[Sync] Move //sync to //components/sync.

sync/internal_api/public/util/weak_handle.h

-// Copyright 2012 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.
-
-// Weak handles provides a way to refer to weak pointers from another
-// thread.  This is useful because it is not safe to reference a weak
-// pointer from a thread other than the thread on which it was
-// created.
-//
-// Weak handles can be passed across threads, so for example, you can
-// use them to do the "real" work on one thread and get notified on
-// another thread:
-//
-// class FooIOWorker {
-//  public:
-//   FooIOWorker(const WeakHandle<Foo>& foo) : foo_(foo) {}
-//
-//   void OnIOStart() {
-//     foo_.Call(FROM_HERE, &Foo::OnIOStart);
-//   }
-//
-//   void OnIOEvent(IOEvent e) {
-//     foo_.Call(FROM_HERE, &Foo::OnIOEvent, e);
-//   }
-//
-//   void OnIOError(IOError err) {
-//     foo_.Call(FROM_HERE, &Foo::OnIOError, err);
-//   }
-//
-//  private:
-//   const WeakHandle<Foo> foo_;
-// };
-//
-// class Foo : public SupportsWeakPtr<Foo>, public NonThreadSafe {
-//  public:
-//   Foo() {
-//     SpawnFooIOWorkerOnIOThread(base::MakeWeakHandle(AsWeakPtr()));
-//   }
-//
-//   /* Will always be called on the correct thread, and only if this
-//      object hasn't been destroyed. */
-//   void OnIOStart() { DCHECK(CalledOnValidThread(); ... }
-//   void OnIOEvent(IOEvent e) { DCHECK(CalledOnValidThread(); ... }
-//   void OnIOError(IOError err) { DCHECK(CalledOnValidThread(); ... }
-// };
-
-#ifndef SYNC_INTERNAL_API_PUBLIC_UTIL_WEAK_HANDLE_H_
-#define SYNC_INTERNAL_API_PUBLIC_UTIL_WEAK_HANDLE_H_
-
-#include <cstddef>
-#include <utility>
-
-#include "base/bind.h"
-#include "base/compiler_specific.h"
-#include "base/gtest_prod_util.h"
-#include "base/location.h"
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
-#include "base/single_thread_task_runner.h"
-#include "sync/base/sync_export.h"
-
-namespace tracked_objects {
-class Location;
-}  // namespace tracked_objects
-
-namespace syncer {
-
-template <typename T> class WeakHandle;
-
-namespace internal {
-// These classes are part of the WeakHandle implementation.  DO NOT
-// USE THESE CLASSES DIRECTLY YOURSELF.
-
-// Base class for WeakHandleCore<T> to avoid template bloat.  Handles
-// the interaction with the owner thread and its message loop.
-class SYNC_EXPORT WeakHandleCoreBase {
- public:
-  // Assumes the current thread is the owner thread.
-  WeakHandleCoreBase();
-
-  // May be called on any thread.
-  bool IsOnOwnerThread() const;
-
- protected:
-  // May be destroyed on any thread.
-  ~WeakHandleCoreBase();
-
-  // May be called on any thread.
-  void PostToOwnerThread(const tracked_objects::Location& from_here,
-                         const base::Closure& fn) const;
-
- private:
-  // May be used on any thread.
-  const scoped_refptr<base::SingleThreadTaskRunner> owner_loop_task_runner_;
-
-  DISALLOW_COPY_AND_ASSIGN(WeakHandleCoreBase);
-};
-
-// WeakHandleCore<T> contains all the logic for WeakHandle<T>.
-template <typename T>
-class WeakHandleCore
-    : public WeakHandleCoreBase,
-      public base::RefCountedThreadSafe<WeakHandleCore<T> > {
- public:
-  // Must be called on |ptr|'s owner thread, which is assumed to be
-  // the current thread.
-  explicit WeakHandleCore(const base::WeakPtr<T>& ptr) : ptr_(ptr) {}
-
-  // Must be called on |ptr_|'s owner thread.
-  base::WeakPtr<T> Get() const {
-    CHECK(IsOnOwnerThread());
-    return ptr_;
-  }
-
-  // Call(...) may be called on any thread, but all its arguments
-  // should be safe to be bound and copied across threads.
-  template <typename Method, typename... Args>
-  void Call(const tracked_objects::Location& from_here,
-            Method method, Args&&... args) const {
-    PostToOwnerThread(
-        from_here, base::Bind(method, ptr_, std::forward<Args>(args)...));
-  }
-
- private:
-  friend class base::RefCountedThreadSafe<WeakHandleCore<T> >;
-
-  // May be destroyed on any thread.
-  ~WeakHandleCore() {}
-
-  // Must be dereferenced only on the owner thread.  May be destroyed
-  // from any thread.
-  base::WeakPtr<T> ptr_;
-
-  DISALLOW_COPY_AND_ASSIGN(WeakHandleCore);
-};
-
-}  // namespace internal
-
-// May be destroyed on any thread.
-// Copying and assignment are welcome.
-template <typename T>
-class WeakHandle {
- public:
-  // Creates an uninitialized WeakHandle.
-  WeakHandle() {}
-
-  // Creates an initialized WeakHandle from |ptr|.
-  explicit WeakHandle(const base::WeakPtr<T>& ptr)
-      : core_(new internal::WeakHandleCore<T>(ptr)) {}
-
-  // Allow conversion from WeakHandle<U> to WeakHandle<T> if U is
-  // convertible to T, but we *must* be on |other|'s owner thread.
-  // Note that this doesn't override the regular copy constructor, so
-  // that one can be called on any thread.
-  template <typename U>
-  WeakHandle(const WeakHandle<U>& other)  // NOLINT
-      : core_(
-          other.IsInitialized() ?
-          new internal::WeakHandleCore<T>(other.Get()) :
-          NULL) {}
-
-  // Returns true iff this WeakHandle is initialized.  Note that being
-  // initialized isn't a guarantee that the underlying object is still
-  // alive.
-  bool IsInitialized() const {
-    return core_.get() != NULL;
-  }
-
-  // Resets to an uninitialized WeakHandle.
-  void Reset() {
-    core_ = NULL;
-  }
-
-  // Must be called only on the underlying object's owner thread.
-  base::WeakPtr<T> Get() const {
-    CHECK(IsInitialized());
-    CHECK(core_->IsOnOwnerThread());
-    return core_->Get();
-  }
-
-  // Call(...) may be called on any thread, but all its arguments
-  // should be safe to be bound and copied across threads.
-  template <typename Method, typename... Args>
-  void Call(const tracked_objects::Location& from_here,
-            Method method, Args&&... args) const {
-    CHECK(IsInitialized());
-    core_->Call(from_here, method, std::forward<Args>(args)...);
-  }
-
- private:
-  FRIEND_TEST_ALL_PREFIXES(WeakHandleTest,
-                           TypeConversionConstructor);
-  FRIEND_TEST_ALL_PREFIXES(WeakHandleTest,
-                           TypeConversionConstructorAssignment);
-
-  scoped_refptr<internal::WeakHandleCore<T> > core_;
-};
-
-// Makes a WeakHandle from a WeakPtr.
-template <typename T>
-WeakHandle<T> MakeWeakHandle(const base::WeakPtr<T>& ptr) {
-  return WeakHandle<T>(ptr);
-}
-
-}  // namespace syncer
-
-#endif  // SYNC_INTERNAL_API_PUBLIC_UTIL_WEAK_HANDLE_H_