1 /*
2 * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2021, Azul Systems, Inc. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "cds/cdsConfig.hpp"
27 #include "classfile/javaClasses.hpp"
28 #include "classfile/javaThreadStatus.hpp"
29 #include "gc/shared/barrierSet.hpp"
30 #include "jfr/jfrEvents.hpp"
31 #include "jvm.h"
32 #include "jvmtifiles/jvmtiEnv.hpp"
33 #include "logging/log.hpp"
34 #include "memory/allocation.inline.hpp"
35 #include "memory/iterator.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "nmt/memTracker.hpp"
38 #include "oops/oop.inline.hpp"
39 #include "runtime/atomic.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/javaThread.inline.hpp"
42 #include "runtime/nonJavaThread.hpp"
43 #include "runtime/orderAccess.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/safepoint.hpp"
46 #include "runtime/safepointMechanism.inline.hpp"
47 #include "runtime/thread.inline.hpp"
48 #include "runtime/threadSMR.inline.hpp"
49 #include "utilities/macros.hpp"
50 #include "utilities/spinYield.hpp"
51 #if INCLUDE_JFR
52 #include "jfr/jfr.hpp"
53 #endif
54
55 #ifndef USE_LIBRARY_BASED_TLS_ONLY
56 // Current thread is maintained as a thread-local variable
57 THREAD_LOCAL Thread* Thread::_thr_current = nullptr;
58 #endif
59
60 // ======= Thread ========
61 // Base class for all threads: VMThread, WatcherThread, ConcurrentMarkSweepThread,
62 // JavaThread
63
64 Thread::Thread(MemTag mem_tag) {
65
66 DEBUG_ONLY(_run_state = PRE_CALL_RUN;)
67
68 // stack and get_thread
69 set_stack_base(nullptr);
70 set_stack_size(0);
71 set_lgrp_id(-1);
72 DEBUG_ONLY(clear_suspendible_thread();)
73 DEBUG_ONLY(clear_indirectly_suspendible_thread();)
74 DEBUG_ONLY(clear_indirectly_safepoint_thread();)
75
76 // allocated data structures
77 set_osthread(nullptr);
78 set_resource_area(new (mem_tag) ResourceArea(mem_tag));
79 DEBUG_ONLY(_current_resource_mark = nullptr;)
80 set_handle_area(new (mem_tag) HandleArea(mem_tag, nullptr));
81 set_metadata_handles(new (mtClass) GrowableArray<Metadata*>(30, mtClass));
82 set_last_handle_mark(nullptr);
83
84 // Initial value of zero ==> never claimed.
85 _threads_do_token = 0;
86 _threads_hazard_ptr = nullptr;
87 _threads_list_ptr = nullptr;
88 _nested_threads_hazard_ptr_cnt = 0;
89 _rcu_counter = 0;
90
91 // the handle mark links itself to last_handle_mark
92 new HandleMark(this);
93
94 // plain initialization
95 debug_only(_owned_locks = nullptr;)
96 NOT_PRODUCT(_skip_gcalot = false;)
97 _jvmti_env_iteration_count = 0;
98 set_allocated_bytes(0);
99 _current_pending_raw_monitor = nullptr;
100 _vm_error_callbacks = nullptr;
101
102 // thread-specific hashCode stream generator state - Marsaglia shift-xor form
103 // If we are dumping, keep ihashes constant. Note that during dumping we only
104 // ever run one java thread, and no other thread should generate ihashes either,
105 // so using a constant seed should work fine.
106 _hashStateX = CDSConfig::is_dumping_static_archive() ? 0x12345678 : os::random();
107 _hashStateY = 842502087;
108 _hashStateZ = 0x8767; // (int)(3579807591LL & 0xffff) ;
109 _hashStateW = 273326509;
110
111 // Many of the following fields are effectively final - immutable
112 // Note that nascent threads can't use the Native Monitor-Mutex
113 // construct until the _MutexEvent is initialized ...
