void DeadlockCycle::print_on(outputStream* st) const {
st->cr();
st->print_cr("Found one Java-level deadlock:");
st->print("=============================");
JavaThread* currentThread;
ObjectMonitor* waitingToLockMonitor;
oop waitingToLockBlocker;
int len = _threads->length();
for (int i = 0; i < len; i++) {
currentThread = _threads->at(i);
waitingToLockMonitor = (ObjectMonitor*)currentThread->current_pending_monitor();
waitingToLockBlocker = currentThread->current_park_blocker();
st->cr();
st->print_cr("\"%s\":", currentThread->get_thread_name());
const char* owner_desc = ",\n which is held by";
if (waitingToLockMonitor != NULL) {
st->print(" waiting to lock monitor " INTPTR_FORMAT, waitingToLockMonitor);
oop obj = (oop)waitingToLockMonitor->object();
if (obj != NULL) {
st->print(" (object "INTPTR_FORMAT ", a %s)", (address)obj,
(instanceKlass::cast(obj->klass()))->external_name());
if (!currentThread->current_pending_monitor_is_from_java()) {
owner_desc = "\n in JNI, which is held by";
}
} else {
// No Java object associated - a JVMTI raw monitor
owner_desc = " (JVMTI raw monitor),\n which is held by";
}
currentThread = Threads::owning_thread_from_monitor_owner(
(address)waitingToLockMonitor->owner(), false /* no locking needed */);
} else {
st->print(" waiting for ownable synchronizer " INTPTR_FORMAT ", (a %s)",
(address)waitingToLockBlocker,
(instanceKlass::cast(waitingToLockBlocker->klass()))->external_name());
assert(waitingToLockBlocker->is_a(SystemDictionary::abstract_ownable_synchronizer_klass()),
"Must be an AbstractOwnableSynchronizer");
oop ownerObj = java_util_concurrent_locks_AbstractOwnableSynchronizer::get_owner_threadObj(waitingToLockBlocker);
currentThread = java_lang_Thread::thread(ownerObj);
}
st->print("%s \"%s\"", owner_desc, currentThread->get_thread_name());
}
st->cr();
st->cr();
// Print stack traces
bool oldJavaMonitorsInStackTrace = JavaMonitorsInStackTrace;
JavaMonitorsInStackTrace = true;
st->print_cr("Java stack information for the threads listed above:");
st->print_cr("===================================================");
for (int j = 0; j < len; j++) {
currentThread = _threads->at(j);
st->print_cr("\"%s\":", currentThread->get_thread_name());
currentThread->print_stack_on(st);
}
JavaMonitorsInStackTrace = oldJavaMonitorsInStackTrace;
}
PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
void markOopDesc::print_on(outputStream* st) const {
if (is_marked()) {
st->print(" marked(" INTPTR_FORMAT ")", value());
} else if (has_monitor()) {
// have to check has_monitor() before is_locked()
st->print(" monitor(" INTPTR_FORMAT ")=", value());
ObjectMonitor* mon = monitor();
if (mon == NULL) {
st->print("NULL (this should never be seen!)");
} else {
st->print("{count=" INTPTR_FORMAT ",waiters=" INTPTR_FORMAT
",recursions=" INTPTR_FORMAT ",owner=" INTPTR_FORMAT "}",
mon->count(), mon->waiters(), mon->recursions(),
p2i(mon->owner()));
}
} else if (is_locked()) {
st->print(" locked(" INTPTR_FORMAT ")->", value());
if (is_neutral()) {
st->print("is_neutral");
if (has_no_hash()) {
st->print(" no_hash");
} else {
st->print(" hash=" INTPTR_FORMAT, hash());
}
st->print(" age=%d", age());
} else if (has_bias_pattern()) {
st->print("is_biased");
JavaThread* jt = biased_locker();
st->print(" biased_locker=" INTPTR_FORMAT, p2i(jt));
} else {
st->print("??");
}
} else {
