--- a/src/hotspot/share/runtime/biasedLocking.cpp Tue Jul 09 10:27:38 2019 -0700
+++ b/src/hotspot/share/runtime/biasedLocking.cpp Tue Jul 09 14:38:48 2019 -0400
@@ -119,6 +119,7 @@
return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
}
+
// Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
@@ -153,9 +154,13 @@
return info;
}
+
// After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
// AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
-static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
+BiasedLocking::Condition BiasedLocking::single_revoke_at_safepoint(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
+ assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
+ assert(Thread::current()->is_VM_thread(), "must be VMThread");
+
markOop mark = obj->mark();
if (!mark->has_bias_pattern()) {
if (log_is_enabled(Info, biasedlocking)) {
@@ -168,7 +173,7 @@
obj->klass()->external_name(),
(intptr_t) requesting_thread);
}
- return BiasedLocking::NOT_BIASED;
+ return NOT_BIASED;
}
uint age = mark->age();
@@ -214,7 +219,7 @@
} else {
log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
}
- return BiasedLocking::BIAS_REVOKED;
+ return BIAS_REVOKED;
}
// Handle case where the thread toward which the object was biased has exited
@@ -239,7 +244,7 @@
log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
PTR_FORMAT ")", p2i(biased_thread));
}
- return BiasedLocking::BIAS_REVOKED;
+ return BIAS_REVOKED;
}
// Log at "info" level if not bulk, else "trace" level
@@ -264,7 +269,7 @@
log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
p2i((void *) mon_info->owner()),
p2i((void *) obj));
- // Assume recursive case and fix up highest lock later
+ // Assume recursive case and fix up highest lock below
markOop mark = markOopDesc::encode((BasicLock*) NULL);
highest_lock = mon_info->lock();
highest_lock->set_displaced_header(mark);
@@ -279,7 +284,7 @@
// object at it
highest_lock->set_displaced_header(unbiased_prototype);
// Reset object header to point to displaced mark.
- // Must release storing the lock address for platforms without TSO
+ // Must release store the lock address for platforms without TSO
// ordering (e.g. ppc).
obj->release_set_mark(markOopDesc::encode(highest_lock));
assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
@@ -309,7 +314,7 @@
*biased_locker = biased_thread;
}
- return BiasedLocking::BIAS_REVOKED;
+ return BIAS_REVOKED;
}
@@ -321,7 +326,7 @@
};
-static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
+static HeuristicsResult update_heuristics(oop o) {
markOop mark = o->mark();
if (!mark->has_bias_pattern()) {
return HR_NOT_BIASED;
@@ -374,11 +379,12 @@
}
-static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
+BiasedLocking::Condition BiasedLocking::bulk_revoke_or_rebias_at_safepoint(oop o,
bool bulk_rebias,
bool attempt_rebias_of_object,
JavaThread* requesting_thread) {
assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
+ assert(Thread::current()->is_VM_thread(), "must be VMThread");
log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
@@ -390,7 +396,6 @@
jlong cur_time = os::javaTimeMillis();
o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
-
Klass* k_o = o->klass();
Klass* klass = k_o;
@@ -432,7 +437,7 @@
// At this point we're done. All we have to do is potentially
// adjust the header of the given object to revoke its bias.
- revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
+ single_revoke_at_safepoint(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
} else {
if (log_is_enabled(Info, biasedlocking)) {
ResourceMark rm;
@@ -454,20 +459,20 @@
oop owner = mon_info->owner();
markOop mark = owner->mark();
if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
- revoke_bias(owner, false, true, requesting_thread, NULL);
+ single_revoke_at_safepoint(owner, false, true, requesting_thread, NULL);
}
}
}
// Must force the bias of the passed object to be forcibly revoked
// as well to ensure guarantees to callers
- revoke_bias(o, false, true, requesting_thread, NULL);
+ single_revoke_at_safepoint(o, false, true, requesting_thread, NULL);
}
} // ThreadsListHandle is destroyed here.
