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8236035: refactor ObjectMonitor::set_owner() and _owner field setting

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Reviewed-by: dholmes, kbarrett, rehn
This commit is contained in:
Daniel D. Daugherty 2020-02-05 11:39:52 -05:00
parent b9e3a4efef
commit 8ff24c55ef
5 changed files with 95 additions and 33 deletions
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55
src/hotspot/share/runtime/objectMonitor.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1998, 2020, 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
@ -245,7 +245,7 @@ void ObjectMonitor::enter(TRAPS) {
// and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
Thread * const Self = THREAD;
void * cur = Atomic::cmpxchg(&_owner, (void*)NULL, Self);
void* cur = try_set_owner_from(NULL, Self);
if (cur == NULL) {
assert(_recursions == 0, "invariant");
return;
@ -260,9 +260,7 @@ void ObjectMonitor::enter(TRAPS) {
if (Self->is_lock_owned((address)cur)) {
assert(_recursions == 0, "internal state error");
_recursions = 1;
// Commute owner from a thread-specific on-stack BasicLockObject address to
// a full-fledged "Thread *".
_owner = Self;
set_owner_from_BasicLock(cur, Self); // Convert from BasicLock* to Thread*.
return;
}
@ -403,7 +401,7 @@ void ObjectMonitor::enter(TRAPS) {
int ObjectMonitor::TryLock(Thread * Self) {
void * own = _owner;
if (own != NULL) return 0;
if (Atomic::replace_if_null(&_owner, Self)) {
if (try_set_owner_from(NULL, Self) == NULL) {
assert(_recursions == 0, "invariant");
return 1;
}
@ -862,15 +860,12 @@ void ObjectMonitor::UnlinkAfterAcquire(Thread *Self, ObjectWaiter *SelfNode) {
// of such futile wakups is low.
void ObjectMonitor::exit(bool not_suspended, TRAPS) {
Thread * const Self = THREAD;
if (THREAD != _owner) {
if (THREAD->is_lock_owned((address) _owner)) {
// Transmute _owner from a BasicLock pointer to a Thread address.
// We don't need to hold _mutex for this transition.
// Non-null to Non-null is safe as long as all readers can
// tolerate either flavor.
Thread* const Self = THREAD;
void* cur = Atomic::load(&_owner);
if (THREAD != cur) {
if (THREAD->is_lock_owned((address)cur)) {
assert(_recursions == 0, "invariant");
_owner = THREAD;
set_owner_from_BasicLock(cur, Self); // Convert from BasicLock* to Thread*.
_recursions = 0;
} else {
// Apparent unbalanced locking ...
@ -914,10 +909,15 @@ void ObjectMonitor::exit(bool not_suspended, TRAPS) {
for (;;) {
assert(THREAD == _owner, "invariant");
// Drop the lock.
// release semantics: prior loads and stores from within the critical section
// must not float (reorder) past the following store that drops the lock.
Atomic::release_store(&_owner, (void*)NULL); // drop the lock
OrderAccess::storeload(); // See if we need to wake a successor
// Uses a storeload to separate release_store(owner) from the
// successor check. The try_set_owner() below uses cmpxchg() so
// we get the fence down there.
release_clear_owner(Self);
OrderAccess::storeload();
if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
return;
}
@ -959,7 +959,7 @@ void ObjectMonitor::exit(bool not_suspended, TRAPS) {
// to reacquire the lock the responsibility for ensuring succession
// falls to the new owner.
//
if (!Atomic::replace_if_null(&_owner, THREAD)) {
if (try_set_owner_from(NULL, Self) != NULL) {
return;
}
@ -1092,8 +1092,9 @@ void ObjectMonitor::ExitEpilog(Thread * Self, ObjectWaiter * Wakee) {
Wakee = NULL;
// Drop the lock
Atomic::release_store(&_owner, (void*)NULL);
OrderAccess::fence(); // ST _owner vs LD in unpark()
// Uses a fence to separate release_store(owner) from the LD in unpark().
release_clear_owner(Self);
OrderAccess::fence();
DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
Trigger->unpark();
@ -1119,10 +1120,11 @@ intx ObjectMonitor::complete_exit(TRAPS) {
assert(InitDone, "Unexpectedly not initialized");
if (THREAD != _owner) {
if (THREAD->is_lock_owned ((address)_owner)) {
void* cur = Atomic::load(&_owner);
if (THREAD != cur) {
if (THREAD->is_lock_owned((address)cur)) {
assert(_recursions == 0, "internal state error");
_owner = THREAD; // Convert from basiclock addr to Thread addr
set_owner_from_BasicLock(cur, Self); // Convert from BasicLock* to Thread*.
_recursions = 0;
}
}
@ -1167,11 +1169,12 @@ void ObjectMonitor::reenter(intx recursions, TRAPS) {
// (IMSE). If there is a pending exception and the specified thread
// is not the owner, that exception will be replaced by the IMSE.
bool ObjectMonitor::check_owner(Thread* THREAD) {
if (_owner == THREAD) {
void* cur = Atomic::load(&_owner);
if (cur == THREAD) {
return true;
}
if (THREAD->is_lock_owned((address)_owner)) {
_owner = THREAD; // convert from BasicLock addr to Thread addr
if (THREAD->is_lock_owned((address)cur)) {
set_owner_from_BasicLock(cur, THREAD); // Convert from BasicLock* to Thread*.
_recursions = 0;
return true;
}
@ -1680,7 +1683,7 @@ int ObjectMonitor::TrySpin(Thread * Self) {
Thread * ox = (Thread *) _owner;
if (ox == NULL) {
ox = (Thread*)Atomic::cmpxchg(&_owner, (void*)NULL, Self);
ox = (Thread*)try_set_owner_from(NULL, Self);
if (ox == NULL) {
// The CAS succeeded -- this thread acquired ownership
// Take care of some bookkeeping to exit spin state.