JDK14/Java14源码在线阅读
/*
* Copyright (c) 2005, 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
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* questions.
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*/
#include "precompiled.hpp"
#include "classfile/classLoaderDataGraph.hpp"
#include "jfr/jfrEvents.hpp"
#include "jfr/support/jfrThreadId.hpp"
#include "logging/log.hpp"
#include "memory/resourceArea.hpp"
#include "oops/klass.inline.hpp"
#include "oops/markWord.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/basicLock.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/handshake.hpp"
#include "runtime/safepointMechanism.hpp"
#include "runtime/task.hpp"
#include "runtime/threadSMR.hpp"
#include "runtime/vframe.hpp"
#include "runtime/vmThread.hpp"
#include "runtime/vmOperations.hpp"
static bool _biased_locking_enabled = false;
BiasedLockingCounters BiasedLocking::_counters;
static GrowableArray<Handle>* _preserved_oop_stack = NULL;
static GrowableArray<markWord>* _preserved_mark_stack = NULL;
static void enable_biased_locking(InstanceKlass* k) {
k->set_prototype_header(markWord::biased_locking_prototype());
}
static void enable_biased_locking() {
_biased_locking_enabled = true;
log_info(biasedlocking)("Biased locking enabled");
}
class VM_EnableBiasedLocking: public VM_Operation {
public:
VM_EnableBiasedLocking() {}
VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
void doit() {
// Iterate the class loader data dictionaries enabling biased locking for all
// currently loaded classes.
ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
// Indicate that future instances should enable it as well
enable_biased_locking();
}
bool allow_nested_vm_operations() const { return false; }
};
// One-shot PeriodicTask subclass for enabling biased locking
class EnableBiasedLockingTask : public PeriodicTask {
public:
EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
virtual void task() {
VM_EnableBiasedLocking op;
VMThread::execute(&op);
// Reclaim our storage and disenroll ourself
delete this;
}
};
void BiasedLocking::init() {
// If biased locking is enabled and BiasedLockingStartupDelay is set,
// schedule a task to fire after the specified delay which turns on
// biased locking for all currently loaded classes as well as future
// ones. This could be a workaround for startup time regressions
// due to large number of safepoints being taken during VM startup for
// bias revocation.
if (UseBiasedLocking) {
if (BiasedLockingStartupDelay > 0) {
EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
task->enroll();
} else {
enable_biased_locking();
}
}
}
bool BiasedLocking::enabled() {
assert(UseBiasedLocking, "precondition");
// We check "BiasedLockingStartupDelay == 0" here to cover the
// possibility of calls to BiasedLocking::enabled() before
// BiasedLocking::init().
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();
if (info != NULL) {
return info;
}
info = new GrowableArray<MonitorInfo*>();
// It's possible for the thread to not have any Java frames on it,
// i.e., if it's the main thread and it's already returned from main()
if (thread->has_last_Java_frame()) {
RegisterMap rm(thread);
for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
GrowableArray<MonitorInfo*> *monitors = vf->monitors();
if (monitors != NULL) {
int len = monitors->length();
// Walk monitors youngest to oldest
for (int i = len - 1; i >= 0; i--) {
MonitorInfo* mon_info = monitors->at(i);
if (mon_info->eliminated()) continue;
oop owner = mon_info->owner();
if (owner != NULL) {
info->append(mon_info);
}
}
}
}
}
thread->set_cached_monitor_info(info);
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).
void BiasedLocking::single_revoke_at_safepoint(oop obj, 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");
markWord mark = obj->mark();
if (!mark.has_bias_pattern()) {
if (log_is_enabled(Info, biasedlocking)) {
ResourceMark rm;
log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
", mark " INTPTR_FORMAT ", type %s"
", requesting thread " INTPTR_FORMAT
" because it's no longer biased)",
p2i((void *)obj), mark.value(),
obj->klass()->external_name(),
(intptr_t) requesting_thread);
}
return;
}
uint age = mark.age();
markWord unbiased_prototype = markWord::prototype().set_age(age);
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
ResourceMark rm;
log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
", requesting thread " INTPTR_FORMAT,
p2i((void *)obj),
mark.value(),
obj->klass()->external_name(),
obj->klass()->prototype_header().value(),
(intptr_t) requesting_thread);
} else {
ResourceMark rm;
log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
" , requesting thread " INTPTR_FORMAT,
p2i((void *)obj),
mark.value(),
obj->klass()->external_name(),
obj->klass()->prototype_header().value(),
(intptr_t) requesting_thread);
}
JavaThread* biased_thread = mark.biased_locker();
if (biased_thread == NULL) {
// Object is anonymously biased. We can get here if, for
// example, we revoke the bias due to an identity hash code
// being computed for an object.