114 // CONSIDER: instead of using a fixed set of purpose-dedicated ParkEvents
115 // we might instead use a stack of ParkEvents that we could provision on-demand.
116 // The stack would act as a cache to avoid calls to ParkEvent::Allocate()
117 // and ::Release()
118 _ParkEvent = ParkEvent::Allocate(this);
119
120 #ifdef CHECK_UNHANDLED_OOPS
121 if (CheckUnhandledOops) {
122 _unhandled_oops = new UnhandledOops(this);
123 }
124 #endif // CHECK_UNHANDLED_OOPS
125
126 // Notify the barrier set that a thread is being created. The initial
127 // thread is created before the barrier set is available. The call to
128 // BarrierSet::on_thread_create() for this thread is therefore deferred
129 // to BarrierSet::set_barrier_set().
130 BarrierSet* const barrier_set = BarrierSet::barrier_set();
131 if (barrier_set != nullptr) {
132 barrier_set->on_thread_create(this);
133 } else {
134 // Only the main thread should be created before the barrier set
135 // and that happens just before Thread::current is set. No other thread
136 // can attach as the VM is not created yet, so they can't execute this code.
137 // If the main thread creates other threads before the barrier set that is an error.
138 assert(Thread::current_or_null() == nullptr, "creating thread before barrier set");
139 }
140
141 MACOS_AARCH64_ONLY(DEBUG_ONLY(_wx_init = false));
142 }
143
144 #ifdef ASSERT
145 address Thread::stack_base() const {
146 // Note: can't report Thread::name() here as that can require a ResourceMark which we
147 // can't use because this gets called too early in the thread initialization.
148 assert(_stack_base != nullptr, "Stack base not yet set for thread id:%d (0 if not set)",
149 osthread() != nullptr ? osthread()->thread_id() : 0);
150 return _stack_base;
151 }
152 #endif
153
154 void Thread::initialize_tlab() {
155 if (UseTLAB) {
156 tlab().initialize();
157 }
158 }
159
160 void Thread::initialize_thread_current() {
161 #ifndef USE_LIBRARY_BASED_TLS_ONLY
162 assert(_thr_current == nullptr, "Thread::current already initialized");
163 _thr_current = this;
164 #endif
165 assert(ThreadLocalStorage::thread() == nullptr, "ThreadLocalStorage::thread already initialized");
166 ThreadLocalStorage::set_thread(this);
167 assert(Thread::current() == ThreadLocalStorage::thread(), "TLS mismatch!");
168 }
169
170 void Thread::clear_thread_current() {
171 assert(Thread::current() == ThreadLocalStorage::thread(), "TLS mismatch!");
172 #ifndef USE_LIBRARY_BASED_TLS_ONLY
173 _thr_current = nullptr;
174 #endif
175 ThreadLocalStorage::set_thread(nullptr);
176 }
177
178 void Thread::record_stack_base_and_size() {
179 // Note: at this point, Thread object is not yet initialized. Do not rely on
180 // any members being initialized. Do not rely on Thread::current() being set.
181 // If possible, refrain from doing anything which may crash or assert since
182 // quite probably those crash dumps will be useless.
183 address base;
184 size_t size;
185 os::current_stack_base_and_size(&base, &size);
186 set_stack_base(base);
187 set_stack_size(size);
188
189 // Set stack limits after thread is initialized.
190 if (is_Java_thread()) {
191 JavaThread::cast(this)->stack_overflow_state()->initialize(stack_base(), stack_end());
192 }
193 }
194
195 void Thread::register_thread_stack_with_NMT() {
196 MemTracker::record_thread_stack(stack_end(), stack_size());
197 }
198
199 void Thread::unregister_thread_stack_with_NMT() {
200 MemTracker::release_thread_stack(stack_end(), stack_size());
201 }
202
203 void Thread::call_run() {
204 DEBUG_ONLY(_run_state = CALL_RUN;)
205
206 // At this point, Thread object should be fully initialized and
207 // Thread::current() should be set.
