1 /*
2 * Copyright (c) 1998, 2025, 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 "compiler/compileBroker.hpp"
26 #include "gc/shared/collectedHeap.hpp"
27 #include "gc/shared/vmThreadCpuTimeScope.inline.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "jfr/support/jfrThreadId.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logConfiguration.hpp"
32 #include "logging/logStream.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "oops/verifyOopClosure.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/cpuTimeCounters.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/javaThread.inline.hpp"
42 #include "runtime/jniHandles.hpp"
43 #include "runtime/mutexLocker.hpp"
44 #include "runtime/os.hpp"
45 #include "runtime/perfData.hpp"
46 #include "runtime/safepoint.hpp"
47 #include "runtime/synchronizer.hpp"
48 #include "runtime/timerTrace.hpp"
49 #include "runtime/vmOperations.hpp"
50 #include "runtime/vmThread.hpp"
51 #include "utilities/dtrace.hpp"
52 #include "utilities/events.hpp"
53 #include "utilities/vmError.hpp"
54
55
56 //------------------------------------------------------------------------------------------------------------------
57 // Timeout machinery
58
59 void VMOperationTimeoutTask::task() {
60 assert(AbortVMOnVMOperationTimeout, "only if enabled");
61 if (is_armed()) {
62 jlong delay = nanos_to_millis(os::javaTimeNanos() - _arm_time);
63 if (delay > AbortVMOnVMOperationTimeoutDelay) {
64 fatal("%s VM operation took too long: " JLONG_FORMAT " ms elapsed since VM-op start (timeout: %zd ms)",
65 _vm_op_name, delay, AbortVMOnVMOperationTimeoutDelay);
66 }
67 }
68 }
69
70 bool VMOperationTimeoutTask::is_armed() {
71 return Atomic::load_acquire(&_armed) != 0;
72 }
73
74 void VMOperationTimeoutTask::arm(const char* vm_op_name) {
75 _vm_op_name = vm_op_name;
76 _arm_time = os::javaTimeNanos();
77 Atomic::release_store_fence(&_armed, 1);
78 }
79
80 void VMOperationTimeoutTask::disarm() {
81 Atomic::release_store_fence(&_armed, 0);
82
83 // The two stores to `_armed` are counted in VM-op, but they should be
84 // insignificant compared to the actual VM-op duration.
85 jlong vm_op_duration = nanos_to_millis(os::javaTimeNanos() - _arm_time);
86
87 // Repeat the timeout-check logic on the VM thread, because
88 // VMOperationTimeoutTask might miss the arm-disarm window depending on
89 // the scheduling.
90 if (vm_op_duration > AbortVMOnVMOperationTimeoutDelay) {
91 fatal("%s VM operation took too long: completed in " JLONG_FORMAT " ms (timeout: %zd ms)",
92 _vm_op_name, vm_op_duration, AbortVMOnVMOperationTimeoutDelay);
93 }
94 _vm_op_name = nullptr;
95 }
96
97 //------------------------------------------------------------------------------------------------------------------
98 // Implementation of VMThread stuff
99
100 static VM_SafepointALot safepointALot_op;
101 static VM_ForceSafepoint no_op;
102
103 bool VMThread::_should_terminate = false;
104 bool VMThread::_terminated = false;
105 Monitor* VMThread::_terminate_lock = nullptr;
106 VMThread* VMThread::_vm_thread = nullptr;
107 VM_Operation* VMThread::_cur_vm_operation = nullptr;
108 VM_Operation* VMThread::_next_vm_operation = &no_op; // Prevent any thread from setting an operation until VM thread is ready.
109 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = nullptr;
110 VMOperationTimeoutTask* VMThread::_timeout_task = nullptr;
111
112
113 void VMThread::create() {
114 assert(vm_thread() == nullptr, "we can only allocate one VMThread");
115 _vm_thread = new VMThread();
116
117 if (AbortVMOnVMOperationTimeout) {
118 // Make sure we call the timeout task frequently enough, but not too frequent.
119 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
120 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
121 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
122 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
123 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
124 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
125
126 _timeout_task = new VMOperationTimeoutTask(interval);
127 _timeout_task->enroll();
128 } else {
129 assert(_timeout_task == nullptr, "sanity");
130 }
131
132 _terminate_lock = new Monitor(Mutex::nosafepoint, "VMThreadTerminate_lock");
