zanmato1984 commented on code in PR #40237:
URL: https://github.com/apache/arrow/pull/40237#discussion_r1503033541
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cpp/src/arrow/array/data.cc:
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@@ -286,8 +286,10 @@ namespace {
template <typename offset_type>
BufferSpan OffsetsForScalar(uint8_t* scratch_space, offset_type value_size) {
auto* offsets = reinterpret_cast<offset_type*>(scratch_space);
- offsets[0] = 0;
- offsets[1] = static_cast<offset_type>(value_size);
+ reinterpret_cast<std::atomic<offset_type>*>(&offsets[0])
+ ->store(0, std::memory_order_relaxed);
+ reinterpret_cast<std::atomic<offset_type>*>(&offsets[1])
+ ->store(static_cast<offset_type>(value_size), std::memory_order_relaxed);
Review Comment:
Well, the reason for the extra reinterpret casts is that: I'm not sure if it
is guaranteed in C++ that `sizeof(std::atomic<offset_type>)` is the same as
`sizeof(offset_type)`. If they are not the same, the pointer will be wrongly
offset-ed.
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