_threads_hazard_ptr();
321 if (current_list == NULL) {
322 return;
323 }
324 // If the hazard ptr is unverified, then ignore it.
325 if (Thread::is_hazard_ptr_tagged(current_list)) return;
326
327 // The current JavaThread has a hazard ptr (ThreadsList reference)
328 // which might be _java_thread_list or it might be an older
329 // ThreadsList that has been removed but not freed. In either case,
330 // the hazard ptr is protecting all the JavaThreads on that
331 // ThreadsList, but we only care about matching a specific JavaThread.
332 JavaThreadIterator jti(current_list);
333 for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) {
334 if (p == _thread) {
335 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));
336 break;
337 }
338 }
339 }
340 };
341
342 // Closure to determine if the specified JavaThread is found by
343 // threads_do().
344 //
345 class VerifyHazardPtrThreadClosure : public ThreadClosure {
346 private:
347 bool _found;
348 Thread *_self;
349
350 public:
351 VerifyHazardPtrThreadClosure(Thread *self) : _found(false), _self(self) {}
352
353 bool found() const { return _found; }
354
355 virtual void do_thread(Thread *thread) {
356 if (thread == _self) {
357 _found = true;
358 }
359 }
360 };
361
362
363 // Acquire a stable ThreadsList.
364 //
365 void SafeThreadsListPtr::acquire_stable_list() {
366 assert(_thread != NULL, "sanity check");
367 _needs_release = true;
368 _previous = _thread->_threads_list_ptr;
369 _thread->_threads_list_ptr = this;
370
371 if (_thread->get_threads_hazard_ptr() == NULL) {
372 // The typical case is first.
373 acquire_stable_list_fast_path();
374 return;
375 }
376
377 // The nested case is rare.
378 acquire_stable_list_nested_path();
379 }
380
381 // Fast path way to acquire a stable ThreadsList.
382 //
383 void SafeThreadsListPtr::acquire_stable_list_fast_path() {
384 assert(_thread != NULL, "sanity check");
385 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
386
387 ThreadsList* threads;
388
389 // Stable recording of a hazard ptr for SMR. This code does not use
390 // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr
391 // fields is racy relative to code that uses those fields with locks.
392 // OrderAccess and Atomic functions are used to deal with those races.
393 //
394 while (true) {
395 threads = ThreadsSMRSupport::get_java_thread_list();
396
397 // Publish a tagged hazard ptr to denote that the hazard ptr is not
398 // yet verified as being stable. Due to the fence after the hazard
399 // ptr write, it will be sequentially consistent w.r.t. the
400 // sequentially consistent writes of the ThreadsList, even on
401 // non-multiple copy atomic machines where stores can be observed
402 // in different order from different observer threads.
403 ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads);
404 _thread->set_threads_hazard_ptr(unverified_threads);
405
406 // If _smr_java_thread_list has changed, we have lost a race with
407 // Threads::add() or Threads::remove() and have to try again.
408 if (ThreadsSMRSupport::get_java_thread_list() != threads) {
409 continue;
410 }
411
412 // We try to remove the tag which will verify the hazard ptr as
413 // being stable. This exchange can race with a scanning thread
414 // which might invalidate the tagged hazard ptr to keep it from
415 // being followed to access JavaThread ptrs. If we lose the race,
416 // we simply retry. If we win the race, then the stable hazard
417 // ptr is officially published.
418 if (_thread->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) {
419 break;
420 }
421 }
422
423 // A stable hazard ptr has been published letting other threads know
424 // that the ThreadsList and the JavaThreads reachable from this list
425 // are protected and hence they should not be deleted until everyone
426 // agrees it is safe to do so.
427
428 _list = threads;
429
430 verify_hazard_ptr_scanned();
431 }
432
433 // Acquire a nested stable ThreadsList; this is rare so it uses
434 // reference counting.
