Tidy DEFINE_(THREAD_SAFE_)STATIC_LOCAL() implementations.

third_party/WebKit/Source/wtf/StdLibExtras.h

Index: third_party/WebKit/Source/wtf/StdLibExtras.h
diff --git a/third_party/WebKit/Source/wtf/StdLibExtras.h b/third_party/WebKit/Source/wtf/StdLibExtras.h
index 26ba1d8d02958298aacfc73daea5743ccbbce201..cf6a5eddd80ff39b3a3378e4f43043b3df6798e6 100644
--- a/third_party/WebKit/Source/wtf/StdLibExtras.h
+++ b/third_party/WebKit/Source/wtf/StdLibExtras.h
@@ -26,26 +26,98 @@
 #ifndef WTF_StdLibExtras_h
 #define WTF_StdLibExtras_h
 
+#include <cstddef>
 #include "base/numerics/safe_conversions.h"
 #include "wtf/Assertions.h"
 #include "wtf/CPU.h"
 #include "wtf/LeakAnnotations.h"
+#include "wtf/Noncopyable.h"
 #include "wtf/TypeTraits.h"
-#include <cstddef>
 
 #if DCHECK_IS_ON()
-#include "wtf/Noncopyable.h"
 #include "wtf/Threading.h"
+#endif
 
-class WTF_EXPORT StaticLocalVerifier {
-  WTF_MAKE_NONCOPYABLE(StaticLocalVerifier);
+// Use |DEFINE_STATIC_LOCAL()| to declare and define a static local variable
+// (|static T;|) so that it is leaked and its destructors are not called at
+// exit. T may also be a Blink garbage collected object, in which case it is
+// wrapped up by an off-heap |Persistent<T>| reference to the object, keeping
+// it alive across GCs.
+//
+#define DEFINE_STATIC_LOCAL(Type, Name, Arguments)            \
+  static WTF::StaticSingleton<Type> s_##Name(                 \
+      new WTF::StaticSingleton<Type>::WrapperType Arguments); \
+  Type& Name = s_##Name.get()
+
+namespace blink {
+template <typename T>
+class Persistent;
+
+}  // namespace blink
+
+namespace WTF {
+
+template <typename Type>
+class StaticSingleton final {
+  WTF_MAKE_NONCOPYABLE(StaticSingleton);
 
  public:
-  StaticLocalVerifier()
-      : m_safelyInitialized(WTF::isBeforeThreadCreated()),
-        m_thread(WTF::internal::currentThreadSyscall()) {}
+  template <typename T,
+            bool = WTF::IsGarbageCollectedType<T>::value &&
+                   !WTF::IsPersistentReferenceType<T>::value>
+  struct Wrapper {
+    using type = T;
+
+    static T& unwrap(T* singleton) { return *singleton; }
+  };
+
+  template <typename T>
+  struct Wrapper<T, true> {
+    using type = blink::Persistent<T>;
+
+    static T& unwrap(blink::Persistent<T>* singleton) {
+      DCHECK(singleton);
+      // If this assert triggers, you're supplying an empty ("()") 'Arguments'
+      // argument to DEFINE_STATIC_LOCAL() - it must be the heap object you wish
+      // to create as a static singleton and wrapped up with a Persistent
+      // reference.
+      DCHECK(*singleton);
+      return **singleton;
+    }
+  };
+
+  using WrapperType = typename Wrapper<Type>::type;
+
+  // To cooperate with leak detection(LSan) for Blink garbage collected objects,
+  // the objects owned by persistent local statics will in some cases have to be
+  // finalized prior to leak checking. This only applies to static references to
+  // Blink heap objects and what they transitively hold on to. Hence the
+  // LEAK_SANITIZER_REGISTER_STATIC_LOCAL() use, it taking care of the grungy
+  // details.
+
+  explicit StaticSingleton(WrapperType* instance)
+      : m_instance(LEAK_SANITIZER_REGISTER_STATIC_LOCAL(WrapperType, instance))
+#if DCHECK_IS_ON()
+        ,
+        m_safelyInitialized(WTF::isBeforeThreadCreated()),
+        m_thread(WTF::internal::currentThreadSyscall())
+#endif
+  {
+  }
+
+  Type& get() const {
+#if DCHECK_IS_ON()
+    DCHECK(isNotRacy());
+#endif
+    return Wrapper<Type>::unwrap(m_instance);
+  }
 