208
209 assert(Thread::current_or_null() != nullptr, "current thread is unset");
210 assert(Thread::current_or_null() == this, "current thread is wrong");
211
212 // Perform common initialization actions
213
214 MACOS_AARCH64_ONLY(this->init_wx());
215
216 register_thread_stack_with_NMT();
217
218 JFR_ONLY(Jfr::on_thread_start(this);)
219
220 log_debug(os, thread)("Thread %zu stack dimensions: "
221 PTR_FORMAT "-" PTR_FORMAT " (%zuk).",
222 os::current_thread_id(), p2i(stack_end()),
223 p2i(stack_base()), stack_size()/1024);
224
225 // Perform <ChildClass> initialization actions
226 DEBUG_ONLY(_run_state = PRE_RUN;)
227 this->pre_run();
228
229 // Invoke <ChildClass>::run()
230 DEBUG_ONLY(_run_state = RUN;)
231 this->run();
232 // Returned from <ChildClass>::run(). Thread finished.
233
234 // Perform common tear-down actions
235
236 assert(Thread::current_or_null() != nullptr, "current thread is unset");
237 assert(Thread::current_or_null() == this, "current thread is wrong");
238
239 // Perform <ChildClass> tear-down actions
240 DEBUG_ONLY(_run_state = POST_RUN;)
241 this->post_run();
242
243 // Note: at this point the thread object may already have deleted itself,
244 // so from here on do not dereference *this*. Not all thread types currently
245 // delete themselves when they terminate. But no thread should ever be deleted
246 // asynchronously with respect to its termination - that is what _run_state can
247 // be used to check.
248
249 // Logically we should do this->unregister_thread_stack_with_NMT() here, but we
250 // had to move that into post_run() because of the `this` deletion issue.
251
252 assert(Thread::current_or_null() == nullptr, "current thread still present");
253 }
254
255 Thread::~Thread() {
256
257 // Attached threads will remain in PRE_CALL_RUN, as will threads that don't actually
258 // get started due to errors etc. Any active thread should at least reach post_run
259 // before it is deleted (usually in post_run()).
260 assert(_run_state == PRE_CALL_RUN ||
261 _run_state == POST_RUN, "Active Thread deleted before post_run(): "
262 "_run_state=%d", (int)_run_state);
263
264 // Notify the barrier set that a thread is being destroyed. Note that a barrier
265 // set might not be available if we encountered errors during bootstrapping.
266 BarrierSet* const barrier_set = BarrierSet::barrier_set();
267 if (barrier_set != nullptr) {
268 barrier_set->on_thread_destroy(this);
269 }
270
271 // deallocate data structures
272 delete resource_area();
273 // since the handle marks are using the handle area, we have to deallocated the root
274 // handle mark before deallocating the thread's handle area,
275 assert(last_handle_mark() != nullptr, "check we have an element");
276 delete last_handle_mark();
277 assert(last_handle_mark() == nullptr, "check we have reached the end");
278
279 ParkEvent::Release(_ParkEvent);
280 // Set to null as a termination indicator for has_terminated().
281 Atomic::store(&_ParkEvent, (ParkEvent*)nullptr);
282
283 delete handle_area();
284 delete metadata_handles();
285
286 // osthread() can be null, if creation of thread failed.
287 if (osthread() != nullptr) os::free_thread(osthread());
288
289 // Clear Thread::current if thread is deleting itself and it has not
290 // already been done. This must be done before the memory is deallocated.
291 // Needed to ensure JNI correctly detects non-attached threads.
292 if (this == Thread::current_or_null()) {
293 Thread::clear_thread_current();
294 }
295
296 CHECK_UNHANDLED_OOPS_ONLY(if (CheckUnhandledOops) delete unhandled_oops();)
297 }
298
299 #ifdef ASSERT
300 // A JavaThread is considered dangling if it not handshake-safe with respect to
301 // the current thread, it is not on a ThreadsList, or not at safepoint.
