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8325303: Replace markWord.is_neutral() with markWord.is_unlocked()

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Reviewed-by: stefank, dcubed
This commit is contained in:
David Holmes 2024-04-05 01:10:03 +00:00
parent 27cfcef99f
commit 34f7974a40
5 changed files with 24 additions and 24 deletions
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6
src/hotspot/share/oops/markWord.cpp
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -80,8 +80,8 @@ void markWord::print_on(outputStream* st, bool print_monitor_info) const {
st->print(" locked(" INTPTR_FORMAT ")", value()); st->print(" locked(" INTPTR_FORMAT ")", value());
} else { } else {
st->print(" mark("); st->print(" mark(");
if (is_neutral()) { // last bits = 01 if (is_unlocked()) { // last bits = 01
st->print("is_neutral"); st->print("is_unlocked");
if (has_no_hash()) { if (has_no_hash()) {
st->print(" no_hash"); st->print(" no_hash");
} else { } else {

4
src/hotspot/share/oops/markWord.hpp
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -143,7 +143,7 @@ class markWord {
bool is_marked() const { bool is_marked() const {
return (mask_bits(value(), lock_mask_in_place) == marked_value); return (mask_bits(value(), lock_mask_in_place) == marked_value);
} }
bool is_neutral() const { bool is_neutral() const { // Not locked, or marked - a "clean" neutral state
return (mask_bits(value(), lock_mask_in_place) == unlocked_value); return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
} }

10
src/hotspot/share/runtime/basicLock.cpp
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -40,10 +40,10 @@ void BasicLock::print_on(outputStream* st, oop owner) const {
void BasicLock::move_to(oop obj, BasicLock* dest) { void BasicLock::move_to(oop obj, BasicLock* dest) {
// Check to see if we need to inflate the lock. This is only needed // Check to see if we need to inflate the lock. This is only needed
// if an object is locked using "this" lightweight monitor. In that // if an object is locked using "this" lightweight monitor. In that
// case, the displaced_header() is unlocked/is_neutral, because the // case, the displaced_header() is unlocked/neutral, because the
// displaced_header() contains the header for the originally unlocked // displaced_header() contains the header for the originally unlocked
// object. However the lock could have already been inflated. But it // object. However the lock could have already been inflated. But it
// does not matter, this inflation will just a no-op. For other cases, // does not matter, this inflation will just be a no-op. For other cases,
// the displaced header will be either 0x0 or 0x3, which are location // the displaced header will be either 0x0 or 0x3, which are location
// independent, therefore the BasicLock is free to move. // independent, therefore the BasicLock is free to move.
// //
@ -63,11 +63,11 @@ void BasicLock::move_to(oop obj, BasicLock* dest) {
// one stack location to another. This avoids inflation. Obviously, // one stack location to another. This avoids inflation. Obviously,
// we need to ensure that both locations refer to the current thread's stack. // we need to ensure that both locations refer to the current thread's stack.
// There are some subtle concurrency issues, however, and since the benefit is // There are some subtle concurrency issues, however, and since the benefit is
// is small (given the support for inflated fast-path locking in the fast_lock, etc) // small (given the support for inflated fast-path locking in the fast_lock, etc)
// we'll leave that optimization for another time. // we'll leave that optimization for another time.
if (LockingMode == LM_LEGACY) { if (LockingMode == LM_LEGACY) {
if (displaced_header().is_neutral()) { if (displaced_header().is_unlocked()) {
// The object is locked and the resulting ObjectMonitor* will also be // The object is locked and the resulting ObjectMonitor* will also be
// locked so it can't be async deflated until ownership is dropped. // locked so it can't be async deflated until ownership is dropped.
ObjectSynchronizer::inflate_helper(obj); ObjectSynchronizer::inflate_helper(obj);

6
src/hotspot/share/runtime/basicLock.hpp
View File

@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -34,6 +34,8 @@ class BasicLock {
friend class VMStructs; friend class VMStructs;
friend class JVMCIVMStructs; friend class JVMCIVMStructs;
private: private:
// This is either the actual displaced header from a locked object, or
// a sentinel zero value indicating a recursive stack-lock.
volatile markWord _displaced_header; volatile markWord _displaced_header;
public: public:
markWord displaced_header() const { markWord displaced_header() const {
@ -46,7 +48,7 @@ class BasicLock {
void print_on(outputStream* st, oop owner) const; void print_on(outputStream* st, oop owner) const;
// move a basic lock (used during deoptimization // move a basic lock (used during deoptimization)
void move_to(oop obj, BasicLock* dest); void move_to(oop obj, BasicLock* dest);
static int displaced_header_offset_in_bytes() { return (int)offset_of(BasicLock, _displaced_header); } static int displaced_header_offset_in_bytes() { return (int)offset_of(BasicLock, _displaced_header); }