-  bool isNotRacy() {
+  operator Type&() { return get(); }
+
+ private:
+#if DCHECK_IS_ON()
+
+  bool isNotRacy() const {
     // Make sure that this 1) is safely initialized, 2) keeps being called
     // on the same thread, or 3) is called within
     // AtomicallyInitializedStatic (i.e. with a lock held).
@@ -53,72 +125,16 @@ class WTF_EXPORT StaticLocalVerifier {
            m_thread == WTF::internal::currentThreadSyscall() ||
            WTF::isAtomicallyInitializedStaticMutexLockHeld();

[dcheng, 2017/02/15 08:29:56]

Since we have threadsafe function-local statics by default now... do we actually
still need these checks? I don't quite understand the history behind these or
what they're trying to verify.

[sof, 2017/02/15 08:44:57]

https://codereview.chromium.org/874203002#msg11 covers that.

   }
+#endif
 
- private:
+  WrapperType* m_instance;
+#if DCHECK_IS_ON()
   bool m_safelyInitialized;
   ThreadIdentifier m_thread;
-};
 #endif
-
-namespace blink {
-template <typename T>
-class Persistent;
 };
 
-template <typename T,
-          bool = WTF::IsGarbageCollectedType<T>::value &&
-                 !WTF::IsPersistentReferenceType<T>::value>
-class StaticLocalWrapper {
- public:
-  using WrapType = T;
-
-  static T& unwrap(T* singleton) { return *singleton; }
-};
-
-template <typename T>
-class StaticLocalWrapper<T, true> {
- public:
-  using WrapType = blink::Persistent<T>;
-
-  static T& unwrap(blink::Persistent<T>* singleton) {
-    DCHECK(singleton);
-    // If this assert triggers, you're supplying an empty ("()") 'Arguments'
-    // argument to DEFINE_STATIC_LOCAL() - it must be the heap object you wish
-    // to create as a static singleton and wrapped up with a Persistent
-    // reference.
-    DCHECK(*singleton);
-    return **singleton;
-  }
-};
-
-#if DCHECK_IS_ON()
-#define DEFINE_STATIC_LOCAL_CHECK_THREADSAFE_ACCESS(Name) \
-  static StaticLocalVerifier Name##StaticLocalVerifier;   \
-  DCHECK(Name##StaticLocalVerifier.isNotRacy())
-#else
-#define DEFINE_STATIC_LOCAL_CHECK_THREADSAFE_ACCESS(Name)
-#endif
-
-// Use DEFINE_STATIC_LOCAL() to declare and define a static local variable
-// (static T;) so that it is leaked and its destructors are not called at exit.
-// T may also be a Blink garbage collected object, in which case it is
-// wrapped up by an off-heap Persistent<T> reference to the object, keeping
-// it alive across GCs.
-//
-// To cooperate with leak detection(LSan) for Blink garbage collected objects,
-// the objects owned by persistent local statics will in some cases have to be
-// finalized prior to leak checking. This only applies to static references to
-// Blink heap objects and what they transitively hold on to. Hence the
-// LEAK_SANITIZER_REGISTER_STATIC_LOCAL() use, it taking care of the grungy
-// details.
-//
-#define DEFINE_STATIC_LOCAL(Type, Name, Arguments)                   \
-  DEFINE_STATIC_LOCAL_CHECK_THREADSAFE_ACCESS(Name);                 \
-  using WrappedTypeFor##Name = StaticLocalWrapper<Type>::WrapType;   \
-  static WrappedTypeFor##Name* WrappedInstanceFor##Name =            \
-      LEAK_SANITIZER_REGISTER_STATIC_LOCAL(                          \
-          WrappedTypeFor##Name, new WrappedTypeFor##Name Arguments); \
-  Type& Name = StaticLocalWrapper<Type>::unwrap(WrappedInstanceFor##Name);
+}  // namespace WTF
 
 // Use this to declare and define a static local pointer to a ref-counted object
 // so that it is leaked so that the object's destructors are not called at