SingletonThreadLocal::try_get()

Summary: Accesses the per-thread singleton if it has already been created.

Reviewed By: amlannayak

Differential Revision: D31003518

fbshipit-source-id: 959418c4bc81da2b0ab7c639cdddb6d0beaf0121

folly/SingletonThreadLocal.h

@@ -132,13 +132,11 @@ class SingletonThreadLocal {
   SingletonThreadLocal() = delete;
 
   FOLLY_ALWAYS_INLINE static WrapperTL& getWrapperTL() {
+    (void)unique; // force the object not to be thrown out as unused
     return detail::createGlobal<WrapperTL, Tag>();
   }
 
-  FOLLY_NOINLINE static Wrapper& getWrapper() {
-    (void)unique; // force the object not to be thrown out as unused
-    return *getWrapperTL();
-  }
+  FOLLY_NOINLINE static Wrapper& getWrapper() { return *getWrapperTL(); }
 
   FOLLY_NOINLINE static Wrapper& getSlow(LocalCache& cache) {
     if (threadlocal_detail::StaticMetaBase::dying()) {
@@ -158,6 +156,11 @@ class SingletonThreadLocal {
     return FOLLY_LIKELY(!!cache.cache) ? *cache.cache : getSlow(cache);
   }
 
+  static T* try_get() {
+    auto* wrapper = getWrapperTL().getIfExist();
+    return wrapper ? &wrapper->object : nullptr;
+  }
+
   class Accessor {
    private:
     using Inner = typename WrapperTL::Accessor;

folly/test/SingletonThreadLocalTest.cpp

@@ -47,6 +47,15 @@ struct Foo {
 using FooSingletonTL = SingletonThreadLocal<Foo>;
 } // namespace
 
+TEST(SingletonThreadLocalTest, TryGet) {
+  struct Foo {};
+  using FooTL = SingletonThreadLocal<Foo>;
+  EXPECT_EQ(nullptr, FooTL::try_get());
+  FooTL::get();
+  EXPECT_NE(nullptr, FooTL::try_get());
+  EXPECT_EQ(&FooTL::get(), FooTL::try_get());
+}
+
 TEST(SingletonThreadLocalTest, OneSingletonPerThread) {
   static constexpr std::size_t targetThreadCount{64};
   std::atomic<std::size_t> completedThreadCount{0};