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8238174: migrate ObjectMonitor::_owner field away from C++ volatile semantics

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Reviewed-by: dholmes, mdoerr
This commit is contained in:
Daniel D. Daugherty 2020-11-18 16:48:17 +00:00
parent 50a2c22ff7
commit 1707d5ca3c
4 changed files with 48 additions and 42 deletions
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64
src/hotspot/share/runtime/objectMonitor.cpp
View file

@ -341,7 +341,7 @@ bool ObjectMonitor::enter(TRAPS) {
// Note that if we acquire the monitor from an initial spin
// we forgo posting JVMTI events and firing DTRACE probes.
if (TrySpin(Self) > 0) {
assert(_owner == Self, "must be Self: owner=" INTPTR_FORMAT, p2i(_owner));
assert(owner_raw() == Self, "must be Self: owner=" INTPTR_FORMAT, p2i(owner_raw()));
assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions);
assert(object()->mark() == markWord::encode(this),
"object mark must match encoded this: mark=" INTPTR_FORMAT
@ -351,7 +351,7 @@ bool ObjectMonitor::enter(TRAPS) {
return true;
}
assert(_owner != Self, "invariant");
assert(owner_raw() != Self, "invariant");
assert(_succ != Self, "invariant");
JavaThread * jt = Self->as_Java_thread();
assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
@ -442,7 +442,7 @@ bool ObjectMonitor::enter(TRAPS) {
// Must either set _recursions = 0 or ASSERT _recursions == 0.
assert(_recursions == 0, "invariant");
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_succ != Self, "invariant");
assert(object()->mark() == markWord::encode(this), "invariant");
@ -480,7 +480,7 @@ bool ObjectMonitor::enter(TRAPS) {
// Callers must compensate as needed.
int ObjectMonitor::TryLock(Thread * Self) {
void * own = _owner;
void* own = owner_raw();
if (own != NULL) return 0;
if (try_set_owner_from(NULL, Self) == NULL) {
assert(_recursions == 0, "invariant");
@ -660,8 +660,8 @@ const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
} else {
ss->print("contentions=0");
}
if (_owner != DEFLATER_MARKER) {
ss->print("owner=" INTPTR_FORMAT, p2i(_owner));
if (!owner_is_DEFLATER_MARKER()) {
ss->print("owner=" INTPTR_FORMAT, p2i(owner_raw()));
} else {
// We report NULL instead of DEFLATER_MARKER here because is_busy()
// ignores DEFLATER_MARKER values.
@ -681,7 +681,7 @@ void ObjectMonitor::EnterI(TRAPS) {
// Try the lock - TATAS
if (TryLock (Self) > 0) {
assert(_succ != Self, "invariant");
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_Responsible != Self, "invariant");
return;
}
@ -714,7 +714,7 @@ void ObjectMonitor::EnterI(TRAPS) {
// effects.
if (TrySpin(Self) > 0) {
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_succ != Self, "invariant");
assert(_Responsible != Self, "invariant");
return;
@ -722,7 +722,7 @@ void ObjectMonitor::EnterI(TRAPS) {
// The Spin failed -- Enqueue and park the thread ...
assert(_succ != Self, "invariant");
assert(_owner != Self, "invariant");
assert(owner_raw() != Self, "invariant");
assert(_Responsible != Self, "invariant");
// Enqueue "Self" on ObjectMonitor's _cxq.
@ -752,7 +752,7 @@ void ObjectMonitor::EnterI(TRAPS) {
// As an optional optimization we retry the lock.
if (TryLock (Self) > 0) {
assert(_succ != Self, "invariant");
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_Responsible != Self, "invariant");
return;
}
@ -804,7 +804,7 @@ void ObjectMonitor::EnterI(TRAPS) {
for (;;) {
if (TryLock(Self) > 0) break;
assert(_owner != Self, "invariant");
assert(owner_raw() != Self, "invariant");
// park self
if (_Responsible == Self) {
@ -873,7 +873,7 @@ void ObjectMonitor::EnterI(TRAPS) {
// The head of cxq is volatile but the interior is stable.
// In addition, Self.TState is stable.
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
UnlinkAfterAcquire(Self, &node);
if (_succ == Self) _succ = NULL;
@ -949,7 +949,7 @@ void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
for (;;) {
ObjectWaiter::TStates v = SelfNode->TState;
guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
assert(_owner != Self, "invariant");
assert(owner_raw() != Self, "invariant");
if (TryLock(Self) > 0) break;
if (TrySpin(Self) > 0) break;
@ -1008,7 +1008,7 @@ void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
// The head of cxq is volatile but the interior is stable.
// In addition, Self.TState is stable.
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(object()->mark() == markWord::encode(this), "invariant");
UnlinkAfterAcquire(Self, SelfNode);
if (_succ == Self) _succ = NULL;
@ -1022,7 +1022,7 @@ void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
// unlinking the thread until ::exit()-time.
void ObjectMonitor::UnlinkAfterAcquire(Thread *Self, ObjectWaiter *SelfNode) {
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(SelfNode->_thread == Self, "invariant");
if (SelfNode->TState == ObjectWaiter::TS_ENTER) {
@ -1142,7 +1142,7 @@ void ObjectMonitor::UnlinkAfterAcquire(Thread *Self, ObjectWaiter *SelfNode) {