133
134 if (UsePerfData) {
135 // jvmstat performance counters
136 JavaThread* THREAD = JavaThread::current(); // For exception macros.
137 _perf_accumulated_vm_operation_time =
138 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
139 PerfData::U_Ticks, CHECK);
140 CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::vm);
141 }
142 }
143
144 VMThread::VMThread() : NamedThread(), _is_running(false) {
145 set_name("VM Thread");
146 }
147
148 void VMThread::destroy() {
149 _vm_thread = nullptr; // VM thread is gone
150 }
151
152 static VM_Halt halt_op;
153
154 void VMThread::run() {
155 assert(this == vm_thread(), "check");
156
157 // Notify_lock wait checks on is_running() to rewait in
158 // case of spurious wakeup, it should wait on the last
159 // value set prior to the notify
160 Atomic::store(&_is_running, true);
161
162 {
163 MutexLocker ml(Notify_lock);
164 Notify_lock->notify();
165 }
166 // Notify_lock is destroyed by Threads::create_vm()
167
168 int prio = (VMThreadPriority == -1)
169 ? os::java_to_os_priority[NearMaxPriority]
170 : VMThreadPriority;
171 // Note that I cannot call os::set_priority because it expects Java
172 // priorities and I am *explicitly* using OS priorities so that it's
173 // possible to set the VM thread priority higher than any Java thread.
174 os::set_native_priority( this, prio );
175
176 // Wait for VM_Operations until termination
177 this->loop();
178
179 // Note the intention to exit before safepointing.
180 // 6295565 This has the effect of waiting for any large tty
181 // outputs to finish.
182 if (xtty != nullptr) {
183 ttyLocker ttyl;
184 xtty->begin_elem("destroy_vm");
185 xtty->stamp();
186 xtty->end_elem();
187 assert(should_terminate(), "termination flag must be set");
188 }
189
190 // 4526887 let VM thread exit at Safepoint
191 _cur_vm_operation = &halt_op;
192 SafepointSynchronize::begin();
193
194 if (VerifyBeforeExit) {
195 HandleMark hm(VMThread::vm_thread());
196 // Among other things, this ensures that Eden top is correct.
197 Universe::heap()->prepare_for_verify();
198 // Silent verification so as not to pollute normal output,
199 // unless we really asked for it.
200 Universe::verify();
201 }
202
203 CompileBroker::set_should_block();
204
205 // wait for threads (compiler threads or daemon threads) in the
206 // _thread_in_native state to block.
207 VM_Exit::wait_for_threads_in_native_to_block();
208
209 // The ObjectMonitor subsystem uses perf counters so do this before
210 // we signal that the VM thread is gone. We don't want to run afoul
211 // of perfMemory_exit() in exit_globals().
212 ObjectSynchronizer::do_final_audit_and_print_stats();
213
214 // signal other threads that VM process is gone
215 {
216 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
217 // VM thread to enter any lock at Safepoint as long as its _owner is null.
218 // If that happens after _terminate_lock->wait() has unset _owner
219 // but before it actually drops the lock and waits, the notification below
220 // may get lost and we will have a hang. To avoid this, we need to use
221 // Mutex::lock_without_safepoint_check().
222 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
223 _terminated = true;
224 ml.notify();
225 }
226
227 // We are now racing with the VM termination being carried out in
228 // another thread, so we don't "delete this". Numerous threads don't
229 // get deleted when the VM terminates
230
231 }
232
233
234 // Notify the VMThread that the last non-daemon JavaThread has terminated,
235 // and wait until operation is performed.
236 void VMThread::wait_for_vm_thread_exit() {
237 assert(JavaThread::current()->is_terminated(), "Should be terminated");
238 {
239 MonitorLocker mu(VMOperation_lock);
240 _should_terminate = true;
241 mu.notify_all();
242 }
243
244 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
245 // because this thread has been removed from the threads list. But anything
246 // that could get blocked by Safepoint should not be used after this point,
247 // otherwise we will hang, since there is no one can end the safepoint.
248
249 // Wait until VM thread is terminated
250 // Note: it should be OK to use Terminator_lock here. But this is called
251 // at a very delicate time (VM shutdown) and we are operating in non- VM
252 // thread at Safepoint. It's safer to not share lock with other threads.
