nice error message if you try to Future<void>

[folly.git] / folly / futures / detail / Core.h

diff --git a/folly/futures/detail/Core.h b/folly/futures/detail/Core.h
index c0e09d099e7a6dfef80dbf9745f6ab2ec5bf416b..a01285fa0420e02dc472331f9f02d1c9f49e15b1 100644 (file)
--- a/folly/futures/detail/Core.h
+++ b/folly/futures/detail/Core.h
@@ -74,11 +74,13 @@ enum class State : uint8_t {
 /// time there won't be any problems.
 template<typename T>
 class Core {
+  static_assert(!std::is_void<T>::value,
+                "void futures are not supported. Use Unit instead.");
  public:
   /// This must be heap-constructed. There's probably a way to enforce that in
   /// code but since this is just internal detail code and I don't know how
   /// off-hand, I'm punting.
-  Core() {}
+  Core() : result_(), fsm_(State::Start), attached_(2) {}
 
   explicit Core(Try<T>&& t)
     : result_(std::move(t)),
@@ -313,8 +315,6 @@ class Core {
   }
 
   void doCallback() {
-    RequestContext::setContext(context_);
-
     Executor* x = executor_;
     int8_t priority;
     if (x) {
@@ -333,19 +333,24 @@ class Core {
         if (LIKELY(x->getNumPriorities() == 1)) {
           x->add([this]() mutable {
             SCOPE_EXIT { detachOne(); };
+            RequestContext::setContext(context_);
             callback_(std::move(*result_));
           });
         } else {
           x->addWithPriority([this]() mutable {
             SCOPE_EXIT { detachOne(); };
+            RequestContext::setContext(context_);
             callback_(std::move(*result_));
           }, priority);
         }
       } catch (...) {
+        --attached_; // Account for extra ++attached_ before try
+        RequestContext::setContext(context_);
         result_ = Try<T>(exception_wrapper(std::current_exception()));
         callback_(std::move(*result_));
       }
     } else {
+      RequestContext::setContext(context_);
       callback_(std::move(*result_));
     }
   }
@@ -364,10 +369,10 @@ class Core {
   char lambdaBuf_[lambdaBufSize];
   // place result_ next to increase the likelihood that the value will be
   // contained entirely in one cache line
-  folly::Optional<Try<T>> result_ {};
+  folly::Optional<Try<T>> result_;
   std::function<void(Try<T>&&)> callback_ {nullptr};
-  FSM<State> fsm_ {State::Start};
-  std::atomic<unsigned char> attached_ {2};
+  FSM<State> fsm_;
+  std::atomic<unsigned char> attached_;
   std::atomic<bool> active_ {true};
   std::atomic<bool> interruptHandlerSet_ {false};
   folly::MicroSpinLock interruptLock_ {0};