void ObjectMonitor::exit(bool not_suspended, TRAPS) {
Thread* const Self = THREAD;
void* cur = Atomic::load(&_owner);
void* cur = owner_raw();
if (THREAD != cur) {
if (THREAD->is_lock_owned((address)cur)) {
assert(_recursions == 0, "invariant");
@ -1188,7 +1188,7 @@ void ObjectMonitor::exit(bool not_suspended, TRAPS) {
#endif
for (;;) {
assert(THREAD == _owner, "invariant");
assert(THREAD == owner_raw(), "invariant");
// Drop the lock.
// release semantics: prior loads and stores from within the critical section
@ -1244,7 +1244,7 @@ void ObjectMonitor::exit(bool not_suspended, TRAPS) {
return;
}
guarantee(_owner == THREAD, "invariant");
guarantee(owner_raw() == THREAD, "invariant");
ObjectWaiter * w = NULL;
@ -1356,7 +1356,7 @@ bool ObjectMonitor::ExitSuspendEquivalent(JavaThread * jSelf) {
void ObjectMonitor::ExitEpilog(Thread * Self, ObjectWaiter * Wakee) {
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
// Exit protocol:
// 1. ST _succ = wakee
@ -1400,7 +1400,7 @@ intx ObjectMonitor::complete_exit(TRAPS) {
assert(InitDone, "Unexpectedly not initialized");
void* cur = Atomic::load(&_owner);
void* cur = owner_raw();
if (THREAD != cur) {
if (THREAD->is_lock_owned((address)cur)) {
assert(_recursions == 0, "internal state error");
@ -1409,11 +1409,11 @@ intx ObjectMonitor::complete_exit(TRAPS) {
}
}
guarantee(Self == _owner, "complete_exit not owner");
guarantee(Self == owner_raw(), "complete_exit not owner");
intx save = _recursions; // record the old recursion count
_recursions = 0; // set the recursion level to be 0
exit(true, Self); // exit the monitor
guarantee(_owner != Self, "invariant");
guarantee(owner_raw() != Self, "invariant");
return save;
}
@ -1423,7 +1423,7 @@ bool ObjectMonitor::reenter(intx recursions, TRAPS) {
Thread * const Self = THREAD;
JavaThread * jt = Self->as_Java_thread();
guarantee(_owner != Self, "reenter already owner");
guarantee(owner_raw() != Self, "reenter already owner");
if (!enter(THREAD)) {
return false;
}
@ -1451,7 +1451,7 @@ bool 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) {
void* cur = Atomic::load(&_owner);
void* cur = owner_raw();
if (cur == THREAD) {
return true;
}
@ -1549,7 +1549,7 @@ void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
_waiters++; // increment the number of waiters
_recursions = 0; // set the recursion level to be 1
exit(true, Self); // exit the monitor
guarantee(_owner != Self, "invariant");
guarantee(owner_raw() != Self, "invariant");
// The thread is on the WaitSet list - now park() it.
// On MP systems it's conceivable that a brief spin before we park
@ -1664,7 +1664,7 @@ void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
assert(Self->_Stalled != 0, "invariant");
Self->_Stalled = 0;
assert(_owner != Self, "invariant");
assert(owner_raw() != Self, "invariant");
ObjectWaiter::TStates v = node.TState;
if (v == ObjectWaiter::TS_RUN) {
enter(Self);
@ -1679,7 +1679,7 @@ void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
// Node is about to go out-of-scope, but even if it were immortal we wouldn't
// want residual elements associated with this thread left on any lists.
guarantee(node.TState == ObjectWaiter::TS_RUN, "invariant");
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_succ != Self, "invariant");
} // OSThreadWaitState()
@ -1691,7 +1691,7 @@ void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
_waiters--; // decrement the number of waiters
// Verify a few postconditions
assert(_owner == Self, "invariant");
assert(owner_raw() == Self, "invariant");
assert(_succ != Self, "invariant");
assert(object()->mark() == markWord::encode(this), "invariant");
@ -1920,7 +1920,7 @@ int ObjectMonitor::TrySpin(Thread * Self) {
ctr = _SpinDuration;
if (ctr <= 0) return 0;
if (NotRunnable(Self, (Thread *) _owner)) {
if (NotRunnable(Self, (Thread *) owner_raw())) {
return 0;
}
@ -1966,7 +1966,7 @@ int ObjectMonitor::TrySpin(Thread * Self) {
// the spin without prejudice or apply a "penalty" to the
// spin count-down variable "ctr", reducing it by 100, say.
Thread * ox = (Thread *) _owner;
Thread * ox = (Thread *) owner_raw();
if (ox == NULL) {
ox = (Thread*)try_set_owner_from(NULL, Self);
if (ox == NULL) {
@ -2092,7 +2092,7 @@ int ObjectMonitor::NotRunnable(Thread * Self, Thread * ox) {
if (BlockedOn == 1) return 1;
if (BlockedOn != 0) {
return BlockedOn != intptr_t(this) && _owner == ox;
return BlockedOn != intptr_t(this) && owner_raw() == ox;
}
assert(sizeof(((JavaThread *)ox)->_thread_state == sizeof(int)), "invariant");
@ -2284,7 +2284,7 @@ void ObjectMonitor::print_debug_style_on(outputStream* st) const {
st->print_cr(" ...");
st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
st->print_cr(" }");
st->print_cr(" _owner = " INTPTR_FORMAT, p2i(_owner));
st->print_cr(" _owner = " INTPTR_FORMAT, p2i(owner_raw()));
st->print_cr(" _previous_owner_tid = " JLONG_FORMAT, _previous_owner_tid);
st->print_cr(" _pad_buf1 = {");
st->print_cr(" [0] = '\\0'");