22
src/hotspot/share/runtime/synchronizer.cpp
View File

@ -602,7 +602,7 @@ bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread
} }
markWord mark = obj()->mark_acquire(); markWord mark = obj()->mark_acquire();
while (mark.is_neutral()) { while (mark.is_unlocked()) {
// Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications. // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
// Try to swing into 'fast-locked' state. // Try to swing into 'fast-locked' state.
assert(!lock_stack.contains(obj()), "thread must not already hold the lock"); assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
@ -625,7 +625,7 @@ bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread
return false; return false;
} else if (LockingMode == LM_LEGACY) { } else if (LockingMode == LM_LEGACY) {
markWord mark = obj->mark(); markWord mark = obj->mark();
if (mark.is_neutral()) { if (mark.is_unlocked()) {
// Anticipate successful CAS -- the ST of the displaced mark must // Anticipate successful CAS -- the ST of the displaced mark must
// be visible <= the ST performed by the CAS. // be visible <= the ST performed by the CAS.
lock->set_displaced_header(mark); lock->set_displaced_header(mark);
@ -696,7 +696,7 @@ void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current)
// Only do diagnostics if we are not racing an inflation. Simply // Only do diagnostics if we are not racing an inflation. Simply
// exiting a recursive enter of a Java Monitor that is being // exiting a recursive enter of a Java Monitor that is being
// inflated is safe; see the has_monitor() comment below. // inflated is safe; see the has_monitor() comment below.
assert(!mark.is_neutral(), "invariant"); assert(!mark.is_unlocked(), "invariant");
assert(!mark.has_locker() || assert(!mark.has_locker() ||
current->is_lock_owned((address)mark.locker()), "invariant"); current->is_lock_owned((address)mark.locker()), "invariant");
if (mark.has_monitor()) { if (mark.has_monitor()) {
@ -1009,7 +1009,7 @@ intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)"); assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked"); guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
} }
if (mark.is_neutral() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) { if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
hash = mark.hash(); hash = mark.hash();
if (hash != 0) { // if it has a hash, just return it if (hash != 0) { // if it has a hash, just return it
return hash; return hash;
@ -1139,7 +1139,7 @@ bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
return monitor->is_entered(current) != 0; return monitor->is_entered(current) != 0;
} }
// Unlocked case, header in place // Unlocked case, header in place
assert(mark.is_neutral(), "sanity check"); assert(mark.is_unlocked(), "sanity check");
return false; return false;
} }
@ -1172,7 +1172,7 @@ JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_ob
// Unlocked case, header in place // Unlocked case, header in place
// Cannot have assertion since this object may have been // Cannot have assertion since this object may have been
// locked by another thread when reaching here. // locked by another thread when reaching here.
// assert(mark.is_neutral(), "sanity check"); // assert(mark.is_unlocked(), "sanity check");
return nullptr; return nullptr;
} }
@ -1423,7 +1423,7 @@ ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oo
// * stack-locked - Coerce it to inflated from stack-locked. // * stack-locked - Coerce it to inflated from stack-locked.
// * INFLATING - Busy wait for conversion from stack-locked to // * INFLATING - Busy wait for conversion from stack-locked to
// inflated. // inflated.
// * neutral - Aggressively inflate the object. // * unlocked - Aggressively inflate the object.
// CASE: inflated // CASE: inflated
if (mark.has_monitor()) { if (mark.has_monitor()) {
@ -1601,7 +1601,7 @@ ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oo
return m; return m;
} }
// CASE: neutral // CASE: unlocked
// TODO-FIXME: for entry we currently inflate and then try to CAS _owner. // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
// If we know we're inflating for entry it's better to inflate by swinging a // If we know we're inflating for entry it's better to inflate by swinging a
// pre-locked ObjectMonitor pointer into the object header. A successful // pre-locked ObjectMonitor pointer into the object header. A successful
@ -1610,9 +1610,7 @@ ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oo
// to inflate and then CAS() again to try to swing _owner from null to current. // to inflate and then CAS() again to try to swing _owner from null to current.
// An inflateTry() method that we could call from enter() would be useful. // An inflateTry() method that we could call from enter() would be useful.
// Catch if the object's header is not neutral (not locked and assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
// not marked is what we care about here).
assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
ObjectMonitor* m = new ObjectMonitor(object); ObjectMonitor* m = new ObjectMonitor(object);
// prepare m for installation - set monitor to initial state // prepare m for installation - set monitor to initial state
m->set_header(mark); m->set_header(mark);
@ -1635,7 +1633,7 @@ ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oo
OM_PERFDATA_OP(Inflations, inc()); OM_PERFDATA_OP(Inflations, inc());
if (log_is_enabled(Trace, monitorinflation)) { if (log_is_enabled(Trace, monitorinflation)) {
ResourceMark rm; ResourceMark rm;
lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
INTPTR_FORMAT ", type='%s'", p2i(object), INTPTR_FORMAT ", type='%s'", p2i(object),
object->mark().value(), object->klass()->external_name()); object->mark().value(), object->klass()->external_name());
} }