Autofill phone number enhancements and integration of Phone Number Util Library: part 1

third_party/libphonenumber/cpp/src/base/lazy_instance.h

+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// The LazyInstance<Type, Traits> class manages a single instance of Type,
+// which will be lazily created on the first time it's accessed.  This class is
+// useful for places you would normally use a function-level static, but you
+// need to have guaranteed thread-safety.  The Type constructor will only ever
+// be called once, even if two threads are racing to create the object.  Get()
+// and Pointer() will always return the same, completely initialized instance.
+// When the instance is constructed it is registered with AtExitManager.  The
+// destructor will be called on program exit.
+//
+// LazyInstance is completely thread safe, assuming that you create it safely.
+// The class was designed to be POD initialized, so it shouldn't require a
+// static constructor.  It really only makes sense to declare a LazyInstance as
+// a global variable using the base::LinkerInitialized constructor.
+//
+// LazyInstance is similar to Singleton, except it does not have the singleton
+// property.  You can have multiple LazyInstance's of the same type, and each
+// will manage a unique instance.  It also preallocates the space for Type, as
+// to avoid allocating the Type instance on the heap.  This may help with the
+// performance of creating the instance, and reducing heap fragmentation.  This
+// requires that Type be a complete type so we can determine the size.
+//
+// Example usage:
+//   static LazyInstance<MyClass> my_instance(base::LINKER_INITIALIZED);
+//   void SomeMethod() {
+//     my_instance.Get().SomeMethod();  // MyClass::SomeMethod()
+//
+//     MyClass* ptr = my_instance.Pointer();
+//     ptr->DoDoDo();  // MyClass::DoDoDo
+//   }
+
+#ifndef BASE_LAZY_INSTANCE_H_
+#define BASE_LAZY_INSTANCE_H_
+#pragma once
+
+#include <new>  // For placement new.
+
+#include "base/atomicops.h"
+#include "base/basictypes.h"
+#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
+#include "base/threading/thread_restrictions.h"
+
+namespace base {
+
+template <typename Type>
+struct DefaultLazyInstanceTraits {
+  static const bool kAllowedToAccessOnNonjoinableThread = false;
+
+  static Type* New(void* instance) {
+    // Use placement new to initialize our instance in our preallocated space.
+    // The parenthesis is very important here to force POD type initialization.
+    return new (instance) Type();
+  }
+  static void Delete(void* instance) {
+    // Explicitly call the destructor.
+    reinterpret_cast<Type*>(instance)->~Type();
+  }
+};
+
+template <typename Type>
+struct LeakyLazyInstanceTraits {
+  static const bool kAllowedToAccessOnNonjoinableThread = true;
+
+  static Type* New(void* instance) {
+    return DefaultLazyInstanceTraits<Type>::New(instance);
+  }
+  // Rather than define an empty Delete function, we make Delete itself
+  // a null pointer.  This allows us to completely sidestep registering
+  // this object with an AtExitManager, which allows you to use
+  // LeakyLazyInstanceTraits in contexts where you don't have an
+  // AtExitManager.
+  static void (*Delete)(void* instance);
+};
+
+template <typename Type>
+void (*LeakyLazyInstanceTraits<Type>::Delete)(void* instance) = NULL;
+
+// We pull out some of the functionality into a non-templated base, so that we
+// can implement the more complicated pieces out of line in the .cc file.
+class LazyInstanceHelper {
+ protected:
+  enum {
+    STATE_EMPTY    = 0,
+    STATE_CREATING = 1,
+    STATE_CREATED  = 2
+  };
+
+  explicit LazyInstanceHelper(LinkerInitialized /*unused*/) {/* state_ is 0 */}
+  // Declaring a destructor (even if it's empty) will cause MSVC to register a
+  // static initializer to register the empty destructor with atexit().
+
+  // Check if instance needs to be created. If so return true otherwise
+  // if another thread has beat us, wait for instance to be created and
+  // return false.
+  bool NeedsInstance();
+
+  // After creating an instance, call this to register the dtor to be called
+  // at program exit and to update the state to STATE_CREATED.
+  void CompleteInstance(void* instance, void (*dtor)(void*));
+
+  base::subtle::Atomic32 state_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LazyInstanceHelper);
+};
+
+template <typename Type, typename Traits = DefaultLazyInstanceTraits<Type> >
+class LazyInstance : public LazyInstanceHelper {
+ public:
+  explicit LazyInstance(LinkerInitialized x) : LazyInstanceHelper(x) { }
+  // Declaring a destructor (even if it's empty) will cause MSVC to register a
+  // static initializer to register the empty destructor with atexit().
+
+  Type& Get() {
+    return *Pointer();
+  }
+
+  Type* Pointer() {
+    if (!Traits::kAllowedToAccessOnNonjoinableThread)
+      base::ThreadRestrictions::AssertSingletonAllowed();
+
+    // We will hopefully have fast access when the instance is already created.
+    if ((base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) &&
+        NeedsInstance()) {
+      // Create the instance in the space provided by |buf_|.
+      instance_ = Traits::New(buf_);
+      // Traits::Delete will be null for LeakyLazyInstanceTraits
+      void (*dtor)(void*) = Traits::Delete;
+      CompleteInstance(this, (dtor == NULL) ? NULL : OnExit);
+    }
+
+    // This annotation helps race detectors recognize correct lock-less
+    // synchronization between different threads calling Pointer().
+    // We suggest dynamic race detection tool that "Traits::New" above
+    // and CompleteInstance(...) happens before "return instance_" below.
+    // See the corresponding HAPPENS_BEFORE in CompleteInstance(...).
+    ANNOTATE_HAPPENS_AFTER(&state_);
+    return instance_;
+  }
+
+  bool operator==(Type* p) {
+    switch (base::subtle::NoBarrier_Load(&state_)) {
+      case STATE_EMPTY:
+        return p == NULL;
+      case STATE_CREATING:
+        return static_cast<int8*>(static_cast<void*>(p)) == buf_;
+      case STATE_CREATED:
+        return p == instance_;
+      default:
+        return false;
+    }
+  }
+
+ private:
+  // Adapter function for use with AtExit.  This should be called single
+  // threaded, so don't use atomic operations.
+  // Calling OnExit while the instance is in use by other threads is a mistake.
+  static void OnExit(void* lazy_instance) {
+    LazyInstance<Type, Traits>* me =
+        reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance);
+    Traits::Delete(me->instance_);
+    me->instance_ = NULL;
+    base::subtle::Release_Store(&me->state_, STATE_EMPTY);
+  }
+
+  int8 buf_[sizeof(Type)];  // Preallocate the space for the Type instance.
+  Type *instance_;
+
+  DISALLOW_COPY_AND_ASSIGN(LazyInstance);
+};
+
+}  // namespace base
+
+#endif  // BASE_LAZY_INSTANCE_H_