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Fix to correct memory ordering for compare_exchange_weak and wait in the intrusive reference counting logic #5381

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Merged
merged 5 commits into from
Apr 4, 2025
Merged

Fix to correct memory ordering for compare_exchange_weak and wait in the intrusive reference counting logic #5381

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cabffcd
switch to memory_order_seq_cst
vlntb Apr 2, 2025
6543027
fixing memory_order instructions
vlntb Apr 2, 2025
3eed7bf
revert memory_order change in test
vlntb Apr 2, 2025
da9e599
revert memory_order change in test
vlntb Apr 2, 2025
58623ad
Merge branch 'develop' into vlntb/ripd-2529-testpartialdelete-win-fix
vlntb Apr 4, 2025
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10 changes: 5 additions & 5 deletions include/xrpl/basics/IntrusiveRefCounts.h
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Original file line number Diff line number Diff line change
Expand Up @@ -294,7 +294,7 @@
}

if (refCounts.compare_exchange_weak(
prevIntVal, nextIntVal, std::memory_order_release))
prevIntVal, nextIntVal, std::memory_order_acq_rel))
{
// Can't be in partial destroy because only decrementing the strong
// count to zero can start a partial destroy, and that can't happen
Expand Down Expand Up @@ -351,7 +351,7 @@
}
}
if (refCounts.compare_exchange_weak(
prevIntVal, nextIntVal, std::memory_order_release))
prevIntVal, nextIntVal, std::memory_order_acq_rel))
{
XRPL_ASSERT(
(!(prevIntVal & partialDestroyStartedMask)),
Expand All @@ -374,15 +374,15 @@
// This case should only be hit if the partialDestroyStartedBit is
// set non-atomically (and even then very rarely). The code is kept
// in case we need to set the flag non-atomically for perf reasons.
refCounts.wait(prevIntVal, std::memory_order_acq_rel);
refCounts.wait(prevIntVal, std::memory_order_acquire);

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include/xrpl/basics/IntrusiveRefCounts.h#L377 

Added line #L377 was not covered by tests
prevIntVal = refCounts.load(std::memory_order_acquire);
prev = RefCountPair{prevIntVal};
}
if (!prev.partialDestroyFinishedBit)
{
// partial destroy MUST finish before running a full destroy (when
// using weak pointers)
refCounts.wait(prevIntVal - weakDelta, std::memory_order_acq_rel);
refCounts.wait(prevIntVal - weakDelta, std::memory_order_acquire);
}
return ReleaseWeakRefAction::destroy;
}
Expand All @@ -396,7 +396,7 @@
auto desiredValue = RefCountPair{2, 1}.combinedValue();

while (!refCounts.compare_exchange_weak(
curValue, desiredValue, std::memory_order_release))
curValue, desiredValue, std::memory_order_acq_rel))
{
RefCountPair const prev{curValue};
if (!prev.strong)
Expand Down
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