obj->set_mark(unbiased_prototype);
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
} else {
log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
}
return;
}
// Handle case where the thread toward which the object was biased has exited
bool thread_is_alive = false;
if (requesting_thread == biased_thread) {
thread_is_alive = true;
} else {
ThreadsListHandle tlh;
thread_is_alive = tlh.includes(biased_thread);
}
if (!thread_is_alive) {
obj->set_mark(unbiased_prototype);
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
PTR_FORMAT ")", p2i(biased_thread));
} else {
log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
PTR_FORMAT ")", p2i(biased_thread));
}
return;
}
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
PTR_FORMAT ")", p2i(biased_thread));
} else {
log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
PTR_FORMAT ")", p2i(biased_thread));
}
// Thread owning bias is alive.
// Check to see whether it currently owns the lock and, if so,
// write down the needed displaced headers to the thread's stack.
// Otherwise, restore the object's header either to the unlocked
// or unbiased state.
GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
BasicLock* highest_lock = NULL;
for (int i = 0; i < cached_monitor_info->length(); i++) {
MonitorInfo* mon_info = cached_monitor_info->at(i);
if (mon_info->owner() == obj) {
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 below
markWord mark = markWord::encode((BasicLock*) NULL);
highest_lock = mon_info->lock();
highest_lock->set_displaced_header(mark);
} else {
log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
p2i((void *) mon_info->owner()),
p2i((void *) 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(markWord::encode(highest_lock));
assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
log_info(biasedlocking)(" Revoked bias of currently-locked object");
} else {
log_trace(biasedlocking)(" Revoked bias of currently-locked object");
}
} else {
// Log at "info" level if not bulk, else "trace" level
if (!is_bulk) {
log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
} else {
log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
}
// Store the unlocked value into the object's header.
obj->set_mark(unbiased_prototype);
}
// If requested, return information on which thread held the bias
if (biased_locker != NULL) {
*biased_locker = biased_thread;
}
}
enum HeuristicsResult {
HR_NOT_BIASED = 1,
HR_SINGLE_REVOKE = 2,
HR_BULK_REBIAS = 3,
HR_BULK_REVOKE = 4
};
static HeuristicsResult update_heuristics(oop o) {
markWord mark = o->mark();
if (!mark.has_bias_pattern()) {
return HR_NOT_BIASED;
}
// Heuristics to attempt to throttle the number of revocations.
// Stages:
// 1. Revoke the biases of all objects in the heap of this type,
// but allow rebiasing of those objects if unlocked.
// 2. Revoke the biases of all objects in the heap of this type
// and don't allow rebiasing of these objects. Disable
// allocation of objects of that type with the bias bit set.
Klass* k = o->klass();
jlong cur_time = os::javaTimeMillis();
jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
int revocation_count = k->biased_lock_revocation_count();
if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
(revocation_count < BiasedLockingBulkRevokeThreshold) &&
(last_bulk_revocation_time != 0) &&
(cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
// This is the first revocation we've seen in a while of an
// object of this type since the last time we performed a bulk
// rebiasing operation. The application is allocating objects in
// bulk which are biased toward a thread and then handing them
// off to another thread. We can cope with this allocation
// pattern via the bulk rebiasing mechanism so we reset the
// klass's revocation count rather than allow it to increase
// monotonically. If we see the need to perform another bulk
// rebias operation later, we will, and if subsequently we see
// many more revocation operations in a short period of time we
// will completely disable biasing for this type.
