From d7d19ad65ca927d42ed143ec99a262d633a0e194 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kchai@redhat.com>
Date: Tue, 21 Jan 2020 12:58:16 +0800
Subject: [PATCH] crimson/thread: generalize Task so it works w/ func returns
 void

Signed-off-by: Kefu Chai <kchai@redhat.com>
---
 src/crimson/thread/ThreadPool.h      | 29 +++++++++++++++++++++-------
 src/test/crimson/test_thread_pool.cc |  8 ++++++++
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/crimson/thread/ThreadPool.h b/src/crimson/thread/ThreadPool.h
index dbc52388217..d648a6b6ed7 100644
--- a/src/crimson/thread/ThreadPool.h
+++ b/src/crimson/thread/ThreadPool.h
@@ -22,28 +22,43 @@ struct WorkItem {
   virtual void process() = 0;
 };
 
-template<typename Func, typename T = std::invoke_result_t<Func>>
+template<typename Func>
 struct Task final : WorkItem {
-  Func func;
-  seastar::future_state<T> state;
-  crimson::thread::Condition on_done;
+  using T = std::invoke_result_t<Func>;
+  using future_state_t = std::conditional_t<std::is_void_v<T>,
+					    seastar::future_state<>,
+					    seastar::future_state<T>>;
+  using futurator_t = seastar::futurize<T>;
 public:
   explicit Task(Func&& f)
     : func(std::move(f))
   {}
   void process() override {
     try {
-      state.set(func());
+      if constexpr (std::is_void_v<T>) {
+        func();
+        state.set();
+      } else {
+        state.set(func());
+      }
     } catch (...) {
       state.set_exception(std::current_exception());
     }
     on_done.notify();
   }
-  seastar::future<T> get_future() {
+  typename futurator_t::type get_future() {
     return on_done.wait().then([this] {
-      return seastar::make_ready_future<T>(state.get0(std::move(state).get()));
+      if (state.failed()) {
+	return futurator_t::make_exception_future(state.get_exception());
+      } else {
+	return futurator_t::from_tuple(state.get_value());
+      }
     });
   }
+private:
+  Func func;
+  future_state_t state;
+  crimson::thread::Condition on_done;
 };
 
 struct SubmitQueue {
diff --git a/src/test/crimson/test_thread_pool.cc b/src/test/crimson/test_thread_pool.cc
index ede6ea1ebe0..b3dd719e29f 100644
--- a/src/test/crimson/test_thread_pool.cc
+++ b/src/test/crimson/test_thread_pool.cc
@@ -25,6 +25,12 @@ seastar::future<> test_accumulate(ThreadPool& tp) {
   });
 }
 
+seastar::future<> test_void_return(ThreadPool& tp) {
+  return tp.submit([=] {
+    std::this_thread::sleep_for(10ns);
+  });
+}
+
 int main(int argc, char** argv)
 {
   ThreadPool tp{2, 128, 0};
@@ -32,6 +38,8 @@ int main(int argc, char** argv)
   return app.run(argc, argv, [&tp] {
       return tp.start().then([&tp] {
           return test_accumulate(tp);
+        }).then([&tp] {
+          return test_void_return(tp);
         }).handle_exception([](auto e) {
           std::cerr << "Error: " << e << std::endl;
           seastar::engine().exit(1);
-- 
2.39.5