assume thread_local in StaticMeta

Reviewed By: Orvid

Differential Revision: D27671636

fbshipit-source-id: 82cab152ecb606235ee66c026ecafecfe52a88a5

folly/detail/ThreadLocalDetail.cpp

@@ -76,10 +76,10 @@ StaticMetaBase::StaticMetaBase(ThreadEntry* (*threadEntry)(), bool strict)
 }
 
 ThreadEntryList* StaticMetaBase::getThreadEntryList() {
-#ifdef FOLLY_TLD_USE_FOLLY_TLS
+  if (kUseThreadLocal) {
     static thread_local ThreadEntryList threadEntryListSingleton;
     return &threadEntryListSingleton;
-#else
+  } else {
     class PthreadKey {
      public:
       PthreadKey() {
@@ -106,7 +106,7 @@ ThreadEntryList* StaticMetaBase::getThreadEntryList() {
     }
 
     return threadEntryList;
-#endif
+  }
 }
 
 bool StaticMetaBase::dying() {
@@ -207,14 +207,14 @@ void StaticMetaBase::onThreadExit(void* ptr) {
       tmp->setElementsCapacity(0);
     }
 
-#ifndef FOLLY_TLD_USE_FOLLY_TLS
+    if (!kUseThreadLocal) {
       delete tmp;
-#endif
+    }
   }
 
-#ifndef FOLLY_TLD_USE_FOLLY_TLS
+  if (!kUseThreadLocal) {
     delete threadEntryList;
-#endif
+  }
 }
 
 uint32_t StaticMetaBase::elementsCapacity() const {

folly/detail/ThreadLocalDetail.h

@@ -41,18 +41,6 @@
 #include <folly/synchronization/MicroSpinLock.h>
 #include <folly/system/ThreadId.h>
 
-// In general, emutls cleanup is not guaranteed to play nice with the way
-// StaticMeta mixes direct pthread calls and the use of __thread. This has
-// caused problems on multiple platforms so don't use __thread there.
-//
-// XXX: Ideally we would instead determine if emutls is in use at runtime as it
-// is possible to configure glibc on Linux to use emutls regardless.
-#if !FOLLY_MOBILE && !defined(__APPLE__) && !defined(_MSC_VER)
-#define FOLLY_TLD_USE_FOLLY_TLS 1
-#else
-#undef FOLLY_TLD_USE_FOLLY_TLS
-#endif
-
 namespace folly {
 
 enum class TLPDestructionMode { THIS_THREAD, ALL_THREADS };
@@ -299,6 +287,14 @@ class PthreadKeyUnregister {
 };
 
 struct StaticMetaBase {
+  // In general, emutls cleanup is not guaranteed to play nice with the way
+  // StaticMeta mixes direct pthread calls and the use of __thread. This has
+  // caused problems on multiple platforms so don't use __thread there.
+  //
+  // XXX: Ideally we would instead determine if emutls is in use at runtime as
+  // it is possible to configure glibc on Linux to use emutls regardless.
+  static constexpr bool kUseThreadLocal = !kIsMobile && !kIsApple && !kMscVer;
+
   // Represents an ID of a thread local object. Initially set to the maximum
   // uint. This representation allows us to avoid a branch in accessing TLS data
   // (because if you test capacity > id if id = maxint then the test will always
@@ -415,13 +411,15 @@ struct FOLLY_EXPORT StaticMeta final : StaticMetaBase {
     // Eliminate as many branches and as much extra code as possible in the
     // cached fast path, leaving only one branch here and one indirection below.
     uint32_t id = ent->getOrInvalid();
-#ifdef FOLLY_TLD_USE_FOLLY_TLS
-    static thread_local ThreadEntry* threadEntry{};
-    static thread_local size_t capacity{};
-#else
-    ThreadEntry* threadEntry{};
-    size_t capacity{};
-#endif
+
+    static thread_local ThreadEntry* threadEntryTL{};
+    ThreadEntry* threadEntryNonTL{};
+    auto& threadEntry = kUseThreadLocal ? threadEntryTL : threadEntryNonTL;
+
+    static thread_local size_t capacityTL{};
+    size_t capacityNonTL{};
+    auto& capacity = kUseThreadLocal ? capacityTL : capacityNonTL;
+
     if (FOLLY_UNLIKELY(capacity <= id)) {
       getSlowReserveAndCache(ent, id, threadEntry, capacity);
     }
@@ -447,12 +445,12 @@ struct FOLLY_EXPORT StaticMeta final : StaticMetaBase {
         static_cast<ThreadEntry*>(pthread_getspecific(key));
     if (!threadEntry) {
       ThreadEntryList* threadEntryList = StaticMeta::getThreadEntryList();
-#ifdef FOLLY_TLD_USE_FOLLY_TLS
+      if (kUseThreadLocal) {
         static thread_local ThreadEntry threadEntrySingleton;
         threadEntry = &threadEntrySingleton;
-#else
+      } else {
         threadEntry = new ThreadEntry();
-#endif
+      }
       // if the ThreadEntry already exists
       // but pthread_getspecific returns NULL
       // do not add the same entry twice to the list