435 //
436 void SafeThreadsListPtr::acquire_stable_list_nested_path() {
437 assert(_thread != NULL, "sanity check");
438 assert(_thread->get_threads_hazard_ptr() != NULL,
439 "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr");
440
441 // The thread already has a hazard ptr (ThreadsList ref) so we need
442 // to create a nested ThreadsListHandle with the current ThreadsList
443 // since it might be different than our current hazard ptr. To remedy
444 // the situation, the ThreadsList pointed to by the pre-existing
445 // stable hazard ptr is reference counted before the hazard ptr may
446 // be released and moved to a new ThreadsList. The old ThreadsList
447 // is remembered in the ThreadsListHandle.
448
449 ThreadsList* current_list = _previous->_list;
450 if (EnableThreadSMRStatistics) {
451 _thread->inc_nested_threads_hazard_ptr_cnt();
452 }
453 current_list->inc_nested_handle_cnt();
454 _previous->_has_ref_count = true; // promote SafeThreadsListPtr to be reference counted
455 _thread->_threads_hazard_ptr = NULL; // clear the hazard ptr so we can go through the fast path below
456
457 if (EnableThreadSMRStatistics && _thread->nested_threads_hazard_ptr_cnt() > ThreadsSMRSupport::_nested_thread_list_max) {
458 ThreadsSMRSupport::_nested_thread_list_max = _thread->nested_threads_hazard_ptr_cnt();
459 }
460
461 acquire_stable_list_fast_path();
462
463 verify_hazard_ptr_scanned();
464
465 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));
466 }
467
468 // Release a stable ThreadsList.
469 //
470 void SafeThreadsListPtr::release_stable_list() {
471 assert(_thread != NULL, "sanity check");
472 assert(_thread->_threads_list_ptr == this, "sanity check");
473 _thread->_threads_list_ptr = _previous;
474
475 if (_has_ref_count) {
476 // If a SafeThreadsListPtr has been promoted to use reference counting
477 // due to nesting of ThreadsListHandles, then the reference count must be
478 // decremented, at which point it may be freed. The forgotten value of
479 // the list no longer matters at this point and should already be NULL.
480 assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
481 if (EnableThreadSMRStatistics) {
482 _thread->dec_nested_threads_hazard_ptr_cnt();
483 }
484 _list->dec_nested_handle_cnt();
485
486 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));
487 } else {
488 // The normal case: a leaf ThreadsListHandle. This merely requires setting
489 // the thread hazard ptr back to NULL.
490 assert(_thread->get_threads_hazard_ptr() != NULL, "sanity check");
491 _thread->set_threads_hazard_ptr(NULL);
492 }
493
494 // After releasing the hazard ptr, other threads may go ahead and
495 // free up some memory temporarily used by a ThreadsList snapshot.
496
497 // We use double-check locking to reduce traffic on the system
498 // wide Thread-SMR delete_lock.
499 if (ThreadsSMRSupport::delete_notify()) {
500 // An exiting thread might be waiting in smr_delete(); we need to
501 // check with delete_lock to be sure.
502 ThreadsSMRSupport::release_stable_list_wake_up(_has_ref_count);
503 }
504 }
505
506 // Verify that the stable hazard ptr used to safely keep threads
507 // alive is scanned by threads_do() which is a key piece of honoring
508 // the Thread-SMR protocol.
509 void SafeThreadsListPtr::verify_hazard_ptr_scanned() {
510 #ifdef ASSERT
511 assert(_list != NULL, "_list must not be NULL");
512
513 // The closure will attempt to verify that the calling thread can
514 // be found by threads_do() on the specified ThreadsList. If it
515 // is successful, then the specified ThreadsList was acquired as
516 // a stable hazard ptr by the calling thread in a way that honored
517 // the Thread-SMR protocol.
518 //
519 // If the calling thread cannot be found by threads_do() and if
520 // it is not the shutdown thread, then the calling thread is not
521 // honoring the Thread-SMR ptotocol. This means that the specified
522 // ThreadsList is not a stable hazard ptr and can be freed by
523 // another thread from the to-be-deleted list at any time.
