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Use a less constraining memory order for all "update" operations on Counter/Gauge. #623

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Use a less constraining memory order for all "update" operations on Counter/Gauge. #623

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12 changes: 8 additions & 4 deletions core/src/gauge.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -14,16 +14,20 @@ void Gauge::Decrement() { Decrement(1.0); }

void Gauge::Decrement(const double value) { Change(-1.0 * value); }

void Gauge::Set(const double value) { value_.store(value); }
void Gauge::Set(const double value) {
value_.store(value, std::memory_order_relaxed);
}

void Gauge::Change(const double value) {
#if __cpp_lib_atomic_float >= 201711L
value_.fetch_add(value);
value_.fetch_add(value, std::memory_order_relaxed);
#else
// Pre-C++ 20 fallback: busy loop (which might be more expansive than using
// fetch_add).
auto current = value_.load();
while (!value_.compare_exchange_weak(current, current + value)) {
auto current = value_.load(std::memory_order_relaxed);
while (!value_.compare_exchange_weak(current, current + value,
std::memory_order_relaxed,
std::memory_order_relaxed)) {
// intentionally empty block
}
#endif
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