[GitHub] [arrow] westonpace commented on a diff in pull request #14257: ARROW-17853: [Python][CI] Timeout in test_dataset.py::test_write_dataset_s3_put_only

[GitBox <gi...@apache.org>]

westonpace commented on code in PR #14257:
URL: https://github.com/apache/arrow/pull/14257#discussion_r989220819


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cpp/src/arrow/util/async_util.cc:
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@@ -98,13 +98,53 @@ 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 {
+    DCHECK(false) << "You should not rely on sub-scheduler's OnFinished.  Use a "
+                     "finished callback when creating the sub-scheduler instead";
+    return Future<>::MakeFinished(Status::UnknownError("Unreachable code encountered"));
+  }
+  AsyncTaskScheduler* MakeSubScheduler(FnOnce<Status(Status)> finish_callback,
+                                       Throttle* throttle,
+                                       std::unique_ptr<Queue> queue) override {
+    return AlreadyFailedScheduler::Make(failure_reason_, std::move(finish_callback));
+  }

Review Comment:
   I'm moving the finish callback passed in and not `finish_callback_` (which is the finish callback for the parent scheduler).  That being said, the very first scheduler doesn't have a finish callback by design.



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