log_info(biasedlocking)("* Ending bulk revocation");
- BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
+ BiasedLocking::Condition status_code = BIAS_REVOKED;
if (attempt_rebias_of_object &&
o->mark()->has_bias_pattern() &&
@@ -475,7 +480,7 @@
markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
klass->prototype_header()->bias_epoch());
o->set_mark(new_mark);
- status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
+ status_code = BIAS_REVOKED_AND_REBIASED;
log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
}
@@ -487,77 +492,125 @@
}
-static void clean_up_cached_monitor_info() {
- // Walk the thread list clearing out the cached monitors
- for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
- thr->set_cached_monitor_info(NULL);
+static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
+ if (thread != NULL) {
+ thread->set_cached_monitor_info(NULL);
+ } else {
+ // Walk the thread list clearing out the cached monitors
+ for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
+ thr->set_cached_monitor_info(NULL);
+ }
}
}
-class VM_RevokeBias : public VM_Operation {
-protected:
+class VM_BulkRevokeBias : public VM_Operation {
+private:
Handle* _obj;
- GrowableArray<Handle>* _objs;
JavaThread* _requesting_thread;
+ bool _bulk_rebias;
+ bool _attempt_rebias_of_object;
BiasedLocking::Condition _status_code;
- traceid _biased_locker_id;
uint64_t _safepoint_id;
public:
- VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
+ VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
+ bool bulk_rebias,
+ bool attempt_rebias_of_object)
: _obj(obj)
- , _objs(NULL)
, _requesting_thread(requesting_thread)
+ , _bulk_rebias(bulk_rebias)
+ , _attempt_rebias_of_object(attempt_rebias_of_object)
, _status_code(BiasedLocking::NOT_BIASED)
- , _biased_locker_id(0)
- , _safepoint_id(0) {}
-
- VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
- : _obj(NULL)
- , _objs(objs)
- , _requesting_thread(requesting_thread)
- , _status_code(BiasedLocking::NOT_BIASED)
- , _biased_locker_id(0)
, _safepoint_id(0) {}
- virtual VMOp_Type type() const { return VMOp_RevokeBias; }
+ virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
+
+ virtual void doit() {
+ _status_code = BiasedLocking::bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
+ _safepoint_id = SafepointSynchronize::safepoint_id();
+ clean_up_cached_monitor_info();
+ }
+
+ bool is_bulk_rebias() const {
+ return _bulk_rebias;
+ }
+
+ BiasedLocking::Condition status_code() const {
+ return _status_code;
+ }
+
+ uint64_t safepoint_id() const {
+ return _safepoint_id;
+ }
+};
+
+
+class RevokeOneBias : public ThreadClosure {
+protected:
+ Handle _obj;
+ JavaThread* _requesting_thread;
+ JavaThread* _biased_locker;
+ BiasedLocking::Condition _status_code;
+ traceid _biased_locker_id;
+
+public:
+ RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
+ : _obj(obj)
+ , _requesting_thread(requesting_thread)
+ , _biased_locker(biased_locker)
+ , _status_code(BiasedLocking::NOT_BIASED)
+ , _biased_locker_id(0) {}
+
+ void do_thread(Thread* target) {
+ assert(target == _biased_locker, "Wrong thread");
- virtual bool doit_prologue() {
- // Verify that there is actual work to do since the callers just
- // give us locked object(s). If we don't find any biased objects
- // there is nothing to do and we avoid a safepoint.
- if (_obj != NULL) {
- markOop mark = (*_obj)()->mark();
- if (mark->has_bias_pattern()) {
- return true;
+ oop o = _obj();
+ markOop mark = o->mark();
+
+ if (!mark->has_bias_pattern()) {
+ return;
+ }
+
+ markOop prototype = o->klass()->prototype_header();
+ if (!prototype->has_bias_pattern()) {
+ // This object has a stale bias from before the handshake
+ // was requested. If we fail this race, the object's bias
+ // has been revoked by another thread so we simply return.
+ markOop biased_value = mark;
+ mark = o->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
+ assert(!o->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
+ if (biased_value == mark) {
+ _status_code = BiasedLocking::BIAS_REVOKED;
}
- } else {
- for ( int i = 0 ; i < _objs->length(); i++ ) {
- markOop mark = (_objs->at(i))()->mark();
- if (mark->has_bias_pattern()) {
- return true;
+ return;
+ }
+
+ if (_biased_locker == mark->biased_locker()) {
+ if (mark->bias_epoch() == prototype->bias_epoch()) {
+ // Epoch is still valid. This means biaser could be currently
+ // synchronized on this object. We must walk its stack looking
+ // for monitor records associated with this object and change
+ // them to be stack locks if any are found.
