1 /*
2 * Copyright (c) 1998, 2024, 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 "compiler/compileBroker.hpp"
27 #include "gc/shared/collectedHeap.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "jfr/support/jfrThreadId.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logStream.hpp"
32 #include "logging/logConfiguration.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/vmThread.hpp"
50 #include "runtime/vmOperations.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: " INTX_FORMAT " 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: " INTX_FORMAT " 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 op->evaluate();
284 if (event.should_commit()) {
285 post_vm_operation_event(&event, op);
286 }
287
288 HOTSPOT_VMOPS_END(
289 (char *) op->name(), strlen(op->name()),
290 op->evaluate_at_safepoint() ? 0 : 1);
291 }
292
293 if (UsePerfData && os::is_thread_cpu_time_supported()) {
294 assert(Thread::current() == this, "Must be called from VM thread");
295 // Update vm_thread_cpu_time after each VM operation.
296 ThreadTotalCPUTimeClosure tttc(CPUTimeGroups::CPUTimeType::vm);
297 tttc.do_thread(this);
298 }
299 }
300
301 class HandshakeALotClosure : public HandshakeClosure {
302 public:
303 HandshakeALotClosure() : HandshakeClosure("HandshakeALot") {}
304 void do_thread(Thread* thread) {
305 #ifdef ASSERT
306 JavaThread::cast(thread)->verify_states_for_handshake();
307 #endif
308 }
309 };
310
311 bool VMThread::handshake_or_safepoint_alot() {
312 assert(_cur_vm_operation == nullptr, "should not have an op yet");
313 assert(_next_vm_operation == nullptr, "should not have an op yet");
314 if (!HandshakeALot && !SafepointALot) {
315 return false;
316 }
317 static jlong last_alot_ms = 0;
318 jlong now_ms = nanos_to_millis(os::javaTimeNanos());
319 // If HandshakeALot or SafepointALot are set, but GuaranteedSafepointInterval is explicitly
320 // set to 0 on the command line, we emit the operation if it's been more than a second
321 // since the last one.
322 jlong interval = GuaranteedSafepointInterval != 0 ? GuaranteedSafepointInterval : 1000;
323 jlong deadline_ms = interval + last_alot_ms;
324 if (now_ms > deadline_ms) {
325 last_alot_ms = now_ms;
326 return true;
327 }
328 return false;
329 }
330
331 bool VMThread::set_next_operation(VM_Operation *op) {
332 if (_next_vm_operation != nullptr) {
333 return false;
334 }
335 log_debug(vmthread)("Adding VM operation: %s", op->name());
336
337 _next_vm_operation = op;
338
339 HOTSPOT_VMOPS_REQUEST(
340 (char *) op->name(), strlen(op->name()),
341 op->evaluate_at_safepoint() ? 0 : 1);
342 return true;
343 }
344
345 void VMThread::wait_until_executed(VM_Operation* op) {
346 MonitorLocker ml(VMOperation_lock,
347 Thread::current()->is_Java_thread() ?
348 Mutex::_safepoint_check_flag :
349 Mutex::_no_safepoint_check_flag);
350 {
351 TraceTime timer("Installing VM operation", TRACETIME_LOG(Trace, vmthread));
352 while (true) {
353 if (VMThread::vm_thread()->set_next_operation(op)) {
354 ml.notify_all();
355 break;
356 }
357 // Wait to install this operation as the next operation in the VM Thread
358 log_trace(vmthread)("A VM operation already set, waiting");
359 ml.wait();
360 }
361 }
362 {
363 // Wait until the operation has been processed
364 TraceTime timer("Waiting for VM operation to be completed", TRACETIME_LOG(Trace, vmthread));
365 // _next_vm_operation is cleared holding VMOperation_lock after it has been
366 // executed. We wait until _next_vm_operation is not our op.
367 while (_next_vm_operation == op) {
368 // VM Thread can process it once we unlock the mutex on wait.
369 ml.wait();
370 }
371 }
372 }
373
374 static void self_destruct_if_needed() {
375 // Support for self destruction
376 if ((SelfDestructTimer != 0.0) && !VMError::is_error_reported() &&
377 (os::elapsedTime() > SelfDestructTimer * 60.0)) {
378 tty->print_cr("VM self-destructed");
379 os::exit(-1);
380 }
381 }
382
383 void VMThread::inner_execute(VM_Operation* op) {
384 assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
385
386 VM_Operation* prev_vm_operation = nullptr;
387 if (_cur_vm_operation != nullptr) {
388 // Check that the VM operation allows nested VM operation.
389 // This is normally not the case, e.g., the compiler
390 // does not allow nested scavenges or compiles.