11
src/hotspot/share/runtime/objectMonitor.hpp
View file

@ -147,13 +147,13 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
sizeof(WeakHandle));
// Used by async deflation as a marker in the _owner field:
#define DEFLATER_MARKER reinterpret_cast<void*>(-1)
void* volatile _owner; // pointer to owning thread OR BasicLock
void* _owner; // pointer to owning thread OR BasicLock
volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
// Separate _owner and _next_om on different cache lines since
// both can have busy multi-threaded access. _previous_owner_tid is only
// changed by ObjectMonitor::exit() so it is a good choice to share the
// cache line with _owner.
DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void*) +
sizeof(volatile jlong));
ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
volatile intx _recursions; // recursion count, 0 for first entry
@ -242,8 +242,8 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
if (contentions() > 0) {
ret_code |= contentions();
}
if (_owner != DEFLATER_MARKER) {
ret_code |= intptr_t(_owner);
if (!owner_is_DEFLATER_MARKER()) {
ret_code |= intptr_t(owner_raw());
}
return ret_code;
}
@ -252,8 +252,9 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
intptr_t is_entered(Thread* current) const;
void* owner() const; // Returns NULL if DEFLATER_MARKER is observed.
void* owner_raw() const;
// Returns true if owner field == DEFLATER_MARKER and false otherwise.
bool owner_is_DEFLATER_MARKER();
bool owner_is_DEFLATER_MARKER() const;
// Returns true if 'this' is being async deflated and false otherwise.
bool is_being_async_deflated();
// Clear _owner field; current value must match old_value.

13
src/hotspot/share/runtime/objectMonitor.inline.hpp
View file

@ -31,7 +31,8 @@
#include "runtime/synchronizer.hpp"
inline intptr_t ObjectMonitor::is_entered(TRAPS) const {
if (THREAD == _owner || THREAD->is_lock_owned((address) _owner)) {
void* owner = owner_raw();
if (THREAD == owner || THREAD->is_lock_owned((address)owner)) {
return 1;
}
return 0;
@ -55,15 +56,19 @@ inline jint ObjectMonitor::waiters() const {
// Returns NULL if DEFLATER_MARKER is observed.
inline void* ObjectMonitor::owner() const {
void* owner = _owner;
void* owner = owner_raw();
return owner != DEFLATER_MARKER ? owner : NULL;
}
inline void* ObjectMonitor::owner_raw() const {
return Atomic::load(&_owner);
}
// Returns true if owner field == DEFLATER_MARKER and false otherwise.
// This accessor is called when we really need to know if the owner
// field == DEFLATER_MARKER and any non-NULL value won't do the trick.
inline bool ObjectMonitor::owner_is_DEFLATER_MARKER() {
return Atomic::load(&_owner) == DEFLATER_MARKER;
inline bool ObjectMonitor::owner_is_DEFLATER_MARKER() const {
return owner_raw() == DEFLATER_MARKER;
}
// Returns true if 'this' is being async deflated and false otherwise.

2
src/hotspot/share/runtime/synchronizer.cpp
View file

@ -341,7 +341,7 @@ bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
if (m->object_peek() == NULL) {
return false;
}
Thread* const owner = (Thread *) m->_owner;
Thread* const owner = (Thread *) m->owner_raw();
// Lock contention and Transactional Lock Elision (TLE) diagnostics
// and observability