--- /dev/null
+// Copyright (c) 2014 Marshall A. Greenblatt. Portions copyright (c) 2012
+// Google Inc. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google Inc. nor the name Chromium Embedded
+// Framework nor the names of its contributors may be used to endorse
+// or promote products derived from this software without specific prior
+// written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Weak pointers are pointers to an object that do not affect its lifetime,
+// and which may be invalidated (i.e. reset to NULL) by the object, or its
+// owner, at any time, most commonly when the object is about to be deleted.
+
+// Weak pointers are useful when an object needs to be accessed safely by one
+// or more objects other than its owner, and those callers can cope with the
+// object vanishing and e.g. tasks posted to it being silently dropped.
+// Reference-counting such an object would complicate the ownership graph and
+// make it harder to reason about the object's lifetime.
+
+// EXAMPLE:
+//
+// class Controller {
+// public:
+// Controller() : weak_factory_(this) {}
+// void SpawnWorker() { Worker::StartNew(weak_factory_.GetWeakPtr()); }
+// void WorkComplete(const Result& result) { ... }
+// private:
+// // Member variables should appear before the WeakPtrFactory, to ensure
+// // that any WeakPtrs to Controller are invalidated before its members
+// // variable's destructors are executed, rendering them invalid.
+// WeakPtrFactory<Controller> weak_factory_;
+// };
+//
+// class Worker {
+// public:
+// static void StartNew(const WeakPtr<Controller>& controller) {
+// Worker* worker = new Worker(controller);
+// // Kick off asynchronous processing...
+// }
+// private:
+// Worker(const WeakPtr<Controller>& controller)
+// : controller_(controller) {}
+// void DidCompleteAsynchronousProcessing(const Result& result) {
+// if (controller_)
+// controller_->WorkComplete(result);
+// }
+// WeakPtr<Controller> controller_;
+// };
+//
+// With this implementation a caller may use SpawnWorker() to dispatch multiple
+// Workers and subsequently delete the Controller, without waiting for all
+// Workers to have completed.
+
+// ------------------------- IMPORTANT: Thread-safety -------------------------
+
+// Weak pointers may be passed safely between threads, but must always be
+// dereferenced and invalidated on the same thread otherwise checking the
+// pointer would be racey.
+//
+// To ensure correct use, the first time a WeakPtr issued by a WeakPtrFactory
+// is dereferenced, the factory and its WeakPtrs become bound to the calling
+// thread, and cannot be dereferenced or invalidated on any other thread. Bound
+// WeakPtrs can still be handed off to other threads, e.g. to use to post tasks
+// back to object on the bound thread.
+//
+// If all WeakPtr objects are destroyed or invalidated then the factory is
+// unbound from the SequencedTaskRunner/Thread. The WeakPtrFactory may then be
+// destroyed, or new WeakPtr objects may be used, from a different sequence.
+//
+// Thus, at least one WeakPtr object must exist and have been dereferenced on
+// the correct thread to enforce that other WeakPtr objects will enforce they
+// are used on the desired thread.
+
+#ifndef CEF_INCLUDE_BASE_CEF_WEAK_PTR_H_
+#define CEF_INCLUDE_BASE_CEF_WEAK_PTR_H_
+#pragma once
+
+#if defined(BASE_MEMORY_WEAK_PTR_H_)
+// Do nothing if the Chromium header has already been included.
+// This can happen in cases where Chromium code is used directly by the
+// client application. When using Chromium code directly always include
+// the Chromium header first to avoid type conflicts.
+#elif defined(USING_CHROMIUM_INCLUDES)
+// When building CEF include the Chromium header directly.
+#include "base/memory/weak_ptr.h"
+#else // !USING_CHROMIUM_INCLUDES
+// The following is substantially similar to the Chromium implementation.
+// If the Chromium implementation diverges the below implementation should be
+// updated to match.
+
+#include "include/base/cef_basictypes.h"
+#include "include/base/cef_logging.h"
+#include "include/base/cef_ref_counted.h"
+#include "include/base/cef_template_util.h"
+#include "include/base/cef_thread_checker.h"
+
+namespace base {
+
+template <typename T> class SupportsWeakPtr;
+template <typename T> class WeakPtr;
+
+namespace cef_internal {
+// These classes are part of the WeakPtr implementation.
+// DO NOT USE THESE CLASSES DIRECTLY YOURSELF.
+
+class WeakReference {
+ public:
+ // Although Flag is bound to a specific thread, it may be deleted from another
+ // via base::WeakPtr::~WeakPtr().
