westonpace commented on a change in pull request #9892:
URL: https://github.com/apache/arrow/pull/9892#discussion_r608834855
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File path: cpp/src/arrow/util/thread_pool.h
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@@ -262,5 +321,40 @@ class ARROW_EXPORT ThreadPool : public Executor {
// Return the process-global thread pool for CPU-bound tasks.
ARROW_EXPORT ThreadPool* GetCpuThreadPool();
+/// \brief Runs a potentially async operation serially
+///
+/// This means that all CPU tasks spawned by the operation will run on the
thread calling
+/// this method and the future will be completed before this call finishes.
+template <typename T = arrow::detail::Empty>
+Result<T> RunSerially(FnOnce<Future<T>(Executor*)> get_future) {
+ struct InnerCallback {
+ void operator()(const Result<T> res) {
std::move(finish_signal)(std::move(res)); }
+ SerialExecutor::FinishSignal<T> finish_signal;
+ };
+ struct OuterCallback {
+ Status operator()(Executor* executor, SerialExecutor::FinishSignal<T>
finish_signal) {
+ auto fut = std::move(get_future)(executor);
+ fut.AddCallback(InnerCallback{std::move(finish_signal)});
+ return Status::OK();
+ }
+ FnOnce<Future<T>(Executor*)> get_future;
+ };
+ return
SerialExecutor::RunInSerialExecutor<T>(OuterCallback{std::move(get_future)});
+}
+
+/// \brief Potentially runs an async operation serially if use_threads is true
+/// \see RunSerially
+///
+/// If `use_threads` is false then the operation is run normally but this
method will
+/// still block the calling thread until the operation has completed.
+template <typename T>
+Result<T> RunSynchronously(FnOnce<Future<T>(Executor*)> get_future, bool
use_threads) {
Review comment:
Hmm...maybe I'm not clear on what you are saying.
I could change TopLevelTask to return a future and then I could get rid of
`FinishSignal`. That would help simplify the code but wouldn't really change
any of the fundamental constraints.
Or are you arguing that `RunSynchronously` should return a finished `Future`
instead of a `Result`. In that case I don't see the advantage since we will
still require that the future be finished before we can return and there is not
much use with a finished future vs a result.
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