/* * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "compiler/compileBroker.hpp" #include "gc/shared/collectedHeap.hpp" #include "jfr/jfrEvents.hpp" #include "jfr/support/jfrThreadId.hpp" #include "logging/log.hpp" #include "logging/logStream.hpp" #include "logging/logConfiguration.hpp" #include "memory/resourceArea.hpp" #include "memory/universe.hpp" #include "oops/method.hpp" #include "oops/oop.inline.hpp" #include "oops/verifyOopClosure.hpp" #include "runtime/atomic.hpp" #include "runtime/handles.inline.hpp" #include "runtime/interfaceSupport.inline.hpp" #include "runtime/mutexLocker.hpp" #include "runtime/os.hpp" #include "runtime/safepoint.hpp" #include "runtime/synchronizer.hpp" #include "runtime/thread.inline.hpp" #include "runtime/vmThread.hpp" #include "runtime/vmOperations.hpp" #include "services/runtimeService.hpp" #include "utilities/dtrace.hpp" #include "utilities/events.hpp" #include "utilities/vmError.hpp" #include "utilities/xmlstream.hpp" VM_QueueHead VMOperationQueue::_queue_head[VMOperationQueue::nof_priorities]; VMOperationQueue::VMOperationQueue() { // The queue is a circular doubled-linked list, which always contains // one element (i.e., one element means empty). for(int i = 0; i < nof_priorities; i++) { _queue_length[i] = 0; _queue_counter = 0; _queue[i] = &_queue_head[i]; _queue[i]->set_next(_queue[i]); _queue[i]->set_prev(_queue[i]); } } bool VMOperationQueue::queue_empty(int prio) { // It is empty if there is exactly one element bool empty = (_queue[prio] == _queue[prio]->next()); assert( (_queue_length[prio] == 0 && empty) || (_queue_length[prio] > 0 && !empty), "sanity check"); return _queue_length[prio] == 0; } // Inserts an element to the right of the q element void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); n->set_prev(q); n->set_next(q->next()); q->next()->set_prev(n); q->set_next(n); } void VMOperationQueue::queue_add(int prio, VM_Operation *op) { _queue_length[prio]++; insert(_queue[prio]->prev(), op); } void VMOperationQueue::unlink(VM_Operation* q) { assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); q->prev()->set_next(q->next()); q->next()->set_prev(q->prev()); } VM_Operation* VMOperationQueue::queue_remove_front(int prio) { if (queue_empty(prio)) return NULL; assert(_queue_length[prio] >= 0, "sanity check"); _queue_length[prio]--; VM_Operation* r = _queue[prio]->next(); assert(r != _queue[prio], "cannot remove base element"); unlink(r); return r; } VM_Operation* VMOperationQueue::queue_drain(int prio) { if (queue_empty(prio)) return NULL; DEBUG_ONLY(int length = _queue_length[prio];); assert(length >= 0, "sanity check"); _queue_length[prio] = 0; VM_Operation* r = _queue[prio]->next(); assert(r != _queue[prio], "cannot remove base element"); // remove links to base element from head and tail r->set_prev(NULL); _queue[prio]->prev()->set_next(NULL); // restore queue to empty state _queue[prio]->set_next(_queue[prio]); _queue[prio]->set_prev(_queue[prio]); assert(queue_empty(prio), "drain corrupted queue"); #ifdef ASSERT int len = 0; VM_Operation* cur; for(cur = r; cur != NULL; cur=cur->next()) len++; assert(len == length, "drain lost some ops"); #endif return r; } //----------------------------------------------------------------- // High-level interface void VMOperationQueue::add(VM_Operation *op) { HOTSPOT_VMOPS_REQUEST( (char *) op->name(), strlen(op->name()), op->evaluate_at_safepoint() ? 0 : 1); // Encapsulates VM queue policy. Currently, that // only involves putting them on the right list queue_add(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op); } VM_Operation* VMOperationQueue::remove_next() { // Assuming VMOperation queue is two-level priority queue. If there are // more than two priorities, we need a different scheduling algorithm. assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, "current algorithm does not work"); // simple counter based scheduling to prevent starvation of lower priority // queue. -- see 4390175 int high_prio, low_prio; if (_queue_counter++ < 10) { high_prio = SafepointPriority; low_prio = MediumPriority; } else { _queue_counter = 0; high_prio = MediumPriority; low_prio = SafepointPriority; } return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); } //------------------------------------------------------------------------------------------------------------------ // Timeout machinery void VMOperationTimeoutTask::task() { assert(AbortVMOnVMOperationTimeout, "only if enabled"); if (is_armed()) { jlong delay = nanos_to_millis(os::javaTimeNanos() - _arm_time); if (delay > AbortVMOnVMOperationTimeoutDelay) { fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)", delay, AbortVMOnVMOperationTimeoutDelay); } } } bool VMOperationTimeoutTask::is_armed() { return Atomic::load_acquire(&_armed) != 0; } void VMOperationTimeoutTask::arm() { _arm_time = os::javaTimeNanos(); Atomic::release_store_fence(&_armed, 1); } void VMOperationTimeoutTask::disarm() { Atomic::release_store_fence(&_armed, 0); } //------------------------------------------------------------------------------------------------------------------ // Implementation