c++|be| fix active events bug in iourinbackend

Summary:
1. inlining this one-liner functions
2. we were setting `gettingEvents_ = true;` after throwing which is deadcode. Instead we are setting right after (if we enter again then do throw). Once we exit the function scope then set flag back to false.

Reviewed By: vishwanath1306

Differential Revision: D92342550

fbshipit-source-id: 21f6a4fd00ca6709963ea66993a06cbba839811d

Author: jlhe97

folly/io/async/IoUringBackend.cpp

@@ -1475,9 +1475,13 @@ int IoUringBackend::cancelOne(IoSqe* ioSqe) {
 size_t IoUringBackend::getActiveEvents(WaitForEventsMode waitForEvents) {
   struct io_uring_cqe* cqe;
 
-  setGetActiveEvents();
+  if (kIsDebug && gettingEvents_) {
+    throw std::runtime_error("getting events is not reentrant");
+  }
+  gettingEvents_ = true;
+
   SCOPE_EXIT {
-    doneGetActiveEvents();
+    gettingEvents_ = false;
   };
 
   auto inner_do_wait = [&]() -> int {

folly/io/async/IoUringBackend.h

@@ -1172,13 +1172,6 @@ class IoUringBackend : public EventBaseBackendBase {
   void dCheckSubmitTid();
   void setSubmitting() noexcept { isSubmitting_++; }
   void doneSubmitting() noexcept { isSubmitting_--; }
-  void setGetActiveEvents() {
-    if (kIsDebug && gettingEvents_) {
-      throw std::runtime_error("getting events is not reentrant");
-      gettingEvents_ = true;
-    }
-  }
-  void doneGetActiveEvents() noexcept { gettingEvents_ = false; }
   bool isSubmitting() const noexcept { return isSubmitting_; }
 };