253 {
254 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
255 while (!VMThread::is_terminated()) {
256 ml.wait();
257 }
258 }
259 }
260
261 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
262 assert(event != nullptr, "invariant");
263 assert(op != nullptr, "invariant");
264 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
265 event->set_operation(op->type());
266 event->set_safepoint(evaluate_at_safepoint);
267 event->set_blocking(true);
268 event->set_caller(JFR_THREAD_ID(op->calling_thread()));
269 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
270 event->commit();
271 }
272
273 void VMThread::evaluate_operation(VM_Operation* op) {
274 ResourceMark rm;
275
276 {
277 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
278 HOTSPOT_VMOPS_BEGIN(
279 (char*) op->name(), strlen(op->name()),
280 op->evaluate_at_safepoint() ? 0 : 1);
281
282 EventExecuteVMOperation event;
283 VMThreadCPUTimeScope CPUTimeScope(this, op->is_gc_operation());
284 op->evaluate();
285 if (event.should_commit()) {
286 post_vm_operation_event(&event, op);
287 }
288
289 HOTSPOT_VMOPS_END(
290 (char*) op->name(), strlen(op->name()),
291 op->evaluate_at_safepoint() ? 0 : 1);
292 }
293 }
294
295 class ALotOfHandshakeClosure : public HandshakeClosure {
296 public:
297 ALotOfHandshakeClosure() : HandshakeClosure("ALotOfHandshakeClosure") {}
298 void do_thread(Thread* thread) {
299 #ifdef ASSERT
300 JavaThread::cast(thread)->verify_states_for_handshake();
301 #endif
302 }
303 };
304
305 bool VMThread::handshake_or_safepoint_alot() {
306 assert(_cur_vm_operation == nullptr, "should not have an op yet");
307 assert(_next_vm_operation == nullptr, "should not have an op yet");
308 if (!HandshakeALot && !SafepointALot) {
309 return false;
310 }
311 static jlong last_alot_ms = 0;
312 jlong now_ms = nanos_to_millis(os::javaTimeNanos());
313 // If HandshakeALot or SafepointALot are set, but GuaranteedSafepointInterval is explicitly
314 // set to 0 on the command line, we emit the operation if it's been more than a second
315 // since the last one.
316 jlong interval = GuaranteedSafepointInterval != 0 ? GuaranteedSafepointInterval : 1000;
317 jlong deadline_ms = interval + last_alot_ms;
318 if (now_ms > deadline_ms) {
319 last_alot_ms = now_ms;
320 return true;
321 }
322 return false;
323 }
324
325 bool VMThread::set_next_operation(VM_Operation *op) {
326 if (_next_vm_operation != nullptr) {
327 return false;
328 }
329 log_debug(vmthread)("Adding VM operation: %s", op->name());
330
331 _next_vm_operation = op;
332
333 HOTSPOT_VMOPS_REQUEST(
334 (char *) op->name(), strlen(op->name()),
335 op->evaluate_at_safepoint() ? 0 : 1);
336 return true;
337 }
338
339 void VMThread::wait_until_executed(VM_Operation* op) {
340 MonitorLocker ml(VMOperation_lock,
341 Thread::current()->is_Java_thread() ?
342 Mutex::_safepoint_check_flag :
343 Mutex::_no_safepoint_check_flag);
344 {
345 TraceTime timer("Installing VM operation", TRACETIME_LOG(Trace, vmthread));
346 while (true) {
347 if (VMThread::vm_thread()->set_next_operation(op)) {
348 ml.notify_all();
349 break;
350 }
351 // Wait to install this operation as the next operation in the VM Thread
352 log_trace(vmthread)("A VM operation already set, waiting");
353 ml.wait();
354 }
355 }
356 {
357 // Wait until the operation has been processed
358 TraceTime timer("Waiting for VM operation to be completed", TRACETIME_LOG(Trace, vmthread));
359 // _next_vm_operation is cleared holding VMOperation_lock after it has been
360 // executed. We wait until _next_vm_operation is not our op.
361 while (_next_vm_operation == op) {
362 // VM Thread can process it once we unlock the mutex on wait.
363 ml.wait();
364 }
365 }
366 }
367
368 static void self_destruct_if_needed() {
369 // Support for self destruction
370 if ((SelfDestructTimer != 0.0) && !VMError::is_error_reported() &&
371 (os::elapsedTime() > SelfDestructTimer * 60.0)) {
372 tty->print_cr("VM self-destructed");
373 os::exit(-1);
374 }
375 }
376
377 void VMThread::inner_execute(VM_Operation* op) {
378 assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
379
380 VM_Operation* prev_vm_operation = nullptr;
381 if (_cur_vm_operation != nullptr) {
382 // Check that the VM operation allows nested VM operation.
383 // This is normally not the case, e.g., the compiler
384 // does not allow nested scavenges or compiles.