of VMThread stuff bool VMThread::_should_terminate = false; bool VMThread::_terminated = false; Monitor* VMThread::_terminate_lock = NULL; VMThread* VMThread::_vm_thread = NULL; VM_Operation* VMThread::_cur_vm_operation = NULL; VMOperationQueue* VMThread::_vm_queue = NULL; PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; uint64_t VMThread::_coalesced_count = 0; VMOperationTimeoutTask* VMThread::_timeout_task = NULL; void VMThread::create() { assert(vm_thread() == NULL, "we can only allocate one VMThread"); _vm_thread = new VMThread(); if (AbortVMOnVMOperationTimeout) { // Make sure we call the timeout task frequently enough, but not too frequent. // Try to make the interval 10% of the timeout delay, so that we miss the timeout // by those 10% at max. Periodic task also expects it to fit min/max intervals. size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10; interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran; interval = MAX2(interval, PeriodicTask::min_interval); interval = MIN2(interval, PeriodicTask::max_interval); _timeout_task = new VMOperationTimeoutTask(interval); _timeout_task->enroll(); } else { assert(_timeout_task == NULL, "sanity"); } // Create VM operation queue _vm_queue = new VMOperationQueue(); guarantee(_vm_queue != NULL, "just checking"); _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true, Monitor::_safepoint_check_never); if (UsePerfData) { // jvmstat performance counters Thread* THREAD = Thread::current(); _perf_accumulated_vm_operation_time = PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", PerfData::U_Ticks, CHECK); } } VMThread::VMThread() : NamedThread() { set_name("VM Thread"); } void VMThread::destroy() { _vm_thread = NULL; // VM thread is gone } static VM_None halt_op("Halt"); void VMThread::run() { assert(this == vm_thread(), "check"); // Notify_lock wait checks on active_handles() to rewait in // case of spurious wakeup, it should wait on the last // value set prior to the notify this->set_active_handles(JNIHandleBlock::allocate_block()); { MutexLocker ml(Notify_lock); Notify_lock->notify(); } // Notify_lock is destroyed by Threads::create_vm() int prio = (VMThreadPriority == -1) ? os::java_to_os_priority[NearMaxPriority] : VMThreadPriority; // Note that I cannot call os::set_priority because it expects Java // priorities and I am *explicitly* using OS priorities so that it's // possible to set the VM thread priority higher than any Java thread. os::set_native_priority( this, prio ); // Wait for VM_Operations until termination this->loop(); // Note the intention to exit before safepointing. // 6295565 This has the effect of waiting for any large tty // outputs to finish. if (xtty != NULL) { ttyLocker ttyl; xtty->begin_elem("destroy_vm"); xtty->stamp(); xtty->end_elem(); assert(should_terminate(), "termination flag must be set"); } if (AsyncDeflateIdleMonitors && log_is_enabled(Info, monitorinflation)) { // AsyncDeflateIdleMonitors does a special deflation at the final // safepoint in order to reduce the in-use monitor population that // is reported by ObjectSynchronizer::log_in_use_monitor_details() // at VM exit. ObjectSynchronizer::set_is_special_deflation_requested(true); } // 4526887 let VM thread exit at Safepoint _cur_vm_operation = &halt_op; SafepointSynchronize::begin(); if (VerifyBeforeExit) { HandleMark hm(VMThread::vm_thread()); // Among other things, this ensures that Eden top is correct. Universe::heap()->prepare_for_verify(); // Silent verification so as not to pollute normal output, // unless we really asked for it. Universe::verify(); } CompileBroker::set_should_block(); // wait for threads (compiler threads or daemon threads) in the // _thread_in_native state to block. VM_Exit::wait_for_threads_in_native_to_block(); // signal other threads that VM process is gone { // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows // VM thread to enter any lock at Safepoint as long as its _owner is NULL. // If that happens after _terminate_lock->wait() has unset _owner // but before it actually drops the lock and waits, the notification below // may get lost and we will have a hang. To avoid this, we need to use // Mutex::lock_without_safepoint_check(). MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag); _terminated = true; ml.notify(); } // We are now racing with the VM termination being carried out in // another thread, so we don't "delete this". Numerous threads don't // get deleted when the VM terminates } // Notify the VMThread that the last non-daemon JavaThread has terminated, // and wait until operation is performed. void VMThread::wait_for_vm_thread_exit() { assert(Thread::current()->is_Java_thread(), "Should be a JavaThread"); assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated"); { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); _should_terminate = true; mu.notify(); } // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint // because this thread has been removed from the threads list. But anything // that could get blocked by Safepoint should not be used after this point, // otherwise