Remove Promise::getFuture from Future-inl.h 3/4 - onError

Summary: Replaces calls to Promise::getFuture in onError calls. Modifies the returned future to complete on the same executor as the caller. No assumption that the future already has an executor (though it should in principle, the codebase is not ready for that yet).

Reviewed By: yfeldblum

Differential Revision: D7104850

fbshipit-source-id: ea152102f8ecd612e322b98a54d9440495b14bf8

folly/futures/Future-inl.h

@@ -835,7 +835,7 @@ Future<T>::onError(F&& func) {
 
   Promise<T> p;
   p.core_->setInterruptHandlerNoLock(this->core_->getInterruptHandler());
-  auto f = p.getFuture();
+  auto sf = p.getSemiFuture();
 
   this->setCallback_(
       [state = futures::detail::makeCoreCallbackState(
@@ -847,7 +847,10 @@ Future<T>::onError(F&& func) {
         }
       });
 
-  return f;
+  // Allow for applying to future with null executor while this is still
+  // possible.
+  auto* e = this->getExecutor();
+  return std::move(sf).via(e ? e : &folly::InlineExecutor::instance());
 }
 
 // onError where the callback returns Future<T>
@@ -868,7 +871,7 @@ Future<T>::onError(F&& func) {
       Exn;
 
   Promise<T> p;
-  auto f = p.getFuture();
+  auto sf = p.getSemiFuture();
 
   this->setCallback_(
       [state = futures::detail::makeCoreCallbackState(
@@ -887,7 +890,10 @@ Future<T>::onError(F&& func) {
         }
       });
 
-  return f;
+  // Allow for applying to future with null executor while this is still
+  // possible.
+  auto* e = this->getExecutor();
+  return std::move(sf).via(e ? e : &folly::InlineExecutor::instance());
 }
 
 template <class T>
@@ -919,7 +925,7 @@ Future<T>::onError(F&& func) {
       "Return type of onError callback must be T or Future<T>");
 
   Promise<T> p;
-  auto f = p.getFuture();
+  auto sf = p.getSemiFuture();
   this->setCallback_(
       [state = futures::detail::makeCoreCallbackState(
            std::move(p), std::forward<F>(func))](Try<T> t) mutable {
@@ -937,7 +943,10 @@ Future<T>::onError(F&& func) {
         }
       });
 
-  return f;
+  // Allow for applying to future with null executor while this is still
+  // possible.
+  auto* e = this->getExecutor();
+  return std::move(sf).via(e ? e : &folly::InlineExecutor::instance());
 }
 
 // onError(exception_wrapper) that returns T
@@ -954,7 +963,7 @@ Future<T>::onError(F&& func) {
       "Return type of onError callback must be T or Future<T>");
 
   Promise<T> p;
-  auto f = p.getFuture();
+  auto sf = p.getSemiFuture();
   this->setCallback_(
       [state = futures::detail::makeCoreCallbackState(
            std::move(p), std::forward<F>(func))](Try<T>&& t) mutable {
@@ -966,7 +975,10 @@ Future<T>::onError(F&& func) {
         }
       });
 
-  return f;
+  // Allow for applying to future with null executor while this is still
+  // possible.
+  auto* e = this->getExecutor();
+  return std::move(sf).via(e ? e : &folly::InlineExecutor::instance());
 }
 
 template <class Func>