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Read Barrier for CompareAndSwapObject #1573

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Apr 3, 2018
Merged

Read Barrier for CompareAndSwapObject #1573

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59 changes: 30 additions & 29 deletions runtime/gc_base/ObjectAccessBarrier.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*******************************************************************************
* Copyright (c) 1991, 2017 IBM Corp. and others
* Copyright (c) 1991, 2018 IBM Corp. and others
*
* This program and the accompanying materials are made available under
* the terms of the Eclipse Public License 2.0 which accompanies this
Expand Down Expand Up @@ -1501,6 +1501,7 @@ MM_ObjectAccessBarrier::compareAndSwapObject(J9VMThread *vmThread, J9Object *des
fj9object_t *actualDestAddress;
fj9object_t compareValue = convertTokenFromPointer(compareObject);
fj9object_t swapValue = convertTokenFromPointer(swapObject);
bool result = false;

/* TODO: To make this API more consistent, it should probably be split into separate
* indexable and non-indexable versions. Currently, when called on an indexable object,
Expand All @@ -1513,25 +1514,22 @@ MM_ObjectAccessBarrier::compareAndSwapObject(J9VMThread *vmThread, J9Object *des
actualDestAddress = J9OAB_MIXEDOBJECT_EA(destObject, ((UDATA)destAddress - (UDATA)destObject), fj9object_t);
}

/* Note: This is a bit of a special case -- we call preObjectStore even though the store
* may not actually occur. This is safe and correct for Metronome.
*/
preObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
protectIfVolatileBefore(vmThread, true, false, false);

/* One of these conditions will evaluate to true at compile time based on whether fields are 32 or 64 bits */
bool result = false;
if (sizeof(fj9object_t) == sizeof(UDATA)) {
result = ((UDATA)compareValue == MM_AtomicOperations::lockCompareExchange((UDATA *)actualDestAddress, (UDATA)compareValue, (UDATA)swapValue));
} else if (sizeof(fj9object_t) == sizeof(U_32)) {
if (preObjectRead(vmThread, destObject, actualDestAddress)) {
/* Note: This is a bit of a special case -- we call preObjectStore even though the store
* may not actually occur. This is safe and correct for Metronome.
*/
preObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
protectIfVolatileBefore(vmThread, true, false, false);

#if defined(J9VM_GC_COMPRESSED_POINTERS)
result = ((U_32)(UDATA)compareValue == MM_AtomicOperations::lockCompareExchangeU32((U_32 *)actualDestAddress, (U_32)(UDATA)compareValue, (U_32)(UDATA)swapValue));
} else {
assume(false, "fj9object_t must be either U_32 (compressed pointers / 32-bit VM) or UDATA");
}

protectIfVolatileAfter(vmThread, true, false, false);
if (result) {
postObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
#else
result = ((UDATA)compareValue == MM_AtomicOperations::lockCompareExchange((UDATA *)actualDestAddress, (UDATA)compareValue, (UDATA)swapValue));
#endif
protectIfVolatileAfter(vmThread, true, false, false);
if (result) {
postObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
}
}

return result;
Expand Down Expand Up @@ -1647,6 +1645,7 @@ MM_ObjectAccessBarrier::compareAndExchangeObject(J9VMThread *vmThread, J9Object
fj9object_t *actualDestAddress;
fj9object_t compareValue = convertTokenFromPointer(compareObject);
fj9object_t swapValue = convertTokenFromPointer(swapObject);
J9Object *result = NULL;

/* TODO: To make this API more consistent, it should probably be split into separate
* indexable and non-indexable versions. Currently, when called on an indexable object,
Expand All @@ -1659,21 +1658,23 @@ MM_ObjectAccessBarrier::compareAndExchangeObject(J9VMThread *vmThread, J9Object
actualDestAddress = J9OAB_MIXEDOBJECT_EA(destObject, ((UDATA)destAddress - (UDATA)destObject), fj9object_t);
}

