Put the current fiber manager behind an accessor

Summary: [Folly] Put the current fiber manager behind an accessor function v.s. having it as a static class member.

Reviewed By: andriigrynenko

Differential Revision: D19229507

fbshipit-source-id: 7cf4eab00ee281bc6104f994a71f5e48d9553852

folly/fibers/FiberManager.cpp

@@ -78,12 +78,15 @@ struct hash<folly::fibers::FiberManager::Options> {
 namespace folly {
 namespace fibers {
 
-FOLLY_TLS FiberManager* FiberManager::currentFiberManager_ = nullptr;
-
 auto FiberManager::FrozenOptions::create(const Options& options) -> ssize_t {
   return std::hash<Options>()(options);
 }
 
+/* static */ FiberManager*& FiberManager::getCurrentFiberManager() {
+  static FOLLY_TLS FiberManager* currentFiberManager;
+  return currentFiberManager;
+}
+
 FiberManager::FiberManager(
     std::unique_ptr<LoopController> loopController,
     Options options)

folly/fibers/FiberManagerInternal-inl.h

@@ -202,7 +202,7 @@ void FiberManager::runFibersHelper(LoopFunc&& loopFunc) {
 #endif
 
   // Support nested FiberManagers
-  auto originalFiberManager = std::exchange(currentFiberManager_, this);
+  auto originalFiberManager = std::exchange(getCurrentFiberManager(), this);
 
   numUncaughtExceptions_ = uncaught_exceptions();
   currentException_ = std::current_exception();
@@ -227,7 +227,7 @@ void FiberManager::runFibersHelper(LoopFunc&& loopFunc) {
     if (!readyFibers_.empty()) {
       ensureLoopScheduled();
     }
-    std::swap(currentFiberManager_, originalFiberManager);
+    std::swap(getCurrentFiberManager(), originalFiberManager);
     CHECK_EQ(this, originalFiberManager);
   };
 
@@ -534,12 +534,12 @@ invoke_result_t<F> FiberManager::runInMainContext(F&& func) {
 }
 
 inline FiberManager& FiberManager::getFiberManager() {
-  assert(currentFiberManager_ != nullptr);
-  return *currentFiberManager_;
+  assert(getCurrentFiberManager() != nullptr);
+  return *getCurrentFiberManager();
 }
 
 inline FiberManager* FiberManager::getFiberManagerUnsafe() {
-  return currentFiberManager_;
+  return getCurrentFiberManager();
 }
 
 inline bool FiberManager::hasActiveFiber() const {
@@ -547,7 +547,7 @@ inline bool FiberManager::hasActiveFiber() const {
 }
 
 inline void FiberManager::yield() {
-  assert(currentFiberManager_ == this);
+  assert(getCurrentFiberManager() == this);
   assert(activeFiber_ != nullptr);
   assert(activeFiber_->state_ == Fiber::RUNNING);
   activeFiber_->preempt(Fiber::YIELDED);

folly/fibers/FiberManagerInternal.h

@@ -490,7 +490,7 @@ class FiberManager : public ::folly::Executor {
    * When we are inside FiberManager loop this points to FiberManager. Otherwise
    * it's nullptr
    */
-  static FOLLY_TLS FiberManager* currentFiberManager_;
+  static FiberManager*& getCurrentFiberManager();
 
   /**
    * Allocator used to allocate stack for Fibers in the pool.