pitrou commented on code in PR #14257:
URL: https://github.com/apache/arrow/pull/14257#discussion_r991262441
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cpp/src/arrow/util/async_util.cc:
##########
@@ -98,13 +98,54 @@ class FifoQueue : public AsyncTaskScheduler::Queue {
std::list<std::unique_ptr<Task>> tasks_;
};
+class AlreadyFailedScheduler : public AsyncTaskScheduler {
+ public:
+ explicit AlreadyFailedScheduler(Status failure_reason,
+ FnOnce<Status(Status)> finish_callback)
+ : failure_reason_(std::move(failure_reason)),
+ finish_callback_(std::move(finish_callback)) {}
+ bool AddTask(std::unique_ptr<Task> task) override { return false; }
+ void End() override {
+ std::ignore = std::move(finish_callback_)(failure_reason_);
+ self.reset();
+ }
+ Future<> OnFinished() const override {
+ Status::UnknownError(
+ "You should not rely on sub-scheduler's OnFinished. Use a "
+ "finished callback when creating the sub-scheduler instead")
+ .Abort();
+ }
+ AsyncTaskScheduler* MakeSubScheduler(FnOnce<Status(Status)> finish_callback,
+ Throttle* throttle,
+ std::unique_ptr<Queue> queue) override {
+ return AlreadyFailedScheduler::Make(failure_reason_,
std::move(finish_callback));
+ }
+ static AsyncTaskScheduler* Make(Status failure,
+ FnOnce<Status(Status)> finish_callback) {
+ DCHECK(!failure.ok());
+ std::unique_ptr<AlreadyFailedScheduler> instance =
+ std::make_unique<AlreadyFailedScheduler>(std::move(failure),
+ std::move(finish_callback));
+ AsyncTaskScheduler* view = instance.get();
+ instance->self = std::move(instance);
+ return view;
+ }
+ // This is deleted when ended so there is no possible way for this to return
true
+ bool IsEnded() override { return false; }
+
+ private:
+ Status failure_reason_;
+ FnOnce<Status(Status)> finish_callback_;
+ std::unique_ptr<AlreadyFailedScheduler> self;
Review Comment:
Thanks for the detailed answer, and +1 from me for the shared_ptr solution.
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