/* Note: This is a bit of a special case -- we call preObjectStore even though the store
* may not actually occur. This is safe and correct for Metronome.
*/
preObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
protectIfVolatileBefore(vmThread, true, false, false);
if (preObjectRead(vmThread, destObject, actualDestAddress)) {
/* Note: This is a bit of a special case -- we call preObjectStore even though the store
* may not actually occur. This is safe and correct for Metronome.
*/
preObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
protectIfVolatileBefore(vmThread, true, false, false);

#if defined(J9VM_GC_COMPRESSED_POINTERS)
J9Object *result = (J9Object *)(UDATA)MM_AtomicOperations::lockCompareExchangeU32((U_32 *)actualDestAddress, (U_32)(UDATA)compareValue, (U_32)(UDATA)swapValue);
J9Object *result = (J9Object *)(UDATA)MM_AtomicOperations::lockCompareExchangeU32((U_32 *)actualDestAddress, (U_32)(UDATA)compareValue, (U_32)(UDATA)swapValue);
#else
J9Object *result = (J9Object *)MM_AtomicOperations::lockCompareExchange((UDATA *)actualDestAddress, (UDATA)compareValue, (UDATA)swapValue);
J9Object *result = (J9Object *)MM_AtomicOperations::lockCompareExchange((UDATA *)actualDestAddress, (UDATA)compareValue, (UDATA)swapValue);
#endif

protectIfVolatileAfter(vmThread, true, false, false);
if (result) {
postObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
protectIfVolatileAfter(vmThread, true, false, false);
if (result) {
postObjectStore(vmThread, destObject, actualDestAddress, swapObject, true);
}
}

return result;
Expand Down
4 changes: 4 additions & 0 deletions runtime/gc_include/ObjectAccessBarrierAPI.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -485,6 +485,7 @@ class MM_ObjectAccessBarrierAPI
if (j9gc_modron_wrtbar_always == _writeBarrierType) {
return (1 == vmThread->javaVM->memoryManagerFunctions->j9gc_objaccess_compareAndSwapObject(vmThread, destObject, (J9Object **)destAddress, compareObject, swapObject));
} else {
preMixedObjectReadObject(vmThread, destObject, destAddress);
preMixedObjectStoreObject(vmThread, destObject, destAddress, swapObject);

protectIfVolatileBefore(isVolatile, false);
Expand Down Expand Up @@ -526,6 +527,7 @@ class MM_ObjectAccessBarrierAPI
if (j9gc_modron_wrtbar_always == _writeBarrierType) {
return vmThread->javaVM->memoryManagerFunctions->j9gc_objaccess_compareAndExchangeObject(vmThread, destObject, (J9Object **)destAddress, compareObject, swapObject);
} else {
preMixedObjectReadObject(vmThread, destObject, destAddress);
preMixedObjectStoreObject(vmThread, destObject, destAddress, swapObject);

protectIfVolatileBefore(isVolatile, false);
Expand Down Expand Up @@ -1887,6 +1889,7 @@ class MM_ObjectAccessBarrierAPI
if (j9gc_modron_wrtbar_always == _writeBarrierType) {
return (1 == vmThread->javaVM->memoryManagerFunctions->j9gc_objaccess_compareAndSwapObject(vmThread, destArray, (J9Object **)actualAddress, compareObject, swapObject));
} else {
preIndexableObjectReadObject(vmThread, destArray, actualAddress);
preIndexableObjectStoreObject(vmThread, destArray, actualAddress, swapObject);

protectIfVolatileBefore(isVolatile, false);
Expand Down Expand Up @@ -1928,6 +1931,7 @@ class MM_ObjectAccessBarrierAPI
if (j9gc_modron_wrtbar_always == _writeBarrierType) {
return vmThread->javaVM->memoryManagerFunctions->j9gc_objaccess_compareAndExchangeObject(vmThread, destArray, (J9Object **)actualAddress, compareObject, swapObject);
} else {
preIndexableObjectReadObject(vmThread, destArray, actualAddress);
preIndexableObjectStoreObject(vmThread, destArray, actualAddress, swapObject);

protectIfVolatileBefore(isVolatile, false);
Expand Down