+ ResourceMark rm;
+ BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
+ _biased_locker->set_cached_monitor_info(NULL);
+ assert(!o->mark()->has_bias_pattern(), "invariant");
+ _biased_locker_id = JFR_THREAD_ID(_biased_locker);
+ _status_code = BiasedLocking::BIAS_REVOKED;
+ return;
+ } else {
+ markOop biased_value = mark;
+ mark = o->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
+ if (mark == biased_value || !mark->has_bias_pattern()) {
+ assert(!o->mark()->has_bias_pattern(), "should be revoked");
+ _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
+ return;
}
}
}
- return false;
- }
- virtual void doit() {
- if (_obj != NULL) {
- log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
- JavaThread* biased_locker = NULL;
- _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
- if (biased_locker != NULL) {
- _biased_locker_id = JFR_THREAD_ID(biased_locker);
- }
- _safepoint_id = SafepointSynchronize::safepoint_id();
- clean_up_cached_monitor_info();
- return;
- } else {
- log_info(biasedlocking)("Revoking bias with global safepoint:");
- BiasedLocking::revoke_at_safepoint(_objs);
- }
+ _status_code = BiasedLocking::NOT_REVOKED;
}
BiasedLocking::Condition status_code() const {
@@ -567,40 +620,9 @@
traceid biased_locker() const {
return _biased_locker_id;
}
-
- uint64_t safepoint_id() const {
- return _safepoint_id;
- }
};
-class VM_BulkRevokeBias : public VM_RevokeBias {
-private:
- bool _bulk_rebias;
- bool _attempt_rebias_of_object;
-
-public:
- VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
- bool bulk_rebias,
- bool attempt_rebias_of_object)
- : VM_RevokeBias(obj, requesting_thread)
- , _bulk_rebias(bulk_rebias)
- , _attempt_rebias_of_object(attempt_rebias_of_object) {}
-
- virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
- virtual bool doit_prologue() { return true; }
-
- virtual void doit() {
- _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
- _safepoint_id = SafepointSynchronize::safepoint_id();
- clean_up_cached_monitor_info();
- }
-
- bool is_bulk_rebias() const {
- return _bulk_rebias;
- }
-};
-
static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
assert(event != NULL, "invariant");
assert(k != NULL, "invariant");
@@ -609,13 +631,13 @@
event->commit();
}
-static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, VM_RevokeBias* op) {
+static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
assert(event != NULL, "invariant");
assert(k != NULL, "invariant");
assert(op != NULL, "invariant");
assert(event->should_commit(), "invariant");
event->set_lockClass(k);
- event->set_safepointId(op->safepoint_id());
+ event->set_safepointId(0);
event->set_previousOwner(op->biased_locker());
event->commit();
}
@@ -631,141 +653,263 @@
event->commit();
}
-BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
- assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
+
+BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
+
+ EventBiasedLockRevocation event;
+ if (PrintBiasedLockingStatistics) {
+ Atomic::inc(handshakes_count_addr());
+ }
+ log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
+ INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
+ p2i(biaser), p2i(obj()));
- // We can revoke the biases of anonymously-biased objects
- // efficiently enough that we should not cause these revocations to
- // update the heuristics because doing so may cause unwanted bulk
- // revocations (which are expensive) to occur.
- markOop mark = obj->mark();
- if (mark->is_biased_anonymously() && !attempt_rebias) {
- // We are probably trying to revoke the bias of this object due to
- // an identity hash code computation. Try to revoke the bias
- // without a safepoint. This is possible if we can successfully
- // compare-and-exchange an unbiased header into the mark word of
- // the object, meaning that no other thread has raced to acquire
- // the bias of the object.