assert(is_unlocked() || has_bias_pattern(), "just checking");
st->print("mark(");
if (has_bias_pattern()) st->print("biased,");
st->print("hash %#lx,", hash());
st->print("age %d)", age());
}
}
jvmtiError
JvmtiEnvBase::get_object_monitor_usage(JavaThread* calling_thread, jobject object, jvmtiMonitorUsage* info_ptr) {
HandleMark hm;
Handle hobj;
bool at_safepoint = SafepointSynchronize::is_at_safepoint();
// Check arguments
{
oop mirror = JNIHandles::resolve_external_guard(object);
NULL_CHECK(mirror, JVMTI_ERROR_INVALID_OBJECT);
NULL_CHECK(info_ptr, JVMTI_ERROR_NULL_POINTER);
hobj = Handle(mirror);
}
JavaThread *owning_thread = NULL;
ObjectMonitor *mon = NULL;
jvmtiMonitorUsage ret = {
NULL, 0, 0, NULL, 0, NULL
};
uint32_t debug_bits = 0;
// first derive the object's owner and entry_count (if any)
{
// Revoke any biases before querying the mark word
if (SafepointSynchronize::is_at_safepoint()) {
BiasedLocking::revoke_at_safepoint(hobj);
} else {
BiasedLocking::revoke_and_rebias(hobj, false, calling_thread);
}
address owner = NULL;
{
markOop mark = hobj()->mark();
if (!mark->has_monitor()) {
// this object has a lightweight monitor
if (mark->has_locker()) {
owner = (address)mark->locker(); // save the address of the Lock word
}
// implied else: no owner
} else {
// this object has a heavyweight monitor
mon = mark->monitor();
// The owner field of a heavyweight monitor may be NULL for no
// owner, a JavaThread * or it may still be the address of the
// Lock word in a JavaThread's stack. A monitor can be inflated
// by a non-owning JavaThread, but only the owning JavaThread
// can change the owner field from the Lock word to the
// JavaThread * and it may not have done that yet.
owner = (address)mon->owner();
}
}
if (owner != NULL) {
// This monitor is owned so we have to find the owning JavaThread.
// Since owning_thread_from_monitor_owner() grabs a lock, GC can
// move our object at this point. However, our owner value is safe
// since it is either the Lock word on a stack or a JavaThread *.
owning_thread = Threads::owning_thread_from_monitor_owner(owner, !at_safepoint);
// Cannot assume (owning_thread != NULL) here because this function
// may not have been called at a safepoint and the owning_thread
// might not be suspended.
if (owning_thread != NULL) {
// The monitor's owner either has to be the current thread, at safepoint
// or it has to be suspended. Any of these conditions will prevent both
// contending and waiting threads from modifying the state of
// the monitor.
if (!at_safepoint && !JvmtiEnv::is_thread_fully_suspended(owning_thread, true, &debug_bits)) {
// Don't worry! This return of JVMTI_ERROR_THREAD_NOT_SUSPENDED
// will not make it back to the JVM/TI agent. The error code will
// get intercepted in JvmtiEnv::GetObjectMonitorUsage() which
// will retry the call via a VM_GetObjectMonitorUsage VM op.
return JVMTI_ERROR_THREAD_NOT_SUSPENDED;
}
HandleMark hm;
Handle th(owning_thread->threadObj());
ret.owner = (jthread)jni_reference(calling_thread, th);
}
// implied else: no owner
}
if (owning_thread != NULL) { // monitor is owned
// The recursions field of a monitor does not reflect recursions
// as lightweight locks before inflating the monitor are not included.
// We have to count the number of recursive monitor entries the hard way.
// We pass a handle to survive any GCs along the way.