391 if (!_cur_vm_operation->allow_nested_vm_operations()) {
392 fatal("Unexpected nested VM operation %s requested by operation %s",
393 op->name(), _cur_vm_operation->name());
394 }
395 op->set_calling_thread(_cur_vm_operation->calling_thread());
396 prev_vm_operation = _cur_vm_operation;
397 }
398
399 _cur_vm_operation = op;
400
401 HandleMark hm(VMThread::vm_thread());
402
403 const char* const cause = op->cause();
404 EventMarkVMOperation em("Executing %sVM operation: %s%s%s%s",
405 prev_vm_operation != nullptr ? "nested " : "",
406 op->name(),
407 cause != nullptr ? " (" : "",
408 cause != nullptr ? cause : "",
409 cause != nullptr ? ")" : "");
410
411 log_debug(vmthread)("Evaluating %s %s VM operation: %s",
412 prev_vm_operation != nullptr ? "nested" : "",
413 _cur_vm_operation->evaluate_at_safepoint() ? "safepoint" : "non-safepoint",
414 _cur_vm_operation->name());
415
416 bool end_safepoint = false;
417 bool has_timeout_task = (_timeout_task != nullptr);
418 if (_cur_vm_operation->evaluate_at_safepoint() &&
419 !SafepointSynchronize::is_at_safepoint()) {
420 SafepointSynchronize::begin();
421 if (has_timeout_task) {
422 _timeout_task->arm(_cur_vm_operation->name());
423 }
424 end_safepoint = true;
425 }
426
427 evaluate_operation(_cur_vm_operation);
428
429 if (end_safepoint) {
430 if (has_timeout_task) {
431 _timeout_task->disarm();
432 }
433 SafepointSynchronize::end();
434 }
435
436 _cur_vm_operation = prev_vm_operation;
437 }
438
439 void VMThread::wait_for_operation() {
440 assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
441 MonitorLocker ml_op_lock(VMOperation_lock, Mutex::_no_safepoint_check_flag);
442
443 // Clear previous operation.
444 // On first call this clears a dummy place-holder.
445 _next_vm_operation = nullptr;
446 // Notify operation is done and notify a next operation can be installed.
447 ml_op_lock.notify_all();
448
449 while (!should_terminate()) {
450 self_destruct_if_needed();
451 if (_next_vm_operation != nullptr) {
452 return;
453 }
454 if (handshake_or_safepoint_alot()) {
455 if (HandshakeALot) {
456 MutexUnlocker mul(VMOperation_lock);
457 HandshakeALotClosure hal_cl;
458 Handshake::execute(&hal_cl);
459 }
460 // When we unlocked above someone might have setup a new op.
461 if (_next_vm_operation != nullptr) {
462 return;
463 }
464 if (SafepointALot) {
465 _next_vm_operation = &safepointALot_op;
466 return;
467 }
468 }
469 assert(_next_vm_operation == nullptr, "Must be");
470 assert(_cur_vm_operation == nullptr, "Must be");
471
472 // We didn't find anything to execute, notify any waiter so they can install an op.
473 ml_op_lock.notify_all();
474 ml_op_lock.wait(GuaranteedSafepointInterval);
475 }
476 }
477
478 void VMThread::loop() {
479 assert(_cur_vm_operation == nullptr, "no current one should be executing");
480
481 SafepointSynchronize::init(_vm_thread);
482
483 // Need to set a calling thread for ops not passed
484 // via the normal way.
485 no_op.set_calling_thread(_vm_thread);
486 safepointALot_op.set_calling_thread(_vm_thread);
487
488 while (true) {
489 if (should_terminate()) break;
490 wait_for_operation();
491 if (should_terminate()) break;
492 assert(_next_vm_operation != nullptr, "Must have one");
493 inner_execute(_next_vm_operation);
494 }
495 }
496
497 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
498 // over a section of execution by a thread. Currently, it's used only to
499 // prevent re-entrant calls to GC.
500 class SkipGCALot : public StackObj {
501 private:
502 bool _saved;
503 Thread* _t;
504
505 public:
506 #ifdef ASSERT
507 SkipGCALot(Thread* t) : _t(t) {
508 _saved = _t->skip_gcalot();
509 _t->set_skip_gcalot(true);
510 }
511
512 ~SkipGCALot() {
513 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
514 _t->set_skip_gcalot(_saved);
515 }
516 #else
517 SkipGCALot(Thread* t) { }
518 ~SkipGCALot() { }
519 #endif
520 };
521
522 void VMThread::execute(VM_Operation* op) {
523 Thread* t = Thread::current();
524
525 if (t->is_VM_thread()) {
526 op->set_calling_thread(t);
527 ((VMThread*)t)->inner_execute(op);
528 return;
529 }
530
531 // Avoid re-entrant attempts to gc-a-lot
532 SkipGCALot sgcalot(t);
533
534 // JavaThread or WatcherThread
535 if (t->is_Java_thread()) {
536 JavaThread::cast(t)->check_for_valid_safepoint_state();
537 }
538
539 // New request from Java thread, evaluate prologue
540 if (!op->doit_prologue()) {
541 return; // op was cancelled
542 }
543
544 op->set_calling_thread(t);
545
546 wait_until_executed(op);
547
548 op->doit_epilogue();
549 }
550
551 void VMThread::verify() {
552 oops_do(&VerifyOopClosure::verify_oop, nullptr);
553 }