Make getGlobalIOExecutor return a KeepAlive<IOExecutor>

Summary: By returning a generic KeepAlive<> the global IO executor was losing the IOExecutor interface. This fixes it by returning the right type.

Reviewed By: yfeldblum

Differential Revision: D27061083

fbshipit-source-id: d57f67982c3467a6b814b17e851e4513ffd33502

folly/executors/GlobalExecutor.cpp

@@ -150,7 +150,7 @@ Executor::KeepAlive<> getGlobalCPUExecutor() {
   return folly::getKeepAliveToken(executorPtrPtr->get());
 }
 
-Executor::KeepAlive<> getGlobalIOExecutor() {
+Executor::KeepAlive<IOExecutor> getGlobalIOExecutor() {
   auto executorPtrPtr = getImmutablePtrPtr<IOExecutor>();
   if (!executorPtrPtr) {
     throw std::runtime_error("Requested global IO executor during shutdown.");

folly/executors/GlobalExecutor.h

@@ -41,7 +41,7 @@ folly::Executor::KeepAlive<> getGlobalCPUExecutor();
  *
  * May return an invalid KeepAlive on shutdown.
  */
-folly::Executor::KeepAlive<> getGlobalIOExecutor();
+folly::Executor::KeepAlive<IOExecutor> getGlobalIOExecutor();
 
 /**
  * Retrieve the global Executor. If there is none, a default InlineExecutor