- markOop biased_value = mark;
- markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
- markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
- if (res_mark == biased_value) {
- return BIAS_REVOKED;
+ RevokeOneBias revoke(obj, requester, biaser);
+ bool executed = Handshake::execute(&revoke, biaser);
+ if (revoke.status_code() == NOT_REVOKED) {
+ return NOT_REVOKED;
+ }
+ if (executed) {
+ log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
+ p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
+ if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
+ post_revocation_event(&event, obj->klass(), &revoke);
}
- } else if (mark->has_bias_pattern()) {
- Klass* k = obj->klass();
- markOop prototype_header = k->prototype_header();
- if (!prototype_header->has_bias_pattern()) {
- // This object has a stale bias from before the bulk revocation
- // for this data type occurred. It's pointless to update the
- // heuristics at this point so simply update the header with a
- // CAS. If we fail this race, the object's bias has been revoked
- // by another thread so we simply return and let the caller deal
- // with it.
- markOop biased_value = mark;
- markOop res_mark = obj->cas_set_mark(prototype_header, mark);
- assert(!obj->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
- return BIAS_REVOKED;
- } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
- // The epoch of this biasing has expired indicating that the
- // object is effectively unbiased. Depending on whether we need
- // to rebias or revoke the bias of this object we can do it
- // efficiently enough with a CAS that we shouldn't update the
- // heuristics. This is normally done in the assembly code but we
- // can reach this point due to various points in the runtime
- // needing to revoke biases.
- if (attempt_rebias) {
- assert(THREAD->is_Java_thread(), "");
- markOop biased_value = mark;
- markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
- markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
- if (res_mark == biased_value) {
- return BIAS_REVOKED_AND_REBIASED;
+ assert(!obj->mark()->has_bias_pattern(), "invariant");
+ return revoke.status_code();
+ } else {
+ // Thread was not alive.
+ // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
+ // created JavaThread (that happens to get the same memory address as biaser) synchronizing
+ // on this object.
+ {
+ MutexLocker ml(Threads_lock);
+ markOop mark = obj->mark();
+ // Check if somebody else was able to revoke it before biased thread exited.
+ if (!mark->has_bias_pattern()) {
+ return NOT_BIASED;
+ }
+ ThreadsListHandle tlh;
+ markOop prototype = obj->klass()->prototype_header();
+ if (!prototype->has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark->biased_locker() &&
+ prototype->bias_epoch() == mark->bias_epoch())) {
+ obj->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
+ if (event.should_commit()) {
+ post_revocation_event(&event, obj->klass(), &revoke);
}
- } else {
- markOop biased_value = mark;
- markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
- markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
- if (res_mark == biased_value) {
- return BIAS_REVOKED;
- }
+ assert(!obj->mark()->has_bias_pattern(), "bias should be revoked by now");
+ return BIAS_REVOKED;
}
}
}
- HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
- if (heuristics == HR_NOT_BIASED) {
- return NOT_BIASED;
- } else if (heuristics == HR_SINGLE_REVOKE) {
- Klass *k = obj->klass();
- markOop prototype_header = k->prototype_header();
- if (mark->biased_locker() == THREAD &&
- prototype_header->bias_epoch() == mark->bias_epoch()) {
- // A thread is trying to revoke the bias of an object biased
- // toward it, again likely due to an identity hash code
- // computation. We can again avoid a safepoint in this case
- // since we are only going to walk our own stack. There are no
- // races with revocations occurring in other threads because we
- // reach no safepoints in the revocation path.
- // Also check the epoch because even if threads match, another thread
- // can come in with a CAS to steal the bias of an object that has a
- // stale epoch.
