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