302 void Thread::check_for_dangling_thread_pointer(Thread *thread) {
303 assert(!thread->is_Java_thread() ||
304 JavaThread::cast(thread)->is_handshake_safe_for(Thread::current()) ||
305 !JavaThread::cast(thread)->on_thread_list() ||
306 SafepointSynchronize::is_at_safepoint() ||
307 ThreadsSMRSupport::is_a_protected_JavaThread_with_lock(JavaThread::cast(thread)),
308 "possibility of dangling Thread pointer");
309 }
310 #endif
311
312 // Is the target JavaThread protected by the calling Thread or by some other
313 // mechanism?
314 //
315 bool Thread::is_JavaThread_protected(const JavaThread* target) {
316 Thread* current_thread = Thread::current();
317
318 // Do the simplest check first:
319 if (SafepointSynchronize::is_at_safepoint()) {
320 // The target is protected since JavaThreads cannot exit
321 // while we're at a safepoint.
322 return true;
323 }
324
325 // If the target hasn't been started yet then it is trivially
326 // "protected". We assume the caller is the thread that will do
327 // the starting.
328 if (target->osthread() == nullptr || target->osthread()->get_state() <= INITIALIZED) {
329 return true;
330 }
331
332 // Now make the simple checks based on who the caller is:
333 if (current_thread == target || Threads_lock->owner() == current_thread) {
334 // Target JavaThread is self or calling thread owns the Threads_lock.
335 // Second check is the same as Threads_lock->owner_is_self(),
336 // but we already have the current thread so check directly.
337 return true;
338 }
339
340 // Check the ThreadsLists associated with the calling thread (if any)
341 // to see if one of them protects the target JavaThread:
342 if (is_JavaThread_protected_by_TLH(target)) {
343 return true;
344 }
345
346 // Use this debug code with -XX:+UseNewCode to diagnose locations that
347 // are missing a ThreadsListHandle or other protection mechanism:
348 // guarantee(!UseNewCode, "current_thread=" INTPTR_FORMAT " is not protecting target="
349 // INTPTR_FORMAT, p2i(current_thread), p2i(target));
350
351 // Note: Since 'target' isn't protected by a TLH, the call to
352 // target->is_handshake_safe_for() may crash, but we have debug bits so
353 // we'll be able to figure out what protection mechanism is missing.
354 assert(target->is_handshake_safe_for(current_thread), "JavaThread=" INTPTR_FORMAT
355 " is not protected and not handshake safe.", p2i(target));
356
357 // The target JavaThread is not protected so it is not safe to query:
358 return false;
359 }
360
361 // Is the target JavaThread protected by a ThreadsListHandle (TLH) associated
362 // with the calling Thread?
363 //
364 bool Thread::is_JavaThread_protected_by_TLH(const JavaThread* target) {
365 Thread* current_thread = Thread::current();
366
367 // Check the ThreadsLists associated with the calling thread (if any)
368 // to see if one of them protects the target JavaThread:
369 for (SafeThreadsListPtr* stlp = current_thread->_threads_list_ptr;
370 stlp != nullptr; stlp = stlp->previous()) {
371 if (stlp->list()->includes(target)) {
372 // The target JavaThread is protected by this ThreadsList:
373 return true;
374 }
375 }
376
377 // The target JavaThread is not protected by a TLH so it is not safe to query:
378 return false;
379 }
380
381 void Thread::set_priority(Thread* thread, ThreadPriority priority) {
382 debug_only(check_for_dangling_thread_pointer(thread);)
383 // Can return an error!
384 (void)os::set_priority(thread, priority);
385 }
386
387
388 void Thread::start(Thread* thread) {
389 // Start is different from resume in that its safety is guaranteed by context or
390 // being called from a Java method synchronized on the Thread object.
391 if (thread->is_Java_thread()) {
392 // Initialize the thread state to RUNNABLE before starting this thread.
393 // Can not set it after the thread started because we do not know the
394 // exact thread state at that time. It could be in MONITOR_WAIT or
395 // in SLEEPING or some other state.