524 //
525 // Note: The shutdown thread has removed itself from the Threads
526 // list and is safe to have a waiver from this check because
527 // VM_Exit::_shutdown_thread is not set until after the VMThread
528 // has started the final safepoint which holds the Threads_lock
529 // for the remainder of the VM's life.
530 //
531 VerifyHazardPtrThreadClosure cl(_thread);
532 ThreadsSMRSupport::threads_do(&cl, _list);
533
534 // If the calling thread is not honoring the Thread-SMR protocol,
535 // then we will either crash in threads_do() above because 'threads'
536 // was freed by another thread or we will fail the assert() below.
537 // In either case, we won't get past this point with a badly placed
538 // ThreadsListHandle.
539
540 assert(cl.found() || _thread == VM_Exit::shutdown_thread(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol.");
541 #endif
542 }
543
544 // 'entries + 1' so we always have at least one entry.
545 ThreadsList::ThreadsList(int entries) :
546 _length(entries),
547 _next_list(NULL),
548 _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)),
549 _nested_handle_cnt(0)
550 {
551 *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
552 }
553
554 ThreadsList::~ThreadsList() {
555 FREE_C_HEAP_ARRAY(JavaThread*, _threads);
556 }
557
558 // Add a JavaThread to a ThreadsList. The returned ThreadsList is a
559 // new copy of the specified ThreadsList with the specified JavaThread
560 // appended to the end.
561 ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) {
562 const uint index = list->_length;
563 const uint new_length = index + 1;
564 const uint head_length = index;
565 ThreadsList *const new_list = new ThreadsList(new_length);
566
567 if (head_length > 0) {
568 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
569 }
570 *(JavaThread**)(new_list->_threads + index) = java_thread;
571
572 return new_list;
573 }
574
575 void ThreadsList::dec_nested_handle_cnt() {
576 // The decrement needs to be MO_ACQ_REL. At the moment, the Atomic::dec
577 // backend on PPC does not yet conform to these requirements. Therefore
578 // the decrement is simulated with an Atomic::sub(1, &addr).
579 // Without this MO_ACQ_REL Atomic::dec simulation, the nested SMR mechanism
580 // is not generally safe to use.
581 Atomic::sub(1, &_nested_handle_cnt);
582 }
583
584 int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
585 if (target == NULL) {
586 return -1;
587 }
588 for (uint i = 0; i < length(); i++) {
589 if (target == thread_at(i)) {
590 return (int)i;
591 }
592 }
593 return -1;
594 }
595
596 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
597 for (uint i = 0; i < length(); i++) {
598 JavaThread* thread = thread_at(i);
599 oop tobj = thread->threadObj();
600 // Ignore the thread if it hasn't run yet, has exited
601 // or is starting to exit.
602 if (tobj != NULL && !thread->is_exiting() &&
603 java_tid == java_lang_Thread::thread_id(tobj)) {
604 // found a match
605 return thread;
606 }
607 }
608 return NULL;
609 }
610
611 void ThreadsList::inc_nested_handle_cnt() {
612 // The increment needs to be MO_SEQ_CST. At the moment, the Atomic::inc
613 // backend on PPC does not yet conform to these requirements. Therefore
614 // the increment is simulated with a load phi; cas phi + 1; loop.
615 // Without this MO_SEQ_CST Atomic::inc simulation, the nested SMR mechanism
616 // is not generally safe to use.
617 intx sample = OrderAccess::load_acquire(&_nested_handle_cnt);
618 for (;;) {
619 if (Atomic::cmpxchg(sample + 1, &_nested_handle_cnt, sample) == sample) {
620 return;
621 } else {
622 sample = OrderAccess::load_acquire(&_nested_handle_cnt);
623 }
624 }
625 }
626
627 bool ThreadsList::includes(const JavaThread * const p) const {
628 if (p == NULL) {
629 return false;
630 }
631 for (uint i = 0; i < length(); i++) {
632 if (thread_at(i) == p) {
633 return true;
634 }
635 }
636 return false;
637 }
638
639 // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a
640 // new copy of the specified ThreadsList with the specified JavaThread
641 // removed.