385 if (!_cur_vm_operation->allow_nested_vm_operations()) {
386 fatal("Unexpected nested VM operation %s requested by operation %s",
387 op->name(), _cur_vm_operation->name());
388 }
389 op->set_calling_thread(_cur_vm_operation->calling_thread());
390 prev_vm_operation = _cur_vm_operation;
391 }
392
393 _cur_vm_operation = op;
394
395 HandleMark hm(VMThread::vm_thread());
396
397 const char* const cause = op->cause();
398 stringStream ss;
399 ss.print("Executing%s%s VM operation: %s",
400 prev_vm_operation != nullptr ? " nested" : "",
401 op->evaluate_at_safepoint() ? " safepoint" : " non-safepoint",
402 op->name());
403 if (cause != nullptr) {
404 ss.print(" (%s)", cause);
405 }
406
407 EventMarkVMOperation em("%s", ss.freeze());
408 log_debug(vmthread)("%s", ss.freeze());
409
410 bool end_safepoint = false;
411 bool has_timeout_task = (_timeout_task != nullptr);
412 if (_cur_vm_operation->evaluate_at_safepoint() &&
413 !SafepointSynchronize::is_at_safepoint()) {
414 SafepointSynchronize::begin();
415 if (has_timeout_task) {
416 _timeout_task->arm(_cur_vm_operation->name());
417 }
418 end_safepoint = true;
419 }
420
421 evaluate_operation(_cur_vm_operation);
422
423 if (end_safepoint) {
424 if (has_timeout_task) {
425 _timeout_task->disarm();
426 }
427 SafepointSynchronize::end();
428 }
429
430 _cur_vm_operation = prev_vm_operation;
431 }
432
433 void VMThread::wait_for_operation() {
434 assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
435 MonitorLocker ml_op_lock(VMOperation_lock, Mutex::_no_safepoint_check_flag);
436
437 // Clear previous operation.
438 // On first call this clears a dummy place-holder.
439 _next_vm_operation = nullptr;
440 // Notify operation is done and notify a next operation can be installed.
441 ml_op_lock.notify_all();
442
443 while (!should_terminate()) {
444 self_destruct_if_needed();
445 if (_next_vm_operation != nullptr) {
446 return;
447 }
448 if (handshake_or_safepoint_alot()) {
449 if (HandshakeALot) {
450 MutexUnlocker mul(VMOperation_lock);
451 ALotOfHandshakeClosure aohc;
452 Handshake::execute(&aohc);
453 }
454 // When we unlocked above someone might have setup a new op.
455 if (_next_vm_operation != nullptr) {
456 return;
457 }
458 if (SafepointALot) {
459 _next_vm_operation = &safepointALot_op;
460 return;
461 }
462 }
463 assert(_next_vm_operation == nullptr, "Must be");
464 assert(_cur_vm_operation == nullptr, "Must be");
465
466 // We didn't find anything to execute, notify any waiter so they can install an op.
467 ml_op_lock.notify_all();
468 ml_op_lock.wait(GuaranteedSafepointInterval);
469 }
470 }
471
472 void VMThread::loop() {
473 assert(_cur_vm_operation == nullptr, "no current one should be executing");
474
475 SafepointSynchronize::init(_vm_thread);
476
477 // Need to set a calling thread for ops not passed
478 // via the normal way.
479 no_op.set_calling_thread(_vm_thread);
480 safepointALot_op.set_calling_thread(_vm_thread);
481
482 while (true) {
483 if (should_terminate()) break;
484 wait_for_operation();
485 if (should_terminate()) break;
486 assert(_next_vm_operation != nullptr, "Must have one");
487 inner_execute(_next_vm_operation);
488 }
489 }
490
491 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
492 // over a section of execution by a thread. Currently, it's used only to
493 // prevent re-entrant calls to GC.
494 class SkipGCALot : public StackObj {
495 private:
496 bool _saved;
497 Thread* _t;
498
499 public:
500 #ifdef ASSERT
501 SkipGCALot(Thread* t) : _t(t) {
502 _saved = _t->skip_gcalot();
503 _t->set_skip_gcalot(true);
504 }
505
506 ~SkipGCALot() {
507 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
508 _t->set_skip_gcalot(_saved);
509 }
510 #else
511 SkipGCALot(Thread* t) { }
512 ~SkipGCALot() { }
513 #endif
514 };
515
516 void VMThread::execute(VM_Operation* op) {
517 Thread* t = Thread::current();
518
519 if (t->is_VM_thread()) {
520 op->set_calling_thread(t);
521 ((VMThread*)t)->inner_execute(op);
522 return;
523 }
524
525 // The current thread must not belong to the SuspendibleThreadSet, because an
526 // on-the-fly safepoint can be waiting for the current thread, and the
527 // current thread will be blocked in wait_until_executed, resulting in
528 // deadlock.
529 assert(!t->is_suspendible_thread(), "precondition");
530 assert(!t->is_indirectly_suspendible_thread(), "precondition");
531
532 // Avoid re-entrant attempts to gc-a-lot
533 SkipGCALot sgcalot(t);
534
535 // JavaThread or WatcherThread
536 if (t->is_Java_thread()) {
537 JavaThread::cast(t)->check_for_valid_safepoint_state();
538 }
539
540 // New request from Java thread, evaluate prologue
541 if (!op->doit_prologue()) {
542 return; // op was cancelled
543 }
544
545 op->set_calling_thread(t);
546
547 wait_until_executed(op);
548
549 op->doit_epilogue();
550 }
551
552 void VMThread::verify() {
553 oops_do(&VerifyOopClosure::verify_oop, nullptr);
554 }