/*
* Copyright (c) 1998, 2019, 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/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]);
}
_drain_list = NULL;
}
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;
}
void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
VM_Operation* cur = _queue[queue];
cur = cur->next();
while (cur != _queue[queue]) {
cur->oops_do(f);
cur = cur->next();
}
}
void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
VM_Operation* cur = _drain_list;
while (cur != NULL) {
cur->oops_do(f);
cur = cur->next();
}
}
//-----------------------------------------------------------------
// 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);
}
void VMOperationQueue::oops_do(OopClosure* f) {
for(int i = 0; i < nof_priorities; i++) {
queue_oops_do(i, f);
}
drain_list_oops_do(f);
}
//------------------------------------------------------------------------------------------------------------------
// Timeout machinery
void VMOperationTimeoutTask::task() {
assert(AbortVMOnVMOperationTimeout, "only if enabled");
if (is_armed()) {
jlong delay = (os::javaTimeMillis() - _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::javaTimeMillis();
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<size_t>(interval, PeriodicTask::min_interval);
interval = MIN2<size_t>(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");
}
// 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 HandshakeALotTC : public ThreadClosure {
public:
virtual 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) {
HandshakeALotTC haltc;
Handshake::execute(&haltc);
}
// 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) {
long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
if (stall > 0)
tty->print_cr("%s stall: %ld", _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());
_vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
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();
_vm_queue->set_drain_list(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);
_vm_queue->set_drain_list(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::javaTimeMillis());
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::oops_do(OopClosure* f, CodeBlobClosure* cf) {
Thread::oops_do(f, cf);
_vm_queue->oops_do(f);
}
//------------------------------------------------------------------------------------------------------------------
#ifndef PRODUCT
void VMOperationQueue::verify_queue(int prio) {
// Check that list is correctly linked
int length = _queue_length[prio];
VM_Operation *cur = _queue[prio];
int i;
// Check forward links
for(i = 0; i < length; i++) {
cur = cur->next();
assert(cur != _queue[prio], "list to short (forward)");
}
assert(cur->next() == _queue[prio], "list to long (forward)");
// Check backwards links
cur = _queue[prio];
for(i = 0; i < length; i++) {
cur = cur->prev();
assert(cur != _queue[prio], "list to short (backwards)");
}
assert(cur->prev() == _queue[prio], "list to long (backwards)");
}
#endif
void VMThread::verify() {
oops_do(&VerifyOopClosure::verify_oop, NULL);
}