- ResourceMark rm;
- log_info(biasedlocking)("Revoking bias by walking my own stack:");
- EventBiasedLockSelfRevocation event;
- BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
- ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
- assert(cond == BIAS_REVOKED, "why not?");
- if (event.should_commit()) {
- post_self_revocation_event(&event, k);
- }
- return cond;
+ return NOT_REVOKED;
+}
+
+
+// Caller should have instantiated a ResourceMark object before calling this method
+void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
+ assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
+ "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
+ assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
+
+ markOop mark = obj->mark();
+ assert(mark->biased_locker() == biased_locker &&
+ obj->klass()->prototype_header()->bias_epoch() == mark->bias_epoch(), "invariant");
+
+ log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
+ INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
+ ", biaser " INTPTR_FORMAT " %s",
+ Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
+ p2i(Thread::current()),
+ p2i(obj),
+ p2i(mark),
+ obj->klass()->external_name(),
+ p2i(obj->klass()->prototype_header()),
+ p2i(biased_locker),
+ Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
+
+ markOop unbiased_prototype = markOopDesc::prototype()->set_age(obj->mark()->age());
+
+ GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
+ BasicLock* highest_lock = NULL;
+ for (int i = 0; i < cached_monitor_info->length(); i++) {
+ MonitorInfo* mon_info = cached_monitor_info->at(i);
+ if (oopDesc::equals(mon_info->owner(), obj)) {
+ log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
+ p2i(mon_info->owner()),
+ p2i(obj));
+ // Assume recursive case and fix up highest lock below
+ markOop mark = markOopDesc::encode((BasicLock*) NULL);
+ highest_lock = mon_info->lock();
+ highest_lock->set_displaced_header(mark);
} else {
- EventBiasedLockRevocation event;
- VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
- VMThread::execute(&revoke);
- if (event.should_commit() && revoke.status_code() != NOT_BIASED) {
- post_revocation_event(&event, k, &revoke);
- }
- return revoke.status_code();
+ log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
+ p2i(mon_info->owner()),
+ p2i(obj));
}
}
+ if (highest_lock != NULL) {
+ // Fix up highest lock to contain displaced header and point
+ // object at it
+ highest_lock->set_displaced_header(unbiased_prototype);
+ // Reset object header to point to displaced mark.
+ // Must release store the lock address for platforms without TSO
+ // ordering (e.g. ppc).
+ obj->release_set_mark(markOopDesc::encode(highest_lock));
+ assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
+ log_info(biasedlocking)(" Revoked bias of currently-locked object");
+ } else {
+ log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
+ // Store the unlocked value into the object's header.
+ obj->set_mark(unbiased_prototype);
+ }
- assert((heuristics == HR_BULK_REVOKE) ||
- (heuristics == HR_BULK_REBIAS), "?");
- EventBiasedLockClassRevocation event;
- VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
- (heuristics == HR_BULK_REBIAS),
- attempt_rebias);
- VMThread::execute(&bulk_revoke);
- if (event.should_commit()) {
- post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
- }
- return bulk_revoke.status_code();
+ assert(!obj->mark()->has_bias_pattern(), "must not be biased");
}
-void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
+BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
- if (objs->length() == 0) {
- return;
+
+ while (true) {
+ // We can revoke the biases of anonymously-biased objects
+ // efficiently enough that we should not cause these revocations to
+ // update the heuristics because doing so may cause unwanted bulk
+ // revocations (which are expensive) to occur.
+ markOop mark = obj->mark();
+ if (mark->is_biased_anonymously() && !attempt_rebias) {
+ // We are probably trying to revoke the bias of this object due to
+ // an identity hash code computation. Try to revoke the bias
+ // without a safepoint. This is possible if we can successfully
+ // compare-and-exchange an unbiased header into the mark word of
+ // the object, meaning that no other thread has raced to acquire
+ // the bias of the object.
+ markOop biased_value = mark;
+ markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
+ markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
+ if (res_mark == biased_value) {
+ return BIAS_REVOKED;
+ }
+ mark = res_mark; // Refresh mark with the latest value.
+ } else if (mark->has_bias_pattern()) {
+ Klass* k = obj->klass();
+ markOop prototype_header = k->prototype_header();
+ if (!prototype_header->has_bias_pattern()) {
+ // This object has a stale bias from before the bulk revocation
+ // for this data type occurred. It's pointless to update the
+ // heuristics at this point so simply update the header with a
+ // CAS. If we fail this race, the object's bias has been revoked
+ // by another thread so we simply return and let the caller deal
+ // with it.
+ obj->cas_set_mark(prototype_header->set_age(mark->age()), mark);
+ assert(!obj->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
+ return BIAS_REVOKED;
+ } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
+ // The epoch of this biasing has expired indicating that the
+ // object is effectively unbiased. Depending on whether we need
+ // to rebias or revoke the bias of this object we can do it
+ // efficiently enough with a CAS that we shouldn't update the
+ // heuristics. This is normally done in the assembly code but we
+ // can reach this point due to various points in the runtime
+ // needing to revoke biases.