+ class Flag : public RefCountedThreadSafe<Flag> {
+ public:
+ Flag();
+
+ void Invalidate();
+ bool IsValid() const;
+
+ private:
+ friend class base::RefCountedThreadSafe<Flag>;
+
+ ~Flag();
+
+ // The current Chromium implementation uses SequenceChecker instead of
+ // ThreadChecker to support SequencedWorkerPools. CEF does not yet expose
+ // the concept of SequencedWorkerPools.
+ ThreadChecker thread_checker_;
+ bool is_valid_;
+ };
+
+ WeakReference();
+ explicit WeakReference(const Flag* flag);
+ ~WeakReference();
+
+ bool is_valid() const;
+
+ private:
+ scoped_refptr<const Flag> flag_;
+};
+
+class WeakReferenceOwner {
+ public:
+ WeakReferenceOwner();
+ ~WeakReferenceOwner();
+
+ WeakReference GetRef() const;
+
+ bool HasRefs() const {
+ return flag_.get() && !flag_->HasOneRef();
+ }
+
+ void Invalidate();
+
+ private:
+ mutable scoped_refptr<WeakReference::Flag> flag_;
+};
+
+// This class simplifies the implementation of WeakPtr's type conversion
+// constructor by avoiding the need for a public accessor for ref_. A
+// WeakPtr<T> cannot access the private members of WeakPtr<U>, so this
+// base class gives us a way to access ref_ in a protected fashion.
+class WeakPtrBase {
+ public:
+ WeakPtrBase();
+ ~WeakPtrBase();
+
+ protected:
+ explicit WeakPtrBase(const WeakReference& ref);
+
+ WeakReference ref_;
+};
+
+// This class provides a common implementation of common functions that would
+// otherwise get instantiated separately for each distinct instantiation of
+// SupportsWeakPtr<>.
+class SupportsWeakPtrBase {
+ public:
+ // A safe static downcast of a WeakPtr<Base> to WeakPtr<Derived>. This
+ // conversion will only compile if there is exists a Base which inherits
+ // from SupportsWeakPtr<Base>. See base::AsWeakPtr() below for a helper
+ // function that makes calling this easier.
+ template<typename Derived>
+ static WeakPtr<Derived> StaticAsWeakPtr(Derived* t) {
+ typedef
+ is_convertible<Derived, cef_internal::SupportsWeakPtrBase&> convertible;
+ COMPILE_ASSERT(convertible::value,
+ AsWeakPtr_argument_inherits_from_SupportsWeakPtr);
+ return AsWeakPtrImpl<Derived>(t, *t);
+ }
+
+ private:
+ // This template function uses type inference to find a Base of Derived
+ // which is an instance of SupportsWeakPtr<Base>. We can then safely
+ // static_cast the Base* to a Derived*.
+ template <typename Derived, typename Base>
+ static WeakPtr<Derived> AsWeakPtrImpl(
+ Derived* t, const SupportsWeakPtr<Base>&) {
+ WeakPtr<Base> ptr = t->Base::AsWeakPtr();
+ return WeakPtr<Derived>(ptr.ref_, static_cast<Derived*>(ptr.ptr_));
+ }
+};
+
+} // namespace cef_internal
+
+template <typename T> class WeakPtrFactory;
+
+// The WeakPtr class holds a weak reference to |T*|.
+//
+// This class is designed to be used like a normal pointer. You should always
+// null-test an object of this class before using it or invoking a method that
+// may result in the underlying object being destroyed.
+//
+// EXAMPLE:
+//
+// class Foo { ... };
+// WeakPtr<Foo> foo;
+// if (foo)
+// foo->method();
+//
+template <typename T>
+class WeakPtr : public cef_internal::WeakPtrBase {
+ public:
+ WeakPtr() : ptr_(NULL) {
+ }
+
+ // Allow conversion from U to T provided U "is a" T. Note that this
+ // is separate from the (implicit) copy constructor.
+ template <typename U>
+ WeakPtr(const WeakPtr<U>& other) : WeakPtrBase(other), ptr_(other.ptr_) {
+ }
+
+ T* get() const { return ref_.is_valid() ? ptr_ : NULL; }
+
+ T& operator*() const {
+ DCHECK(get() != NULL);
+ return *get();
+ }
+ T* operator->() const {
+ DCHECK(get() != NULL);
+ return get();
+ }
+
+ // Allow WeakPtr<element_type> to be used in boolean expressions, but not
+ // implicitly convertible to a real bool (which is dangerous).
+ //
+ // Note that this trick is only safe when the == and != operators
+ // are declared explicitly, as otherwise "weak_ptr1 == weak_ptr2"
+ // will compile but do the wrong thing (i.e., convert to Testable
+ // and then do the comparison).