ResourceMark rm;
ret.entry_count = count_locked_objects(owning_thread, hobj);
}
// implied else: entry_count == 0
}
jint nWant, nWait;
if (mon != NULL) {
// this object has a heavyweight monitor
nWant = mon->contentions(); // # of threads contending for monitor
nWait = mon->waiters(); // # of threads in Object.wait()
ret.waiter_count = nWant + nWait;
ret.notify_waiter_count = nWait;
} else {
// this object has a lightweight monitor
ret.waiter_count = 0;
ret.notify_waiter_count = 0;
}
// Allocate memory for heavyweight and lightweight monitor.
jvmtiError err;
err = allocate(ret.waiter_count * sizeof(jthread *), (unsigned char**)&ret.waiters);
if (err != JVMTI_ERROR_NONE) {
return err;
}
err = allocate(ret.notify_waiter_count * sizeof(jthread *),
(unsigned char**)&ret.notify_waiters);
if (err != JVMTI_ERROR_NONE) {
deallocate((unsigned char*)ret.waiters);
return err;
}
// now derive the rest of the fields
if (mon != NULL) {
// this object has a heavyweight monitor
// Number of waiters may actually be less than the waiter count.
// So NULL out memory so that unused memory will be NULL.
memset(ret.waiters, 0, ret.waiter_count * sizeof(jthread *));
memset(ret.notify_waiters, 0, ret.notify_waiter_count * sizeof(jthread *));
if (ret.waiter_count > 0) {
// we have contending and/or waiting threads
HandleMark hm;
if (nWant > 0) {
// we have contending threads
ResourceMark rm;
// get_pending_threads returns only java thread so we do not need to
// check for non java threads.
GrowableArray<JavaThread*>* wantList = Threads::get_pending_threads(
nWant, (address)mon, !at_safepoint);
if (wantList->length() < nWant) {
// robustness: the pending list has gotten smaller
nWant = wantList->length();
}
for (int i = 0; i < nWant; i++) {
JavaThread *pending_thread = wantList->at(i);
// If the monitor has no owner, then a non-suspended contending
// thread could potentially change the state of the monitor by
// entering it. The JVM/TI spec doesn't allow this.
if (owning_thread == NULL && !at_safepoint &
!JvmtiEnv::is_thread_fully_suspended(pending_thread, true, &debug_bits)) {
if (ret.owner != NULL) {
destroy_jni_reference(calling_thread, ret.owner);
}
for (int j = 0; j < i; j++) {
destroy_jni_reference(calling_thread, ret.waiters[j]);
}
deallocate((unsigned char*)ret.waiters);
deallocate((unsigned char*)ret.notify_waiters);
return JVMTI_ERROR_THREAD_NOT_SUSPENDED;
}
Handle th(pending_thread->threadObj());
ret.waiters[i] = (jthread)jni_reference(calling_thread, th);
}
}
if (nWait > 0) {
// we have threads in Object.wait()
int offset = nWant; // add after any contending threads
ObjectWaiter *waiter = mon->first_waiter();
for (int i = 0, j = 0; i < nWait; i++) {
if (waiter == NULL) {
// robustness: the waiting list has gotten smaller
nWait = j;
break;
}
Thread *t = mon->thread_of_waiter(waiter);
if (t != NULL && t->is_Java_thread()) {
JavaThread *wjava_thread = (JavaThread *)t;
// If the thread was found on the ObjectWaiter list, then
// it has not been notified. This thread can't change the
// state of the monitor so it doesn't need to be suspended.
Handle th(wjava_thread->threadObj());
ret.waiters[offset + j] = (jthread)jni_reference(calling_thread, th);
ret.notify_waiters[j++] = (jthread)jni_reference(calling_thread, th);
}
waiter = mon->next_waiter(waiter);
}
}
}
// Adjust count. nWant and nWait count values may be less than original.
ret.waiter_count = nWant + nWait;
ret.notify_waiter_count = nWait;
} else {
// this object has a lightweight monitor and we have nothing more
// to do here because the defaults are just fine.