642 ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) {
643 assert(list->_length > 0, "sanity");
644
645 uint i = (uint)list->find_index_of_JavaThread(java_thread);
646 assert(i < list->_length, "did not find JavaThread on the list");
647 const uint index = i;
648 const uint new_length = list->_length - 1;
649 const uint head_length = index;
650 const uint tail_length = (new_length >= index) ? (new_length - index) : 0;
651 ThreadsList *const new_list = new ThreadsList(new_length);
652
653 if (head_length > 0) {
654 Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
655 }
656 if (tail_length > 0) {
657 Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length);
658 }
659
660 return new_list;
661 }
662
663 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list_ptr(self, /* acquire */ true) {
664 assert(self == Thread::current(), "sanity check");
665 if (EnableThreadSMRStatistics) {
666 _timer.start();
667 }
668 }
669
670 ThreadsListHandle::~ThreadsListHandle() {
671 if (EnableThreadSMRStatistics) {
672 _timer.stop();
673 uint millis = (uint)_timer.milliseconds();
674 ThreadsSMRSupport::update_tlh_stats(millis);
675 }
676 }
677
678 // Convert an internal thread reference to a JavaThread found on the
679 // associated ThreadsList. This ThreadsListHandle "protects" the
680 // returned JavaThread *.
681 //
682 // If thread_oop_p is not NULL, then the caller wants to use the oop
683 // after this call so the oop is returned. On success, *jt_pp is set
684 // to the converted JavaThread * and true is returned. On error,
685 // returns false.
686 //
687 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
688 JavaThread ** jt_pp,
689 oop * thread_oop_p) {
690 assert(this->list() != NULL, "must have a ThreadsList");
691 assert(jt_pp != NULL, "must have a return JavaThread pointer");
692 // thread_oop_p is optional so no assert()
693
694 // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI
695 // allows a NULL thread parameter to signify "current thread" which
696 // allows us to avoid calling cv_external_thread_to_JavaThread().
697 // The JVM_* interfaces have no such leeway.
698
699 oop thread_oop = JNIHandles::resolve_non_null(jthread);
700 // Looks like an oop at this point.
701 if (thread_oop_p != NULL) {
702 // Return the oop to the caller; the caller may still want
703 // the oop even if this function returns false.
704 *thread_oop_p = thread_oop;
705 }
706
707 JavaThread *java_thread = java_lang_Thread::thread(thread_oop);
708 if (java_thread == NULL) {
709 // The java.lang.Thread does not contain a JavaThread * so it has
710 // not yet run or it has died.
711 return false;
712 }
713 // Looks like a live JavaThread at this point.
714
715 if (java_thread != JavaThread::current()) {
716 // jthread is not for the current JavaThread so have to verify
717 // the JavaThread * against the ThreadsList.
718 if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) {
719 // Not on the JavaThreads list so it is not alive.
720 return false;
721 }
722 }
723
724 // Return a live JavaThread that is "protected" by the
725 // ThreadsListHandle in the caller.
726 *jt_pp = java_thread;
727 return true;
728 }
729
730 void ThreadsSMRSupport::add_thread(JavaThread *thread){
731 ThreadsList *new_list = ThreadsList::add_thread(get_java_thread_list(), thread);
732 if (EnableThreadSMRStatistics) {
733 inc_java_thread_list_alloc_cnt();
734 update_java_thread_list_max(new_list->length());
735 }
736 // Initial _java_thread_list will not generate a "Threads::add" mesg.
737 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
738
739 ThreadsList *old_list = xchg_java_thread_list(new_list);
740 free_list(old_list);
741 }
742
743 // set_delete_notify() and clear_delete_notify() are called
744 // under the protection of the delete_lock, but we also use an
745 // Atomic operation to ensure the memory update is seen earlier than
746 // when the delete_lock is dropped.