+ private:
+ typedef T* WeakPtr::*Testable;
+
+ public:
+ operator Testable() const { return get() ? &WeakPtr::ptr_ : NULL; }
+
+ void reset() {
+ ref_ = cef_internal::WeakReference();
+ ptr_ = NULL;
+ }
+
+ private:
+ // Explicitly declare comparison operators as required by the bool
+ // trick, but keep them private.
+ template <class U> bool operator==(WeakPtr<U> const&) const;
+ template <class U> bool operator!=(WeakPtr<U> const&) const;
+
+ friend class cef_internal::SupportsWeakPtrBase;
+ template <typename U> friend class WeakPtr;
+ friend class SupportsWeakPtr<T>;
+ friend class WeakPtrFactory<T>;
+
+ WeakPtr(const cef_internal::WeakReference& ref, T* ptr)
+ : WeakPtrBase(ref),
+ ptr_(ptr) {
+ }
+
+ // This pointer is only valid when ref_.is_valid() is true. Otherwise, its
+ // value is undefined (as opposed to NULL).
+ T* ptr_;
+};
+
+// A class may be composed of a WeakPtrFactory and thereby
+// control how it exposes weak pointers to itself. This is helpful if you only
+// need weak pointers within the implementation of a class. This class is also
+// useful when working with primitive types. For example, you could have a
+// WeakPtrFactory<bool> that is used to pass around a weak reference to a bool.
+template <class T>
+class WeakPtrFactory {
+ public:
+ explicit WeakPtrFactory(T* ptr) : ptr_(ptr) {
+ }
+
+ ~WeakPtrFactory() {
+ ptr_ = NULL;
+ }
+
+ WeakPtr<T> GetWeakPtr() {
+ DCHECK(ptr_);
+ return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_);
+ }
+
+ // Call this method to invalidate all existing weak pointers.
+ void InvalidateWeakPtrs() {
+ DCHECK(ptr_);
+ weak_reference_owner_.Invalidate();
+ }
+
+ // Call this method to determine if any weak pointers exist.
+ bool HasWeakPtrs() const {
+ DCHECK(ptr_);
+ return weak_reference_owner_.HasRefs();
+ }
+
+ private:
+ cef_internal::WeakReferenceOwner weak_reference_owner_;
+ T* ptr_;
+ DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory);
+};
+
+// A class may extend from SupportsWeakPtr to let others take weak pointers to
+// it. This avoids the class itself implementing boilerplate to dispense weak
+// pointers. However, since SupportsWeakPtr's destructor won't invalidate
+// weak pointers to the class until after the derived class' members have been
+// destroyed, its use can lead to subtle use-after-destroy issues.
+template <class T>
+class SupportsWeakPtr : public cef_internal::SupportsWeakPtrBase {
+ public:
+ SupportsWeakPtr() {}
+
+ WeakPtr<T> AsWeakPtr() {
+ return WeakPtr<T>(weak_reference_owner_.GetRef(), static_cast<T*>(this));
+ }
+
+ protected:
+ ~SupportsWeakPtr() {}
+
+ private:
+ cef_internal::WeakReferenceOwner weak_reference_owner_;
+ DISALLOW_COPY_AND_ASSIGN(SupportsWeakPtr);
+};
+
+// Helper function that uses type deduction to safely return a WeakPtr<Derived>
+// when Derived doesn't directly extend SupportsWeakPtr<Derived>, instead it
+// extends a Base that extends SupportsWeakPtr<Base>.
+//
+// EXAMPLE:
+// class Base : public base::SupportsWeakPtr<Producer> {};
+// class Derived : public Base {};
+//
+// Derived derived;
+// base::WeakPtr<Derived> ptr = base::AsWeakPtr(&derived);
+//
+// Note that the following doesn't work (invalid type conversion) since
+// Derived::AsWeakPtr() is WeakPtr<Base> SupportsWeakPtr<Base>::AsWeakPtr(),
+// and there's no way to safely cast WeakPtr<Base> to WeakPtr<Derived> at
+// the caller.
+//
+// base::WeakPtr<Derived> ptr = derived.AsWeakPtr(); // Fails.
+
+template <typename Derived>
+WeakPtr<Derived> AsWeakPtr(Derived* t) {
+ return cef_internal::SupportsWeakPtrBase::StaticAsWeakPtr<Derived>(t);
+}
+
+} // namespace base
+
+#endif // !USING_CHROMIUM_INCLUDES
+
+#endif // CEF_INCLUDE_BASE_CEF_WEAK_PTR_H_
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