bkietz commented on a change in pull request #8680:
URL: https://github.com/apache/arrow/pull/8680#discussion_r534357174
##########
File path: cpp/src/arrow/util/future.h
##########
@@ -264,11 +335,125 @@ class Future {
}
/// \brief Make a finished Future<> with the provided Status.
- template <typename E = ValueType, typename = detail::Empty::EnableIfSame<E>>
+ template <typename E = ValueType, typename = typename std::enable_if<
+ std::is_same<E,
detail::Empty>::value>::type>
static Future<> MakeFinished(Status s = Status::OK()) {
return MakeFinished(E::ToResult(std::move(s)));
}
+ /// \brief Consumer API: Register a callback to run when this future
completes
+ template <typename OnComplete>
+ void AddCallback(OnComplete&& on_complete) const {
+ struct Callback {
+ void operator()() && {
+ auto self = weak_self.get();
+ std::move(on_complete)(*self.GetResult());
+ }
+
+ WeakFuture<T> weak_self;
+ OnComplete on_complete;
+ };
+
+ // We know impl_ will not be dangling when invoking callbacks because at
least one
+ // thread will be waiting for MarkFinished to return. Thus it's safe to
keep a
+ // weak reference to impl_ here
+ impl_->AddCallback(
+ Callback{WeakFuture<T>(*this), std::forward<OnComplete>(on_complete)});
+ }
+
+ /// \brief Consumer API: Register a continuation to run when this future
completes
+ ///
+ /// The continuation will run in the same thread that called MarkFinished
(whatever
+ /// callback is registered with this function will run before MarkFinished
returns).
+ /// Avoid long-running callbacks in favor of submitting a task to an
Executor and
+ /// returning the future.
+ ///
+ /// Two callbacks are supported:
+ /// - OnSuccess, called against the result (const ValueType&) on successul
completion.
+ /// - OnFailure, called against the error (const Status&) on failed
completion.
+ ///
+ /// Then() returns a Future whose ValueType is derived from the return type
of the
+ /// callbacks. If a callback returns:
+ /// - void, a Future<> will be produced which will completes successully as
soon
Review comment:
yes, I'll s/produced/returned
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