+ markOop res_mark;
+ if (attempt_rebias) {
+ assert(THREAD->is_Java_thread(), "");
+ markOop biased_value = mark;
+ markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
+ res_mark = obj->cas_set_mark(rebiased_prototype, mark);
+ if (res_mark == biased_value) {
+ return BIAS_REVOKED_AND_REBIASED;
+ }
+ } else {
+ markOop biased_value = mark;
+ markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
+ res_mark = obj->cas_set_mark(unbiased_prototype, mark);
+ if (res_mark == biased_value) {
+ return BIAS_REVOKED;
+ }
+ }
+ mark = res_mark; // Refresh mark with the latest value.
+ }
+ }
+
+ HeuristicsResult heuristics = update_heuristics(obj());
+ if (heuristics == HR_NOT_BIASED) {
+ return NOT_BIASED;
+ } else if (heuristics == HR_SINGLE_REVOKE) {
+ JavaThread *blt = mark->biased_locker();
+ assert(blt != NULL, "invariant");
+ if (blt == THREAD) {
+ // A thread is trying to revoke the bias of an object biased
+ // toward it, again likely due to an identity hash code
+ // computation. We can again avoid a safepoint/handshake in this case
+ // since we are only going to walk our own stack. There are no
+ // races with revocations occurring in other threads because we
+ // reach no safepoints in the revocation path.
+ EventBiasedLockSelfRevocation event;
+ ResourceMark rm;
+ walk_stack_and_revoke(obj(), blt);
+ blt->set_cached_monitor_info(NULL);
+ assert(!obj->mark()->has_bias_pattern(), "invariant");
+ if (event.should_commit()) {
+ post_self_revocation_event(&event, obj->klass());
+ }
+ return BIAS_REVOKED;
+ } else {
+ BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
+ if (cond != NOT_REVOKED) {
+ return cond;
+ }
+ }
+ } else {
+ assert((heuristics == HR_BULK_REVOKE) ||
+ (heuristics == HR_BULK_REBIAS), "?");
+ EventBiasedLockClassRevocation event;
+ VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
+ (heuristics == HR_BULK_REBIAS),
+ attempt_rebias);
+ VMThread::execute(&bulk_revoke);
+ if (event.should_commit()) {
+ post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
+ }
+ return bulk_revoke.status_code();
+ }
}
- VM_RevokeBias revoke(objs, JavaThread::current());
- VMThread::execute(&revoke);
+}
+
+// All objects in objs should be locked by biaser
+void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
+ bool clean_my_cache = false;
+ for (int i = 0; i < objs->length(); i++) {
+ oop obj = (objs->at(i))();
+ markOop mark = obj->mark();
+ if (mark->has_bias_pattern()) {
+ walk_stack_and_revoke(obj, biaser);
+ clean_my_cache = true;
+ }
+ }
+ if (clean_my_cache) {
+ clean_up_cached_monitor_info(biaser);
+ }
}
void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
oop obj = h_obj();
- HeuristicsResult heuristics = update_heuristics(obj, false);
+ HeuristicsResult heuristics = update_heuristics(obj);
if (heuristics == HR_SINGLE_REVOKE) {
- revoke_bias(obj, false, false, NULL, NULL);
+ JavaThread* biased_locker = NULL;
+ single_revoke_at_safepoint(obj, false, false, NULL, &biased_locker);
+ if (biased_locker) {
+ clean_up_cached_monitor_info(biased_locker);
+ }
} else if ((heuristics == HR_BULK_REBIAS) ||
(heuristics == HR_BULK_REVOKE)) {
bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
+ clean_up_cached_monitor_info();
}
- clean_up_cached_monitor_info();
}
@@ -774,9 +918,9 @@
int len = objs->length();
for (int i = 0; i < len; i++) {
oop obj = (objs->at(i))();
- HeuristicsResult heuristics = update_heuristics(obj, false);
+ HeuristicsResult heuristics = update_heuristics(obj);
if (heuristics == HR_SINGLE_REVOKE) {
- revoke_bias(obj, false, false, NULL, NULL);
+ single_revoke_at_safepoint(obj, false, false, NULL, NULL);
} else if ((heuristics == HR_BULK_REBIAS) ||
(heuristics == HR_BULK_REVOKE)) {
bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
@@ -862,6 +1006,7 @@
int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
+int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
@@ -885,6 +1030,7 @@
tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
+ tty->print_cr("# handshakes entries: %d", _handshakes_count);
tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
}