Enforce non-reentrancy of ExecutorLoopController::runLoop()

Summary: `runLoop()` is not supposed to be reentrant, but we never enforced it. After having verified that it is indeed not called re-entrantly, we can make the `loopThread_` check stricter.

Reviewed By: Gownta

Differential Revision: D52575247

fbshipit-source-id: 6e3da3b132033b7023a336b5b26fb3eb991302f4

Author: ot

third-party/folly/src/folly/fibers/ExecutorLoopController-inl.h

@@ -52,10 +52,8 @@ inline void ExecutorLoopController::schedule() {
 
 inline void ExecutorLoopController::runLoop() {
   auto oldLoopThread = loopThread_.exchange(std::this_thread::get_id());
-  DCHECK(
-      oldLoopThread == std::thread::id{} ||
-      oldLoopThread == std::this_thread::get_id());
-  SCOPE_EXIT { loopThread_ = oldLoopThread; };
+  DCHECK(oldLoopThread == std::thread::id{});
+  SCOPE_EXIT { loopThread_ = std::thread::id{}; };
 
   if (!executorKeepAlive_) {
     if (!fm_->hasTasks()) {