we will hang, since there is no one can end the safepoint. // Wait until VM thread is terminated // Note: it should be OK to use Terminator_lock here. But this is called // at a very delicate time (VM shutdown) and we are operating in non- VM // thread at Safepoint. It's safer to not share lock with other threads. { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag); while(!VMThread::is_terminated()) { ml.wait(); } } } static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { assert(event != NULL, "invariant"); assert(event->should_commit(), "invariant"); assert(op != NULL, "invariant"); const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); event->set_operation(op->type()); event->set_safepoint(evaluate_at_safepoint); event->set_blocking(true); event->set_caller(JFR_THREAD_ID(op->calling_thread())); event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0); event->commit(); } void VMThread::evaluate_operation(VM_Operation* op) { ResourceMark rm; { PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); HOTSPOT_VMOPS_BEGIN( (char *) op->name(), strlen(op->name()), op->evaluate_at_safepoint() ? 0 : 1); EventExecuteVMOperation event; op->evaluate(); if (event.should_commit()) { post_vm_operation_event(&event, op); } HOTSPOT_VMOPS_END( (char *) op->name(), strlen(op->name()), op->evaluate_at_safepoint() ? 0 : 1); } // Mark as completed op->calling_thread()->increment_vm_operation_completed_count(); } static VM_None safepointALot_op("SafepointALot"); static VM_Cleanup cleanup_op; class HandshakeALotClosure : public HandshakeClosure { public: HandshakeALotClosure() : HandshakeClosure("HandshakeALot") {} void do_thread(Thread* thread) { #ifdef ASSERT assert(thread->is_Java_thread(), "must be"); JavaThread* jt = (JavaThread*)thread; jt->verify_states_for_handshake(); #endif } }; void VMThread::check_for_forced_cleanup() { MonitorLocker mq(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); mq.notify(); } VM_Operation* VMThread::no_op_safepoint() { // Check for handshakes first since we may need to return a VMop. if (HandshakeALot) { HandshakeALotClosure hal_cl; Handshake::execute(&hal_cl); } // Check for a cleanup before SafepointALot to keep stats correct. long interval_ms = SafepointTracing::time_since_last_safepoint_ms(); bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval_ms >= GuaranteedSafepointInterval); if ((max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) || SafepointSynchronize::is_forced_cleanup_needed()) { return &cleanup_op; } if (SafepointALot) { return &safepointALot_op; } // Nothing to be done. return NULL; } void VMThread::loop() { assert(_cur_vm_operation == NULL, "no current one should be executing"); SafepointSynchronize::init(_vm_thread); while(true) { VM_Operation* safepoint_ops = NULL; // // Wait for VM operation // // use no_safepoint_check to get lock without attempting to "sneak" { MonitorLocker mu_queue(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); // Look for new operation assert(_cur_vm_operation == NULL, "no current one should be executing"); _cur_vm_operation = _vm_queue->remove_next(); // Stall time tracking code if (PrintVMQWaitTime && _cur_vm_operation != NULL) { jlong stall = nanos_to_millis(os::javaTimeNanos() - _cur_vm_operation->timestamp()); if (stall > 0) tty->print_cr("%s stall: " JLONG_FORMAT, _cur_vm_operation->name(), stall); } while (!should_terminate() && _cur_vm_operation == NULL) { // wait with a timeout to guarantee safepoints at regular intervals // (if there is cleanup work to do) (void)mu_queue.wait(GuaranteedSafepointInterval); // Support for self destruction if ((SelfDestructTimer != 0) && !VMError::is_error_reported() && (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { tty->print_cr("VM self-destructed"); exit(-1); } // If the queue contains a safepoint VM op, // clean up will be done so we can skip this part. if (!_vm_queue->peek_at_safepoint_priority()) { // Have to unlock VMOperationQueue_lock just in case no_op_safepoint() // has to do a handshake when HandshakeALot is enabled. MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) { // Force a safepoint since we have not had one for at least // 'GuaranteedSafepointInterval' milliseconds and we need to clean // something. This will run all the clean-up processing that needs // to be done at a safepoint. SafepointSynchronize::begin(); #ifdef ASSERT if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); #endif SafepointSynchronize::end(); _cur_vm_operation = NULL; } } _cur_vm_operation = _vm_queue->remove_next(); // If we are at a safepoint we will evaluate all the operations that // follow that also require a safepoint if (_cur_vm_operation != NULL && _cur_vm_operation->evaluate_at_safepoint()) { safepoint_ops = _vm_queue->drain_at_safepoint_priority(); } } if (should_terminate()) break; } // Release mu_queue_lock // // Execute VM operation // { HandleMark hm(VMThread::vm_thread()); EventMark em("Executing VM operation: %s", vm_operation()->name()); assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); // If we are at a safepoint we will evaluate