747 //
748 void ThreadsSMRSupport::clear_delete_notify() {
749 Atomic::dec(&_delete_notify);
750 }
751
752 bool ThreadsSMRSupport::delete_notify() {
753 // Use load_acquire() in order to see any updates to _delete_notify
754 // earlier than when delete_lock is grabbed.
755 return (OrderAccess::load_acquire(&_delete_notify) != 0);
756 }
757
758 // Safely free a ThreadsList after a Threads::add() or Threads::remove().
759 // The specified ThreadsList may not get deleted during this call if it
760 // is still in-use (referenced by a hazard ptr). Other ThreadsLists
761 // in the chain may get deleted by this call if they are no longer in-use.
762 void ThreadsSMRSupport::free_list(ThreadsList* threads) {
763 assert_locked_or_safepoint(Threads_lock);
764
765 threads->set_next_list(_to_delete_list);
766 _to_delete_list = threads;
767 if (EnableThreadSMRStatistics) {
768 _to_delete_list_cnt++;
769 if (_to_delete_list_cnt > _to_delete_list_max) {
770 _to_delete_list_max = _to_delete_list_cnt;
771 }
772 }
773
774 // Hash table size should be first power of two higher than twice the length of the ThreadsList
775 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
776 hash_table_size--;
777 hash_table_size |= hash_table_size >> 1;
778 hash_table_size |= hash_table_size >> 2;
779 hash_table_size |= hash_table_size >> 4;
780 hash_table_size |= hash_table_size >> 8;
781 hash_table_size |= hash_table_size >> 16;
782 hash_table_size++;
783
784 // Gather a hash table of the current hazard ptrs:
785 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
786 ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
787 threads_do(&scan_cl);
788 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
789 // nested reference counters
790
791 // Walk through the linked list of pending freeable ThreadsLists
792 // and free the ones that are not referenced from hazard ptrs.
793 ThreadsList* current = _to_delete_list;
794 ThreadsList* prev = NULL;
795 ThreadsList* next = NULL;
796 bool threads_is_freed = false;
797 while (current != NULL) {
798 next = current->next_list();
799 if (!scan_table->has_entry((void*)current) && current->_nested_handle_cnt == 0) {
800 // This ThreadsList is not referenced by a hazard ptr.
801 if (prev != NULL) {
802 prev->set_next_list(next);
803 }
804 if (_to_delete_list == current) {
805 _to_delete_list = next;
806 }
807
808 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current));
809 if (current == threads) threads_is_freed = true;
810 delete current;
811 if (EnableThreadSMRStatistics) {
812 _java_thread_list_free_cnt++;
813 _to_delete_list_cnt--;
814 }
815 } else {
816 prev = current;
817 }
818 current = next;
819 }
820
821 if (!threads_is_freed) {
822 // Only report "is not freed" on the original call to
823 // free_list() for this ThreadsList.
824 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads));
825 }
826
827 delete scan_table;
828 }
829
830 // Return true if the specified JavaThread is protected by a hazard
831 // pointer (ThreadsList reference). Otherwise, returns false.
832 //
833 bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) {
834 assert_locked_or_safepoint(Threads_lock);
835
836 // Hash table size should be first power of two higher than twice
837 // the length of the Threads list.
838 int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
839 hash_table_size--;
840 hash_table_size |= hash_table_size >> 1;
841 hash_table_size |= hash_table_size >> 2;
842 hash_table_size |= hash_table_size >> 4;
843 hash_table_size |= hash_table_size >> 8;
844 hash_table_size |= hash_table_size >> 16;
845 hash_table_size++;
846
847 // Gather a hash table of the JavaThreads indirectly referenced by
848 // hazard ptrs.
849 ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
850 ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table);
851 threads_do(&scan_cl);
852 OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
853 // nested reference counters
854
855 // Walk through the linked list of pending freeable ThreadsLists
856 // and include the ones that are currently in use by a nested
857 // ThreadsListHandle in the search set.
