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..9c2d45744f754091bead5ea4c82687101c395c93 100644
--- a/third_party/WebKit/Source/wtf/StdLibExtras.h
+++ b/third_party/WebKit/Source/wtf/StdLibExtras.h
@@ -26,26 +26,141 @@
 #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
+
+// 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_STATIC_LOCAL()| takes an optional fourth argument of type
+// |CheckScriptWrappable|. Rarely needed, but the argument serves to
+// selectively disable verification |DCHECK()|s that the declared
+// singleton doesn't contain any embedded |ScriptWrappable| instances.
+// Having singletons retain such objects risks leaking v8 wrapper objects
+// across contexts in a renderer process, which must not happen.
+// However, if the singleton definition and use can be shown not to
+// leak its |ScriptWrappable|s, the check can be disabled by supplying
+// |CheckScriptWrappable::No| as a fourth argument. Its use isn't
+// encouraged, so please consider alternatives to declaring a singleton.
+//
+#define DEFINE_STATIC_LOCAL(Type, Name, Arguments, ...)                        \
+  static WTF::StaticSingleton<Type, ##__VA_ARGS__> s_##Name(                   \
+      (WTF::StaticSingleton<Type, ##__VA_ARGS__>::enterScope(),                \
+       new WTF::StaticSingleton<Type, ##__VA_ARGS__>::WrapperType Arguments)); \
+  Type& Name = s_##Name.get()
+
+namespace blink {
+template <typename T>
+class Persistent;
+class ScriptWrappable;
+
+}  // namespace blink
+
+namespace WTF {
+
+enum class CheckScriptWrappable {
+  No,
+  Yes,
+};
 
-class WTF_EXPORT StaticLocalVerifier {
-  WTF_MAKE_NONCOPYABLE(StaticLocalVerifier);
+template <typename Type,
+          CheckScriptWrappable checkScriptWrappable = CheckScriptWrappable::Yes>
+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;
+
+  static_assert(
+      !WTF::IsPersistentReferenceType<WrapperType>::value ||
+          !WTF::IsSubclass<
+              typename WTF::RemoveTemplate<WrapperType,
+                                           blink::Persistent>::type,
+              blink::ScriptWrappable>::value,
+      "It is unsafe to keep a static singleton to a ScriptWrappable-derived "
+      "object");
+
+  // 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
+  {
+    leaveScope();
+  }
+
+  Type& get() const {
+#if DCHECK_IS_ON()
+    DCHECK(isNotRacy());
+#endif
+    return Wrapper<Type>::unwrap(m_instance);
+  }
+
+  operator Type&() { return get(); }
+
+  static void enterScope() {
+#if DCHECK_IS_ON()
+    if (checkScriptWrappable == CheckScriptWrappable::Yes)
+      NoScriptWrappableScope<WrapperType>::enter();
+#endif
+  }
+
+  static void leaveScope() {
+#if DCHECK_IS_ON()
+    if (checkScriptWrappable == CheckScriptWrappable::Yes)
+      NoScriptWrappableScope<WrapperType>::leave();
+#endif
+  }
+
+ private:
+#if DCHECK_IS_ON()
 
-  bool isNotRacy() {
+  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).
@@ -54,71 +169,29 @@ class WTF_EXPORT StaticLocalVerifier {
            WTF::isAtomicallyInitializedStaticMutexLockHeld();
   }
 
- private:
+  template <typename T, bool = WTF::IsPersistentReferenceType<T>::value>
+  struct NoScriptWrappableScope {
+    static void enter() {}
+    static void leave() {}
+  };
+
+  template <typename T>
+  struct NoScriptWrappableScope<T, true> {
+    static void enter() { T::enterNoScriptWrappableScope(); }
+    static void leave() { T::leaveNoScriptWrappableScope(); }
+  };
+#endif
+  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
+}  // namespace WTF
 
-// 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);
+using WTF::CheckScriptWrappable;
 
 // 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