all the operations that // follow that also require a safepoint if (_cur_vm_operation->evaluate_at_safepoint()) { log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); SafepointSynchronize::begin(); if (_timeout_task != NULL) { _timeout_task->arm(); } evaluate_operation(_cur_vm_operation); // now process all queued safepoint ops, iteratively draining // the queue until there are none left do { _cur_vm_operation = safepoint_ops; if (_cur_vm_operation != NULL) { do { EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name()); log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); // evaluate_operation deletes the op object so we have // to grab the next op now VM_Operation* next = _cur_vm_operation->next(); evaluate_operation(_cur_vm_operation); _cur_vm_operation = next; _coalesced_count++; } while (_cur_vm_operation != NULL); } // There is a chance that a thread enqueued a safepoint op // since we released the op-queue lock and initiated the safepoint. // So we drain the queue again if there is anything there, as an // optimization to try and reduce the number of safepoints. // As the safepoint synchronizes us with JavaThreads we will see // any enqueue made by a JavaThread, but the peek will not // necessarily detect a concurrent enqueue by a GC thread, but // that simply means the op will wait for the next major cycle of the // VMThread - just as it would if the GC thread lost the race for // the lock. if (_vm_queue->peek_at_safepoint_priority()) { // must hold lock while draining queue MutexLocker mu_queue(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); safepoint_ops = _vm_queue->drain_at_safepoint_priority(); } else { safepoint_ops = NULL; } } while(safepoint_ops != NULL); if (_timeout_task != NULL) { _timeout_task->disarm(); } // Complete safepoint synchronization SafepointSynchronize::end(); } else { // not a safepoint operation log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); if (TraceLongCompiles) { elapsedTimer t; t.start(); evaluate_operation(_cur_vm_operation); t.stop(); double secs = t.seconds(); if (secs * 1e3 > LongCompileThreshold) { // XXX - _cur_vm_operation should not be accessed after // the completed count has been incremented; the waiting // thread may have already freed this memory. tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); } } else { evaluate_operation(_cur_vm_operation); } _cur_vm_operation = NULL; } } // // Notify (potential) waiting Java thread(s) { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag); mu.notify_all(); } } } // A SkipGCALot object is used to elide the usual effect of gc-a-lot // over a section of execution by a thread. Currently, it's used only to // prevent re-entrant calls to GC. class SkipGCALot : public StackObj { private: bool _saved; Thread* _t; public: #ifdef ASSERT SkipGCALot(Thread* t) : _t(t) { _saved = _t->skip_gcalot(); _t->set_skip_gcalot(true); } ~SkipGCALot() { assert(_t->skip_gcalot(), "Save-restore protocol invariant"); _t->set_skip_gcalot(_saved); } #else SkipGCALot(Thread* t) { } ~SkipGCALot() { } #endif }; void VMThread::execute(VM_Operation* op) { Thread* t = Thread::current(); if (!t->is_VM_thread()) { SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot // JavaThread or WatcherThread t->check_for_valid_safepoint_state(); // New request from Java thread, evaluate prologue if (!op->doit_prologue()) { return; // op was cancelled } // Setup VM_operations for execution op->set_calling_thread(t); // Get ticket number for the VM operation int ticket = t->vm_operation_ticket(); // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests // to be queued up during a safepoint synchronization. { MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); log_debug(vmthread)("Adding VM operation: %s", op->name()); _vm_queue->add(op); op->set_timestamp(os::javaTimeNanos()); ml.notify(); } { // Wait for completion of request // Note: only a JavaThread triggers the safepoint check when locking MonitorLocker ml(VMOperationRequest_lock, t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag); while(t->vm_operation_completed_count() < ticket) { ml.wait(); } } op->doit_epilogue(); } else { // invoked by VM thread; usually nested VM operation assert(t->is_VM_thread(), "must be a VM thread"); VM_Operation* prev_vm_operation = vm_operation(); if (prev_vm_operation != NULL) { // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler // does not allow nested scavenges or compiles. if (!prev_vm_operation->allow_nested_vm_operations()) { fatal("Nested VM operation %s requested by operation %s", op->name(), vm_operation()->name()); } op->set_calling_thread(prev_vm_operation->calling_thread()); } EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); // Release all internal handles after operation is evaluated HandleMark hm(t); _cur_vm_operation = op; if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { SafepointSynchronize::begin(); op->evaluate(); SafepointSynchronize::end(); } else { op->evaluate(); } _cur_vm_operation = prev_vm_operation; } } void VMThread::verify() { oops_do(&VerifyOopClosure::verify_oop, NULL); }