858 ThreadsList* current = _to_delete_list;
859 while (current != NULL) {
860 if (current->_nested_handle_cnt != 0) {
861 // 'current' is in use by a nested ThreadsListHandle so the hazard
862 // ptr is protecting all the JavaThreads on that ThreadsList.
863 AddThreadHazardPointerThreadClosure add_cl(scan_table);
864 current->threads_do(&add_cl);
865 }
866 current = current->next_list();
867 }
868
869 bool thread_is_protected = false;
870 if (scan_table->has_entry((void*)thread)) {
871 thread_is_protected = true;
872 }
873 delete scan_table;
874 return thread_is_protected;
875 }
876
877 // Wake up portion of the release stable ThreadsList protocol;
878 // uses the delete_lock().
879 //
880 void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) {
881 const char* log_str = is_nested ? "nested hazard ptr" : "regular hazard ptr";
882
883 // Note: delete_lock is held in smr_delete() for the entire
884 // hazard ptr search so that we do not lose this notify() if
885 // the exiting thread has to wait. That code path also holds
886 // Threads_lock (which was grabbed before delete_lock) so that
887 // threads_do() can be called. This means the system can't start a
888 // safepoint which means this thread can't take too long to get to
889 // a safepoint because of being blocked on delete_lock.
890 //
891 MonitorLockerEx ml(ThreadsSMRSupport::delete_lock(), Monitor::_no_safepoint_check_flag);
892 if (ThreadsSMRSupport::delete_notify()) {
893 // Notify any exiting JavaThreads that are waiting in smr_delete()
894 // that we've released a ThreadsList.
895 ml.notify_all();
896 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str);
897 }
898 }
899
900 void ThreadsSMRSupport::remove_thread(JavaThread *thread) {
901 ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_java_thread_list(), thread);
902 if (EnableThreadSMRStatistics) {
903 ThreadsSMRSupport::inc_java_thread_list_alloc_cnt();
904 // This list is smaller so no need to check for a "longest" update.
905 }
906
907 // Final _java_thread_list will not generate a "Threads::remove" mesg.
908 log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
909
910 ThreadsList *old_list = ThreadsSMRSupport::xchg_java_thread_list(new_list);
911 ThreadsSMRSupport::free_list(old_list);
912 }
913
914 // See note for clear_delete_notify().
915 //
916 void ThreadsSMRSupport::set_delete_notify() {
917 Atomic::inc(&_delete_notify);
918 }
919
920 // Safely delete a JavaThread when it is no longer in use by a
921 // ThreadsListHandle.
922 //
923 void ThreadsSMRSupport::smr_delete(JavaThread *thread) {
924 assert(!Threads_lock->owned_by_self(), "sanity");
925
926 bool has_logged_once = false;
927 elapsedTimer timer;
928 if (EnableThreadSMRStatistics) {
929 timer.start();
930 }
931
932 while (true) {
933 {
934 // No safepoint check because this JavaThread is not on the
935 // Threads list.
936 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
937 // Cannot use a MonitorLockerEx helper here because we have
938 // to drop the Threads_lock first if we wait.
939 ThreadsSMRSupport::delete_lock()->lock_without_safepoint_check();
940 // Set the delete_notify flag after we grab delete_lock
941 // and before we scan hazard ptrs because we're doing
942 // double-check locking in release_stable_list().
943 ThreadsSMRSupport::set_delete_notify();
944
945 if (!is_a_protected_JavaThread(thread)) {
946 // This is the common case.
947 ThreadsSMRSupport::clear_delete_notify();
948 ThreadsSMRSupport::delete_lock()->unlock();
949 break;
950 }
951 if (!has_logged_once) {
952 has_logged_once = true;
953 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread));
954 if (log_is_enabled(Debug, os, thread)) {
955 ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread);
956 threads_do(&scan_cl);
957 ThreadsList* current = _to_delete_list;
958 while (current != NULL) {
959 if (current->_nested_handle_cnt != 0 && current->includes(thread)) {
960 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: found nested hazard pointer to thread=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread));
961 }
962 current = current->next_list();
963 }
964 }
965 }
966 } // We have to drop the Threads_lock to wait or delete the thread
967
968 if (EnableThreadSMRStatistics) {
969 _delete_lock_wait_cnt++;
970 if (_delete_lock_wait_cnt > _delete_lock_wait_max) {
971 _delete_lock_wait_max = _delete_lock_wait_cnt;
972 }
973 }
974 // Wait for a release_stable_list() call before we check again. No
975 // safepoint check, no timeout, and not as suspend equivalent flag
976 // because this JavaThread is not on the Threads list.
