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ARROW-10196: [C++] Add Future::DeferNotOk #8362

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ARROW-10196: [C++] Add Future::DeferNotOk #8362

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ARROW-10196: [C++] Add Future::DeferNotOk
bkietz Oct 6, 2020
1f54d61
add doccomment
bkietz Oct 7, 2020
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29 changes: 13 additions & 16 deletions cpp/src/arrow/util/future.h
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Original file line number Diff line number Diff line change
Expand Up @@ -154,9 +154,8 @@ class FutureStorage : public FutureStorageBase {

Status status() const { return result_.status(); }

template <typename U>
void MarkFinished(U&& value) {
result_ = std::forward<U>(value);
void MarkFinished(Result<T> result) {
result_ = std::move(result);
if (ARROW_PREDICT_TRUE(result_.ok())) {
impl_->MarkFinished();
} else {
Expand Down Expand Up @@ -250,7 +249,7 @@ class Future {
// The default constructor creates an invalid Future. Use Future::Make()
// for a valid Future. This constructor is mostly for the convenience
// of being able to presize a vector of Futures.
Future() : impl_(NULLPTR) {}
Future() = default;

// Consumer API

Expand Down Expand Up @@ -311,6 +310,15 @@ class Future {
return impl_->Wait(seconds);
}

/// If a Result<Future> holds an error instead of a Future, construct a finished Future
/// holding that error.
static Future DeferNotOk(Result<Future> maybe_future) {
if (ARROW_PREDICT_FALSE(!maybe_future.ok())) {
return MakeFinished(std::move(maybe_future).status());
}
return std::move(maybe_future).MoveValueUnsafe();
}

// Producer API

/// \brief Producer API: execute function and mark Future finished
Expand Down Expand Up @@ -368,7 +376,7 @@ class Future {
}

std::shared_ptr<FutureStorage<T>> storage_;
FutureImpl* impl_;
FutureImpl* impl_ = NULLPTR;

friend class FutureWaiter;
};
Expand Down Expand Up @@ -419,15 +427,4 @@ inline std::vector<int> WaitForAny(const std::vector<Future<T>*>& futures,
return waiter->MoveFinishedFutures();
}

#define ARROW_ASSIGN_OR_RETURN_FUTURE_IMPL(result_name, lhs, T, rexpr) \
auto result_name = (rexpr); \
if (ARROW_PREDICT_FALSE(!(result_name).ok())) { \
return Future<T>::MakeFinished(std::move(result_name).status()); \
} \
lhs = std::move(result_name).MoveValueUnsafe();

#define ARROW_ASSIGN_OR_RETURN_FUTURE(lhs, T, rexpr) \
ARROW_ASSIGN_OR_RETURN_FUTURE_IMPL( \
ARROW_ASSIGN_OR_RAISE_NAME(_error_or_value, __COUNTER__), lhs, T, rexpr);

} // namespace arrow
4 changes: 1 addition & 3 deletions cpp/src/arrow/util/thread_pool.h
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Original file line number Diff line number Diff line change
Expand Up @@ -143,10 +143,8 @@ class ARROW_EXPORT Executor {
typename RT = typename detail::ExecutorResultTraits<FunctionRetType>,
typename ValueType = typename RT::ValueType>
Future<ValueType> SubmitAsFuture(Function&& func, Args&&... args) {
ARROW_ASSIGN_OR_RETURN_FUTURE(
auto future, ValueType,
return Future<ValueType>::DeferNotOk(
Submit(std::forward<Function>(func), std::forward<Args>(args)...));
return future;
}

// Return the level of parallelism (the number of tasks that may be executed
Expand Down