k->set_biased_lock_revocation_count(0);
revocation_count = 0;
}
// Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
revocation_count = k->atomic_incr_biased_lock_revocation_count();
}
if (revocation_count == BiasedLockingBulkRevokeThreshold) {
return HR_BULK_REVOKE;
}
if (revocation_count == BiasedLockingBulkRebiasThreshold) {
return HR_BULK_REBIAS;
}
return HR_SINGLE_REVOKE;
}
void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, 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",
(bulk_rebias ? "rebias" : "revoke"),
p2i((void *) o),
o->mark().value(),
o->klass()->external_name());
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;
{
JavaThreadIteratorWithHandle jtiwh;
if (bulk_rebias) {
// Use the epoch in the klass of the object to implicitly revoke
// all biases of objects of this data type and force them to be
// reacquired. However, we also need to walk the stacks of all
// threads and update the headers of lightweight locked objects
// with biases to have the current epoch.
// If the prototype header doesn't have the bias pattern, don't
// try to update the epoch -- assume another VM operation came in
// and reset the header to the unbiased state, which will
// implicitly cause all existing biases to be revoked
if (klass->prototype_header().has_bias_pattern()) {
int prev_epoch = klass->prototype_header().bias_epoch();
klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
int cur_epoch = klass->prototype_header().bias_epoch();
// Now walk all threads' stacks and adjust epochs of any biased
// and locked objects of this data type we encounter
for (; JavaThread *thr = jtiwh.next(); ) {
GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
for (int i = 0; i < cached_monitor_info->length(); i++) {
MonitorInfo* mon_info = cached_monitor_info->at(i);
oop owner = mon_info->owner();
markWord mark = owner->mark();
if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
// We might have encountered this object already in the case of recursive locking
assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
owner->set_mark(mark.set_bias_epoch(cur_epoch));
}
}
}
}
// At this point we're done. All we have to do is potentially
// adjust the header of the given object to revoke its bias.
single_revoke_at_safepoint(o, true, requesting_thread, NULL);
} else {
if (log_is_enabled(Info, biasedlocking)) {
ResourceMark rm;
log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
}
// Disable biased locking for this data type. Not only will this
// cause future instances to not be biased, but existing biased
// instances will notice that this implicitly caused their biases
// to be revoked.
klass->set_prototype_header(markWord::prototype());
// Now walk all threads' stacks and forcibly revoke the biases of
// any locked and biased objects of this data type we encounter.
for (; JavaThread *thr = jtiwh.next(); ) {
GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
for (int i = 0; i < cached_monitor_info->length(); i++) {
MonitorInfo* mon_info = cached_monitor_info->at(i);
oop owner = mon_info->owner();
markWord mark = owner->mark();
if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
single_revoke_at_safepoint(owner, true, requesting_thread, NULL);
}
}
}
// Must force the bias of the passed object to be forcibly revoked
// as well to ensure guarantees to callers
single_revoke_at_safepoint(o, true, requesting_thread, NULL);
}
} // ThreadsListHandle is destroyed here.
log_info(biasedlocking)("* Ending bulk revocation");
assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation");
}
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_BulkRevokeBias : public VM_Operation {
private:
Handle* _obj;
JavaThread* _requesting_thread;
bool _bulk_rebias;
uint64_t _safepoint_id;
public:
VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
bool bulk_rebias)
: _obj(obj)
, _requesting_thread(requesting_thread)
, _bulk_rebias(bulk_rebias)
, _safepoint_id(0) {}
virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
virtual void doit() {
BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread);
_safepoint_id = SafepointSynchronize::safepoint_id();
clean_up_cached_monitor_info();
}
bool is_bulk_rebias() const {
return _bulk_rebias;
}
uint64_t safepoint_id() const {
return _safepoint_id;
}
};
class RevokeOneBias : public HandshakeClosure {
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)
: HandshakeClosure("RevokeOneBias")
, _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");
oop o = _obj();
markWord mark = o->mark();
if (!mark.has_bias_pattern()) {
return;
}
markWord 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.