977 ThreadsSMRSupport::delete_lock()->wait(Mutex::_no_safepoint_check_flag, 0,
978 !Mutex::_as_suspend_equivalent_flag);
979 if (EnableThreadSMRStatistics) {
980 _delete_lock_wait_cnt--;
981 }
982
983 ThreadsSMRSupport::clear_delete_notify();
984 ThreadsSMRSupport::delete_lock()->unlock();
985 // Retry the whole scenario.
986 }
987
988 delete thread;
989 if (EnableThreadSMRStatistics) {
990 timer.stop();
991 uint millis = (uint)timer.milliseconds();
992 ThreadsSMRSupport::inc_deleted_thread_cnt();
993 ThreadsSMRSupport::add_deleted_thread_times(millis);
994 ThreadsSMRSupport::update_deleted_thread_time_max(millis);
995 }
996
997 log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread));
998 }
999
1000 // Apply the closure to all threads in the system, with a snapshot of
1001 // all JavaThreads provided by the list parameter.
1002 void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) {
1003 list->threads_do(tc);
1004 Threads::non_java_threads_do(tc);
1005 }
1006
1007 // Apply the closure to all threads in the system.
1008 void ThreadsSMRSupport::threads_do(ThreadClosure *tc) {
1009 threads_do(tc, _java_thread_list);
1010 }
1011
1012
1013 // Debug, logging, and printing stuff at the end:
1014
1015 // Print SMR info for a SafeThreadsListPtr to a given output stream.
1016 void SafeThreadsListPtr::print_on(outputStream* st) {
1017 if (this == _thread->_threads_list_ptr) {
1018 // The top level hazard ptr.
1019 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1020 } else {
1021 // Nested hazard ptrs.
1022 st->print(", _nested_threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
1023 }
1024 }
1025
1026 // Log Threads class SMR info.
1027 void ThreadsSMRSupport::log_statistics() {
1028 LogTarget(Info, thread, smr) log;
1029 if (log.is_enabled()) {
1030 LogStream out(log);
1031 print_info_on(&out);
1032 }
1033 }
1034
1035 // Print SMR info for a thread to a given output stream.
1036 void ThreadsSMRSupport::print_info_on(const Thread* thread, outputStream* st) {
1037 if (thread->_threads_hazard_ptr != NULL) {
1038 st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(thread->_threads_hazard_ptr));
1039 }
1040 if (EnableThreadSMRStatistics && thread->_threads_list_ptr != NULL) {
1041 // The count is only interesting if we have a _threads_list_ptr.
1042 st->print(", _nested_threads_hazard_ptr_cnt=%u", thread->_nested_threads_hazard_ptr_cnt);
1043 }
1044 if (SafepointSynchronize::is_at_safepoint() || Thread::current() == thread) {
1045 // It is only safe to walk the list if we're at a safepoint or the
1046 // calling thread is walking its own list.
1047 SafeThreadsListPtr* current = thread->_threads_list_ptr;
1048 if (current != NULL) {
1049 // Skip the top nesting level as it is always printed above.
1050 current = current->previous();
1051 }
1052 while (current != NULL) {
1053 current->print_on(st);
1054 current = current->previous();
1055 }
1056 }
1057 }
1058
1059 // Print Threads class SMR info.
1060 void ThreadsSMRSupport::print_info_on(outputStream* st) {
1061 // Only grab the Threads_lock if we don't already own it and if we
1062 // are not reporting an error.
