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ARROW-16743: [C++] Add short-circuit version of logical Status AND #13304

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ARROW-16743: [C++] Add short-circuit version of logical Status AND #13304

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9 changes: 5 additions & 4 deletions cpp/src/arrow/scalar.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -75,15 +75,16 @@ struct ScalarHashImpl {
}

Status Visit(const DayTimeIntervalScalar& s) {
return StdHash(s.value.days) & StdHash(s.value.milliseconds);
return StdHash(s.value.days) && StdHash(s.value.milliseconds);

@cyb70289 cyb70289 Jun 3, 2022

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To me, && is easier to understand. Just like a bash script, I know LHS will be evaluated before RHS, and RHS will only be evaluated if LHS is true.

}

Status Visit(const MonthDayNanoIntervalScalar& s) {
return StdHash(s.value.days) & StdHash(s.value.months) & StdHash(s.value.nanoseconds);
return StdHash(s.value.days) && StdHash(s.value.months) &&
StdHash(s.value.nanoseconds);
}

Status Visit(const Decimal128Scalar& s) {
return StdHash(s.value.low_bits()) & StdHash(s.value.high_bits());
return StdHash(s.value.low_bits()) && StdHash(s.value.high_bits());
}

Status Visit(const Decimal256Scalar& s) {
Expand Down Expand Up @@ -140,7 +141,7 @@ struct ScalarHashImpl {
Status ArrayHash(const Array& a) { return ArrayHash(*a.data()); }

Status ArrayHash(const ArrayData& a) {
RETURN_NOT_OK(StdHash(a.length) & StdHash(a.GetNullCount()));
RETURN_NOT_OK(StdHash(a.length) && StdHash(a.GetNullCount()));
if (a.buffers[0] != nullptr) {
// We can't visit values without unboxing the whole array, so only hash
// the null bitmap for now.
Expand Down
18 changes: 18 additions & 0 deletions cpp/src/arrow/status.h
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Expand Up @@ -150,6 +150,8 @@ class ARROW_MUST_USE_TYPE ARROW_EXPORT Status : public util::EqualityComparable<
// AND the statuses.
inline Status operator&(const Status& s) const noexcept;
inline Status operator&(Status&& s) const noexcept;
inline Status operator&&(const Status& s) const noexcept;
inline Status operator&&(Status&& s) const noexcept;
inline Status& operator&=(const Status& s) noexcept;
inline Status& operator&=(Status&& s) noexcept;

Expand Down Expand Up @@ -424,6 +426,22 @@ Status Status::operator&(Status&& s) const noexcept {
}
}

Status Status::operator&&(const Status& s) const noexcept {
if (ok()) {
return s;
} else {
return *this;
}
}

Status Status::operator&&(Status&& s) const noexcept {

@cyb70289 cyb70289 Jun 3, 2022

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Nit: doesn't it make sense if we combine these two overloads into one function accepting a value parameter?

Status Status::operator&&(Status s) {
  if (ok()) {
    return s;
  } else {
    return *this;
  }
}

As s is a direct arugment, return s is same as return std::move(s) if RVO doesn't apply (a direct argument or stack variable returned is treated as rvalue, IIRC).
This function may introduce at most one additonal move to both the const& and && overloads. Maybe even no this overhead if RVO can apply to argument, or compiler can do some tricks, I'm not sure.

@bkietz bkietz Jun 6, 2022

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I agree that having a non-reference parameter is preferable. We might still want two overloads, however, since we're copying in the case that *this is not ok:

Status Status::operator&&(Status s) const& noexcept {
  if (!ok()) return *this;
  return s;
}

Status Status::operator&&(Status s) && noexcept {
  if (!ok()) return std::move(*this);
  return s;
}

if (ok()) {
return std::move(s);
} else {
return *this;
}
}

Status& Status::operator&=(const Status& s) noexcept {
if (ok() && !s.ok()) {
CopyFrom(s);
Expand Down
19 changes: 16 additions & 3 deletions cpp/src/arrow/status_test.cc
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Expand Up @@ -93,11 +93,11 @@ TEST(StatusTest, AndStatus) {
ASSERT_TRUE(res.IsInvalid());

// With rvalues
res = Status::OK() & Status::Invalid("foo");
res = Status::OK() && Status::Invalid("foo");
ASSERT_TRUE(res.IsInvalid());
res = Status::Invalid("foo") & Status::OK();
res = Status::Invalid("foo") && Status::OK();
ASSERT_TRUE(res.IsInvalid());
res = Status::Invalid("foo") & Status::IOError("bar");
res = Status::Invalid("foo") && Status::IOError("bar");
ASSERT_TRUE(res.IsInvalid());

res = Status::OK();
Expand All @@ -109,6 +109,19 @@ TEST(StatusTest, AndStatus) {
ASSERT_TRUE(res.IsInvalid());
}

Status PassingTaskWithSideEffect(bool* hit_side_effect) {
*hit_side_effect = true;
return Status::OK();
}

Status FailingTask() { return Status::Invalid("err"); }

TEST(StatusTest, SortCircuitAndStatus) {
bool hit_side_effect = false;
Status res = PassingTaskWithSideEffect(&hit_side_effect) && FailingTask();
ASSERT_TRUE(hit_side_effect);
}

TEST(StatusTest, TestEquality) {
ASSERT_EQ(Status(), Status::OK());
ASSERT_EQ(Status::Invalid("error"), Status::Invalid("error"));
Expand Down