396 java_lang_Thread::set_thread_status(JavaThread::cast(thread)->threadObj(),
397 JavaThreadStatus::RUNNABLE);
398 }
399 os::start_thread(thread);
400 }
401
402 // GC Support
403 bool Thread::claim_par_threads_do(uintx claim_token) {
404 uintx token = _threads_do_token;
405 if (token != claim_token) {
406 uintx res = Atomic::cmpxchg(&_threads_do_token, token, claim_token);
407 if (res == token) {
408 return true;
409 }
410 guarantee(res == claim_token, "invariant");
411 }
412 return false;
413 }
414
415 void Thread::oops_do_no_frames(OopClosure* f, NMethodClosure* cf) {
416 // Do oop for ThreadShadow
417 f->do_oop((oop*)&_pending_exception);
418 handle_area()->oops_do(f);
419 }
420
421 // If the caller is a NamedThread, then remember, in the current scope,
422 // the given JavaThread in its _processed_thread field.
423 class RememberProcessedThread: public StackObj {
424 NamedThread* _cur_thr;
425 public:
426 RememberProcessedThread(Thread* thread) {
427 Thread* self = Thread::current();
428 if (self->is_Named_thread()) {
429 _cur_thr = (NamedThread *)self;
430 assert(_cur_thr->processed_thread() == nullptr, "nesting not supported");
431 _cur_thr->set_processed_thread(thread);
432 } else {
433 _cur_thr = nullptr;
434 }
435 }
436
437 ~RememberProcessedThread() {
438 if (_cur_thr) {
439 assert(_cur_thr->processed_thread() != nullptr, "nesting not supported");
440 _cur_thr->set_processed_thread(nullptr);
441 }
442 }
443 };
444
445 void Thread::oops_do(OopClosure* f, NMethodClosure* cf) {
446 // Record JavaThread to GC thread
447 RememberProcessedThread rpt(this);
448 oops_do_no_frames(f, cf);
449 oops_do_frames(f, cf);
450 }
451
452 void Thread::metadata_handles_do(void f(Metadata*)) {
453 // Only walk the Handles in Thread.
454 if (metadata_handles() != nullptr) {
455 for (int i = 0; i< metadata_handles()->length(); i++) {
456 f(metadata_handles()->at(i));
457 }
458 }
459 }
460
461 void Thread::print_on(outputStream* st, bool print_extended_info) const {
462 // get_priority assumes osthread initialized
463 if (osthread() != nullptr) {
464 int os_prio;
465 if (os::get_native_priority(this, &os_prio) == OS_OK) {
466 st->print("os_prio=%d ", os_prio);
467 }
468
469 st->print("cpu=%.2fms ",
470 (double)os::thread_cpu_time(const_cast<Thread*>(this), true) / 1000000.0
471 );
472 st->print("elapsed=%.2fs ",
473 (double)_statistical_info.getElapsedTime() / 1000.0
474 );
475 if (is_Java_thread() && (PrintExtendedThreadInfo || print_extended_info)) {
476 size_t allocated_bytes = (size_t) const_cast<Thread*>(this)->cooked_allocated_bytes();
477 st->print("allocated=%zu%s ",
478 byte_size_in_proper_unit(allocated_bytes),
479 proper_unit_for_byte_size(allocated_bytes)
480 );
481 st->print("defined_classes=" INT64_FORMAT " ", _statistical_info.getDefineClassCount());
482 }
483
484 st->print("tid=" INTPTR_FORMAT " ", p2i(this));
485 if (!is_Java_thread() || !JavaThread::cast(this)->is_vthread_mounted()) {
486 osthread()->print_on(st);
487 }
488 }
489 ThreadsSMRSupport::print_info_on(this, st);
490 st->print(" ");
491 debug_only(if (WizardMode) print_owned_locks_on(st);)
492 }
493
494 void Thread::print() const { print_on(tty); }
495
496 // Thread::print_on_error() is called by fatal error handler. Don't use
497 // any lock or allocate memory.