1063 // Note: Not grabbing the Threads_lock during error reporting is
1064 // dangerous because the data structures we want to print can be
1065 // freed concurrently. However, grabbing the Threads_lock during
1066 // error reporting can be equally dangerous since this thread might
1067 // block during error reporting or a nested error could leave the
1068 // Threads_lock held. The classic no win scenario.
1069 //
1070 MutexLockerEx ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock);
1071
1072 st->print_cr("Threads class SMR info:");
1073 st->print_cr("_java_thread_list=" INTPTR_FORMAT ", length=%u, "
1074 "elements={", p2i(_java_thread_list),
1075 _java_thread_list->length());
1076 print_info_elements_on(st, _java_thread_list);
1077 st->print_cr("}");
1078 if (_to_delete_list != NULL) {
1079 st->print_cr("_to_delete_list=" INTPTR_FORMAT ", length=%u, "
1080 "elements={", p2i(_to_delete_list),
1081 _to_delete_list->length());
1082 print_info_elements_on(st, _to_delete_list);
1083 st->print_cr("}");
1084 for (ThreadsList *t_list = _to_delete_list->next_list();
1085 t_list != NULL; t_list = t_list->next_list()) {
1086 st->print("next-> " INTPTR_FORMAT ", length=%u, "
1087 "elements={", p2i(t_list), t_list->length());
1088 print_info_elements_on(st, t_list);
1089 st->print_cr("}");
1090 }
1091 }
1092 if (!EnableThreadSMRStatistics) {
1093 return;
1094 }
1095 st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ", "
1096 "_java_thread_list_free_cnt=" UINT64_FORMAT ", "
1097 "_java_thread_list_max=%u, "
1098 "_nested_thread_list_max=%u",
1099 _java_thread_list_alloc_cnt,
1100 _java_thread_list_free_cnt,
1101 _java_thread_list_max,
1102 _nested_thread_list_max);
1103 if (_tlh_cnt > 0) {
1104 st->print_cr("_tlh_cnt=%u"
1105 ", _tlh_times=%u"
1106 ", avg_tlh_time=%0.2f"
1107 ", _tlh_time_max=%u",
1108 _tlh_cnt, _tlh_times,
1109 ((double) _tlh_times / _tlh_cnt),
1110 _tlh_time_max);
1111 }
1112 if (_deleted_thread_cnt > 0) {
1113 st->print_cr("_deleted_thread_cnt=%u"
1114 ", _deleted_thread_times=%u"
1115 ", avg_deleted_thread_time=%0.2f"
1116 ", _deleted_thread_time_max=%u",
1117 _deleted_thread_cnt, _deleted_thread_times,
1118 ((double) _deleted_thread_times / _deleted_thread_cnt),
1119 _deleted_thread_time_max);
1120 }
1121 st->print_cr("_delete_lock_wait_cnt=%u, _delete_lock_wait_max=%u",
1122 _delete_lock_wait_cnt, _delete_lock_wait_max);
1123 st->print_cr("_to_delete_list_cnt=%u, _to_delete_list_max=%u",
1124 _to_delete_list_cnt, _to_delete_list_max);
1125 }
1126
1127 // Print ThreadsList elements (4 per line).
1128 void ThreadsSMRSupport::print_info_elements_on(outputStream* st, ThreadsList* t_list) {
1129 uint cnt = 0;
1130 JavaThreadIterator jti(t_list);
1131 for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
1132 st->print(INTPTR_FORMAT, p2i(jt));
1133 if (cnt < t_list->length() - 1) {
1134 // Separate with comma or comma-space except for the last one.
1135 if (((cnt + 1) % 4) == 0) {
1136 // Four INTPTR_FORMAT fit on an 80 column line so end the
1137 // current line with just a comma.
1138 st->print_cr(",");
1139 } else {
1140 // Not the last one on the current line so use comma-space:
1141 st->print(", ");
1142 }
1143 } else {
1144 // Last one so just end the current line.
1145 st->cr();
1146 }
1147 cnt++;
1148 }
1149 }