}
// we don't update return parameter unless everything worked
*info_ptr = ret;
return JVMTI_ERROR_NONE;
}
// Find deadlocks involving object monitors and concurrent locks if concurrent_locks is true
DeadlockCycle* ThreadService::find_deadlocks_at_safepoint(bool concurrent_locks) {
// This code was modified from the original Threads::find_deadlocks code.
int globalDfn = 0, thisDfn;
ObjectMonitor* waitingToLockMonitor = NULL;
oop waitingToLockBlocker = NULL;
bool blocked_on_monitor = false;
JavaThread *currentThread, *previousThread;
int num_deadlocks = 0;
for (JavaThread* p = Threads::first(); p != NULL; p = p->next()) {
// Initialize the depth-first-number
p->set_depth_first_number(-1);
}
DeadlockCycle* deadlocks = NULL;
DeadlockCycle* last = NULL;
DeadlockCycle* cycle = new DeadlockCycle();
for (JavaThread* jt = Threads::first(); jt != NULL; jt = jt->next()) {
if (jt->depth_first_number() >= 0) {
// this thread was already visited
continue;
}
thisDfn = globalDfn;
jt->set_depth_first_number(globalDfn++);
previousThread = jt;
currentThread = jt;
cycle->reset();
// When there is a deadlock, all the monitors involved in the dependency
// cycle must be contended and heavyweight. So we only care about the
// heavyweight monitor a thread is waiting to lock.
waitingToLockMonitor = (ObjectMonitor*)jt->current_pending_monitor();
if (concurrent_locks) {
waitingToLockBlocker = jt->current_park_blocker();
}
while (waitingToLockMonitor != NULL || waitingToLockBlocker != NULL) {
cycle->add_thread(currentThread);
if (waitingToLockMonitor != NULL) {
address currentOwner = (address)waitingToLockMonitor->owner();
if (currentOwner != NULL) {
currentThread = Threads::owning_thread_from_monitor_owner(
currentOwner,
false /* no locking needed */);
if (currentThread == NULL) {
// This function is called at a safepoint so the JavaThread
// that owns waitingToLockMonitor should be findable, but
// if it is not findable, then the previous currentThread is
// blocked permanently. We record this as a deadlock.
num_deadlocks++;
cycle->set_deadlock(true);
// add this cycle to the deadlocks list
if (deadlocks == NULL) {
deadlocks = cycle;
} else {
last->set_next(cycle);
}
last = cycle;
cycle = new DeadlockCycle();
break;
}
}
} else {
if (concurrent_locks) {
if (waitingToLockBlocker->is_a(SystemDictionary::abstract_ownable_synchronizer_klass())) {
oop threadObj = java_util_concurrent_locks_AbstractOwnableSynchronizer::get_owner_threadObj(waitingToLockBlocker);
currentThread = threadObj != NULL ? java_lang_Thread::thread(threadObj) : NULL;
} else {
currentThread = NULL;
}
}
}
if (currentThread == NULL) {
// No dependency on another thread
break;
}
if (currentThread->depth_first_number() < 0) {
// First visit to this thread
currentThread->set_depth_first_number(globalDfn++);
} else if (currentThread->depth_first_number() < thisDfn) {
// Thread already visited, and not on a (new) cycle
break;
} else if (currentThread == previousThread) {
// Self-loop, ignore
break;
} else {
// We have a (new) cycle
num_deadlocks++;
cycle->set_deadlock(true);
// add this cycle to the deadlocks list
if (deadlocks == NULL) {
deadlocks = cycle;
} else {
last->set_next(cycle);
}
last = cycle;
cycle = new DeadlockCycle();
break;
}
previousThread = currentThread;
waitingToLockMonitor = (ObjectMonitor*)currentThread->current_pending_monitor();
if (concurrent_locks) {
waitingToLockBlocker = currentThread->current_park_blocker();
}
}
}
delete cycle;
return deadlocks;
}