498 void Thread::print_on_error(outputStream* st, char* buf, int buflen) const {
499 assert(!(is_Compiler_thread() || is_Java_thread()), "Can't call name() here if it allocates");
500
501 st->print("%s \"%s\"", type_name(), name());
502
503 OSThread* os_thr = osthread();
504 if (os_thr != nullptr) {
505 st->fill_to(67);
506 if (os_thr->get_state() != ZOMBIE) {
507 // Use raw field members for stack base/size as this could be
508 // called before a thread has run enough to initialize them.
509 st->print(" [id=%d, stack(" PTR_FORMAT "," PTR_FORMAT ") (" PROPERFMT ")]",
510 osthread()->thread_id(), p2i(_stack_base - _stack_size), p2i(_stack_base),
511 PROPERFMTARGS(_stack_size));
512 } else {
513 st->print(" terminated");
514 }
515 } else {
516 st->print(" unknown state (no osThread)");
517 }
518 ThreadsSMRSupport::print_info_on(this, st);
519 }
520
521 void Thread::print_value_on(outputStream* st) const {
522 if (is_Named_thread()) {
523 st->print(" \"%s\" ", name());
524 }
525 st->print(INTPTR_FORMAT, p2i(this)); // print address
526 }
527
528 #ifdef ASSERT
529 void Thread::print_owned_locks_on(outputStream* st) const {
530 Mutex* cur = _owned_locks;
531 if (cur == nullptr) {
532 st->print(" (no locks) ");
533 } else {
534 st->print_cr(" Locks owned:");
535 while (cur) {
536 cur->print_on(st);
537 cur = cur->next();
538 }
539 }
540 }
541
542 Thread* Thread::_starting_thread = nullptr;
543
544 bool Thread::is_starting_thread(const Thread* t) {
545 assert(_starting_thread != nullptr, "invariant");
546 return t == _starting_thread;
547 }
548 #endif // ASSERT
549
550 bool Thread::set_as_starting_thread(JavaThread* jt) {
551 assert(jt != nullptr, "invariant");
552 assert(_starting_thread == nullptr, "already initialized: "
553 "_starting_thread=" INTPTR_FORMAT, p2i(_starting_thread));
554 // NOTE: this must be called from Threads::create_vm().
555 DEBUG_ONLY(_starting_thread = jt;)
556 return os::create_main_thread(jt);
557 }
558
559 // Ad-hoc mutual exclusion primitive: spin lock
560 //
561 // We employ a spin lock _only for low-contention, fixed-length
562 // short-duration critical sections where we're concerned
563 // about native mutex_t or HotSpot Mutex:: latency.
564
565 void Thread::SpinAcquire(volatile int * adr, const char * LockName) {
566 if (Atomic::cmpxchg(adr, 0, 1) == 0) {
567 return; // normal fast-path return
568 }
569
570 // Slow-path : We've encountered contention -- Spin/Yield/Block strategy.
571 int ctr = 0;
572 int Yields = 0;
573 for (;;) {
574 while (*adr != 0) {
575 ++ctr;
576 if ((ctr & 0xFFF) == 0 || !os::is_MP()) {
577 if (Yields > 5) {
578 os::naked_short_sleep(1);
579 } else {
580 os::naked_yield();
581 ++Yields;
582 }
583 } else {
584 SpinPause();
585 }
586 }
587 if (Atomic::cmpxchg(adr, 0, 1) == 0) return;
588 }
589 }
590
591 void Thread::SpinRelease(volatile int * adr) {
592 assert(*adr != 0, "invariant");
593 OrderAccess::fence(); // guarantee at least release consistency.
594 // Roach-motel semantics.
595 // It's safe if subsequent LDs and STs float "up" into the critical section,
596 // but prior LDs and STs within the critical section can't be allowed
597 // to reorder or float past the ST that releases the lock.
598 // Loads and stores in the critical section - which appear in program
599 // order before the store that releases the lock - must also appear
600 // before the store that releases the lock in memory visibility order.
601 // Conceptually we need a #loadstore|#storestore "release" MEMBAR before
602 // the ST of 0 into the lock-word which releases the lock, so fence
603 // more than covers this on all platforms.
604 *adr = 0;
605 }