markWord biased_value = mark;
mark = o->cas_set_mark(markWord::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;
}
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 {
markWord biased_value = mark;
mark = o->cas_set_mark(markWord::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;
}
}
}
_status_code = BiasedLocking::NOT_REVOKED;
}
BiasedLocking::Condition status_code() const {
return _status_code;
}
traceid biased_locker() const {
return _biased_locker_id;
}
};
static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
assert(event != NULL, "invariant");
assert(k != NULL, "invariant");
assert(event->should_commit(), "invariant");
event->set_lockClass(k);
event->commit();
}
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(0);
event->set_previousOwner(op->biased_locker());
event->commit();
}
static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
assert(event != NULL, "invariant");
assert(k != NULL, "invariant");
assert(op != NULL, "invariant");
assert(event->should_commit(), "invariant");
event->set_revokedClass(k);
event->set_disableBiasing(!op->is_bulk_rebias());
event->set_safepointId(op->safepoint_id());
event->commit();
}
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()));
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);
}
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);
markWord 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;
markWord 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(markWord::prototype().set_age(mark.age()), mark);
if (event.should_commit()) {
post_revocation_event(&event, obj->klass(), &revoke);
}
assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now");
return BIAS_REVOKED;
}
}
}
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() || !SafepointMechanism::uses_thread_local_poll(),
"if SafepointMechanism::uses_thread_local_poll() is enabled this should always be executed outside safepoints");
assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
markWord 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),
mark.value(),
obj->klass()->external_name(),
obj->klass()->prototype_header().value(),
p2i(biased_locker),
Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
markWord unbiased_prototype = markWord::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 (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
markWord mark = markWord::encode((BasicLock*) NULL);
highest_lock = mon_info->lock();
highest_lock->set_displaced_header(mark);
} else {
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(markWord::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(!obj->mark().has_bias_pattern(), "must not be biased");
}
void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) {
assert(THREAD->is_Java_thread(), "must be called by a JavaThread");
JavaThread* thread = (JavaThread*)THREAD;
markWord mark = obj->mark();
if (!mark.has_bias_pattern()) {
return;
}
Klass *k = obj->klass();
assert(mark.biased_locker() == thread &&
k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state");
ResourceMark rm;
log_info(biasedlocking)("Revoking bias by walking my own stack:");
EventBiasedLockSelfRevocation event;
BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread);
thread->set_cached_monitor_info(NULL);
assert(!obj->mark().has_bias_pattern(), "invariant");
if (event.should_commit()) {
post_self_revocation_event(&event, k);
}
}
void BiasedLocking::revoke(Handle obj, TRAPS) {
assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
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.
markWord mark = obj->mark();
if (!mark.has_bias_pattern()) {
return;
}
if (mark.is_biased_anonymously()) {
// 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.
markWord biased_value = mark;
markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
if (res_mark == biased_value) {
return;
}
mark = res_mark; // Refresh mark with the latest value.
} else {
Klass* k = obj->klass();
markWord 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;
} else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
// The epoch of this biasing has expired indicating that the
// object is effectively unbiased. We can revoke the bias of this
// object 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.
markWord res_mark;
markWord biased_value = mark;
markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
res_mark = obj->cas_set_mark(unbiased_prototype, mark);
if (res_mark == biased_value) {
return;
}
mark = res_mark; // Refresh mark with the latest value.
}
}
HeuristicsResult heuristics = update_heuristics(obj());
if (heuristics == HR_NOT_BIASED) {
return;
} 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;
} else {
BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
if (cond != NOT_REVOKED) {
return;
}
}
} else {
assert((heuristics == HR_BULK_REVOKE) ||
(heuristics == HR_BULK_REBIAS), "?");
EventBiasedLockClassRevocation event;
VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
(heuristics == HR_BULK_REBIAS));
VMThread::execute(&bulk_revoke);
if (event.should_commit()) {
post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
}
return;
}
}
}
// 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))();
markWord 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);
if (heuristics == HR_SINGLE_REVOKE) {
JavaThread* biased_locker = NULL;
single_revoke_at_safepoint(obj, 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_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL);
clean_up_cached_monitor_info();
}
}
void BiasedLocking::preserve_marks() {
if (!UseBiasedLocking)
return;
assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
assert(_preserved_oop_stack == NULL, "double initialization");
assert(_preserved_mark_stack == NULL, "double initialization");
// In order to reduce the number of mark words preserved during GC
// due to the presence of biased locking, we reinitialize most mark
// words to the class's prototype during GC -- even those which have
// a currently valid bias owner. One important situation where we
// must not clobber a bias is when a biased object is currently
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